線程回收

pthread_join函數

阻塞等待線程退出，獲取線程退出狀態????????? 其作用，對應進程中 waitpid() 函數。

?????? int pthread_join(pthread_t thread, void **retval); 成功：0；失敗：錯誤號

?????? 參數：thread：線程ID （【注意】：不是指針）；retval：存儲線程結束狀態。

?????? 對比記憶：

????????????? 進程中：main返回值、exit參數-->int；等待子進程結束 wait 函數參數-->int *

????????????? 線程中：線程主函數返回值、pthread_exit-->void *；等待線程結束 pthread_join 函數參數-->void **

【練習】：參數 retval 非空用法。??????????????????????????????????????????????????????????????????????????????? ?????? 【pthrd_exit_join.c】

調用該函數的線程將掛起等待，直到id為thread的線程終止。thread線程以不同的方法終止，通過pthread_join得到的終止狀態是不同的，總結如下：

1. 如果thread線程通過return返回，retval所指向的單元里存放的是thread線程函數的返回值。
2. 如果thread線程被別的線程調用pthread_cancel異常終止掉，retval所指向的單元里存放的是常數PTHREAD_CANCELED。
3. 如果thread線程是自己調用pthread_exit終止的，retval所指向的單元存放的是傳給pthread_exit的參數。
4. 如果對thread線程的終止狀態不感興趣，可以傳NULL給retval參數。

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【練習】：使用pthread_join函數將循環創建的多個子線程回收。? ? ? ? ? ??

/***
thread_join.c
***/
#include<stdio.h>
#include<error.h>
#include<string.h>
#include<unistd.h>
#include<stdlib.h>
#include<pthread.h>typedef struct 
{char ch;int var;char str[64];
}exit_t;void *thrd_func(void *arg)
{pthread_exit((void *)1);
}int main()
{pthread_t tid;int ret;int *retval;printf("In main 1 : thread id = %lu, pid = %u\n",pthread_self(),getpid());ret = pthread_create(&tid,NULL,thrd_func,NULL);if(0 != ret){fprintf(stderr,"pthread_create error : %s \n",strerror(ret));exit(1);}pthread_join(tid,(void **)&retval);printf("--------------%d\n",(int)retval);pthread_exit((void*)1);
}

運行結果：

ubuntu1604@ubuntu:~/wangqinghe/linux/20190819$ ./thread_join

In main 1 : thread id = 139721544345344, pid = 12974

--------------1

/***
pthread_join_struct.c
***/
#include<stdio.h>
#include<error.h>
#include<string.h>
#include<unistd.h>
#include<stdlib.h>
#include<pthread.h>typedef struct 
{char ch;int var;char str[64];
}exit_t;void *thrd_func(void *arg)
{exit_t *retvar = (exit_t *)malloc(sizeof(exit_t));retvar->ch = 'm';retvar->var = 200;strcpy(retvar->str,"my thread\n");pthread_exit((exit_t *)retvar);
}int main()
{pthread_t tid;int ret;exit_t *retval;printf("In main 1 : thread id = %lu, pid = %u\n",pthread_self(),getpid());ret = pthread_create(&tid,NULL,thrd_func,NULL);if(0 != ret){fprintf(stderr,"pthread_create error : %s \n",strerror(ret));exit(1);}pthread_join(tid,(void **)&retval);printf("ch = %c,var = %d,str = %s\n--------------%d\n",retval->ch,retval->var,retval->str);free(retval);pthread_exit((void*)1);
}

運行結果：

ubuntu1604@ubuntu:~/wangqinghe/linux/20190819$ ./thread_join

In main 1 : thread id = 140316487100160, pid = 13121

ch = m,var = 200,str = my thread

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--------------202

/***
thread_join_loop.c
***/
#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<pthread.h>int var = 100;void *tfn(void *arg)
{int i;i = (int)arg;sleep(i);if(1 == i){var = 333;printf("var = %d\n",var);return (void*)var;}else if( 3 == i){var = 888;printf("i'm %dth pthread,pthread id = %lu ,var = %d\n",i+1,pthread_self(),var);pthread_exit((void*)var);}else{printf("i'm %dth pthread,pthread id = %lu ,var = %d\n",i+1,pthread_self(),var);pthread_exit((void*)var);        }return NULL;    
}int main()
{pthread_t tid[5];int i;int *ret[5];for(i = 0; i < 5; i++){pthread_create(&tid[i],NULL,tfn,(void*)i);}for(i = 0; i < 5; i++){pthread_join(tid[i],(void**)&ret[i]);printf("-----------%d's ret = %d\n",(int)ret[i]);}printf("I'm main pthread tid = %lu var = %d\n",pthread_self(),var);sleep(i);return 0;
}

運行結果：

ubuntu1604@ubuntu:~/wangqinghe/linux/20190819$ ./thread_loop

i'm 1th pthread,pthread id = 139809124009728 ,var = 100

-----------100's ret = -645238160

var = 333

-----------333's ret = -651408960

i'm 3th pthread,pthread id = 139809107224320 ,var = 333

-----------333's ret = -659801664

i'm 4th pthread,pthread id = 139809098831616 ,var = 888

-----------888's ret = -668194368

i'm 5th pthread,pthread id = 139809090438912 ,var = 888

-----------888's ret = 0

I'm main pthread tid = 139809132349184 var = 888

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