C中的切換上下文

Question

我正在學習如何在C中使用ucontext_t，並編寫了以下代碼。我希望使用無限循環來觀察兩個上下文之間的切換（ctx_main和ctx_thread）。但是，上下文似乎卡在while循環中。我正在尋找一些幫助糾正代碼。我把我的意見在下面的代碼：

#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

你的主程序建立了一個新的環境，但從來沒有切換到它，所以revert_main從來沒有運行。

您只想爲給u_context對象調用makecontext一次。因此請將呼叫移至makecontext之外。