c – prctl(PR_SET_PDEATHSIG,SIGNAL)在父线程退出时调用,而不是

这是我的代码：

parent.cpp：

#include <sys/prctl.h>
#include <signal.h>
#include <unistd.h>
#include <pthread.h>
#include <iostream>

void* run(void* ptr) {

    std::cout << "thread:" << getpid() << ":" << std::hex << pthread_self() << ":" << std::dec << getppid() << std::endl;
    auto pid = fork();
    if ( pid != 0 ) {
        sleep(1);
    }
    else {
        char* arg = NULL;
        execv("./child",&arg);
    }
    return NULL;
}

int main() {

    std::cout << "main:" << getpid() << ":" << std::hex << pthread_self() << ":" << std::dec << getppid() << std::endl;

    pthread_t threadid;
    pthread_attr_t attr;

    ::pthread_attr_init( &attr );
    ::pthread_attr_setdetachstate( &attr,PTHREAD_CREATE_DETACHED );
    ::pthread_create(&threadid,&attr,run,NULL);

    sleep(6);

    return 0;
}

child.cpp：

#include <sys/prctl.h>
#include <signal.h>
#include <unistd.h>
#include <iostream>

int main() {
    std::cout << "child:" << getpid() << ":" << std::hex << pthread_self() << ":" << std::dec << getppid() << std::endl;
    ::prctl( PR_SET_PDEATHSIG,SIGKILL );
    sleep(6);


    return 0;
}

在命令行上运行以下命令：

$./parent

同时,运行以下命令查找child的状态：

$for i in {1..10000}; do ps aux | grep child ; sleep .5; done

孩子已经不复存在了.如果你在孩子身上取出prctl电话,它就不会失效.

在http://www.kernel.org/doc/man-pages/online/pages/man2/prctl.2.html的prctl页面似乎描述了这个调用应该在父进程死亡时调用SIGKILL,而不是父线程.当父进程死而不是父线程时,有没有办法让prctl终止子进程？