c - pthread_cancel() 没有取消线程，因为它应该

Question

我正在为我的 OS 类项目测试信号处理程序。基本上我的信号处理程序(在它自己的线程中运行)必须处理 SIGINT，这意味着它必须“杀死”所有其他线程然后退出。

不幸的是我的代码不起作用。

这是我的虚拟线程任务，我想用 SIGINT 停止

 static void * dummyTask(){
   pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
   pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
   while(1){
      pthread_testcancel();
      printf(" Hello!\n");
      sleep(2);
   }
   return NULL;
}

这是我的主要内容。如您所见，我创建了信号处理程序，然后创建了最多 2 个虚拟线程。我将它们的 thID 保存在一个数组中，稍后在信号处理程序线程的任务中需要它，如您所见

 int main(){
   //need to the signal handler thread, so it can kill all the threads with cancel
   pthread_t **thids = malloc( 2 * sizeof(pthread_t *));
   sigset_t set;
   pthread_t signalHandlerThread;

   sigemptyset(&set);
   sigaddset(&set, SIGINT);
   //s is for error checking, not importanto now
   int s = pthread_sigmask(SIG_BLOCK, &set, NULL);

   //shParam: signalHandlerParam
   signalHParam *shParam = malloc(sizeof(signalHParam));
    shParam->set = &set;
    shParam->arrayOfThIDs = thids;
   s = pthread_create(&signalHandlerThread, NULL, signalHandlerTask, (void *) shParam);

   for(int i = 0; i < 2; i ++){
     pthread_t dummyThread;
     pthread_create(&dummyThread, NULL, &dummyTask, NULL);
     thids[i] = &dummyThread;
   }

   pause();
   //pthread_join(signalHandlerThread, NULL);
   return 1;
}

正如你所看到的，signalHandlerThread 执行了一个名为 signalHandlerTask 的函数，它是:

static void *signalHandlerTask(void *shParam){
   signalHParam *tmp = (signalHParam *) shParam;
   sigset_t *set = tmp->set;
   int s, sig;

    int i = sigismember(set, SIGINT);
    if(i != 1)
      printf("error\n");
   while(1 == 1){
      s = sigwait(set, &sig);
        
        if(sig == SIGINT){
            printf("\n----- signal recived ----\n");
         //function that use the array to kill threads
            killThreads(tmp->arrayOfThIDs);
            pthread_exit(NULL); //kill the signal handler thread
        }
    }
}

shParam 是我用来将多个参数传递给线程任务 (signalHandlerTask) 的结构体，它是这样的

typedef struct{
   pthread_t **arrayOfThIDs;
   sigset_t *set;
} signalHParam;

终于到了真正的问题了。我按如下方式创建了 killThreads 函数:

void killThreads(pthread_t **thids){
    for(int i = 0; i < 2; i++){
        int r = pthread_cancel(*thids[i]);
        if(r != 0)
            printf("error!! %d\n", r);
            //r is 3, why??
            pthread_join(*thids[i], NULL);
    }
}

问题是，如前所述，pthread_cancel(*thids[i]) 不起作用，线程保持事件状态，我不明白为什么

这里是给想要运行它的人的完整代码:

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <error.h>
#include <unistd.h>
#include <errno.h>

typedef struct{
   pthread_t **arrayOfThIDs;
   sigset_t *set;
} signalHParam;

void killThreads(pthread_t **thids){
    //termino il threadListener, e tutti i thread nel thread pool 
    for(int i = 0; i < 2; i++){

        //FAI ANCHE SU PROGETTO!!
        int r = pthread_cancel(*thids[i]);
        if(r != 0)
         printf("pthread_cancel failed: %s\n", strerror(r));
        //FAI ANCHE SU PROGETTO!!
        pthread_join(*thids[i], NULL);
    }

}

static void *signalHandlerTask(void *shParam){
    signalHParam *tmp = (signalHParam *) shParam;
   sigset_t *set = tmp->set;
   int s, sig;

    int i = sigismember(set, SIGINT);
    if(i != 1)
      printf("error\n");
   while(1 == 1){
      s = sigwait(set, &sig);
        
        if(sig == SIGINT){
            printf("\n----- signal recived ----\n");
         //function that use the array to kill threads
            killThreads(tmp->arrayOfThIDs);
            pthread_exit(NULL); //kill the signal handler thread
        }
    }
}
static void * dummyTask(){
   pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
   pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
   //printf("mo aspetto 10s\n");
   //sleep(10);
   while(1){
      pthread_testcancel();
      printf(" Ciao!\n");
      sleep(2);
   }
   return NULL;
}

int main(){
   //need to the signal handler thread, so it can kill all the threads with cancel
   pthread_t **thids = malloc( 2 * sizeof(pthread_t *));
   sigset_t set;
   pthread_t signalHandlerThread;

   sigemptyset(&set);
   sigaddset(&set, SIGINT);
   //s is for error checking, not importanto now
   int s = pthread_sigmask(SIG_BLOCK, &set, NULL);

   //shParam: signalHandlerParam
   signalHParam *shParam = malloc(sizeof(signalHParam));
    shParam->set = &set;
    shParam->arrayOfThIDs = thids;
   s = pthread_create(&signalHandlerThread, NULL, signalHandlerTask, (void *) shParam);

   for(int i = 0; i < 2; i ++){
     pthread_t dummyThread;
     pthread_create(&dummyThread, NULL, &dummyTask, NULL);
     thids[i] = &dummyThread;
   }

   pthread_join(signalHandlerThread, NULL);
   return 1;
}

Answer 1

我自己运行了整个程序，结果发现唯一重要的错误是我最初在评论中指出的错误。 (有很多样式问题和我不会那样做的地方，但它们都没有上升到“错误”的级别。是一个不相关的小错误:你忘了包括 stdio.h 和 signal.h。)

for(int i = 0; i < 2; i ++){
  pthread_t dummyThread;
  pthread_create(&dummyThread, NULL, &dummyTask, NULL);
  thids[i] = &dummyThread;
}

这将创建一个名为 dummyThread 的变量(无论它是否在循环内声明)并将 所有 线程句柄写入该变量。所有 thids[i] 指针都设置为指向那个变量。由于单个 pthread_t 变量只能保存一个线程句柄，因此除了循环​​的最后一次迭代之外，您将丢失在所有线程上创建的线程句柄。稍后，信号处理程序线程将反复尝试取消同一个线程，第一次成功，其余 N-1 次失败。 (为了使发生的事情更明显，增加线程数并注意程序打印“pthread_cancel failed: No such process”恰好 N-1 次，无论 N 是多少。)

更正的是简单的用pthread_t数组代替pthread_t *数组，把线程句柄直接写入数组:

typedef struct{
   pthread_t *arrayOfThIDs;
   sigset_t *set;
} signalHParam;

void killThreads(pthread_t **thids){
    //termino il threadListener, e tutti i thread nel thread pool 
    for(int i = 0; i < 2; i++){
        //FAI ANCHE SU PROGETTO!!
        int r = pthread_cancel(thids[i]);
        if(r != 0)
         printf("pthread_cancel failed: %s\n", strerror(r));
        //FAI ANCHE SU PROGETTO!!
        pthread_join(*thids[i], NULL);
    }

}

// ...

int main(){
   //need to the signal handler thread, so it can kill all the threads with cancel
   pthread_t *thids = malloc( 2 * sizeof(pthread_t));
   sigset_t set;
   pthread_t signalHandlerThread;

   sigemptyset(&set);
   sigaddset(&set, SIGINT);
   //s is for error checking, not importanto now
   int s = pthread_sigmask(SIG_BLOCK, &set, NULL);

   //shParam: signalHandlerParam
   signalHParam *shParam = malloc(sizeof(signalHParam));
    shParam->set = &set;
    shParam->arrayOfThIDs = thids;
   s = pthread_create(&signalHandlerThread, NULL, signalHandlerTask,
                      (void *) shParam);

   for(int i = 0; i < 2; i ++){
     pthread_create(&thids[i], NULL, &dummyTask, NULL);
   }

   pthread_join(signalHandlerThread, NULL);
   return 1;
}

signalHandlerTask 和 dummyTask 基本上是正确的。