Thread recycling

pthread_join function

Quit waiting thread, the thread gets its role exit status, the corresponding process waitpid () function.

       int pthread_join (pthread_t thread, void ** retval); Success: 0; failed: No.

       Parameters: Thread: Thread ID ([Note]: not a pointer); retval: storing thread end state.

       Contrast Memory:

              Process: main return values, exit parameters -> int; wait for the child ended the wait function parameters -> int *

              Thread: thread main function return values, pthread_exit -> void *; waiting thread ends pthread_join function parameters -> void **

[Practice]: non-null parameters retval usage. [Pthrd_exit_join.c]

The function is called thread hangs wait until terminated as thread id thread. thread thread terminated in different ways, by terminating the state is different pthread_join obtained, summarized as follows:

1. If the thread through the thread return return retval unit pointed in the return value is stored in thread thread function.
2. If the thread is called a thread pthread_cancel another thread terminates abnormally out, retval unit is pointing in the store is constant PTHREAD_CANCELED.
3. If the thread is a thread calls himself pthread_exit terminated, retval pointed unit is stored in the parameters passed to pthread_exit.
4. If you are not interested in the state of thread to terminate the thread, you can pass NULL to retval parameter.

 

[Practice]: using multiple child threads pthread_join recovery function will cycle created.            

/***
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);
}

operation result:

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);
}

operation result:

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

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

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

 

--------------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;
}

operation result:

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

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

----------- 100's right = -645238160

was = 333

----------- 333's right = -651,408,960

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

----------- 333's right = -659,801,664

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

----------- 888 K = -668194368

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

----------- 888 K = 0

I'm main pthread tid = 139809132349184 var = 888