linux 线程属性控制

本节主要讲 pthread_create 函数的第二个参数——线程的属性。之前设为 NULL，也就是采用默认属性。现在讲一下修改线程属性的方法。

这些属性主要包括绑定属性、分离属性、堆栈地址、堆栈大小、优先级。其中系统默认的属性为非绑定、非分离、缺省1M 的堆栈、与父进程同样级别的优先级。

具体属性的含义请参考手册，本文只讲如何使用这些函数。其实挺简单的，

跟普通的线程调用只需多加三步：

1、调用pthread_attr_init初始化线程属性。

2、调用相应的设置属性的函数，如下文用到的pthread_attr_setschedparam设置线程优先级。

3、然后将pthread_create的第二个参数传进去。

来看看设置线程属性的一些相关函数：

pthread_attr_init函数：

#include <pthread.h>
int pthread_attr_init(pthread_attr_t *attr)

返回值：若成功，返回0；若出错，返回-1

参数：

attr：线程属性

pthread_attr_setscope函数：

#include <pthread.h>
int pthread_attr_setscope(pthread_attr_t *attr, int scope)

返回值：若成功，返回0；若出错，返回-1

参数：

attr：线程属性

scope

PTHREAD_SCOPE_SYSTEM：绑定

PTHREAD_SCOPE_PROCESS：非绑定

pthread_attr_setdetachstate函数：

#include <pthread.h>
int pthread_attr_setscope(pthread_attr_t *attr, int detachstate)

返回值：若成功，返回0；若出错，返回-1

参数：

attr：线程属性

detachstate：

PTHREAD_CREATE_DETACHED：分离

PTHREAD _CREATE_JOINABLE：非分离

pthread_attr_getschedparam函数：

#include <pthread.h>
int pthread_attr_getschedparam (pthread_attr_t *attr, struct sched_param *param)

返回值：若成功，返回0；若出错，返回-1

参数：

attr：线程属性

param：线程优先级

pthread_attr_setschedparam函数：

#include <pthread.h>
int pthread_attr_setschedparam (pthread_attr_t *attr, struct sched_param *param)

返回值：若成功，返回0；若出错，返回-1

参数：

attr：线程属性

param：线程优先级

示例程序：

主要看看线程属性是如何使用的。

/* pthread_attr_control.c*/

#include <stdio.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <semaphore.h>
#include <sched.h>
#include <assert.h>

sem_t sem;
static int count = 0 ;
#define FILENAME "pthread_attr_control_file"
/*线程一*/
void thread1(void * arg)
{
char write_buf[] = "1";
int fd = *(int *)arg;
printf("this is pthread1,fd = %d\n",fd);
int i = 0;
while(1)
{
/*信号量减一，P 操作*/
sem_wait(&sem);
for(i = 0;i<5;i++)
{
if (write(fd,write_buf,sizeof(write_buf)))
{
perror("write");
}
count++;
}
printf("This is a pthread1....and count = %d\n",count);
/*信号量加一，V 操作*/
sem_post(&sem);
sleep(2);
}
}
/*线程二*/
void thread2(void * arg)
{
char write_buf[] = "2";
int fd = *(int *)arg;
printf("this is pthread2 and fd = %d\n",fd);
int i = 0;
while(1)
{
/*信号量减一，P 操作*/
sem_wait(&sem);
for(i = 0;i<5;i++)
{
if (write(fd,write_buf,sizeof(write_buf)))
{
perror("write");
}
count++;
}

printf("This is a pthread2.... count = %d\n",count);
/*信号量加一，V 操作*/
sem_post(&sem);
sleep(2);
}
}

static int api_get_thread_policy (pthread_attr_t *attr)
{
int policy;
int rs = pthread_attr_getschedpolicy (attr, &policy);
assert (rs == 0);

switch (policy)
{
case SCHED_FIFO:
printf ("policy = SCHED_FIFO\n");
break;
case SCHED_RR:
printf ("policy = SCHED_RR");
break;
case SCHED_OTHER:
printf ("policy = SCHED_OTHER\n");
break;
default:
printf ("policy = UNKNOWN\n");
break;
}
return policy;
}
int main(void)
{
int fd = open(FILENAME,O_RDWR | O_CREAT,0777);
if(fd < 0)
{
perror("open");
}
printf("open success!\n");
int i,ret;
/*初始化信号量为 1*/
ret=sem_init(&sem,0,1);
if(ret!=0)
{
perror("sem_init");
}

pthread_t id1,id2;
pthread_attr_t attr;
//获取线程调度优先级
struct sched_param param;
int rs = pthread_attr_getschedparam (&attr, ¶m);
assert (rs == 0);
printf ("current priority = %d\n", param.__sched_priority);

/* 获得当前调度策略 */
int policy = api_get_thread_policy (&attr);

int priority_max = sched_get_priority_max (policy);
assert (priority_max != -1);
printf ("max_priority = %d\n", priority_max);

int priority_min = sched_get_priority_min (policy);
assert (priority_min != -1);
printf ("min_priority = %d\n", priority_min);
int priority = priority_min + 1;
printf("the priority of pthread1 is %d",priority);
/*初始化线程属性*/
pthread_attr_init(&attr);
//设置线程一优先级
rs = pthread_attr_setschedpolicy (&attr, priority);
assert (rs == 0);

//  rs = pthread_attr_getschedparam (&attr, ¶m);
//  assert (rs == 0);
//  printf ("show show ------priority = %d\n", param.__sched_priority);

/*创建线程一*/
ret=pthread_create(&id1,&attr,(void *) thread1,&fd);
if(ret!=0){
perror("Create pthread error!\n");
}
//设置线程二优先级
priority = priority_min;
printf("the priority of pthread1 is %d",priority);
rs = pthread_attr_setschedpolicy (&attr, priority);
assert (rs == 0);
/*创建线程二*/
ret=pthread_create(&id2,&attr,(void *) thread2,&fd);
if(ret!=0){
perror ("Create pthread error!\n");
}

/*等待线程结束*/
pthread_join(id1,NULL);
pthread_join(id2,NULL);
return 0;
}

实验结果：

ubuntu:~/test/pthread_test$ gcc pthread_attr_control.c -o pthread_attr_control -lpthread
ubuntu:~/test/pthread_test$ ./pthread_attr_control
open success!
current priority = 0
policy = SCHED_OTHER
max_priority = 0
min_priority = 0
the priority of pthread1 is 1the priority of pthread1 is 0this is pthread2 and fd = 3
this is pthread1,fd = 3
write: Success
write: Success
write: Success
write: Success
write: Success
This is a pthread2.... count = 5
write: Success
write: Success
write: Success
write: Success
write: Success
This is a pthread1....and count = 10
write: Success
write: Success
write: Success
write: Success
write: Success
This is a pthread2.... count = 15
write: Success
write: Success
write: Success
write: Success
write: Success
This is a pthread1....and count = 20