c++ - pthread_sigmask :unusual behavior

Question

我正在使用 Linux 并尝试与信号处理相关的代码。我正在尝试以下代码，但我无法理解此代码的行为。

/**Globally declared variable**/

    time_t start, finish;
    struct sigaction sact;
    sigset_t new_set, old_set,test;
    double diff;

/**Function to Catch Signal**/
void catcher( int sig )
{
    cout<< "inside catcher() function\n"<<endl;
}


void Initialize_Signalhandler()
{

    sigemptyset( &sact.sa_mask );
    sact.sa_flags = 0;
    sact.sa_handler = catcher;
    sigaction( SIGALRM, &sact, NULL );

    sigemptyset( &new_set );
    sigaddset( &new_set, SIGALRM );

}


/**Function called by thread**/
void *threadmasked(void *parm)
{

/**To produce delay of 10sec**/
        do {
         time( &finish );
         diff = difftime( finish, start );
    } while (diff < 10);

    cout<<"Thread Exit"<<endl;

}


int main( int argc, char *argv[] ) {

    Initialize_Signalhandler();

    pthread_t a;
    pthread_create(&a, NULL, threadmasked, NULL);

    pthread_sigmask( SIG_BLOCK, &new_set, &old_set);

    time( &start );
    cout<<"SIGALRM signals blocked at %s\n"<< ctime(&start) <<endl;


    alarm(2); //to raise SIGALM signal


/**To produce delay of 10sec**/
        do {
         time( &finish );
         diff = difftime( finish, start );
    } while (diff < 10);


return( 0 );
}

甚至认为我正在使用“pthread_sigmask(SIG_BLOCK, &new_set, &old_set)”。它没有阻挡信号。但是如果我删除“pthread_create(&a, NULL, threadmasked, NULL);”它工作正常并阻止了信号。我在这里观察到的另一件事是，如果我将 pthread_sigmask 更改为 sigprocmask，行为保持不变。

Answer 1

线程从创建它们的线程继承信号掩码。

因此，当您的代码调用 pthread_sigmask() after 它调用 pthread_create() 时，新创建的线程不会修改其信号掩码.

像这样更改你的代码，让事情按你预期的那样工作:

...

pthread_sigmask( SIG_BLOCK, &new_set, &old_set);

pthread_t a;
pthread_create(&a, NULL, threadmasked, NULL);

...