在用pthread函数库实现一个线程池的过程中,遇到了几个小小的问题:
(1)pthread_cond_signal对一个已经被cancel的线程发信号时,会导致死锁的发生。实验的代码如下:
- #include <stdio.h>
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#include <unistd.h>
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#include <pthread.h>
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int x = 10, y;
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pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
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pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
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void* fun1(void *arg)
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{
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pthread_mutex_lock(&lock);
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printf("x: %d\ty: %d\n", x, y);
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while(x >= y){
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pthread_cond_wait(&cond, &lock);
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}
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printf("OH, My God, y is bigger than x.\n");
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pthread_mutex_unlock(&lock);
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return NULL;
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}
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void* fun2(void *arg)
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{
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pthread_mutex_lock(&lock);
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while(1){
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y++;
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printf("x: %d\ty: %d\n", x, y);
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sleep(1);
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if(y == 5){
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pthread_mutex_unlock(&lock);
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sleep(1);
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pthread_mutex_lock(&lock);
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}
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if(x < y){
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pthread_cond_signal(&cond);
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pthread_mutex_unlock(&lock);
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break;
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}
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}
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return NULL;
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}
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int main()
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{
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pthread_t tid1, tid2;
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pthread_create(&tid2, NULL, fun2, NULL);
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sleep(1);
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pthread_create(&tid1, NULL, fun1, NULL);
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sleep(1);
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pthread_cancel(tid1);
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sleep(1);
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pthread_join(tid1, NULL);
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pthread_join(tid2, NULL);
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return 0;
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}
当我们将main()函数中的:pthread_cancel(tid1); 注释掉时,编译运行的结果为:
- digdeep@ubuntu:~/pthread/threadpool$ gcc -Wall -lpthread -o cond cond.c
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digdeep@ubuntu:~/pthread/threadpool$ ./cond
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x: 10 y: 1
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x: 10 y: 2
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x: 10 y: 3
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x: 10 y: 4
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x: 10 y: 5
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x: 10 y: 5
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x: 10 y: 6
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x: 10 y: 7
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x: 10 y: 8
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x: 10 y: 9
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x: 10 y: 10
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x: 10 y: 11
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OH, My God, y is bigger than x.
当我们没有将main()函数中的:pthread_cancel(tid1); 注释掉时,编译运行的结果为:
- digdeep@ubuntu:~/pthread/threadpool$ gcc -Wall -lpthread -o cond cond.c
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digdeep@ubuntu:~/pthread/threadpool$ ./cond
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x: 10 y: 1
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x: 10 y: 2
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x: 10 y: 3
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x: 10 y: 4
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x: 10 y: 5
在输出:x: 10 y: 5 之后,发生了死锁。
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