這兩天在看Pthread 資料的時候，無意中看到這樣一句話(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.)
也就是說：每個進程創建以后都應該調用pthread_join 或 pthread_detach 函數，只有這樣在線程結束的時候資源(線程的描述信息和stack)才能被釋放.
之后又查了pthread_join 但是沒有明確說明必須調用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.
才知道如果在新線程里面沒有調用pthread_join 或 pthread_detach會導致內存泄漏, 如果你創建的線程越多，你的內存利用率就會越高, 直到你再無法創建線程，最終只能結束進程。
解決方法有三個:
1. 線程里面調用 pthread_detach(pthread_self()) 這個方法最簡單
2. 在創建線程的設置PTHREAD_CREATE_DETACHED屬性
3. 創建線程后用 pthread_join() 一直等待子線程結束。
下面是幾個簡單的例子
1. 調用 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. 在創建線程的設置PTHREAD_CREATE_DETACHED屬性
#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. 創建線程后用 pthread_join() 一直等待子線程結束。
#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);
}