linux多进/线程编程(7)——多线程1(线程的创建,回收,分离,设置线程属性等)
2024-08-28 23:55:21
参考资料:
1.博客1:https://blog.csdn.net/zhou1021jian/article/details/71531699
2.博客2:https://blog.csdn.net/weixin_40039738/article/details/81145247
本文主要介绍下面函数的用法和代码示例
pthread_create 创建线程
pthread_exit 终止线程
pthread_join 回收进程
pthread_detach 线程分离
pthread_attr_setdetachstate 设置线程属性
注意:在linux下查看线程相关的方法时,man 出来可以非常多,所以要想查阅资料搞清楚到底需要啥
pthread_create 创建线程
函数原型:
#include <pthread.h> int pthread_create(pthread_t *thread, const pthread_attr_t *attr,void *(*start_routine) (void *), void *arg);
创建出的新线程退出的可能情况:
* It calls pthread_exit(3), specifying an exit status value that is available to another thread in the same process that calls pthread_join(3). * It returns from start_routine(). This is equivalent to calling pthread_exit(3) with the value supplied in the return statement. * It is canceled (see pthread_cancel(3)). * Any of the threads in the process calls exit(3), or the main thread performs a return from main().
简言之就是以下几种可能:
1.执行新线程的函数“走完了”;
2.新线程本身或者与之join的线程执行“终止线程”的方法pthread_exit;
3.取消创建该线程pthread_cancel;
4.其他线程执行推出exit,或者主线程return弹(函数)栈
pthread_exit 终止进程
终止调用它的线程并返回一个指向某个对象的指针。
创建进程 代码示例:
#include <stdio.h>
#include <unistd.h>
#include <pthread.h> void* thr(void* arg) {
printf("i am a thread! pid = %d, tid = %ld\n", getpid(), pthread_self());
//pthread_exit((void*)100);
// return nullptr;
} int main(int argc, char* argv[]) {
/*
* int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
*/ pthread_t tid { 0 };
pthread_create(&tid, nullptr, thr, nullptr);
printf("i am a main thread! pid = %d, tid = %ld\n", getpid(), pthread_self()); //sleep(1);
/*1. 如果添加pthread_exit()在主线程,则主线程马上退出,不在执行主线程下面的程序,但是主线程中启动的其他线程继续执行,程序不会马上退出,等待子线程执行完毕退出。
2. 如果不添加,主线程不等待子线程执行完毕,程序直接退出,子线程可能没有执行完毕。*/
pthread_exit(nullptr); //return 0;// no use, never exec
}
线程joinable
上面的代码中子线程创建成功依赖于,主线程要么是推出的很慢(有耗时操作)来保证一定会创建子线程,要么是加上pthread_exit,我们往往不想这么做,因此介绍
pthread_join
pthread_join
函数原型:
#include <pthread.h> int pthread_join(pthread_t thread, void **retval);
描述:
The pthread_join() function waits for the thread specified by thread to terminate. wait()方法用来回收进程,是阻塞的,类比,pthread_join也是阻塞的,直至指定的进程终止才会执行后面的代码。 If that thread has already terminated, then pthread_join() returns immediately. The thread specified by thread must be joinable.
代码示例:
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <stdlib.h> void* thr(void* arg) {
printf("i am a thread! pid = %d, tid = %ld\n", getpid(), pthread_self());
sleep(3);
pthread_exit((void*)1004);
// return (void*)100;
} int main(int argc, char* argv[]) {
/*
* int pthread_join(pthread_t thread, void **retval);
*/
pthread_t tid { 0 };
pthread_create(&tid, nullptr, thr, nullptr);
printf("i am a main thread! pid = %d, tid = %ld\n", getpid(), pthread_self()); void* ret = nullptr;
pthread_join(tid, &ret);//回收子线程,pthread_join会阻塞,直到子线程退出
printf("ret exit with %ld\n", (long)ret); //sleep(1);
/*
* 此处主线程加pthread_exit仅用来回收主线程,不影响子线程创建,因为pthread_join的作用*/
pthread_exit(nullptr); //return 0; no use there
}
线程detached
线程默认属性就是joinable,依赖于创建该线程的“父线程”(其实线程之间不存在父子关系),但是可以修改线程属性。
修改方法有两种,1是使用函数pthread_detach,2是设置属性pthread_attr_setdetachstate。
当线程被分离(detached)后,这个线程的回收就交给操作系统,就不是用户可以控制的了。
pthread_detach
函数原型:
#include <pthread.h> int pthread_detach(pthread_t thread);
描述:
The pthread_detach() function marks the thread identified by thread as detached.
When a detached thread terminates, its resources are automatically released back to the system without the
need for another thread to join with the terminated thread.
pthread_attr_setdetachstate
函数原型:
#include <pthread.h> int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);
int pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detachstate);
描述:
The pthread_attr_setdetachstate() function sets the detach state attribute of the thread attributes object referred to by attr to the value specified in detachstate.
The detach state attribute determines whether a thread created using the thread attributes object attr will be created in a joinable or a detached state.
The following values may be specified in detachstate: PTHREAD_CREATE_DETACHED
Threads that are created using attr will be created in a detached state. PTHREAD_CREATE_JOINABLE
Threads that are created using attr will be created in a joinable state. The default setting of the detach state attribute in a newly initialized thread attributes object is PTHREAD_CREATE_JOINABLE.(默认是joinable,可以设置为detached) The pthread_attr_getdetachstate() returns the detach state attribute of the thread attributes object attr in the buffer pointed to by detachstate.
代码示例:
#include <stdio.h>
#include <pthread.h>
#include <string.h> void * thr(void * arg) {
printf("i am child thread \n");
return nullptr;
} int main(int argc, char* argv[]) { pthread_attr_t attr;
pthread_attr_init(&attr);
/*
* 当设置为PTHREAD_CREATE_JOINABLE时,下面可以用pthread_join回收,但是如果设置为PTHREAD_CREATE_DETACHED则不可以
* */
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); pthread_t tid {0};
pthread_create(&tid, &attr, thr, nullptr); int ret = 0;
if ((ret = pthread_join(tid, nullptr)) > 0) {
//printf("join err:%ld, %s\n", (long)ret, strerror((long)ret));
printf("join err:%d, %s\n", ret, strerror(ret));
} pthread_attr_destroy(&attr); return 0;
}
其他代码:
#include <stdio.h>
#include <unistd.h>
#include <pthread.h> void * thr(void * arg) { // malloc();
printf("i am child thread, tid = %ld, arg = %ld\n", pthread_self(), (long)arg);
//return nullptr;
return (void *)(100 + (long)arg);
} int main(int argc, char* argv[]) { pthread_t tid[5]; int length = sizeof(tid) / sizeof(pthread_t); printf("**********************length = %d\n", length); for (long i = 0; i < length; ++i) {
/* (void*)i :
* 这里不能这样写,最好是先在堆区创建,再传进去,用完了在外面释放,这样保证数据没问题。
* 如果直接传地址,可能在创建子线程的过程中,数据发生了变化(指向的地址也变了),这样传参不稳定,有问题。
* */
pthread_create(&tid[i], nullptr, thr, (void*)i);
} for (int i = 0; i < length; ++i) {
void* ret = nullptr;
pthread_join(tid[i], &ret);
printf("i == %d, ret == %ld\n", i, (long)ret);
} return 0;
}
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