1. 程式人生 > >執行緒優先順序的設定pthread_setschedparam

執行緒優先順序的設定pthread_setschedparam

參考:

在linux下我們可以通過

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
    void *(*start_routine)(void*), void *arg);
來建立執行緒,但是如何設定執行緒的優先順序呢?
在討論這個問題的時候,我們先要確定當前執行緒使用的排程策略,posix提供了
int pthread_attr_getschedpolicy(const pthread_attr_t *attr, int *policy);函式來獲取所
使用的排程策略,它們是:SCHED_FIFO, SCHED_RR 和 SCHED_OTHER。
我們可以使用
int sched_get_priority_max(int policy);
int sched_get_priority_min(int policy);
來獲取執行緒執行緒可是設定的最大和最小的優先順序值,如果呼叫成功就返回最大和最小的優先順序值,否則返回-1。
從我現在執行的linux系統中,我使用下列程式獲取了對應三種排程策略中的最大和最小優先順序:
policy = SCHED_OTHER
Show current configuration of priority
max_priority = 0
min_priority = 0
Show SCHED_FIFO of priority
max_priority = 99
min_priority = 1
Show SCHED_RR of priority
max_priority = 99
min_priority = 1
Show priority of current thread
priority = 0
Set thread policy
Set SCHED_FIFO policy
policy = SCHED_FIFO
Set SCHED_RR policy
policy = SCHED_RR
Restore current policy
policy = SCHED_OTHER

我們可以看到
SCHED_OTHER是不支援優先順序使用的,而SCHED_FIFO和SCHED_RR支援優先順序的使用,他們分別為1和99, 數值越大優先順序越高。 從上面的結果我們可以看出,如果程式控制執行緒的優先順序,一般是用 pthread_attr_getschedpolicy來獲取系統使用的排程策略,如果是SCHED_OTHER的話,表明當前策略 不支援執行緒優先順序的使用,否則可以。當然所設定的優先順序範圍必須在最大和最小值之間。我們可以通過 sched_get_priority_maxsched_get_priority_min來獲取。 可能網友會問,是否我們可以通過 int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);來設定自己所需的 排程策略呢?我覺得是完全可以的(有些系統需要定義
_POSIX_THREAD_PRIORITY_SCHEDULING),只要 系統實現了對應的呼叫策略。 說了半天,我們還沒有說,在系統允許使用執行緒優先級別的時候,如何設定優先級別呢? 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); 上面兩個函式分別用於設定執行緒的優先順序,struct sched_param的定義如下 struct sched_param { int __sched_priority; //所要設定的執行緒優先順序 }; 使用的測試程式:
#include <iostream>
#include <pthread.h>
#include <sched.h>
#include <assert.h>
using namespace std;
static int get_thread_policy( pthread_attr_t &attr )
{
        int policy;
        int rs = pthread_attr_getschedpolicy( &attr, &policy );
        assert( rs == 0 );
        switch ( policy )
        {
        case SCHED_FIFO:
                cout << "policy = SCHED_FIFO" << endl;
                break;
        case SCHED_RR:
                cout << "policy = SCHED_RR" << endl;
                break;
        case SCHED_OTHER:
                cout << "policy = SCHED_OTHER" << endl;
                break;
        default:
                cout << "policy = UNKNOWN" << endl;
                break;
        }
        return policy;
}

static void show_thread_priority( pthread_attr_t &attr, int policy )
{
        int priority = sched_get_priority_max( policy );
        assert( priority != -1 );
        cout << "max_priority = " << priority << endl;
        priority = sched_get_priority_min( policy );
        assert( priority != -1 );
        cout << "min_priority = " << priority << endl;
}

static int get_thread_priority( pthread_attr_t &attr )
{
        struct sched_param param;
        int rs = pthread_attr_getschedparam( &attr, &param );
        assert( rs == 0 );
        cout << "priority = " << param.__sched_priority << endl;
        return param.__sched_priority;
}

static void set_thread_policy( pthread_attr_t &attr,  int policy )
{
        int rs = pthread_attr_setschedpolicy( &attr, policy );
        assert( rs == 0 );
        get_thread_policy( attr );
}

int main( void )
{
        pthread_attr_t attr;
        struct sched_param sched;
        int rs;
        rs = pthread_attr_init( &attr );
        assert( rs == 0 );
        int policy = get_thread_policy( attr );
        cout << "Show current configuration of priority" << endl;
        show_thread_priority( attr, policy );
        cout << "Show SCHED_FIFO of priority" << endl;
        show_thread_priority( attr, SCHED_FIFO );

        cout << "Show SCHED_RR of priority" << endl;
        show_thread_priority( attr, SCHED_RR );

        cout << "Show priority of current thread" << endl;
        int priority = get_thread_priority( attr );

        cout << "Set thread policy" << endl;
        cout << "Set SCHED_FIFO policy" << endl;
        set_thread_policy( attr, SCHED_FIFO );
        cout << "Set SCHED_RR policy" << endl;
        set_thread_policy( attr, SCHED_RR );
        cout << "Restore current policy" << endl;
        set_thread_policy( attr, policy );


        rs = pthread_attr_destroy( &attr );
        assert( rs == 0 );

        return 0;
}