在 C 中切换上下文

Question

我正在学习如何在 C 中使用 ucontext_t，并编写了以下代码。我希望使用无限 while 循环来观察两个上下文（ctx_main 和 ctx_thread）之间的切换。但是，上下文似乎停留在 while 循环中。我正在寻找更正代码的帮助。我将我的 cmets 放在下面的代码中：

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ucontext.h>


#define MEM 64000

ucontext_t ctx_main, ctx_thread;
static int thread_id = 0;

/* the function thread_init() will initialize the ctx_main context
*  this is the first function to be called in main() */

void thread_init()
{
    getcontext(&ctx_main);
    ctx_main.uc_link = 0;
    ctx_main.uc_stack.ss_sp = malloc(MEM);
    ctx_main.uc_stack.ss_size = MEM;
    ctx_main.uc_stack.ss_flags = 0;

    printf("printed in thread_init()\n");
}

/* This function revert_main is supposed to increment the global variable thread_id,
*  then switch back to ctx_main context */

void *revert_main(void *n)  
{
    thread_id += *(int *) n;
    printf("printed in the revert_main()\n");
    swapcontext(&ctx_thread, &ctx_main); /* now switch back to ctx_main context */
}

int main()
{
    thread_init();   /* Initialize the ctx_main context */

    getcontext(&ctx_thread);  /* Initialize the ctx_thread context */

    ctx_thread.uc_link = 0;
    ctx_thread.uc_stack.ss_sp = malloc(MEM);
    ctx_thread.uc_stack.ss_size = MEM;
    ctx_thread.uc_stack.ss_flags = 0;

    int *j = (int *) malloc(sizeof(int));
    *j = 1;
    while(1)  /* Infinite loop to switch between ctx_main and ctx_thread */
    {
        printf("printed in the main while loop\n");

        printf("the thread id is %d\n", thread_id);
        makecontext(&ctx_thread, (void *)&revert_main, 1, (void *)j);  /* hopefully this will trigger the revert_main() function */
    }

    return 0;
}

Answer 1

您的主例程设置了一个新上下文，但从不切换到它，因此revert_main 永远不会运行。

您只想为给定的 u_context 对象调用一次makecontext。所以把对makecontext的调用移出循环。