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 */}
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