一、建立分離執行緒

有兩種方式建立分離執行緒：

（1）線上程建立時將其屬性設為分離狀態(detached)；

（2）線上程建立後將其屬性設為分離的(detached)。

二、分離執行緒的作用

由系統來回收執行緒所佔用資源。

三、例項

#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>
#include <sys/types.h>
#include <dirent.h>
#include <pthread.h>
#include <errno.h>
#include <signal.h>
#include <time.h>

void* thread1(void *arg)
{
    while (1)
    {
        usleep(100 * 1000);
        printf("thread1 running...!\n");
    }
    printf("Leave thread1!\n");

    return NULL;
}

int main(int argc, char** argv)
{
    pthread_t tid;

    pthread_create(&tid, NULL, (void*)thread1, NULL);
    pthread_detach(tid);  // 使執行緒處於分離狀態
    sleep(1);
    printf("Leave main thread!\n");
    pthread_exit("end"); //這個地方執行後，子程序並沒有退出
//    return 0; //return後，系統會呼叫_exit

，所有程序都會退出。
}

#gcc a.c -lpthread

#./a.out
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
Leave main thread!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!

可以看出main執行緒退出後，thread_1並沒有退出。

$ cat a.c
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>
#include <sys/types.h>
#include <dirent.h>
#include <pthread.h>
#include <errno.h>
#include <signal.h>
#include <time.h>

void* thread1(void *arg)
{
    while (1)
    {
        usleep(100 * 1000);
        printf("thread1 running...!\n");
    }
    printf("Leave thread1!\n");

    return NULL;
}

int main(int argc, char** argv)
{
    pthread_t tid;

    pthread_create(&tid, NULL, (void*)thread1, NULL);
    pthread_detach(tid);  // 使執行緒處於分離狀態
    sleep(1);
    printf("Leave main thread!\n");
    return 0;
}

$ ./a.out
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
Leave main thread!

可以看出main執行緒return後，子執行緒也退出了。

如果把pthread_deteach改為pthread_join，因為子執行緒是while(1）所有主執行緒也不會退出。

[email protected]:~/work/mt8516-p1v2/build/tmp/deploy/images/aud8516p1v2-slc-bluez$ cat a.c
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>
#include <sys/types.h>
#include <dirent.h>
#include <pthread.h>
#include <errno.h>
#include <signal.h>
#include <time.h>

void* thread1(void *arg)
{
    while (1)
    {
        usleep(100 * 1000);
        printf("thread1 running...!\n");
    }
    printf("Leave thread1!\n");

    return NULL;
}

int main(int argc, char** argv)
{
    pthread_t tid;

    pthread_create(&tid, NULL, (void*)thread1, NULL);
    //pthread_detach(tid);  // 使執行緒處於分離狀態
    pthread_join(tid,NULL);  // 使執行緒處於分離狀態
    sleep(1);
    printf("Leave main thread!\n");
    return 0;
}

[email protected]:~/work/mt8516-p1v2/build/tmp/deploy/images/aud8516p1v2-slc-bluez$ ./a.out
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!
thread1 running...!

^

這可以在main中使用pthread_cancel，明確退出子執行緒。