epoll_wait是線程退出點嗎？
2010年04月02日 星期五 上午 10:46
在Linux上,epoll_wait是否cancellation point,取決于glibc的版本. 好像在glibc-2.4以上版本中才支持. 假如系統epoll_wait不是cancellation point,那么在某線程執行epoll_wait時,另一線程通過pthread_cancel發出cancel信號,那么表現為： 1. 在epoll_wait返回之前,線程阻塞該信號,并不響應; 2. 當epoll_wait返回時,線程立即退出(所有資源不會被釋放),在此之前即使通過pthread_cleanup_push注冊了銷毀時的回調函數也不會被執行;同時,如果有線程阻塞在pthread_join等待此線程退出的話,則會返回. 測試代碼如下：
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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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