113 lines
3.4 KiB
C
113 lines
3.4 KiB
C
#include <assert.h>
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#include <mmu.h>
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#include <errno.h>
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#include <x86.h>
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#include <kern/syscall.h>
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#include <kern/wait.h>
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#include <kern/process.h>
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#include <kern/pmap.h>
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#include <kern/sche.h>
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#include <kern/kmalloc.h>
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/*
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The wait() system call suspends execution of the calling thread
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until one of its children terminates.
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RETURN VALUE
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on success, returns the process ID of the terminated child;
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on failure, -1 is returned.
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! however the testwait.bin expects a valued return other than simply -1
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*/
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ssize_t
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kern_wait(int *wstatus)
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{
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// 相比于fork来说，wait的实现简单很多
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// 语义实现比较清晰，没有fork那么多难点要处理，所以这里并不会给大家太多引导
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// 需要大家自己思考wait怎么实现。
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// 在实现之前你必须得读一遍文档`man 2 wait`
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// 了解到wait大概要做什么
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// panic("Unimplement! Read The F**king Manual");
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// 当然读文档是一方面，最重要的还是代码实现
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// wait系统调用与exit系统调用关系密切，所以在实现wait之前需要先读一遍exit为好
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// 可能读完exit的代码你可能知道wait该具体做什么了
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// panic("Unimplement! Read The F**king Source Code");
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again:
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while (xchg(&p_proc_ready->pcb.lock, 1) == 1)
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schedule();
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PROCESS_0 *p_fa = &p_proc_ready->pcb;
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int child_pid = -1;
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struct son_node* p_son = p_fa->fork_tree.sons;
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if (p_son == NULL) {
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xchg(&p_fa->lock, 0);
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return -ECHILD;
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}
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assert(p_son->pre == NULL); // make sure it is the head of the list
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while (p_son != NULL) {
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if (p_son->p_son->statu == ZOMBIE) {
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/*
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struct s_proc {
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user_regs; // let it be
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kern_regs; // let it be
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lock; // get and release before kfree
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statu; // set to IDLE
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pid; // keep it util return
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cr3; // let it be
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page_list; // recycle it
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exit_code; // set to wstatus
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priority; // let it be
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ticks; // let it be
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fork_tree; // already cleared
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};
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*/
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while (xchg(&p_son->p_son->lock, 1) == 1)
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schedule();
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// just use this value, which is '(status & 0xFF) << 8' in exit.c::do_exit
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if (wstatus != NULL)
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*wstatus = p_son->p_son->exit_code;
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// recycle_pages in pmap.c
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recycle_pages(p_son->p_son->page_list);
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// free it in proc table, 'cause in fork I judge free by statu
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p_son->p_son->statu = IDLE;
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// remove p_son from p_fa's son list
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if (p_son->pre != NULL) {
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p_son->pre->nxt = p_son->nxt;
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}
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else {
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p_fa->fork_tree.sons = p_son->nxt;
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}
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if (p_son->nxt != NULL) {
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p_son->nxt->pre = p_son->pre;
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}
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// keep p_son's pid for retval, 'cause the pointer will get freed before return
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child_pid = p_son->p_son->pid;
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xchg(&p_son->p_son->lock, 0);
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kfree(p_son);
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goto done;
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}
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p_son = p_son->nxt;
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}
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p_fa->statu = SLEEP;
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xchg(&p_fa->lock, 0);
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schedule();
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goto again;
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// 接下来就是你自己的实现了，我们在设计的时候这段代码不会有太大问题
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// 在实现完后你任然要对自己来个灵魂拷问
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// 1. 上锁上了吗？所有临界情况都考虑到了吗？（永远要相信有各种奇奇怪怪的并发问题）
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// 2. 所有错误情况都判断到了吗？错误情况怎么处理？（RTFM->`man 2 wait`）
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// 3. 是否所有的资源都正确回收了？
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// 4. 你写的代码真的符合wait语义吗？
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done:
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xchg(&p_fa->lock, 0);
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// panic("Unimplement! soul torture");
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return child_pid;
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}
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ssize_t
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do_wait(int *wstatus)
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{
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assert((uintptr_t)wstatus < KERNBASE);
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assert((uintptr_t)wstatus + sizeof(wstatus) < KERNBASE);
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return kern_wait(wstatus);
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} |