linux下设置线程优先级
2009-09-11 21:21
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在linux下我们可以通过
int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void*), void *arg); 来创建线程,但是如何设置线程的优先级呢? 在讨论这个问题的时候,我们先要确定当前线程使用的调度策略,posix提供了
int pthread_attr_getschedpolicy(const pthread_attr_t *attr, int *policy);函数来获取所 使用的调度策略,它们是:SCHED_FIFO, SCHED_RR 和 SCHED_OTHER。我们可以使用
int sched_get_priority_max(int policy); int sched_get_priority_min(int policy); 来获取线程线程可是设置的最大和最小的优先级值,如果调用成功就返回最大和最小的优先级值,否则返回-1。 从我现在运行的linux系统中,我使用下列程序获取了对应三种调度策略中的最大和最小优先级: 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 我们可以看到
SCHED_OTHER是不支持优先级使用的,而
SCHED_FIFO和SCHED_RR支持优先级的使用,他们分别为1和99, 数值越大优先级越高。 从上面的结果我们可以看出,如果程序控制线程的优先级,一般是用
pthread_attr_getschedpolicy来获取系统使用的调度策略,如果是SCHED_OTHER的话,表明当前策略 不支持线程优先级的使用,否则可以。当然所设定的优先级范围必须在最大和最小值之间。我们可以通过
sched_get_priority_max和
sched_get_priority_min来获取。 可能网友会问,是否我们可以通过
int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);来设定自己所需的 调度策略呢?我觉得是完全可以的(有些系统需要定义_POSIX_THREAD_PRIORITY_SCHEDULING),只要系统实现了对应的调用策略。说了半天,我们还没有说,在系统允许使用线程优先级别的时候,如何设置优先级别呢?
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);上面两个函数分别用于设置线程的优先级,struct sched_param的定义如下struct sched_param{int __sched_priority; //所要设定的线程优先级};
使用的测试程序:#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, ¶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;}
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