執行緒優先順序的設定pthread_setschedparam
阿新 • • 發佈:2019-02-19
參考:
在linux下我們可以通過
#include <iostream>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_max
和sched_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 <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, ¶m );
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;
}