c++ Pthread创建线程后必须使用join或detach释放线程资源

http://www.cppblog.com/prayer/archive/2012/04/23/172427.html

这两天在看Pthread 资料的时候，无意中看到这样一句话(man pthread_detach):

Either pthread_join(3) or pthread_detach() should be called for each thread
       that an application creates, so that system resources for the thread can be
       released.  (But note that the resources of all threads are freed when the
       process terminates.)

也就是说：每个进程创建以后都应该调用pthread_join 或 pthread_detach 函数，只有这样在线程结束的时候资源(线程的描述信息和stack)才能被释放.

之后又查了pthread_join 但是没有明确说明必须调用pthread_join 或 pthread_detach.

但是再查了 Pthread for win32 pthread_join

When a joinable thread terminates, its memory resources (thread descriptor and stack) are not deallocated until another thread performs pthread_join on it. Therefore, pthread_join must be called  once  for each joinable thread created to avoid memory leaks.

 

才知道如果在新线程里面没有调用pthread_join 或 pthread_detach会导致内存泄漏, 如果你创建的线程越多，你的内存利用率就会越高, 直到你再无法创建线程，最终只能结束进程。

 

解决方法有三个:

1.   线程里面调用 pthread_detach(pthread_self()) 这个方法最简单

2. 在创建线程的设置PTHREAD_CREATE_DETACHED属性

3. 创建线程后用 pthread_join() 一直等待子线程结束。

 

下面是几个简单的例子

1. 调用  pthread_detach(pthread_self())

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

void *PrintHello(void)

{

pthread_detach(pthread_self());

int stack[1024 * 20] = {0,};

//sleep(1);

long tid = 0;

//printf(“Hello World! It’s me, thread #%ld!\n”, tid);

//pthread_exit(NULL);

}

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

{

pthread_t pid;

int rc;

long t;

while (1) {

printf(“In main: creating thread %ld\n”, t);

rc = pthread_create(&pid, NULL, PrintHello, NULL);

if (rc){

printf(“ERROR; return code from pthread_create() is %d\n”, rc);

//exit(-1);

}

sleep(1);

}

printf(” \n— main End —- \n”);

pthread_exit(NULL);

}

2. 在创建线程的设置PTHREAD_CREATE_DETACHED属性

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

void *PrintHello(void)

{

int stack[1024 * 20] = {0,};

//pthread_exit(NULL);

//pthread_detach(pthread_self());

}

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

{

pthread_t pid;

int rc;

long t;

while (1) {

printf(“In main: creating thread %ld\n”, t);

pthread_attr_t attr;

pthread_t thread;

pthread_attr_init (&attr);

pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);

rc = pthread_create(&pid, &attr, PrintHello, NULL);

pthread_attr_destroy (&attr);

if (rc){

printf(“ERROR; return code from pthread_create() is %d\n”, rc);

//exit(-1);

}

sleep(1);

}

printf(” \n— main End —- \n”);

pthread_exit(NULL);

}

3. 创建线程后用 pthread_join() 一直等待子线程结束。

 

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

void *PrintHello(void)

{

int stack[1024 * 20] = {0,};

//sleep(1);

long tid = 0;

//pthread_exit(NULL);

//pthread_detach(pthread_self());

}

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

{

pthread_t pid;

int rc;

long t;

while (1) {

printf(“In main: creating thread %ld\n”, t);

rc = pthread_create(&pid, NULL, PrintHello, NULL);

if (rc){

printf(“ERROR; return code from pthread_create() is %d\n”, rc);

//exit(-1);

}

pthread_join(pid, NULL);

sleep(1);

}

printf(” \n— main End —- \n”);

pthread_exit(NULL);

}