c - timer_create 是否为处理程序创建新线程

Question

timer_settime() 每秒建立一个计时器。信号处理程序是 traffic_measurement_handler。 traffic_measurement_handler 是否在新线程中运行？如何在处理程序运行时让 callback 停止？

#define CLOCKID CLOCK_REALTIME
#define SIG SIGUSR1
timer_t timerid;

int main(void)
{
    ..

    build_timer();
    pcap_loop(pcap_handle, -1, callback, NULL);
}

void callback() // callback of Libpcap API: pcap_loop()
{
    detect_network_traffic(); // stop when timer expires, and then continue                 
                              // to run when traffic_measurement_handler has finished.
}

// timer handler runs every second to update database
void traffic_measurement_handler() 
{
    .. // This block will fetch global variables, so I want to
       // let callback stop when this handler is running.


    // rebuild the timer
    build_timer();

}

// set timer
void build_timer()
{
    sa.sa_flags = SA_SIGINFO;
    sa.sa_sigaction = traffic_measurement_handler;
    sigemptyset(&sa.sa_mask);
    sigaction(SIG, &sa, NULL);

    sev.sigev_notify = SIGEV_SIGNAL;
    sev.sigev_signo = SIG;
    sev.sigev_value.sival_ptr = &timerid;
    timer_create(CLOCKID, &sev, &timerid);

    its.it_value.tv_sec = 1;
    its.it_value.tv_nsec = 0;
    its.it_interval.tv_sec = its.it_value.tv_sec;
    its.it_interval.tv_nsec = its.it_value.tv_nsec;

    timer_settime(timerid, 0, &its, NULL);
}

信号处理程序在只有一个线程的进程中安全吗？

添加:第二个版本
这样对吗？

pthread_t thread_global;

int main(void)
{
    // register SIGUSR1 handler
    sa.sa_flags = SA_SIGINFO;
    sa.sa_sigaction = traffic_measurement_handler;
    sigemptyset(&sa.sa_mask);
    sigaction(SIG, &sa, NULL);

    pthread_create(&thread1, NULL, processing_thread, (void *) thread_id1);
    pthread_create(&thread2, NULL, timer_thread, (void *) thread_id2);
    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);    
}

void *processing_thread(void *thread_id)
{
    pcap_loop(pcap_handle, -1, callback, NULL);
}

void callback() // callback of Libpcap API: pcap_loop()
{
    thread_global = pthread_self();
    detect_network_traffic(); // stop when SIGUSR1 is caught, and then continue                 
                              // to run when traffic_measurement_handler has finished.
}

//update database every second when SIGUSR1 is caught
void traffic_measurement_handler()
{
    ..
}

//This thread is used to notify updating database every second.
void *timer_thread(void *thread_id)
{
    for (; ;) {
        sleep(1);
        pthread_kill(thread_global, SIGUSR1);
    }
}

Answer 1

1. Does traffic_measurement_handler run in a new thread?

在POSIX threads当 sigev_notify = SIGEV_SIGNAL 时，不会因为信号而创建新线程。因此，在您的代码中，您不会创建新线程。

1. How to let callback stop when the handler is running?

您可以将信号设置为由运行回调的同一线程处理。

POSIX.1 distinguishes the notions of signals that are directed to the process as a whole and signals that are directed to individual threads.

阅读Unix pthreads and signals: per thread signal handlers