线程fork进程

 一个多线程进程的某个线程fork出一个子进程，那么子进程完整复制调用fork的线程，且子进程不会拥有原进程那么多的线程，这里出现一个潜在的死锁条件，就是子进程继承了父进程的互斥锁但是并不知道该互斥锁的状态，若该互斥锁以上锁且子进程再次加锁该互斥量，此时子进程将死锁。

#include <pthread.h>#include <unistd.h>#include <stdio.h>#include <stdlib.h>#include <wait.h>pthread_mutex_t mutex;void* another( void* arg ){    printf( "in child thread, lock the mutex\n" );    pthread_mutex_lock( &mutex );    sleep( 5 );    pthread_mutex_unlock( &mutex );}void prepare(){    pthread_mutex_lock( &mutex );}void infork(){    pthread_mutex_unlock( &mutex );}int main(){    pthread_mutex_init( &mutex, NULL );    pthread_t id;    pthread_create( &id, NULL, another, NULL );    //pthread_atfork( prepare, infork, infork );//pthread_atfork()可以确保fork后父进程和子进程都拥有一个清楚的锁状态，prepare将父进程所有互斥锁锁住，infork释放prepare锁住的互斥锁，调用这行时子进程就不会死锁了    sleep( 1 );    int pid = fork();    if( pid < 0 )    {        pthread_join( id, NULL );        pthread_mutex_destroy( &mutex );        return 1;    }    else if( pid == 0 )    {        printf( "I anm in the child, want to get the lock\n" );        pthread_mutex_lock( &mutex );        printf( "I can not run to here, oop...\n" );        pthread_mutex_unlock( &mutex );        exit( 0 );    }    else    {        pthread_mutex_unlock( &mutex );        wait( NULL );    }    pthread_join( id, NULL );    pthread_mutex_destroy( &mutex );    return 0;}