在Linux上,epoll_wait是否cancellation point,取决于glibc的版本.
好像在glibc-2.4以上版本中才支持.
假如系统epoll_wait不是cancellation point,那么在某线程执行epoll_wait时,另一线程通过pthread_cancel发出cancel信号,那么表现为：
1. 在epoll_wait返回之前,线程阻塞该信号,并不响应;
2. 当epoll_wait返回时,线程立即退出(所有资源不会被释放),在此之前即使通过pthread_cleanup_push注册了销毁时的回调函数也不会被执行;同时,如果有线程阻塞在pthread_join等待此线程退出的话,则会返回.
测试代码如下：
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/*
test epoll_wait is a cancellation point.
glibc-2.4 or later support.
fedora 5 support.
*/
#include <sys/epoll.h>
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
void * run (int * events) {
struct epoll_event storage;
printf("Wait start.\n");
/* block forever */
epoll_wait(*events, &storage, 1, -1/*10000*/);
printf("Wait stop.\n");
return NULL;
}
int main (void) {
int events;
pthread_t new_thread;
events = epoll_create(1);
pthread_create(&new_thread, NULL, (void * (*) (void *))run, &events);
/* wait for enter keypress to try pthread cancellation */
getchar();
printf("Cleanup start.\n");
pthread_cancel(new_thread);
/* let's see if this returns or not */
pthread_join(new_thread, NULL);
/* if to here, the epoll_wait is a cancellation point. */
printf("Cleanup stop.\n");
close(events);
return 0;
}
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