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OSTEP 34

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This commit is contained in:
ridethepig 2023-04-13 10:16:50 +08:00
parent 083bb41b59
commit 11facbf2ef
9 changed files with 2086 additions and 492 deletions
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70
assets/ostep_1681115599584_0.edn
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@ -2836,5 +2836,73 @@
:height 1209.6}),
:page 440},
:content {:text "implicit blocking "},
:properties {:color "yellow"}}
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:y1 639.015625,
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:page 448},
:content {:text "obstinate "},
:properties {:color "green"}}
{:id #uuid "6436caa1-6fe0-4de8-9ad4-2a057960fc1a",
:page 448,
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:page 448},
:content {:text "pickle"},
:properties {:color "green"}}
{:id #uuid "6436cb20-ee0b-4359-a39a-4178a4e8a4f7",
:page 448,
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:x2 259.7266540527344,
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:page 448},
:content {:text "segue"},
:properties {:color "green"}}
{:id #uuid "6436cc2e-b1af-4555-9d1d-808e6de120b1",
:page 450,
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:content {:text "System Architecture"},
:properties {:color "yellow"}}],
:extra {:page 351}}
:extra {:page 450}}

12
logseq/bak/logseq/config/2023-04-04T13_20_29.426Z.Desktop.edn → logseq/bak/logseq/config/2023-04-12T13_46_13.393Z.Desktop.edn
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@ -34,6 +34,9 @@
;; Enable showing the body of blocks when referencing them.
:ui/show-full-blocks? false
;; Expand block references automatically when zoom-in
:ui/auto-expand-block-refs? true
;; Enable Block timestamp
:feature/enable-block-timestamps? false
@ -127,7 +130,7 @@
;; 2. ` ` empty space between keys represents key chords. eg: `t s` means press `t` followed by `s`
;; 3. `mod` means `Ctrl` for Windows/Linux and `Command` for Mac
;; 4. use `false` to disable particular shortcut
;; 4. you can define multiple bindings for one action, eg `["ctrl+j" "down"]`
;; 5. you can define multiple bindings for one action, eg `["ctrl+j" "down"]`
;; full list of configurable shortcuts are available below:
;; https://github.com/logseq/logseq/blob/master/src/main/frontend/modules/shortcut/config.cljs
;; Example:
@ -135,7 +138,7 @@
;; {:editor/new-block "enter"
;; :editor/new-line "shift+enter"
;; :editor/insert-link "mod+shift+k"
;; :editor/hightlight false
;; :editor/highlight false
;; :ui/toggle-settings "t s"
;; :editor/up ["ctrl+k" "up"]
;; :editor/down ["ctrl+j" "down"]
@ -267,7 +270,7 @@
;; :property/separated-by-commas #{}
;; Properties that are ignored when parsing property values for references
;; :ignored-page-references-keywords #{"author" "startup"}
;; :ignored-page-references-keywords #{:author :startup}
;; logbook setup
;; :logbook/settings
@ -310,7 +313,7 @@
;; :media "[[quick capture]] **{time}**: {url}"}
;; Quick capture options
;; :quick-capture-options {:insert-today? false :redirect-page? false :default-page nil}
;; :quick-capture-options {:insert-today? false :redirect-page? false :default-page "my page"}
;; File sync options
;; Ignore these files when syncing, regexp is supported.
@ -339,6 +342,7 @@
;; ;use triple underscore `___` for slash `/` in page title
;; ;use Percent-encoding for other invalid characters
:file/name-format :triple-lowbar
:ui/show-brackets? false
;; specify the format of the filename for journal files
;; :journal/file-name-format "yyyy_MM_dd"

5
logseq/bak/logseq/config/2023-04-06T03_47_03.642Z.Desktop.edn → logseq/bak/logseq/config/2023-04-12T14_59_38.087Z.Desktop.edn
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@ -9,7 +9,7 @@
;; Preferred workflow style.
;; Value is either ":now" for NOW/LATER style,
;; or ":todo" for TODO/DOING style.
:preferred-workflow :now
:preferred-workflow :todo
;; The app will ignore those directories or files.
;; E.g. :hidden ["/archived" "/test.md" "../assets/archived"]
@ -35,7 +35,7 @@
:ui/show-full-blocks? false
;; Expand block references automatically when zoom-in
:ui/auto-expand-block-refs? true
:ui/auto-expand-block-refs? false
;; Enable Block timestamp
:feature/enable-block-timestamps? false
@ -342,6 +342,7 @@
;; ;use triple underscore `___` for slash `/` in page title
;; ;use Percent-encoding for other invalid characters
:file/name-format :triple-lowbar
:ui/show-brackets? false
;; specify the format of the filename for journal files
;; :journal/file-name-format "yyyy_MM_dd"

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logseq/bak/logseq/config/2023-04-12T15_07_19.432Z.Desktop.edn Normal file
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@ -0,0 +1,350 @@
{:meta/version 1
;; Currently, we support either "Markdown" or "Org".
;; This can overwrite your global preference so that
;; maybe your personal preferred format is Org but you'd
;; need to use Markdown for some projects.
;; :preferred-format ""
;; Preferred workflow style.
;; Value is either ":now" for NOW/LATER style,
;; or ":todo" for TODO/DOING style.
:preferred-workflow :todo
;; The app will ignore those directories or files.
;; E.g. :hidden ["/archived" "/test.md" "../assets/archived"]
:hidden []
;; When creating the new journal page, the app will use your template if there is one.
;; You only need to input your template name here.
:default-templates
{:journals ""}
;; Set a custom date format for journal page title
;; Example:
;; :journal/page-title-format "EEE, do MMM yyyy"
;; Whether to enable hover on tooltip preview feature
;; Default is true, you can also toggle this via setting page
:ui/enable-tooltip? true
;; Show brackets around page references
;; :ui/show-brackets? true
;; Enable showing the body of blocks when referencing them.
:ui/show-full-blocks? false
;; Expand block references automatically when zoom-in
:ui/auto-expand-block-refs? false
;; Enable Block timestamp
:feature/enable-block-timestamps? false
;; Enable remove accents when searching.
;; After toggle this option, please remember to rebuild your search index by press (cmd+c cmd+s).
:feature/enable-search-remove-accents? true
;; Enable journals
;; :feature/enable-journals? true
;; Enable flashcards
;; :feature/enable-flashcards? true
;; Enable Whiteboards
;; :feature/enable-whiteboards? true
;; Disable the built-in Scheduled tasks and deadlines query
;; :feature/disable-scheduled-and-deadline-query? true
;; Specify the number of days in the future to display in the
;; scheduled tasks and deadlines query, with a default value of 0 which
;; only displays tasks for today.
;; Example usage:
;; Display all scheduled tasks and deadlines in the next 7 days
;; :scheduled/future-days 7
;; Specify the date on which the week starts.
;; Goes from 0 to 6 (Monday to Sunday), default to 6
:start-of-week 6
;; Specify a custom CSS import
;; This option take precedence over your local `logseq/custom.css` file
;; You may find a list of awesome logseq themes here:
;; https://github.com/logseq/awesome-logseq#css-themes
;; Example:
;; :custom-css-url "@import url('https://cdn.jsdelivr.net/gh/dracula/logseq@master/custom.css');"
;; Specify a custom js import
;; This option take precedence over your local `logseq/custom.js` file
;; :custom-js-url ""
;; Set a custom Arweave gateway
;; Default gateway: https://arweave.net
;; :arweave/gateway ""
;; Set Bullet indentation when exporting
;; default option: tab
;; Possible options are for `:sidebar` are
;; 1. `:eight-spaces` as eight spaces
;; 2. `:four-spaces` as four spaces
;; 3. `:two-spaces` as two spaces
;; :export/bullet-indentation :tab
;; When :all-pages-public? true, export repo would export all pages within that repo.
;; Regardless of whether you've set any page to public or not.
;; Example:
;; :publishing/all-pages-public? true
;; Specify default home page and sidebar status for Logseq
;; If not specified, Logseq default opens journals page on startup
;; value for `:page` is name of page
;; Possible options for `:sidebar` are
;; 1. `"Contents"` to open up `Contents` in sidebar by default
;; 2. `page name` to open up some page in sidebar
;; 3. Or multiple pages in an array ["Contents" "Page A" "Page B"]
;; If `:sidebar` is not set, sidebar will be hidden
;; Example:
;; 1. Setup page "Changelog" as home page and "Contents" in sidebar
;; :default-home {:page "Changelog", :sidebar "Contents"}
;; 2. Setup page "Jun 3rd, 2021" as home page without sidebar
;; :default-home {:page "Jun 3rd, 2021"}
;; 3. Setup page "home" as home page with multiple pages in sidebar
;; :default-home {:page "home" :sidebar ["page a" "page b"]}
;; Tell logseq to use a specific folder in the repo as a default location for notes
;; if not specified, notes are stored in `pages` directory
;; :pages-directory "your-directory"
;; Tell logseq to use a specific folder in the repo as a default location for journals
;; if not specified, journals are stored in `journals` directory
;; :journals-directory "your-directory"
;; Set this to true will convert
;; `[[Grant Ideas]]` to `[[file:./grant_ideas.org][Grant Ideas]]` for org-mode
;; For more, see https://github.com/logseq/logseq/issues/672
;; :org-mode/insert-file-link? true
;; Setup custom shortcuts under `:shortcuts` key
;; Syntax:
;; 1. `+` means keys pressing simultaneously. eg: `ctrl+shift+a`
;; 2. ` ` empty space between keys represents key chords. eg: `t s` means press `t` followed by `s`
;; 3. `mod` means `Ctrl` for Windows/Linux and `Command` for Mac
;; 4. use `false` to disable particular shortcut
;; 5. you can define multiple bindings for one action, eg `["ctrl+j" "down"]`
;; full list of configurable shortcuts are available below:
;; https://github.com/logseq/logseq/blob/master/src/main/frontend/modules/shortcut/config.cljs
;; Example:
;; :shortcuts
;; {:editor/new-block "enter"
;; :editor/new-line "shift+enter"
;; :editor/insert-link "mod+shift+k"
;; :editor/highlight false
;; :ui/toggle-settings "t s"
;; :editor/up ["ctrl+k" "up"]
;; :editor/down ["ctrl+j" "down"]
;; :editor/left ["ctrl+h" "left"]
;; :editor/right ["ctrl+l" "right"]}
:shortcuts {}
;; By default, pressing `Enter` in the document mode will create a new line.
;; Set this to `true` so that it's the same behaviour as the usual outliner mode.
:shortcut/doc-mode-enter-for-new-block? false
;; Block content larger than `block/content-max-length` will not be searchable
;; or editable for performance.
:block/content-max-length 10000
;; Whether to show command doc on hover
:ui/show-command-doc? true
;; Whether to show empty bullets for non-document mode (the default mode)
:ui/show-empty-bullets? false
;; Pre-defined :view function to use with advanced queries
:query/views
{:pprint
(fn [r] [:pre.code (pprint r)])}
;; Pre-defined :result-transform function for use with advanced queries
:query/result-transforms
{:sort-by-priority
(fn [result] (sort-by (fn [h] (get h :block/priority "Z")) result))}
;; The app will show those queries in today's journal page,
;; the "NOW" query asks the tasks which need to be finished "now",
;; the "NEXT" query asks the future tasks.
:default-queries
{:journals
[{:title "🔨 NOW"
:query [:find (pull ?h [*])
:in $ ?start ?today
:where
[?h :block/marker ?marker]
[(contains? #{"NOW" "DOING"} ?marker)]
[?h :block/page ?p]
[?p :block/journal? true]
[?p :block/journal-day ?d]
[(>= ?d ?start)]
[(<= ?d ?today)]]
:inputs [:14d :today]
:result-transform (fn [result]
(sort-by (fn [h]
(get h :block/priority "Z")) result))
:collapsed? false}
{:title "📅 NEXT"
:query [:find (pull ?h [*])
:in $ ?start ?next
:where
[?h :block/marker ?marker]
[(contains? #{"NOW" "LATER" "TODO"} ?marker)]
[?h :block/page ?p]
[?p :block/journal? true]
[?p :block/journal-day ?d]
[(> ?d ?start)]
[(< ?d ?next)]]
:inputs [:today :7d-after]
:collapsed? false}]}
;; Add your own commands to slash menu to speedup.
;; E.g.
;; :commands
;; [
;; ["js" "Javascript"]
;; ["md" "Markdown"]
;; ]
:commands
[]
;; By default, a block can only be collapsed if it has some children.
;; `:outliner/block-title-collapse-enabled? true` enables a block with a title
;; (multiple lines) can be collapsed too. For example:
;; - block title
;; block content
:outliner/block-title-collapse-enabled? false
;; Macros replace texts and will make you more productive.
;; For example:
;; Change the :macros value below to:
;; {"poem" "Rose is $1, violet's $2. Life's ordered: Org assists you."}
;; input "{{poem red,blue}}"
;; becomes
;; Rose is red, violet's blue. Life's ordered: Org assists you.
:macros {}
;; The default level to be opened for the linked references.
;; For example, if we have some example blocks like this:
;; - a [[page]] (level 1)
;; - b (level 2)
;; - c (level 3)
;; - d (level 4)
;;
;; With the default value of level 2, `b` will be collapsed.
;; If we set the level's value to 3, `b` will be opened and `c` will be collapsed.
:ref/default-open-blocks-level 2
:ref/linked-references-collapsed-threshold 50
;; Favorites to list on the left sidebar
:favorites []
;; any number between 0 and 1 (the greater it is the faster the changes of the next-interval of card reviews) (default 0.5)
;; :srs/learning-fraction 0.5
;; the initial interval after the first successful review of a card (default 4)
;; :srs/initial-interval 4
;; hide specific properties for blocks
;; E.g. :block-hidden-properties #{:created-at :updated-at}
;; :block-hidden-properties #{}
;; Enable all your properties to have corresponding pages
:property-pages/enabled? true
;; Properties to exclude from having property pages
;; E.g.:property-pages/excludelist #{:duration :author}
;; :property-pages/excludelist
;; By default, property value separated by commas will not be treated as
;; page references. You can add properties to enable it.
;; E.g. :property/separated-by-commas #{:alias :tags}
;; :property/separated-by-commas #{}
;; Properties that are ignored when parsing property values for references
;; :ignored-page-references-keywords #{:author :startup}
;; logbook setup
;; :logbook/settings
;; {:with-second-support? false ;limit logbook to minutes, seconds will be eliminated
;; :enabled-in-all-blocks true ;display logbook in all blocks after timetracking
;; :enabled-in-timestamped-blocks false ;don't display logbook at all
;; }
;; Mobile photo uploading setup
;; :mobile/photo
;; {:allow-editing? true
;; :quality 80}
;; Mobile features options
;; Gestures
;; :mobile
;; {:gestures/disabled-in-block-with-tags ["kanban"]}
;; Extra CodeMirror options
;; See https://codemirror.net/5/doc/manual.html#config for possible options
;; :editor/extra-codemirror-options {:keyMap "emacs" :lineWrapping true}
;; Enable logical outdenting
;; :editor/logical-outdenting? true
;; When both text and a file are in the clipboard, paste the file
;; :editor/preferred-pasting-file? true
;; Quick capture templates for receiving contents from other apps.
;; Each template contains three elements {time}, {text} and {url}, which can be auto-expanded
;; by received contents from other apps. Note: the {} cannot be omitted.
;; - {time}: capture time
;; - {date}: capture date using current date format, use `[[{date}]]` to get a page reference
;; - {text}: text that users selected before sharing.
;; - {url}: url or assets path for media files stored in Logseq.
;; You can also reorder them, or even only use one or two of them in the template.
;; You can also insert or format any text in the template as shown in the following examples.
;; :quick-capture-templates
;; {:text "[[quick capture]] **{time}**: {text} from {url}"
;; :media "[[quick capture]] **{time}**: {url}"}
;; Quick capture options
;; :quick-capture-options {:insert-today? false :redirect-page? false :default-page "my page"}
;; File sync options
;; Ignore these files when syncing, regexp is supported.
;; :file-sync/ignore-files []
;; dwim (do what I mean) for Enter key when editing.
;; Context-awareness of Enter key makes editing more easily
; :dwim/settings {
; :admonition&src? true
; :markup? false
; :block-ref? true
; :page-ref? true
; :properties? true
; :list? true
; }
;; Decide the way to escape the special characters in the page title.
;; Warning:
;; This is a dangerous operation. If you want to change the setting,
;; should access the setting `Filename format` and follow the instructions.
;; Or you have to rename all the affected files manually then re-index on all
;; clients after the files are synced. Wrong handling may cause page titles
;; containing special characters to be messy.
;; Available values:
;; :file/name-format :triple-lowbar
;; ;use triple underscore `___` for slash `/` in page title
;; ;use Percent-encoding for other invalid characters
:file/name-format :triple-lowbar
:ui/show-brackets? true
;; specify the format of the filename for journal files
;; :journal/file-name-format "yyyy_MM_dd"
}

350
logseq/bak/logseq/config/2023-04-12T15_07_28.101Z.Desktop.edn Normal file
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@ -0,0 +1,350 @@
{:meta/version 1
;; Currently, we support either "Markdown" or "Org".
;; This can overwrite your global preference so that
;; maybe your personal preferred format is Org but you'd
;; need to use Markdown for some projects.
;; :preferred-format ""
;; Preferred workflow style.
;; Value is either ":now" for NOW/LATER style,
;; or ":todo" for TODO/DOING style.
:preferred-workflow :todo
;; The app will ignore those directories or files.
;; E.g. :hidden ["/archived" "/test.md" "../assets/archived"]
:hidden []
;; When creating the new journal page, the app will use your template if there is one.
;; You only need to input your template name here.
:default-templates
{:journals ""}
;; Set a custom date format for journal page title
;; Example:
;; :journal/page-title-format "EEE, do MMM yyyy"
;; Whether to enable hover on tooltip preview feature
;; Default is true, you can also toggle this via setting page
:ui/enable-tooltip? true
;; Show brackets around page references
;; :ui/show-brackets? true
;; Enable showing the body of blocks when referencing them.
:ui/show-full-blocks? false
;; Expand block references automatically when zoom-in
:ui/auto-expand-block-refs? false
;; Enable Block timestamp
:feature/enable-block-timestamps? false
;; Enable remove accents when searching.
;; After toggle this option, please remember to rebuild your search index by press (cmd+c cmd+s).
:feature/enable-search-remove-accents? true
;; Enable journals
;; :feature/enable-journals? true
;; Enable flashcards
;; :feature/enable-flashcards? true
;; Enable Whiteboards
;; :feature/enable-whiteboards? true
;; Disable the built-in Scheduled tasks and deadlines query
;; :feature/disable-scheduled-and-deadline-query? true
;; Specify the number of days in the future to display in the
;; scheduled tasks and deadlines query, with a default value of 0 which
;; only displays tasks for today.
;; Example usage:
;; Display all scheduled tasks and deadlines in the next 7 days
;; :scheduled/future-days 7
;; Specify the date on which the week starts.
;; Goes from 0 to 6 (Monday to Sunday), default to 6
:start-of-week 6
;; Specify a custom CSS import
;; This option take precedence over your local `logseq/custom.css` file
;; You may find a list of awesome logseq themes here:
;; https://github.com/logseq/awesome-logseq#css-themes
;; Example:
;; :custom-css-url "@import url('https://cdn.jsdelivr.net/gh/dracula/logseq@master/custom.css');"
;; Specify a custom js import
;; This option take precedence over your local `logseq/custom.js` file
;; :custom-js-url ""
;; Set a custom Arweave gateway
;; Default gateway: https://arweave.net
;; :arweave/gateway ""
;; Set Bullet indentation when exporting
;; default option: tab
;; Possible options are for `:sidebar` are
;; 1. `:eight-spaces` as eight spaces
;; 2. `:four-spaces` as four spaces
;; 3. `:two-spaces` as two spaces
;; :export/bullet-indentation :tab
;; When :all-pages-public? true, export repo would export all pages within that repo.
;; Regardless of whether you've set any page to public or not.
;; Example:
;; :publishing/all-pages-public? true
;; Specify default home page and sidebar status for Logseq
;; If not specified, Logseq default opens journals page on startup
;; value for `:page` is name of page
;; Possible options for `:sidebar` are
;; 1. `"Contents"` to open up `Contents` in sidebar by default
;; 2. `page name` to open up some page in sidebar
;; 3. Or multiple pages in an array ["Contents" "Page A" "Page B"]
;; If `:sidebar` is not set, sidebar will be hidden
;; Example:
;; 1. Setup page "Changelog" as home page and "Contents" in sidebar
;; :default-home {:page "Changelog", :sidebar "Contents"}
;; 2. Setup page "Jun 3rd, 2021" as home page without sidebar
;; :default-home {:page "Jun 3rd, 2021"}
;; 3. Setup page "home" as home page with multiple pages in sidebar
;; :default-home {:page "home" :sidebar ["page a" "page b"]}
;; Tell logseq to use a specific folder in the repo as a default location for notes
;; if not specified, notes are stored in `pages` directory
;; :pages-directory "your-directory"
;; Tell logseq to use a specific folder in the repo as a default location for journals
;; if not specified, journals are stored in `journals` directory
;; :journals-directory "your-directory"
;; Set this to true will convert
;; `[[Grant Ideas]]` to `[[file:./grant_ideas.org][Grant Ideas]]` for org-mode
;; For more, see https://github.com/logseq/logseq/issues/672
;; :org-mode/insert-file-link? true
;; Setup custom shortcuts under `:shortcuts` key
;; Syntax:
;; 1. `+` means keys pressing simultaneously. eg: `ctrl+shift+a`
;; 2. ` ` empty space between keys represents key chords. eg: `t s` means press `t` followed by `s`
;; 3. `mod` means `Ctrl` for Windows/Linux and `Command` for Mac
;; 4. use `false` to disable particular shortcut
;; 5. you can define multiple bindings for one action, eg `["ctrl+j" "down"]`
;; full list of configurable shortcuts are available below:
;; https://github.com/logseq/logseq/blob/master/src/main/frontend/modules/shortcut/config.cljs
;; Example:
;; :shortcuts
;; {:editor/new-block "enter"
;; :editor/new-line "shift+enter"
;; :editor/insert-link "mod+shift+k"
;; :editor/highlight false
;; :ui/toggle-settings "t s"
;; :editor/up ["ctrl+k" "up"]
;; :editor/down ["ctrl+j" "down"]
;; :editor/left ["ctrl+h" "left"]
;; :editor/right ["ctrl+l" "right"]}
:shortcuts {}
;; By default, pressing `Enter` in the document mode will create a new line.
;; Set this to `true` so that it's the same behaviour as the usual outliner mode.
:shortcut/doc-mode-enter-for-new-block? false
;; Block content larger than `block/content-max-length` will not be searchable
;; or editable for performance.
:block/content-max-length 10000
;; Whether to show command doc on hover
:ui/show-command-doc? true
;; Whether to show empty bullets for non-document mode (the default mode)
:ui/show-empty-bullets? false
;; Pre-defined :view function to use with advanced queries
:query/views
{:pprint
(fn [r] [:pre.code (pprint r)])}
;; Pre-defined :result-transform function for use with advanced queries
:query/result-transforms
{:sort-by-priority
(fn [result] (sort-by (fn [h] (get h :block/priority "Z")) result))}
;; The app will show those queries in today's journal page,
;; the "NOW" query asks the tasks which need to be finished "now",
;; the "NEXT" query asks the future tasks.
:default-queries
{:journals
[{:title "🔨 NOW"
:query [:find (pull ?h [*])
:in $ ?start ?today
:where
[?h :block/marker ?marker]
[(contains? #{"NOW" "DOING"} ?marker)]
[?h :block/page ?p]
[?p :block/journal? true]
[?p :block/journal-day ?d]
[(>= ?d ?start)]
[(<= ?d ?today)]]
:inputs [:14d :today]
:result-transform (fn [result]
(sort-by (fn [h]
(get h :block/priority "Z")) result))
:collapsed? false}
{:title "📅 NEXT"
:query [:find (pull ?h [*])
:in $ ?start ?next
:where
[?h :block/marker ?marker]
[(contains? #{"NOW" "LATER" "TODO"} ?marker)]
[?h :block/page ?p]
[?p :block/journal? true]
[?p :block/journal-day ?d]
[(> ?d ?start)]
[(< ?d ?next)]]
:inputs [:today :7d-after]
:collapsed? false}]}
;; Add your own commands to slash menu to speedup.
;; E.g.
;; :commands
;; [
;; ["js" "Javascript"]
;; ["md" "Markdown"]
;; ]
:commands
[]
;; By default, a block can only be collapsed if it has some children.
;; `:outliner/block-title-collapse-enabled? true` enables a block with a title
;; (multiple lines) can be collapsed too. For example:
;; - block title
;; block content
:outliner/block-title-collapse-enabled? false
;; Macros replace texts and will make you more productive.
;; For example:
;; Change the :macros value below to:
;; {"poem" "Rose is $1, violet's $2. Life's ordered: Org assists you."}
;; input "{{poem red,blue}}"
;; becomes
;; Rose is red, violet's blue. Life's ordered: Org assists you.
:macros {}
;; The default level to be opened for the linked references.
;; For example, if we have some example blocks like this:
;; - a [[page]] (level 1)
;; - b (level 2)
;; - c (level 3)
;; - d (level 4)
;;
;; With the default value of level 2, `b` will be collapsed.
;; If we set the level's value to 3, `b` will be opened and `c` will be collapsed.
:ref/default-open-blocks-level 2
:ref/linked-references-collapsed-threshold 50
;; Favorites to list on the left sidebar
:favorites []
;; any number between 0 and 1 (the greater it is the faster the changes of the next-interval of card reviews) (default 0.5)
;; :srs/learning-fraction 0.5
;; the initial interval after the first successful review of a card (default 4)
;; :srs/initial-interval 4
;; hide specific properties for blocks
;; E.g. :block-hidden-properties #{:created-at :updated-at}
;; :block-hidden-properties #{}
;; Enable all your properties to have corresponding pages
:property-pages/enabled? true
;; Properties to exclude from having property pages
;; E.g.:property-pages/excludelist #{:duration :author}
;; :property-pages/excludelist
;; By default, property value separated by commas will not be treated as
;; page references. You can add properties to enable it.
;; E.g. :property/separated-by-commas #{:alias :tags}
;; :property/separated-by-commas #{}
;; Properties that are ignored when parsing property values for references
;; :ignored-page-references-keywords #{:author :startup}
;; logbook setup
;; :logbook/settings
;; {:with-second-support? false ;limit logbook to minutes, seconds will be eliminated
;; :enabled-in-all-blocks true ;display logbook in all blocks after timetracking
;; :enabled-in-timestamped-blocks false ;don't display logbook at all
;; }
;; Mobile photo uploading setup
;; :mobile/photo
;; {:allow-editing? true
;; :quality 80}
;; Mobile features options
;; Gestures
;; :mobile
;; {:gestures/disabled-in-block-with-tags ["kanban"]}
;; Extra CodeMirror options
;; See https://codemirror.net/5/doc/manual.html#config for possible options
;; :editor/extra-codemirror-options {:keyMap "emacs" :lineWrapping true}
;; Enable logical outdenting
;; :editor/logical-outdenting? true
;; When both text and a file are in the clipboard, paste the file
;; :editor/preferred-pasting-file? true
;; Quick capture templates for receiving contents from other apps.
;; Each template contains three elements {time}, {text} and {url}, which can be auto-expanded
;; by received contents from other apps. Note: the {} cannot be omitted.
;; - {time}: capture time
;; - {date}: capture date using current date format, use `[[{date}]]` to get a page reference
;; - {text}: text that users selected before sharing.
;; - {url}: url or assets path for media files stored in Logseq.
;; You can also reorder them, or even only use one or two of them in the template.
;; You can also insert or format any text in the template as shown in the following examples.
;; :quick-capture-templates
;; {:text "[[quick capture]] **{time}**: {text} from {url}"
;; :media "[[quick capture]] **{time}**: {url}"}
;; Quick capture options
;; :quick-capture-options {:insert-today? false :redirect-page? false :default-page "my page"}
;; File sync options
;; Ignore these files when syncing, regexp is supported.
;; :file-sync/ignore-files []
;; dwim (do what I mean) for Enter key when editing.
;; Context-awareness of Enter key makes editing more easily
; :dwim/settings {
; :admonition&src? true
; :markup? false
; :block-ref? true
; :page-ref? true
; :properties? true
; :list? true
; }
;; Decide the way to escape the special characters in the page title.
;; Warning:
;; This is a dangerous operation. If you want to change the setting,
;; should access the setting `Filename format` and follow the instructions.
;; Or you have to rename all the affected files manually then re-index on all
;; clients after the files are synced. Wrong handling may cause page titles
;; containing special characters to be messy.
;; Available values:
;; :file/name-format :triple-lowbar
;; ;use triple underscore `___` for slash `/` in page title
;; ;use Percent-encoding for other invalid characters
:file/name-format :triple-lowbar
:ui/show-brackets? false
;; specify the format of the filename for journal files
;; :journal/file-name-format "yyyy_MM_dd"
}

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file:: [ostep_1681115599584_0.pdf](../assets/ostep_1681115599584_0.pdf)
file-path:: ../assets/ostep_1681115599584_0.pdf
- # Part II
- thread
ls-type:: annotation
hl-page:: 311
hl-color:: yellow
id:: 6433ca28-1bdf-433d-8ed9-0d54bf5ba940
collapsed:: true
- share the same address space and thus can access the same data
- context switch: the address space remains the same
hl-page:: 311
ls-type:: annotation
id:: 6433cb70-d168-4863-8268-1e969df6ce06
hl-color:: yellow
- thread control blocks
ls-type:: annotation
hl-page:: 311
hl-color:: yellow
id:: 6433cb56-fbef-46da-83c2-13fa2dba2967
- thread-local storage: one stack per thread in the address space
hl-page:: 312
ls-type:: annotation
id:: 6433cba2-61bd-4549-a29f-2ad85b3e30cd
hl-color:: yellow
- Why thread?
- possible speedup through parallelization
- enable overlap of IO in a single program
- Though these could be done through multi-processing, threading makes share data easier
- KEY CONCURRENCY TERMS
ls-type:: annotation
hl-page:: 323
hl-color:: yellow
id:: 6433eabf-48d6-4776-b66f-a5f7804d1ddc
collapsed:: true
- **indeterminate**: the results depend on the timing execution of the code.
- race condition
ls-type:: annotation
hl-page:: 320
hl-color:: yellow
id:: 6433e4cc-69e4-4057-8cc6-1766240d82f4
- A **critical section** is a piece of code that accesses a shared variable (or resource) and must not be concurrently executed by more than one thread.
hl-page:: 320
ls-type:: annotation
id:: 6433e52b-1f38-4f7c-b168-0aed624f9bdf
hl-color:: yellow
- **mutual exclusion**: This property guarantees that if one thread is executing within the *critical section*, the others will be prevented from doing so.
hl-page:: 320
ls-type:: annotation
id:: 6433e566-e6ef-45b3-84b1-eba981be914a
hl-color:: yellow
- Atomicity: *as a unit*, or, *all or none*
hl-page:: 321
ls-type:: annotation
id:: 6433e6a1-407c-4936-b184-dee868ef4107
hl-color:: yellow
- synchronization primitives
ls-type:: annotation
hl-page:: 322
hl-color:: yellow
id:: 6433e729-7043-453b-8d60-6e6c41560543
- sane 精神健全的；神志正常的；明智的；理智的
ls-type:: annotation
hl-page:: 322
hl-color:: green
id:: 6433e6e7-d995-4b69-96b3-261b79f94c1d
- Thread API
hl-page:: 327
ls-type:: annotation
id:: 6433f35b-403b-4b25-b9f9-076e9e34777e
hl-color:: yellow
collapsed:: true
- `pthread_create` `pthread_join` `pthread_mutex_lock` `pthread_cond_*`
- Locks
ls-type:: annotation
hl-page:: 339
hl-color:: yellow
id:: 6433f45b-0345-4790-8379-3d1a94e57ef5
- A lock is just a variable
hl-page:: 339
ls-type:: annotation
id:: 6433f4ba-f2e4-4743-a536-e2b7747433b7
hl-color:: yellow
collapsed:: true
- **lock variable**: some type of variable, which holds the *state* of the lock(and maybe additional data such as its holder or a queue for acquisition)
- **lock state**: available (or unlocked or free); acquired (or locked or held)
- **lock routines**:
- `lock()` tries to acquire the lock. If no other thread holds the lock, the thread will acquire the lock and enter the critical section(become the owner of the lock). Otherwise, it will not return while the lock is held by another thread.
- `unlock()` : The owner of the lock calls `unlock()`, then it is *available* again. If there are waiting threads, one of them will (eventually) notice (or be informed of) this change of the lock's state, acquire the lock, and enter the critical section.
- Locks help transform the chaos that is traditional OS scheduling into a more controlled activity
hl-page:: 340
ls-type:: annotation
id:: 6433f5e6-bc06-42a9-866e-e9a3053f528f
hl-color:: yellow
- Controlling Interrupts
ls-type:: annotation
hl-page:: 342
hl-color:: yellow
id:: 6433fbfd-a1bf-4fd9-a54d-e15189c77b15
collapsed:: true
- For *single-processor* systems, **disable interrupts** for critical sections.
- Problems
- disable interrupts is privileged. In the worst case, the OS may never regain control when the interrupt isn't going to be enabled.
- does NOT work on multi-processor systems, each CPU has its own interrupt state
- importance interrupts may get lost
- inefficient
- Just Using Loads/Stores(Fail)
hl-page:: 343
ls-type:: annotation
id:: 6433fe7e-2221-41ee-ad6b-7deaa4459aa5
hl-color:: yellow
collapsed:: true
- use a simple variable (flag) to indicate whether some thread has possession of a lock
hl-page:: 343
ls-type:: annotation
id:: 6433ff4a-856d-4e4b-af30-6cb600aefeb5
hl-color:: yellow
- On acquisition, load, test the flag. If free, set the flag; If not free, spin-wait(loop load and test).
- On releasing, clear the flag.
- Problem
- When interrupted between load and test, *mutual exclusion* is broken.
- Low efficiency because of spin-waiting.
- **spin lock**
- ```c
void lock(lock_t *lock) {
while (TestAndSet(&lock->status, 1) == 1);
}
void unlock(lock_t *lock) { lock->status = 0; }
```
- Requires a preemptive scheduler(or it may spin forever)
- No fairness guarantee
- For single processor systems, terrible performance, because the thread holding the lock cannot make any progress to release the lock until it is scheduled again and thus all other threads waiting for the lock can do nothing but spinning even they are scheduled.
- For multi-processor systems, spin lock may work well when thread B on CPU1 waits for thread A on CPU0, and the critical section is short. Because lock owner keeps making progress, spinning doesn't waste many cycles.
- **Priority Inversion**: Threads with high priority wait for locks held by threads with low priority.
hl-page:: 355
ls-type:: annotation
id:: 6435099b-0834-483e-9ef2-98a0b795cf00
hl-color:: yellow
Solution: **priority inheritance** or give up the priority?
- **Test-And-Set (Atomic Exchange)**
hl-page:: 344
ls-type:: annotation
id:: 643401e0-fcec-41d3-9898-d5c4175ac464
hl-color:: yellow
collapsed:: true
- Returns the old value pointed to by the `old_ptr`, and simultaneously updates said value to `new`.
- "test" the old value (which is what is returned) while simultaneously "set" the memory location to a new value
- ```c
int TestAndSet(int *old_ptr, int new) {
int old = *old_ptr;
*old_ptr = new;
return old;
}
```
- **Compare-And-Swap**
hl-page:: 348
ls-type:: annotation
id:: 6434f8ac-d762-40a4-abb0-2955c2c8b396
hl-color:: yellow
collapsed:: true
- Test whether the value at the address specified by `ptr` is equal to `expected`.
hl-page:: 348
ls-type:: annotation
id:: 6434fab0-08de-4f28-8d8e-f48f7e04aaaa
hl-color:: yellow
If so, update the memory location with the `new` value.
If not, do nothing.
Return the old value at the memory location.
- ```c
int CompareAndSwap(int *ptr, int expected, int new) {
int original = *ptr;
if (original == expected) *ptr = new;
return orginial
}
```
- Compare-and-swap flavor spin lock
```C
void lock(lock_t *lock) {
while (CompareAndSwap(&lock->status, 0, 1) == 1) ;
}
```
- **load-linked** and **store-conditional**
hl-page:: 349
ls-type:: annotation
id:: 6434fde1-9d19-4381-805e-f2a972875dc2
hl-color:: yellow
collapsed:: true
- The **load-linked** operates much like a typical load instruction, and simply fetches a value from memory and places it in a register.
ls-type:: annotation
hl-page:: 349
hl-color:: yellow
id:: 6434fe1c-47f3-422c-a317-be72f08d6aef
- **store-conditional** only succeeds if no intervening store to the address has taken place.
hl-page:: 349
ls-type:: annotation
id:: 6434fe62-0e92-4414-86cc-b0c37fcf51ec
hl-color:: yellow
On success, return 1 and update the value at `ptr` to value.
On failure, return 0 and the value at `ptr` is not updated.
- ```c
int LL(int *ptr) { return *ptr; }
int SC(int *ptr, int value) {
if (/*no update to *ptr since LoadLinked to this address*/) {
*ptr = value;
return 1; // success!
} else {
return 0; // failed to update
}
}
```
- LL/SC flavor spin lock: very similar to the errant Load/Store lock, but the special instructions here can detect intervening
```c
void lock(lock_t *lock) {
while (true) {
while (LL(&lock->status) == 1) ; // test
if (SC(&lock->status, 1) == 1) // set
break;
// else retry, in case lock->status is changed
}
}
```
- **Fetch-And-Add**
ls-type:: annotation
hl-page:: 350
hl-color:: yellow
id:: 64350170-c853-4080-9ed1-2777ea3a18c8
collapsed:: true
- Atomically increments a value while returning the old value at a particular address
- ```c
int FetchAndAdd(int *ptr) {
int old = *ptr;
*ptr = old + 1;
return old;
}
```
- **ticket lock**
hl-page:: 351
ls-type:: annotation
id:: 64350331-8fbb-4c41-9ac1-1a4ba852f772
hl-color:: yellow
- ```C
struct lock_t{
int ticket;
int turn;
};
void lock(lock_t *lock) {
int myturn = FetchAndAdd(&lock->ticket);
// atomically allocate a ticket as the thread's turn
while (lock->turn != myturn) ;
// wait for its turn
}
void unlock(lock_t *lock) {
lock->turn += 1;
}
```
- Ensure progress for all threads. Once a thread is assigned its ticket value, it will be scheduled at some point in the future (i.e. it will definitely get its turn as `unlock()` operations increase global `turn` value).
hl-page:: 351
ls-type:: annotation
id:: 64350420-ca8a-4cac-af2f-f4e7deb5d1be
hl-color:: yellow
In contrast, test-and-set spin lock may starve, if it is very unlucky.(never succeeds in contention)
- Simple Yield Lock
hl-page:: 353
ls-type:: annotation
id:: 64350781-6995-41db-8b8e-2de0eb84136a
hl-color:: yellow
collapsed:: true
- `yield`: a system call that moves the caller from the running state to the ready state, and thus promotes another thread to running.
hl-page:: 353
ls-type:: annotation
id:: 643507af-1153-46c1-b232-31a9a203e5df
hl-color:: yellow
- ```C
void lock(lock_t *lock) {
while (TestAndSet(&lock->status, 1) == 1)
yield();
}
```
- Problem: Starvation is still possible; Context switch overhead, though better than spinning
- Lock With Queues, Test-and-set, Yield, And Wakeup
ls-type:: annotation
hl-page:: 354
hl-color:: yellow
id:: 64350b44-dfae-4544-93f9-ff2b343fefd4
- The real problem is: We have not much control over which thread to run next and thus causes potential waste.
hl-page:: 353
ls-type:: annotation
id:: 64350b4e-9559-49d9-aa37-eda9fe425b7f
hl-color:: yellow
- `park()`: put a calling thread to sleep
hl-page:: 354
ls-type:: annotation
id:: 64350bfb-64f7-4d41-8cc2-260dbec3372d
hl-color:: yellow
- `unpark(threadID)`: wake a particular thread
hl-page:: 354
ls-type:: annotation
id:: 64350c01-39bb-4d15-b554-0287b13806ee
hl-color:: yellow
- implement
```C
struct lock_t{
int lk;
int guard; // spin lock for the whole lock
queue_t *q; // control who gets the lock next
};
void lock(lock_t *lock) {
while (TestAndSet(&m->guard, 1) == 1) ;
if (m->lk == 0) {
m->lk = 1;
m->guard = 0;
}
else {
m->q->add(get_tid());
setpark(); // newly added
m->guard = 0;
// ---- wakeup/waiting race ----
park();
}
}
void unlock(lock_t *lock) {
while (TestAndSet(&m->guard, 1) == 1) ;
if (m->q->empty())
m->flag = 0;
else
unpark(m->q->pop()); // should not clear flag here
// Wake up Only one waiting thread
m->guard = 0;
}
```
- When a thread is woken up, it will be as if it is returning from `park()`. Thus when `unpark` a thread, pass the lock directly from the thread releasing the lock to the next thread acquiring it; flag is not set to 0 in-between.
- wakeup/waiting race: If the thread is scheduled out just before it calls `park`, and then the lock owner calls `unpark` on that thread, it would sleep forever.
hl-page:: 356
ls-type:: annotation
id:: 64351ba3-d4b5-4999-bc61-7733d5e0a061
hl-color:: yellow
- One solution is to use `setpark()`: indicate the thread is about to `park`. If it happens to be interrupted and another thread calls `unpark` before `park` is actually called, the subsequent park returns immediately instead of sleeping.
- Peterson's algorithm: mutual exclusion lock for 2 threads without hardware atomic instruction. Use 2 intention flags and a turn flag.
hl-page:: 345
ls-type:: annotation
id:: 6434edd3-2a7b-4e11-af18-29854e628bc6
hl-color:: yellow
- **two-phase lock**
hl-page:: 358
ls-type:: annotation
id:: 643522a7-4b16-4998-9b2f-47a852681a16
hl-color:: yellow
- A combination of spin lock and sleep lock
- In the first phase, the lock spins for a while, hoping that it can acquire the lock.
hl-page:: 358
ls-type:: annotation
id:: 6435230e-d84a-4c91-8329-b7608b0d543a
hl-color:: yellow
- A second phase is entered if the lock is not acquired, where the caller is put to sleep, and only woken up when the lock becomes free later.
ls-type:: annotation
hl-page:: 358
hl-color:: yellow
id:: 64352344-d140-468c-987c-e8afa05c2171
- Linux System Call **futex**
hl-page:: 356
ls-type:: annotation
id:: 64351e9a-6505-4176-a6fb-ddf63f3245a8
hl-color:: yellow
- each `futex` is associated with ==a specific physical memory location==, and ==an in-kernel queue==
- `futex_wake(address)` wakes one thread that is waiting on the queue.
- `futex_wait(address, expected)` puts the calling thread to sleep, assuming the value at `address` is equal to `expected`. If it is not equal, the call returns immediately.
- Figure 28.10: Linux-based Futex Locks
ls-type:: annotation
hl-page:: 357
hl-color:: yellow
id:: 64352221-d590-4371-a5f0-29e9cfa75ccb
- efficacy 功效，效力
ls-type:: annotation
hl-page:: 341
hl-color:: green
id:: 6433fb69-1425-46b4-996f-f91da5d3e8d0
- foil
ls-type:: annotation
hl-page:: 347
hl-color:: green
id:: 6434f523-44b7-40ab-8fea-528969c5acfd
- delve 钻研；探究；挖
ls-type:: annotation
hl-page:: 349
hl-color:: green
id:: 6434fb8c-2b3b-4d80-83fb-3b34da4dcd28
- brag 吹嘘；自吹自擂
ls-type:: annotation
hl-page:: 351
hl-color:: green
id:: 643501c1-f11b-4e85-8125-d2a5a31f69b0
- scourge
- 鞭打；鞭笞；折磨；使受苦难
- Lock-based Concurrent Data Structures
ls-type:: annotation
hl-page:: 361
hl-color:: yellow
id:: 643525b0-e245-489b-877d-a2a1d63e7ea6
- **Concurrent Counters**
hl-page:: 361
ls-type:: annotation
id:: 643525e5-fb85-48d4-905a-2a88b9ac0b0d
hl-color:: yellow
collapsed:: true
- **Counter with lock**
- Wrap the all the operations with a single lock.
- Performance is bad due to lock contention and it gets worse when the number of threads increases.
- **perfect scaling**: the increase in thread number doesn't harm the performance
hl-page:: 363
ls-type:: annotation
id:: 64352751-d9bd-4d5e-a8ba-cd18f86b1a15
hl-color:: yellow
- **approximate counter**
hl-page:: 363
ls-type:: annotation
id:: 64352794-d7c8-42f9-8321-f874967cebf2
hl-color:: yellow
- represent a single logical counter via ==numerous local physical counters==(one per CPU core), as well as ==a single global counter==. Each actual counter has a ==lock==.
- To add the counter, acquire the ==local lock== and increase it, thus avoiding contention.
- To read the counter, acquire the ==global lock== and read.
- To keep the global counter up to date, the local values are periodically transferred to the global counter and reset, which requires ==global lock and local lock==. A threshold `S` determines how often this transfer happens, tuning the trade-off between scalability and precision.
- **Concurrent Linked Lists**
ls-type:: annotation
hl-page:: 367
hl-color:: yellow
id:: 643530d8-9d09-4c8a-9e92-47dfe814ef50
collapsed:: true
- Again, the simplest way to implement this is to wrap all operations on the list with a single lock.
- Assuming the `malloc` is ==thread-safe==, we can improve the code a little by narrowing critical section: only operations on global structure need to be locked.
- **hand-over-hand locking**: a lock per node.
hl-page:: 369
ls-type:: annotation
id:: 64353237-4b74-4148-b7c1-5854d83a18c7
hl-color:: yellow
- When traversing the list, the code first grabs the next node's lock and then releases the current node's lock.
- In practice, it ==doesn't work== due to prohibitive overhead
- **Concurrent Queues**
ls-type:: annotation
hl-page:: 370
hl-color:: yellow
id:: 64353353-9de2-421b-967d-dc80a597eecd
- Two locks, head and tail, for `enqueue` and `dequeue` operation.
- Add a dummy node to separate head and tail operation. Without this, `dequeue` operation needs to acquire both locks in case the queue is empty.
- **Concurrent Hash Table**
hl-page:: 372
ls-type:: annotation
id:: 6435360d-c176-494a-9d61-b1fd0107a9bd
hl-color:: yellow
- instead of having a single lock for the entire structure, it uses a lock per hash bucket
ls-type:: annotation
hl-page:: 372
hl-color:: yellow
id:: 6435363d-c697-42a6-bfd0-8a2332cef394
- ubiquitous 似乎无所不在的；十分普遍的
ls-type:: annotation
hl-page:: 372
hl-color:: green
id:: 6435365a-b5d6-46fc-a9a1-25b0d23aa529
- humble 谦逊；低声下气；虚心；贬低
ls-type:: annotation
hl-page:: 373
hl-color:: green
id:: 6435367f-dd9e-449d-b0e4-3d8c9e14f6c2
- sloppy 马虎的，草率的；（衣服）宽松肥大的；太稀的，不够稠的；
hl-page:: 376
ls-type:: annotation
id:: 643536c8-fc05-4bbe-8d1d-0f4f6d1c4fee
hl-color:: green
- gross 总的，毛的；严重的，极端的；粗鲁的；臃肿的；粗略的；
hl-page:: 378
ls-type:: annotation
id:: 643537d3-7d01-442b-b47e-59433c2aa6db
hl-color:: green
- **condition variable**
hl-page:: 378
ls-type:: annotation
id:: 643537ff-1028-4725-8d7a-c0338cc946d3
hl-color:: yellow
- A ==condition variable== is an explicit queue that threads can put themselves on when some state of execution(condition) is not as desired (by *waiting on the condition*); some other thread, when it changes said state, can then wake one (or more) of those waiting threads and thus allow them to continue (by *signaling*).
hl-page:: 378
ls-type:: annotation
id:: 64353882-7697-4c16-8e53-c8f59ea256c1
hl-color:: yellow
- Operations
- `wait()` put the caller to sleep. `pthread_cond_wait(pthread_cond_t *c, pthread_mutex_t *m)`
hl-page:: 378
ls-type:: annotation
id:: 643538d5-9ea3-4399-9fa2-d75fdf0e1dd4
hl-color:: yellow
- `signal()` wake up a sleeping thread waiting on this condition. `pthread_cond_signal(pthread_cond_t *c);`
hl-page:: 379
ls-type:: annotation
id:: 643538de-cc40-4dd2-8f03-9492004f209b
hl-color:: yellow
- The `wait()` also takes a mutex as a parameter; it assumes that this mutex is locked when `wait()` is called. The responsibility of `wait()` is to ==release the lock and put the calling thread to sleep== (atomically); when the thread wakes up, it must ==re-acquire the lock before returning== to the caller. The design is helpful to avoid some race conditions when trying to sleep.
- use a while loop instead of just an if statement when deciding whether to wait on the condition.
ls-type:: annotation
hl-page:: 380
hl-color:: yellow
id:: 643547c5-1613-49e9-899e-0e86f59a1462
- stem (花草的)茎；(花或叶的)梗,柄；阻止；封堵；遏止；
hl-page:: 379
ls-type:: annotation
id:: 64353eb8-8ed8-4680-a3c0-91608b429408
hl-color:: green
- **stem from sth ** 是…的结果；起源于；根源是
- **producer/consumer problem**
hl-page:: 382
ls-type:: annotation
id:: 64354974-adea-4b20-90f4-a12ebe1e4d5b
hl-color:: yellow
- **Mesa semantics**: Signaling a thread only wakes them up; it is thus a hint that the state of the world has ==changed==, but there is ==no guarantee== that when the woken thread runs, the state will ==still be as desired==. (Another guy may run before the thread and change the state again)
hl-page:: 385
ls-type:: annotation
id:: 64354cc4-14c5-408d-b879-7d4d011b2b5c
hl-color:: yellow
- So, always use while loops. While loops make sure the thread wake up in the desired state of world, which tackles the ((64355502-f41f-40dd-b71f-e0abdbc76716)) and provides support for ((64355441-5a1b-4015-baa1-65917526079c))
hl-page:: 386
ls-type:: annotation
id:: 64354db0-8c74-4c14-b063-d26378a10555
hl-color:: yellow
- **Hoare semantics**: provides a stronger guarantee that the woken thread will run immediately upon being woken
hl-page:: 386
ls-type:: annotation
id:: 64354d46-4286-44fd-9e82-2ba562a50f25
hl-color:: yellow
- Incorrect Solution: single condition variable. The problem arises from the ==undirected wakeup operation==: God knows which thread is to be woken up.
- Envision multiple consumers and one producer:
1. producer `P1` increases count to 1, signals the CV and sleeps
2. consumer `C1` is awaken, reduces count to 0, signals the CV and sleeps
3. another consumer `C2` is woken up ==by accident==, finds out count is 0, sleeps
4. In this case, they all sleep and thus nobody will signal any of them
- If in step 3, the producer `P1` is woken up, everything is fine. Obviously, one solution is to ==exert control over which thread is to be woken up==. Well, wake up all threads may also solve this problem, see ((64355441-5a1b-4015-baa1-65917526079c)).
- Correct solution: 2 condition variable.
- Producer threads wait on the condition `empty`, and signals `fill`. Conversely, consumer threads wait on `fill` and signal `empty`.
- Code
```C
cond_t empty, fill;
mutex_t mutex;
void *producer(void *arg) {
int i;
for (i = 0; i < loops; i++) {
Pthread_mutex_lock(&mutex);
while (count == MAX)
Pthread_cond_wait(&empty, &mutex);
put(i);
Pthread_cond_signal(&fill);
Pthread_mutex_unlock(&mutex);
}
}
void *consumer(void *arg) {
int i;
for (i = 0; i < loops; i++) {
Pthread_mutex_lock(&mutex);
while (count == 0)
Pthread_cond_wait(&fill, &mutex);
int tmp = get();
Pthread_cond_signal(&empty);
Pthread_mutex_unlock(&mutex);
printf("%d\n", tmp);
}
}
```
- **spurious wakeups**
hl-page:: 390
ls-type:: annotation
id:: 64355502-f41f-40dd-b71f-e0abdbc76716
hl-color:: yellow
- In some thread packages, due to details of the implementation, it is possible that two threads get woken up though just a single signal has taken place.
- **covering condition**
hl-page:: 391
ls-type:: annotation
id:: 64355441-5a1b-4015-baa1-65917526079c
hl-color:: yellow
- covers all the cases where a thread needs to wake up, those unneeded simply wake up, re-check condition and go back to sleep
- `pthread_cond_broadcast()` wakes up all waiting threads
- albeit 尽管；虽然
ls-type:: annotation
hl-page:: 390
hl-color:: green
id:: 64354f54-b26c-48dc-a328-4ae355b680f3
- spurious 虚假的；伪造的；建立在错误的观念（或思想方法）之上的；谬误的
hl-page:: 390
ls-type:: annotation
id:: 643554f4-75a7-48fa-9366-87058ee723fb
hl-color:: green
- Semaphores
ls-type:: annotation
hl-page:: 396
hl-color:: yellow
id:: 64356d96-cce8-48ad-80f1-e3e02a1a4684
- A semaphore is an ==object with an integer value== that we can manipulate with two routines `sem_wait()` and `sem_post()`. The initial value determines its behavior, so we need to give it an initial value through `sem_init()`
hl-page:: 396
ls-type:: annotation
id:: 64356dba-48b4-49b8-8182-c962f12f03a5
hl-color:: yellow
- Semaphore: Definitions Of **Wait And Post**
ls-type:: annotation
hl-page:: 397
hl-color:: yellow
id:: 6435744b-a300-40ad-ba91-157666d8cd2a
collapsed:: true
- `sem_wait(sem_t *s)`: First decrement the value of the semaphore by one. Then wait if the value of semaphore is negative
- `sem_post(sem_t*s)`: First increment the value of the semaphore by one. If there is any thread waiting, wait up one of them
- The value of the semaphore, *when negative*, is equal to the ==number of waiting threads==
hl-page:: 397
ls-type:: annotation
id:: 64357512-e25b-4226-961a-caec367fc8a3
hl-color:: yellow
- **Binary Semaphores (Locks)**
ls-type:: annotation
hl-page:: 398
hl-color:: yellow
id:: 6435753a-65b5-4e46-82bc-54c11c1cd533
collapsed:: true
- Initialize semaphore to 1, indicating we only have one piece of resource (the critical section).
- Wrap the critical section with `sem_wait` and `sem_post`
- When the lock is acquired, the semaphore is 0. On another acquisition request, the value goes to -1, which makes the caller sleep. When the lock is free, the value is decreased to 0 on acquisition, which will not get stuck.
- **Semaphores For Ordering (Condition Variable, or Ordering Primitive)**
hl-page:: 399
ls-type:: annotation
id:: 64357930-2d96-4867-bc3d-2fe89990ce5f
hl-color:: yellow
collapsed:: true
- Initialize the semaphore to 0
- Consider the *join* operation. The parent calls `sem_wait`and the child calls `sem_post`. In either case, no matter which thread is scheduled first, the semaphore guarantees the desired result.
- **The Producer/Consumer (Bounded Buffer) Problem (Again)**
hl-page:: 401
ls-type:: annotation
id:: 64357c6d-381e-492e-b901-095454f5315e
hl-color:: yellow
collapsed:: true
- 2 semaphores `empty` and `full` for coordination between consumer and producer, and 1 semaphore for lock
- Initialize `empty <- MAX`, and `full <- 0`
- Consumer waits for `full` and posts `empty` and conversely, produce waits for `empty` and posts `full`
- Special case for `MAX=1`
- When only one slot is available in the buffer, we don't even need a lock! Actually, it is binary semaphore which not only controls the buffer entry but also works as a lock.
- Otherwise, there will be a ==data race== inside the `put/get` operation due to potential multi-thread access to these procedures (when `MAX > 1`, the `sem_wait(&empty)` may allow in more than one thread).
- Deadlock avoidance
- If the lock semaphore is the outmost semaphore, deadlock occurs (the thread may sleep in `sem_wait(&empty)` with `mutex` unrelease). Therefore, put the lock inside the `empty/full` semaphore pair.
- Implement
```C
int empty = MAX, full = 0, mutex = 1;
void *producer() {
for (int i = 0; i < loops; ++ i) {
sem_wait(&empty);
sem_wait(&mutex);
put(i);
sem_post(&mutex);
sem_post(&full);
}
}
void *consumer() {
for (int i = 0; i < loops; ++ i) {
sem_wait(&full);
sem_wait(&mutex);
int tmp = get();
sem_post(&mutex);
sem_post(&empty);
printf("%d\n", tmp);
}
}
```
- **Reader-Writer Locks**
ls-type:: annotation
hl-page:: 406
hl-color:: yellow
id:: 643583b4-26b1-4cbf-801c-11ed6e63976e
- Either allow ==multiple readers to read== concurrently, or allow ==only one writer to write==.
- Two sets of operation
- `rwlock_acquire/release_writelock()`: simply `wait/post` the `writelock`
- `rwlock_acquire/release_readlock()`: acquire `writelock` when the ==first reader acquires==, and release it when the ==last reader releases==
- Implement
```C
typedef struct _rwlock_t {
sem_t guard; // binary semaphore (basic lock)
sem_t writelock; // allow ONE writer/MANY readers
int readers; // #readers in critical section
} rwlock_t;
void rwlock_acquire_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (++rw->readers == 1) sem_wait(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_release_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (--rw->readers == 0) sem_post(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_acquire_writelock(rwlock_t *rw) { sem_wait(&rw->writelock); }
void rwlock_release_writelock(rwlock_t *rw) { sem_post(&rw->writelock); }
```
- Problem: More overhead; Unfairness, writer is much more likely to starve.
- To tackle the writer starvation problem, we may manually wake up the writers (if ever suspended) on read lock release. [Wiki](https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock)
- **The Dining Philosophers**
hl-page:: 408
ls-type:: annotation
id:: 643587a7-ade4-4f09-be50-aea233ff02c0
hl-color:: yellow
- Background setting
hl-page:: 408
ls-type:: annotation
id:: 6435889f-1375-4b94-8630-b3d0d7bdfa56
hl-color:: yellow
- 5 "philosophers" around a table.
Between each pair of philosophers is a single fork (and thus, 5 total).
The philosophers each have times where they think (don’t need forks), and times where they eat.
In order to eat, a philosopher needs two forks (left and right).
The contention for these forks is our synchronization problem.
- Solution
- A semaphore per fork, and helper function `left/right(p)` which is the fork on philosopher `p`'s left/right.
- Deadlock: if each philosopher tries to grab the fork on their left first, there will be a deadlock. When all of them get their left-side forks, all of the forks are locked and no one could get their right-side fork.
- Non-deadlock: force one philosopher to try to grab the right-side fork first
- Implement
```C
void put_forks(int p) {
sem_post(&forks[left(p)]);
sem_post(&forks[right(p)]);
}
void get_forks(int p) {
if (p == 4) {
sem_wait(&forks[right(p)]);
sem_wait(&forks[left(p)]);
} else {
sem_wait(&forks[left(p)]);
sem_wait(&forks[right(p)]);
}
}
void philosopher() {
while (1) {
think();
get_forks(p);
eat();
put_forks(p);
}
}
```
- Implement Semaphores
ls-type:: annotation
hl-page:: 411
hl-color:: yellow
id:: 643589a6-31e6-4603-9259-999e9c8860f7
- Implementing Zemaphores With One Lock And One CV: the book authors provide us a simple implement for semaphore, though somewhat different from its definition.
hl-page:: 412
ls-type:: annotation
id:: 64358de1-f418-44fd-8a77-bc0faa368059
hl-color:: yellow
- salient 最重要的；显着的；突出的:
ls-type:: annotation
hl-page:: 397
hl-color:: green
id:: 64357404-d348-42b3-96a3-ba28575baa66
- ensue 跟着发生，接着发生；
ls-type:: annotation
hl-page:: 408
hl-color:: green
id:: 64358802-3b22-46ed-a0e2-71cc9df69a7b
- Throttle 节流阀；风门；喉咙；使窒息；使节流；
hl-page:: 411
ls-type:: annotation
id:: 64358758-cb9c-4e8d-aaa4-f8e50457db88
hl-color:: green
- bog 沼泽；泥塘；使陷于泥沼；使动弹不得
hl-page:: 411
ls-type:: annotation
id:: 64358755-1fae-4ea2-93a3-8c9d3d3e11c3
hl-color:: green
- ramification (众多复杂而又难以预料的)结果,后果
hl-page:: 410
ls-type:: annotation
id:: 64358b0c-e441-4d0a-852d-ecfde369306c
hl-color:: green

2
logseq/config.edn
View File

@ -342,7 +342,7 @@
;; ;use triple underscore `___` for slash `/` in page title
;; ;use Percent-encoding for other invalid characters
:file/name-format :triple-lowbar
:ui/show-brackets? false
:ui/show-brackets? true
;; specify the format of the filename for journal files
;; :journal/file-name-format "yyyy_MM_dd"

127
pages/OSTEP Code Snippets.md
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@ -117,3 +117,130 @@
}
}
```
- Dining Philosopher Solution with Semaphore
id:: 6436bebd-0681-4f94-9d04-4d8e4a554512
- ```C
void put_forks(int p) {
sem_post(&forks[left(p)]);
sem_post(&forks[right(p)]);
}
void get_forks(int p) {
if (p == 4) {
sem_wait(&forks[right(p)]);
sem_wait(&forks[left(p)]);
} else {
sem_wait(&forks[left(p)]);
sem_wait(&forks[right(p)]);
}
}
void philosopher() {
while (1) {
think();
get_forks(p);
eat();
put_forks(p);
}
}
```
- Simple Semaphore Implement
id:: 6436c47e-dc86-4452-b9b5-4e7997dbfbfb
- ```C
struct sem_t{
int value;
cond_t cond;
mutex_t lock;
};
void sem_wait(sem_t *sem) {
mutex_lock(&sem->lock);
while (s->value <= 0)
cond_wait(&sem->cond, &sem->lock);
s->value --;
mutex_unlock(&sem->lock);
}
void sem_post(sem_t *sem) {
mutex_lock(&sem->lock);
sem->value ++;
cond_signal(&sem->cond);
mutex_unlock(&sem->lock);
}
```
- Compare-And-Swap Code Description
id:: 6436c5c7-32e7-4071-b909-4fdc14bb479d
- ```c
int CompareAndSwap(int *ptr, int expected, int new) {
int original = *ptr;
if (original == expected) *ptr = new;
return orginial
}
```
- Compare-and-swap flavor spin lock
id:: b7679e9b-aabe-4bd3-8c2c-eb0a23fad491
- ```C
void lock(lock_t *lock) {
while (CompareAndSwap(&lock->status, 0, 1) == 1) ;
}
```
- LL/SC Code Description
id:: 6436c620-4884-45a7-9273-b7952a6521ae
- ```c
int LL(int *ptr) { return *ptr; }
int SC(int *ptr, int value) {
if (/*no update to *ptr since LoadLinked to this address*/) {
*ptr = value;
return 1; // success!
} else {
return 0; // failed to update
}
}
```
- LL/SC flavor spin lock
id:: c38274a9-22dd-40e2-b74a-d3a9be63600e
- very similar to the errant Load/Store lock, but the special instructions here can detect intervening
```c
void lock(lock_t *lock) {
while (true) {
while (LL(&lock->status) == 1) ; // test
if (SC(&lock->status, 1) == 1) // set
break;
// else retry, in case lock->status is changed
}
}
```
- Simple Yield Lock Code
id:: 6436c684-ac4a-4144-9e7e-b4cb8f976c1f
- ```C
void lock(lock_t *lock) {
while (TestAndSet(&lock->status, 1) == 1)
yield();
}
```
- Fetch-And-Add Code Description
id:: 6436c66c-807b-4e9d-93ed-b1d9703e6dc2
- ```C
int FetchAndAdd(int *ptr) {
int old = *ptr;
*ptr = old + 1;
return old;
}
```
- Readers-Writer Lock Implement
id:: 6436c668-5be8-4ce1-b701-1f2a00d34cc9
- ```C
typedef struct _rwlock_t {
sem_t guard; // binary semaphore (basic lock)
sem_t writelock; // allow ONE writer/MANY readers
int readers; // #readers in critical section
} rwlock_t;
void rwlock_acquire_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (++rw->readers == 1) sem_wait(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_release_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (--rw->readers == 0) sem_post(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_acquire_writelock(rwlock_t *rw) { sem_wait(&rw->writelock); }
void rwlock_release_writelock(rwlock_t *rw) { sem_post(&rw->writelock); }
```

193
pages/hls__ostep_1681115599584_0.md
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@ -2,11 +2,12 @@ file:: [ostep_1681115599584_0.pdf](../assets/ostep_1681115599584_0.pdf)
file-path:: ../assets/ostep_1681115599584_0.pdf
- # Part II
- thread
- ## thread
ls-type:: annotation
hl-page:: 311
hl-color:: yellow
id:: 6433ca28-1bdf-433d-8ed9-0d54bf5ba940
collapsed:: true
- share the same address space and thus can access the same data
- context switch: the address space remains the same
hl-page:: 311
@ -24,6 +25,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
id:: 6433cba2-61bd-4549-a29f-2ad85b3e30cd
hl-color:: yellow
- Why thread?
collapsed:: true
- possible speedup through parallelization
- enable overlap of IO in a single program
- Though these could be done through multi-processing, threading makes share data easier
@ -32,6 +34,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
hl-page:: 323
hl-color:: yellow
id:: 6433eabf-48d6-4776-b66f-a5f7804d1ddc
collapsed:: true
- **indeterminate**: the results depend on the timing execution of the code.
- race condition
ls-type:: annotation
@ -68,12 +71,14 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 6433f35b-403b-4b25-b9f9-076e9e34777e
hl-color:: yellow
collapsed:: true
- `pthread_create` `pthread_join` `pthread_mutex_lock` `pthread_cond_*`
- Locks
- ## Locks
ls-type:: annotation
hl-page:: 339
hl-color:: yellow
id:: 6433f45b-0345-4790-8379-3d1a94e57ef5
collapsed:: true
- A lock is just a variable
hl-page:: 339
ls-type:: annotation
@ -96,8 +101,8 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
id:: 6433fbfd-a1bf-4fd9-a54d-e15189c77b15
- For *single-processor* systems, **disable interrupts** for critical sections.
- Problems
- disable interrupts is privileged. In the worst case, the OS may never regain control when the interrupt isn't going to be enabled.
- does NOT work on multi-processor systems, each CPU has its own interrupt state
- Disable interrupts is a privileged instruction. In the worst case, the OS may never regain control when the interrupt isn't going to be enabled.
- NOT work on multi-processor systems, each CPU has its own interrupt state
- importance interrupts may get lost
- inefficient
- Just Using Loads/Stores(Fail)
@ -147,19 +152,8 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
If so, update the memory location with the `new` value.
If not, do nothing.
Return the old value at the memory location.
- ```c
int CompareAndSwap(int *ptr, int expected, int new) {
int original = *ptr;
if (original == expected) *ptr = new;
return orginial
}
```
- Compare-and-swap flavor spin lock
```C
void lock(lock_t *lock) {
while (CompareAndSwap(&lock->status, 0, 1) == 1) ;
}
```
- ((6436c5c7-32e7-4071-b909-4fdc14bb479d))
- ((b7679e9b-aabe-4bd3-8c2c-eb0a23fad491))
- **load-linked** and **store-conditional**
hl-page:: 349
ls-type:: annotation
@ -177,41 +171,15 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
hl-color:: yellow
On success, return 1 and update the value at `ptr` to value.
On failure, return 0 and the value at `ptr` is not updated.
- ```c
int LL(int *ptr) { return *ptr; }
int SC(int *ptr, int value) {
if (/*no update to *ptr since LoadLinked to this address*/) {
*ptr = value;
return 1; // success!
} else {
return 0; // failed to update
}
}
```
- LL/SC flavor spin lock: very similar to the errant Load/Store lock, but the special instructions here can detect intervening
```c
void lock(lock_t *lock) {
while (true) {
while (LL(&lock->status) == 1) ; // test
if (SC(&lock->status, 1) == 1) // set
break;
// else retry, in case lock->status is changed
}
}
```
- ((6436c620-4884-45a7-9273-b7952a6521ae))
- ((c38274a9-22dd-40e2-b74a-d3a9be63600e))
- **Fetch-And-Add**
ls-type:: annotation
hl-page:: 350
hl-color:: yellow
id:: 64350170-c853-4080-9ed1-2777ea3a18c8
- Atomically increments a value while returning the old value at a particular address
- ```c
int FetchAndAdd(int *ptr) {
int old = *ptr;
*ptr = old + 1;
return old;
}
```
- ((6436c66c-807b-4e9d-93ed-b1d9703e6dc2))
- **ticket lock**
hl-page:: 351
ls-type:: annotation
@ -224,7 +192,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
id:: 64350420-ca8a-4cac-af2f-f4e7deb5d1be
hl-color:: yellow
In contrast, test-and-set spin lock may starve, if it is very unlucky.(never succeeds in contention)
- Simple Yield Lock
- Simple **Yield Lock**
hl-page:: 353
ls-type:: annotation
id:: 64350781-6995-41db-8b8e-2de0eb84136a
@ -234,14 +202,9 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 643507af-1153-46c1-b232-31a9a203e5df
hl-color:: yellow
- ```C
void lock(lock_t *lock) {
while (TestAndSet(&lock->status, 1) == 1)
yield();
}
```
- ((6436c684-ac4a-4144-9e7e-b4cb8f976c1f))
- Problem: Starvation is still possible; Context switch overhead, though better than spinning
- Lock With Queues, Test-and-set, Yield, And Wakeup
- **Lock With Queues**, Test-and-set, Yield, And Wakeup
ls-type:: annotation
hl-page:: 354
hl-color:: yellow
@ -324,11 +287,12 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
hl-color:: green
id:: 643501c1-f11b-4e85-8125-d2a5a31f69b0
- scourge 鞭打；鞭笞；折磨；使受苦难
- Lock-based Concurrent Data Structures
- ## Lock-based Concurrent Data Structures
ls-type:: annotation
hl-page:: 361
hl-color:: yellow
id:: 643525b0-e245-489b-877d-a2a1d63e7ea6
collapsed:: true
- **Concurrent Counters**
hl-page:: 361
ls-type:: annotation
@ -372,6 +336,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
hl-page:: 370
hl-color:: yellow
id:: 64353353-9de2-421b-967d-dc80a597eecd
collapsed:: true
- Two locks, head and tail, for `enqueue` and `dequeue` operation.
- Add a dummy node to separate head and tail operation. Without this, `dequeue` operation needs to acquire both locks in case the queue is empty.
- **Concurrent Hash Table**
@ -379,6 +344,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 6435360d-c176-494a-9d61-b1fd0107a9bd
hl-color:: yellow
collapsed:: true
- instead of having a single lock for the entire structure, it uses a lock per hash bucket
ls-type:: annotation
hl-page:: 372
@ -404,7 +370,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 643537d3-7d01-442b-b47e-59433c2aa6db
hl-color:: green
- **condition variable**
- ## condition variable
hl-page:: 378
ls-type:: annotation
id:: 643537ff-1028-4725-8d7a-c0338cc946d3
@ -437,7 +403,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
id:: 64353eb8-8ed8-4680-a3c0-91608b429408
hl-color:: green
- **stem from sth ** 是…的结果；起源于；根源是
- **producer/consumer problem**
- **Producer/Consumer Problem**
hl-page:: 382
ls-type:: annotation
id:: 64354974-adea-4b20-90f4-a12ebe1e4d5b
@ -478,7 +444,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 64355441-5a1b-4015-baa1-65917526079c
hl-color:: yellow
- covers all the cases where a thread needs to wake up, those unneeded simply wake up, re-check condition and go back to sleep
- covers all the cases where a thread needs to wake up, other threads simply wake up, re-check condition and go back to sleep
- `pthread_cond_broadcast()` wakes up all waiting threads
- albeit 尽管；虽然
ls-type:: annotation
@ -490,11 +456,12 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 643554f4-75a7-48fa-9366-87058ee723fb
hl-color:: green
- Semaphores
ls-type:: annotation
- ## Semaphores
hl-page:: 396
hl-color:: yellow
ls-type:: annotation
id:: 64356d96-cce8-48ad-80f1-e3e02a1a4684
hl-color:: yellow
collapsed:: true
- A semaphore is an ==object with an integer value== that we can manipulate with two routines `sem_wait()` and `sem_post()`. The initial value determines its behavior, so we need to give it an initial value through `sem_init()`
hl-page:: 396
ls-type:: annotation
@ -540,8 +507,8 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
- Otherwise, there will be a ==data race== inside the `put/get` operation due to potential multi-thread access to these procedures (when `MAX > 1`, the `sem_wait(&empty)` may allow in more than one thread).
- Deadlock avoidance
- If the lock semaphore is the outmost semaphore, deadlock occurs (the thread may sleep in `sem_wait(&empty)` with `mutex` unrelease). Therefore, put the lock inside the `empty/full` semaphore pair.
- Implement
- **Reader-Writer Locks**
- ((6436bebd-0681-4f94-9d04-4d8e4a554512))
- **Readers-Writer Locks**
ls-type:: annotation
hl-page:: 406
hl-color:: yellow
@ -550,26 +517,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
- Two sets of operation
- `rwlock_acquire/release_writelock()`: simply `wait/post` the `writelock`
- `rwlock_acquire/release_readlock()`: acquire `writelock` when the ==first reader acquires==, and release it when the ==last reader releases==
- Implement
```C
typedef struct _rwlock_t {
sem_t guard; // binary semaphore (basic lock)
sem_t writelock; // allow ONE writer/MANY readers
int readers; // #readers in critical section
} rwlock_t;
void rwlock_acquire_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (++rw->readers == 1) sem_wait(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_release_readlock(rwlock_t *rw) {
sem_wait(&rw->guard);
if (--rw->readers == 0) sem_post(&rw->writelock);
sem_post(&rw->guard);
}
void rwlock_acquire_writelock(rwlock_t *rw) { sem_wait(&rw->writelock); }
void rwlock_release_writelock(rwlock_t *rw) { sem_post(&rw->writelock); }
```
- ((6436c668-5be8-4ce1-b701-1f2a00d34cc9))
- Problem: More overhead; Unfairness, writer is much more likely to starve.
- To tackle the writer starvation problem, we may manually wake up the writers (if ever suspended) every time read lock releases. [Wiki](https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock)
- **The Dining Philosophers**
@ -591,30 +539,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
- A semaphore per fork, and helper function `left/right(p)` which is the fork on philosopher `p`'s left/right.
- Deadlock: if each philosopher tries to grab the fork on their left first, there will be a deadlock. When all of them get their left-side forks, all of the forks are locked and no one could get their right-side fork.
- Non-deadlock: force one philosopher to try to grab the right-side fork first
- Implement
```C
void put_forks(int p) {
sem_post(&forks[left(p)]);
sem_post(&forks[right(p)]);
}
void get_forks(int p) {
if (p == 4) {
sem_wait(&forks[right(p)]);
sem_wait(&forks[left(p)]);
} else {
sem_wait(&forks[left(p)]);
sem_wait(&forks[right(p)]);
}
}
void philosopher() {
while (1) {
think();
get_forks(p);
eat();
put_forks(p);
}
}
```
- ((6436bebd-0681-4f94-9d04-4d8e4a554512))
- Implement Semaphores
ls-type:: annotation
hl-page:: 411
@ -625,27 +550,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 64358de1-f418-44fd-8a77-bc0faa368059
hl-color:: yellow
- Implement
```C
struct sem_t{
int value;
cond_t cond;
mutex_t lock;
};
void sem_wait(sem_t *sem) {
mutex_lock(&sem->lock);
while (s->value <= 0)
cond_wait(&sem->cond, &sem->lock);
s->value --;
mutex_unlock(&sem->lock);
}
void sem_post(sem_t *sem) {
mutex_lock(&sem->lock);
sem->value ++;
cond_signal(&sem->cond);
mutex_unlock(&sem->lock);
}
```
- ((6436c47e-dc86-4452-b9b5-4e7997dbfbfb))
- salient 最重要的；显着的；突出的:
ls-type:: annotation
hl-page:: 397
@ -671,16 +576,17 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
ls-type:: annotation
id:: 64358b0c-e441-4d0a-852d-ecfde369306c
hl-color:: green
- Non-Deadlock Bugs: A large fraction (97%) of non-deadlock bugs studied by Lu et al. are either ==atomicity violations== or ==order violations==.
- **Non-Deadlock Bugs**: A large fraction (97%) of non-deadlock bugs studied by Lu et al. are either ==atomicity violations== or ==order violations==.
hl-page:: 420
ls-type:: annotation
id:: 64361e4c-62eb-4599-9809-0f77f9ce1cd0
hl-color:: yellow
- **Deadlock**
ls-type:: annotation
- ## Deadlock
hl-page:: 420
hl-color:: yellow
ls-type:: annotation
id:: 64361fb7-5aa6-45cd-8b1e-aa0d0c300ad2
hl-color:: yellow
collapsed:: true
- **Conditions for Deadlock**
hl-page:: 422
ls-type:: annotation
@ -769,11 +675,11 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
hl-page:: 432
hl-color:: green
id:: 64364569-01b4-45e1-83f8-ac1bd8af5850
- **Event-based Concurrency**
ls-type:: annotation
- ## Event-based Concurrency
hl-page:: 432
hl-color:: yellow
ls-type:: annotation
id:: 64364585-ace4-4920-87fe-87aad004dffd
hl-color:: yellow
- event loop: waits for something to do and then, for each event returned, processes them, one at a time
hl-page:: 433
ls-type:: annotation
@ -825,7 +731,7 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
- Checking IO completion is inefficient, perhaps we need interrupt-based approaches (e.g. UNIX signals) to inform applications when async IO completes.
- Problems
- State management
- manual stack management: when an event handler issues an asynchronous I/O, it must package up some program state for the next event handler to use when the I/O finally completes; this additional work is not needed in thread-based programs, as the state the program needs is on the stack of the thread.
- manual stack management: when an event handler issues an asynchronous I/O, it must package up some ==program state for the next event handler== to use when the I/O finally completes; this additional work is ==not needed in thread-based programs==, as the state the program needs is on the stack of the thread.
hl-page:: 438
ls-type:: annotation
id:: 6436a3d9-ee29-4378-af79-4efc770cc209
@ -846,3 +752,18 @@ file-path:: ../assets/ostep_1681115599584_0.pdf
id:: 6436a485-7a70-4974-93d2-9e11b010a948
hl-color:: yellow
- Messy code base due to complicated asynchronous logic
- obstinate 固执的；棘手的；难以去除的；
hl-page:: 448
ls-type:: annotation
id:: 6436ca1f-f4e7-431e-9620-be7764825acd
hl-color:: green
- pickle 泡菜；腌菜
ls-type:: annotation
hl-page:: 448
hl-color:: green
id:: 6436caa1-6fe0-4de8-9ad4-2a057960fc1a
- System Architecture
ls-type:: annotation
hl-page:: 450
hl-color:: yellow
id:: 6436cc2e-b1af-4555-9d1d-808e6de120b1