一个sigprocmask和sigsuspend函数的综合应用

头文件：	#include <signal.h>
函数：		int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
功能：		用于获取或者改变当前进程的信号掩码（当前进程屏蔽的信号集）。
返回值：	0成功，-1失败（具体原因由errno值表示）。

头文件：	#include <signal.h>
函数：		int sigsuspend(const sigset_t *mask);
功能：		阻塞当前进程（TASK_INTERRUPTIBLE可中断状态），等待mask信号集（信号掩码）之外的任何信号的到来。
			在收到pendmask之外）信号后，先调用该信号的处理函数，然后把信号集mask还原为原来的信号集，接着从sigsuspend调用处返回（进程恢复执行）。
返回值：	该系统调用始终返回-1，并将errno设置为EINTR。

/**
 * @FileName    sigprocmask_sigsuspend.c
 * @Describe    A simple example for using sigprocmask and sigsuspend functions in linux.
 * @Author      vfhky 2016-02-29 11:21 https://typecodes.com/cseries/sigprocmasksigsuspendapp.html
 * @Compile 	gcc sigprocmask_sigsuspend.c -o sigprocmask_sigsuspend
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>

//Signal handle function.
void sig_handler( int signal )
{
	printf( "Receive signal=[%d].\n", signal );
	return;
}

int main( int argc, char *argv[] )
{
	printf( "getpid=[%d].\n", getpid() );
	int i = 0;
	
	//Register a signal.
	struct sigaction new_act;
	sigemptyset( &new_act.sa_mask );
	new_act.sa_handler = sig_handler;
	new_act.sa_flags = 0;
	sigaction( SIGUSR1, &new_act, 0 );
	sigaction( SIGUSR2, &new_act, 0 );
	sigaction( SIGINT, &new_act, 0 );
	
	//Add SIGINT, SIGUSR1/SIGUSR2 signals to the signal-set of new_set.
	sigset_t new_set, old_set;
	sigemptyset( &new_set );
	sigaddset( &new_set, SIGINT );				//2
	sigaddset( &new_set, SIGUSR1 );				//10
	//sigaddset( &new_set, SIGUSR2 );			//12
	
	/**
	 * Repalce the old mask set with the new mask set.Thus the process will block the signal of SIGINT and SIGUSR1, 
	 * but it will excute the function of sig_handler when the signal such as SIGUSR2 other than SIGINT, SIGUSR1 arrives.
	 */
	sigprocmask( SIG_SETMASK, &new_set, &old_set );
	
	//Add SIGUSR1 and SIGUSR2 signals to the signal-set of pendmask.
	sigset_t pendmask;
	sigemptyset( &pendmask );
	sigaddset( &pendmask, SIGUSR1 );			//10
	sigaddset( &pendmask, SIGUSR2 );			//12
	
	//Replaces the signal mask of the process with pendmask temporarily and suspends the process until delivery of a signal whose action is to invoke a signal handler or to terminate a process.
	i = sigsuspend( &pendmask );
	printf( "Sigsuspend returned with value[%d].\n", i );
	if( errno == EINTR )
	{
		printf( "[%d]Interrupted by a signal.\n", errno );
	}
	
	while(1)
	{
		printf( "--while.\n" );
		sleep(3);
	}
	return 0;
}