1. 休眠sleep(unsigned int)为线程内操作
　　所以如果不同线程，信号量SIGALRM是不能中断sleep()；
　　编写程序进行测试

//timercreate_demo.cpp

#include <unistd.h>

#include <stdio.h>

#include <signal.h>

#include <time.h>

#include <pthread.h>  

void SignHandler(int iSignNo);

void testTimerSign();

void printTime();

void *function(void *arg);

int main() {

    pthread_t thread1;

    pthread_create(&thread1,NULL,function,(char*)"");

    testTimerSign();

    while(true);

    return ;

}

void SignHandler(int iSignNo){

    if(iSignNo == SIGUSR1){

        printf("Capture sign no : SIGUSR1\n");

    }else if(SIGALRM == iSignNo){

        //printf("Capture sign no : SIGALRM\n");

    }else{

        printf("Capture sign no:%d\n",iSignNo);

    }

}

void testTimerSign(){

    struct sigevent evp;

    struct itimerspec ts;

    timer_t timer;

    int ret;

    evp.sigev_value.sival_ptr = &timer;

    evp.sigev_notify = SIGEV_SIGNAL;

    evp.sigev_signo = SIGALRM;

    signal(evp.sigev_signo, SignHandler);

    ret = timer_create(CLOCK_REALTIME, &evp, &timer);

    if(ret) {

        perror("timer_create");

    }

    ts.it_interval.tv_sec = ;

    ts.it_interval.tv_nsec = ;

    ts.it_value.tv_sec = ;

    ts.it_value.tv_nsec = ;

    printTime();

    printf("start\n");

    ret = timer_settime(timer, , &ts, NULL);

    if(ret) {

        perror("timer_settime");

    }

}

void printTime(){

    struct tm *cursystem;

    time_t tm_t;

    time(&tm_t);

    cursystem = localtime(&tm_t);

    char tszInfo[] ;

    sprintf(tszInfo, "%02d:%02d:%02d",

        cursystem->tm_hour,

        cursystem->tm_min,

        cursystem->tm_sec);

        printf("[%s]",tszInfo);

}

void *function(void *arg){

    char *m;

    m = (char *)arg;

    while(true) {

        while(true){

            int left = sleep();

            printTime();

            printf("sleep(3)(left=%d)\n", left);

            }

    }

}

可以看出，在主线程的定时器中的信号量SIGALRM是无法中断子线程thread1的休眠；

在同一线程中, sleep()函数会被SIGALARM信号中断

使用SIGALRM信号量定时

上面程序中使用了信号量SIGUSR1；
如果使用信号量SIGALRM；
(对 CLOCK_REALTIMER来说，默认信号就是SIGALRM)
sleep()函数使用的就是实时时钟CLOCK_REALTIMER
所以使用信号值SIGALRM会中断sleep(int second)函数的休眠；

//timercreate_demo.cpp

#include <unistd.h>

#include <stdio.h>

#include <signal.h>

#include <time.h>

void SignHandler(int iSignNo);

void testTimerSign();

void printTime();

int main() {

    testTimerSign();

    while(true){

         int left = sleep();

         printTime();

         printf("sleep(5)(left=%d)\n", left);

    }

    return ;

}

void SignHandler(int iSignNo){

    //printTime();

    if(iSignNo == SIGUSR1){

        printf("Capture sign no : SIGUSR1\n");

    }else if(SIGALRM == iSignNo){

        //printf("Capture sign no : SIGALRM\n");

    }else{

        printf("Capture sign no:%d\n",iSignNo);

    }

}

void testTimerSign(){

    struct sigevent evp;

    struct itimerspec ts;

    timer_t timer;

    int ret;

    evp.sigev_value.sival_ptr = &timer;

    evp.sigev_notify = SIGEV_SIGNAL;

    evp.sigev_signo = SIGALRM;

    signal(evp.sigev_signo, SignHandler);

    ret = timer_create(CLOCK_REALTIME, &evp, &timer);

    if(ret) {

        perror("timer_create");

    }

    ts.it_interval.tv_sec = ;

    ts.it_interval.tv_nsec = ;

    ts.it_value.tv_sec = ;

    ts.it_value.tv_nsec = ;

    printTime();

    printf("start\n");

    ret = timer_settime(timer, , &ts, NULL);

    if(ret) {

        perror("timer_settime");

    }

}

void printTime(){

    struct tm *cursystem;

    time_t tm_t;

    time(&tm_t);

    cursystem = localtime(&tm_t);

    char tszInfo[] ;

    sprintf(tszInfo, "%02d:%02d:%02d",

        cursystem->tm_hour,

        cursystem->tm_min,

        cursystem->tm_sec);

        printf("[%s]",tszInfo);

}

因为timer_settime()中定时器间隔时间为1秒
于是sleep(5)每次都被打断不能按时休眠，剩余4秒未能执行;

巴特西

Linux下 sleep函数的注意事项

使用SIGALRM信号量定时

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