POSIX多线程编程(二)--pthread_join

To explicitly create a thread as joinable or detached, the attr argument in the pthread_create() routine is used. The typical 4 step process is:

1. Declare a pthread attribute variable of the pthread_attr_t data type
2. Initialize the attribute variable with pthread_attr_init()
3. Set the attribute detached status with pthread_attr_setdetachstate()
4. When done, free library resources used by the attribute with pthread_attr_destroy()

/** * NAME * pthread_join - wait for thread termination * SYNOPSIS * #include <pthread.h> * int pthread_join(pthread_t thread, void **value_ptr); * DESCRIPTION * The  pthread_join()  function  shall  suspend  execution of the calling * thread until the target thread terminates, unless the target thread has * already  terminated.  On  return  from a successful pthread_join() call * with a non-NULL value_ptr argument, the value passed to  pthread_exit() * by  the terminating thread shall be made available in the location ref- * erenced by value_ptr. When a pthread_join() returns  successfully,  the * target thread has been terminated. The results of multiple simultaneous * calls to pthread_join() specifying the same  target  thread  are  unde- * fined.  If the thread calling pthread_join() is canceled, then the tar- * get thread shall not be detached. * It is unspecified whether a thread that has exited but remains unjoined * counts against {PTHREAD_THREADS_MAX}. * RETURN VALUE * If  successful,  the  pthread_join() function shall return zero; other- * wise, an error number shall be returned to indicate the error. */#include <pthread.h>#include <stdio.h>#include <stdlib.h>#define NUM_THREADS4//线程执行的函数void *BusyWork(void *t){int i;long tid;double result = 0.0;tid = (long) t;printf("Thread %ld starting...\n", tid);for (i = 0; i < 1000000; i++){result = result + sin(i) * tan(i);}printf("Thread %ld done. Result = %e\n", tid, result);pthread_exit((void*) t);return NULL ;}int main(int argc, char *argv[]){pthread_t thread[NUM_THREADS];//定义pthread_attr_t变量pthread_attr_t attr;int rc;long t;void *status;/* Initialize and set thread detached attribute *//** * 主要注意一下两个方法 * 初始化attr * pthread_attr_init * 设置这个线程是可以joinable * pthread_attr_setdetachstate */pthread_attr_init(&attr);pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);for (t = 0; t < NUM_THREADS; t++){printf("Main: creating thread %ld\n", t);//主要是函数的第二个参数//把设置好的attr传入rc = pthread_create(&thread[t], &attr, BusyWork, (void *) t);if (rc){printf("ERROR; return code from pthread_create() is %d\n", rc);exit(-1);}}/* Free attribute and wait for the other threads *///释放attributepthread_attr_destroy(&attr);for (t = 0; t < NUM_THREADS; t++){rc = pthread_join(thread[t], &status);if (rc){printf("ERROR; return code from pthread_join() is %d\n", rc);exit(-1);}printf("Main: completed join with thread %ld having a status of %ld\n",t, (long) status);}printf("Main: program completed. Exiting.\n");pthread_exit(NULL );}