基础知识
- Linux 内核当中有 3 种调度策略：
- SCHED_OTHER 分时调度策略；
- SCHED_FIFO 实时调度策略，先到先服务；
- SCHED_RR 实时调度策略，时间片轮转。
如果有相同优先级的实时进程（根据优先级计算的调度权值是一样的）已经准备好，FIFO 时必须等待该进程主动放弃之后才可以运行这个优先级相同的任务。而 RR 可以每个任务都执行一段时间。
- 获取线程设置的最高和最低优先级函数
- int sched_get_priority_max(int policy)获取实时优先级的最大值；
- int sched_get_priority_min(int policy)获取实时优先级的最小值；
SCHED_OTHER它 不 支 持 优 先 级 使 用 ， 而SCHED_RR/SCHED_FIFO 支持优先级使用，它们分别为 1-99，数值越大优先级越高。
实时调度策略（SCHED_FIFO/SCHED_RR）优先级最大值为99；普通调度策略
（SCHED_NORMAL/SCHED_BATCH/SCHED_IDLE），始终返回0，即普通任务调度的函数。
- 设置和获取优先级的2个主要核心参数
- int pthread_attr_setschedparam(pthread_attr_t* attr, const struct sched_param* param);设置线程优先级；
- int pthread_attr_getschedparam(pthread_attr_t* attr, const struct sched_param* param)；获取线程优先级；
struct sched_param { int __sched_priority; // 所有设定的线程优先级 } param.sched_priority = 11; // 设置优先级
- 当操作系统创建线程时，默认线程是 SCHED_OTHER，我们也可以通过改变调度策略，使用如下函数：
- int pthread_attr_setschedpolicy(pthread_attr_t* attr, int policy);设置线程调度策略；
基础案例分析
- 操作系统所支持优先级测试程序分析：
#include <stdio.h> #include <pthread.h> #include <sched.h> #include <assert.h> static int GetThreadPolicyFunc(pthread_attr_t *pAttr) { int iPlicy; int igp=pthread_attr_getschedpolicy(pAttr,&iPlicy); assert(igp==0); switch (iPlicy) { case SCHED_FIFO: printf("Policy is --> SCHED_FIFO.\n"); break; case SCHED_RR: printf("Policy is --> SCHED_RR.\n"); break; case SCHED_OTHER: printf("Policy is --> SCHED_OTHER.\n"); break; default: printf("Policy is --> Unknown.\n"); break; } return iPlicy; } static void PrintThreadPriorityFunc(pthread_attr_t *pAttr,int iPolicy) { int iPriority=sched_get_priority_max(iPolicy); assert(iPriority!=-1); printf("Max_priority is : %d\n",iPriority); iPriority=sched_get_priority_min(iPolicy); assert(iPriority!=-1); printf("Min_priority is : %d\n",iPriority); } static int GetThreadPriorityFunc(pthread_attr_t *pAttr) { struct sched_param sParam; int irs=pthread_attr_getschedparam(pAttr,&sParam); assert(irs==0); printf("Priority=%d\n",sParam.__sched_priority); return sParam.__sched_priority; } static void SetThreadPolicyFunc(pthread_attr_t *pAttr,int iPolicy) { int irs=pthread_attr_setschedpolicy(pAttr,iPolicy); assert(irs==0); GetThreadPolicyFunc(pAttr); } int main(int argc,char *argv[]) { pthread_attr_t pAttr; struct sched_param sched; int irs=pthread_attr_init(&pAttr); assert(irs==0); int iPlicy=GetThreadPolicyFunc(&pAttr); printf("\nExport current Configuration of priority.\n"); PrintThreadPriorityFunc(&pAttr,iPlicy); printf("\nExport SCHED_FIFO of prioirty.\n"); PrintThreadPriorityFunc(&pAttr,SCHED_FIFO); printf("\nExport SCHED_RR of prioirty.\n"); PrintThreadPriorityFunc(&pAttr,SCHED_RR); printf("\nExport priority of current thread.\n"); int iPriority=GetThreadPriorityFunc(&pAttr); printf("Set thread policy.\n"); printf("\nSet SCHED_FIFO policy.\n"); SetThreadPolicyFunc(&pAttr,SCHED_FIFO); printf("\nSet SCHED_RR policy.\n"); SetThreadPolicyFunc(&pAttr,SCHED_RR); printf("\nRestore current policy.\n"); SetThreadPolicyFunc(&pAttr,iPlicy); irs=pthread_attr_destroy(&pAttr); assert(irs==0); return 0; }
- 简单线程调度策略，我们创建三个线程，默认创建的线程它的调度策略为SCHED_OTHER，另外两个线程调度策略为 SCHED_RR/FIFO：
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <pthread.h> void ThreadFunc1() { sleep(1); int i, j; int policy; struct sched_param param; pthread_getschedparam(pthread_self(), &policy, ¶m); switch (policy) { case SCHED_OTHER: printf("SCHED_OTHER\n"); break; case SCHED_FIFO: printf("SCHED_FIFO\n"); case SCHED_RR: printf("SCHED_RR Thread1\n"); default: break; } for(i = 1; i <= 5; i++){ for(j = 1; j <= 5000000; j++){} printf("Execute thread function 1.\n"); } printf("ThreadFunc1 Exit\n"); } void ThreadFunc2() { sleep(2); int policy; struct sched_param param; pthread_getschedparam(pthread_self(), &policy, ¶m); switch(policy) { case SCHED_OTHER: printf("SCHED_OTHER\n"); break; case SCHED_FIFO: printf("SCHED_FIFO\n"); break; case SCHED_RR: printf("SCHED_RR Thread2"); break; } for(int i = 1; i <= 6; i++){ for(int j = 1; j <= 6000000; j++){} printf("Execute thread function 2.\n"); } printf("ThreadFunc2 Exit\n"); } void ThreadFunc3() { sleep(3); int policy; struct sched_param param; pthread_getschedparam(pthread_self(), &policy, ¶m); switch(policy) { case SCHED_OTHER: printf("SCHED_OTHER\n"); break; case SCHED_FIFO: printf("SCHED_FIFO\n"); break; case SCHED_RR: printf("SCHED_RR\n"); break; } for(int i = 1; i <= 7; i++) { for(int j = 0; j <= 7000000; j++){} printf("Execute thread function 3.\n"); } printf("ThreadFunc3 Exit\n"); } int main(int argc, char* argv[]) { int i = 0; i = getuid(); if(i == 0) { printf("The current user is root.\n\n"); } else { printf("The current user is not root.\n\n"); } pthread_t pid1, pid2, pid3; struct sched_param param; pthread_attr_t attr1, attr2, attr3; pthread_attr_init(&attr1); pthread_attr_init(&attr2); pthread_attr_init(&attr3); param.sched_priority = 31; pthread_attr_setschedpolicy(&attr2, SCHED_RR); pthread_attr_setschedparam(&attr2, ¶m); pthread_attr_setinheritsched(&attr2, PTHREAD_EXPLICIT_SCHED); param.sched_priority = 11; pthread_attr_setschedpolicy(&attr1, SCHED_FIFO); pthread_attr_setschedparam(&attr1, ¶m); pthread_attr_setinheritsched(&attr1, PTHREAD_EXPLICIT_SCHED); pthread_create(&pid3, &attr3, (void*)ThreadFunc3, NULL); pthread_create(&pid2, &attr2, (void*)ThreadFunc2, NULL); pthread_create(&pid1, &attr1, (void*)ThreadFunc1, NULL); pthread_join(pid3, NULL); pthread_join(pid2, NULL); pthread_join(pid1, NULL); pthread_attr_destroy(&attr3); pthread_attr_destroy(&attr2); pthread_attr_destroy(&attr1); return 0; }
- 超级用户运行
