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(xiàn)程執行epoll_wait時(shí),另一線(xiàn)程通過(guò)pthread_cancel發(fā)出cancel信號,那么表現為：
1. 在epoll_wait返回之前,線(xiàn)程阻塞該信號,并不響應;
2. 當epoll_wait返回時(shí),線(xiàn)程立即退出(所有資源不會(huì )被釋放),在此之前即使通過(guò)pthread_cleanup_push注冊了銷(xiāo)毀時(shí)的回調函數也不會(huì )被執行;同時(shí),如果有線(xiàn)程阻塞在pthread_join等待此線(xiàn)程退出的話(huà),則會(huì )返回.
測試代碼如下：
| /*
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;
}
|
