thread 线程属性 脱离线程

thread 线程属性 脱离线程

线程的属性

脱离线程:不向主线程返回信息,不需要主线程等待.
通过两种方法创建:
调用pthread_detach;
修改线程的属性. <- 这里使用

#include <pthread.h>
int pthread_attr_init(pthread_attr_t *attr);
初始化一个线程属性对象.
pthread_destroy
回收一个线程属性对象.

#include <pthread.h>
int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);
int pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detachstate);
这个属性允许我们无需对线程进行合并:
| PTHREAD_CREATE_JOINABLE 默认.
| PTHREAD_CREATE_DETACHED 不能调用pthread_join来获得另一个线程的退出状态.

int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
int pthread_attr_getschedpolicy(const pthread_attr_t *attr, int *policy);
控制线程的调度方式:
| SCHED_OTHER 默认
| SCHED_RP   循环(round_robin) <- 下面2个调度方式具备实时调度功能,需要root权限.
| SCHED_FIFO 先进先出

int pthread_attr_setschedparam(pthread_attr_t *attr, const struct sched_param *param);
int pthread_attr_getschedparam(const pthread_attr_t *attr, struct sched_param *param);
和schedpolicy配合使用,控制SCHED_OTHER线程的调度策略.

int pthread_attr_setinheritsched(pthread_attr_t *attr, int inherit);
int pthread_attr_getinheritsched(const pthread_attr_t *attr, int *inherit);
| PTHREAD_EXPLICIT_SCHED 调度由属性明确设置.
| PTHREAD_INHERIT_SCHED  新线程沿用创建者的属性.

int pthread_attr_setscope(pthread_attr_t *attr, int scope);
int pthread_attr_getscope(const pthread_attr_t *attr, int *scope);
控制一个线程调度的计算方式,目前Linux只支持PTHREAD_SCOPE_SYSTEM.

int pthread_attr_setstacksize(pthread_attr_t *attr, int scope);
int pthread_attr_getstacksize(const pthread_attr_t *attr, int *scope);
控制线程创建的栈大小,单位字节.可选.
Linux在实现线程时,默认的栈很大,这个属性有点多余.

创建脱离线程:

/*
 * 线程属性-创建脱离线程
 * 主线程不等待子线程结束,只通过thread_finished标志来检测子线程是否已结束,并显示线程之间仍然共享的变量.
  */
#include  < stdio.h >
#include  < unistd.h >
#include  < stdlib.h >
#include  < pthread.h >

void   * thread_function( void   * arg);

char  g_message[]  =   " Hello World! " ;
int  g_thread_finished  =   0 ;

int  main(){
     int  res;
    pthread_t a_thread;
    pthread_attr_t thread_attr;

    res  =  pthread_attr_init( & thread_attr);
     if (res  !=   0 ){
        perror( " Attribute creation failed " );
        exit(EXIT_FAILURE);
    }

    res  =  pthread_attr_setdetachstate( & thread_attr, PTHREAD_CREATE_DETACHED);
     if (res  !=   0 ){
        perror( " Setting detached attribute failed " );
        exit(EXIT_FAILURE);
    }

    res  =  pthread_create( & a_thread,  & thread_attr,
            thread_function, ( void   * )g_message);
     if (res  !=   0 ){
        perror( " Thread creation failed " );
        exit(EXIT_FAILURE);
    }

    ( void )pthread_attr_destroy( & thread_attr);
     while ( ! g_thread_finished){
        printf( " Waiting for thread to say it's finished\n " );
        sleep( 1 );
    }
    printf( " Other thread finished, bye!\n " );
    exit(EXIT_SUCCESS);
}

void   * thread_function( void   * arg){
    printf( " thread_function is running. Argument was %s\n " , ( char   * )arg);
    sleep( 4 );
    printf( " Second thread setting finished flag, and exit now\n " );
    g_thread_finished  =   1 ;
    pthread_exit(NULL);
}

执行结果:

$ gcc  - D_REENTRANT thread5.c  - o thread5  - lpthread  
$ . / thread5 
Waiting  for  thread to say it ' s finished
thread_function  is  running. Argument was Hello World !
Waiting  for  thread to say it ' s finished
Waiting  for  thread to say it ' s finished
Waiting  for  thread to say it ' s finished
Second thread setting finished flag, and exit now
Other thread finished, bye !

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FROM: Linux程序设计