在阅读ltp/testcases/kernel/io/disktest/signals.c代码时,setup_sig_mask()调用了pthread_sigmask()函数,好久没有写代码了,关于这部分代码竟没看明白,故查阅linux自带的manual手册(#man pthread_sigmask)以下代码就是man手册中给出的例子,为了理解信号的处理机制,稍作修改,废话不多说了,请看运行case。
编译:gcc pthread_sigmask.c -lpthread
运行结果
$ ./a.out &
[3] 3782$ kill -USR1 3782
$ kill -USR1 3782
[sig_thread] Signal handling thread got signal 10
$ kill -QUIT 3782
[main] Signal handling thread got signal 3
$ kill -USR1 3782
[sig_thread] Signal handling thread got signal 10
$ kill -QUIT 3782
[sig_thread] Signal handling thread got signal 3
$ kill -TERM 3782
[3]+ Terminated ./a.out
结果分析
主线程创建子线程sig_thread后,调用sleep(10)休眠10秒(在这10秒钟,子线程sig_thread已经阻塞在sigwait()函数获取set集合中的信号),主线程在没有执行到sigwait时,执行kill -USR1 3782,子线程获取该信号;一旦主线程和子线程sig_thread都阻塞在sigwait()函数时,当执行kill -QUIT 3782向PID=3782的进程发送信号时,主线程可以获取到,而子线程获取不到,由此可见主线程的优先级高于子线程的。主线程最后执行pause()函数,只有发送QUIT, USR1以外的信号,主线程才可以唤醒,退出,进而进程退出。
/* File: pthread_sigmask.c */ /* Date: 20140609 */ #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <signal.h> #include <errno.h> /* Simple error handling functions */ #define handle_error_en(en, msg) \ do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0) static void * sig_thread(void *arg) { sigset_t *set = (sigset_t *) arg; int s, sig; for (;;) { s = sigwait(set, &sig); if (s != 0) handle_error_en(s, "sigwait"); printf("[sig_thread] Signal handling thread got signal %d\n", sig); } printf("exit sig_thread\n"); } int main(int argc, char *argv[]) { pthread_t thread; sigset_t set; int s, sig; /* Block SIGINT; other threads created by main() will inherit a copy of the signal mask. */ sigemptyset(&set); sigaddset(&set, SIGQUIT); sigaddset(&set, SIGUSR1); s = pthread_sigmask(SIG_SETMASK, &set, NULL); if (s != 0) handle_error_en(s, "pthread_sigmask"); s = pthread_create(&thread, NULL, &sig_thread, (void *) &set); if (s != 0) handle_error_en(s, "pthread_create"); /* Main thread carries on to create other threads and/or do other work */ sleep(10); s = sigwait(&set, &sig); if (s != 0) handle_error_en(s, "sigwait"); printf("[main] Signal handling thread got signal %d\n", sig); pause(); /* Dummy pause so we can test program */ }