SCHED_FIFO线程被Linux中的SCHED_OTHER线程抢占

概述我已经编写了测试程序来测试SCHED_FIFO.我了解到SCHED_FIFO线程无法抢占SCHED_FIFO.但我无法解释同一个程序多次运行时获得的结果. /* Includes */#include <unistd.h> /* Symbolic Constants */#include <sys/types.h> /* Primitive System Data Types */ 我已经编写了测试程序来测试SCHED_FIFO.我了解到SCHED_FIFO线程无法抢占SCHED_FIFO.但我无法解释同一个程序多次运行时获得的结果.

/* Includes */#include <unistd.h>     /* Symbolic Constants */#include <sys/types.h>  /* Primitive System Data Types */ #include <errno.h>      /* Errors */#include <stdio.h>      /* input/Output */#include <stdlib.h>     /* General UtilitIEs */#include <pthread.h>    /* POSIX Threads */#include <string.h>     /* String handling */#include <sched.h>/* prototype for thread routine */voID print_message_function ( voID *ptr );voID print_message_function1 ( voID *ptr );/* struct to hold data to be passed to a threadthis shows how multiple data items can be passed to a thread */typedef struct str_thdata{int thread_no;int thread_value;char message[100];  } thdata;int main()  {pthread_t thread1,thread2;  /* thread variables */thdata data1,data2;         /* structs to be passed to threads *//* initialize data to pass to thread 1 */data1.thread_no = 1;data1.thread_value = 0;strcpy(data1.message,"Hello!");/* initialize data to pass to thread 2 */data2.thread_no = 2;data2.thread_value = 10000;strcpy(data2.message,"Hi!");/* create threads 1 and 2 */    pthread_create (&thread1,NulL,(voID *) &print_message_function,(voID *) &data1);pthread_create (&thread2,(voID *) &print_message_function1,(voID *) &data2);/* Main block Now waits for both threads to terminate,before it exits   If main block exits,both threads exit,even if the threads have not   finished their work */ pthread_join(thread1,NulL);pthread_join(thread2,NulL);/* exit */  exit(0);} /* main() *//** * print_message_function is used as the start routine for the threads used* it accepts a voID pointer **/voID print_message_function ( voID *ptr ){thdata *data;            data = (thdata *) ptr;  /* type cast to a pointer to thdata */struct sched_param param;//int priority=10;/* sched_priority will be the priority of the thread *///param.sched_priority = priority;/* only supported policy,others will result in ENOTSUP */int policy = SCHED_OTHER;/* scheduling parameters of target thread */pthread_setschedparam(pthread_self(),policy,&param);printf("Thread %d says sched policy  %d \n",data->thread_no,SCHED_OTHER);pthread_getschedparam(pthread_self(),&policy,&param);printf("Thread %d says %s  %d \n",data->message,policy);int i=0;/* do the work */printf("Thread %d says %s %d \n",(int)pthread_self());for(i=0;i<100;i++)printf("Thread %d says %d \n",data->thread_value++);pthread_exit(0); /* exit */} /* print_message_function ( voID *ptr ) */voID print_message_function1 ( voID *ptr ){thdata *data;            data = (thdata *) ptr;  /* type cast to a pointer to thdata */struct sched_param param;int priority=10;/* sched_priority will be the priority of the thread */param.sched_priority = priority;/* only supported policy,others will result in ENOTSUP * /int policy = SCHED_FIFO;/* scheduling parameters of target thread */pthread_setschedparam(pthread_self(),&param);printf("Thread %d says sched policy %d \n",SCHED_FIFO);pthread_getschedparam(pthread_self(),policy);int i=0;/* do the work */printf("Thread %d says %s  %d \n",data->thread_value++);pthread_exit(0); /* exit */} /* print_message_function ( voID *ptr ) */

我在多次运行中得到了意想不到的结果,我看到SCHED_FIFO被SCHED_OTHER线程抢占,即按程序,线程2处于FIFO模式,而线程1处于SCHED_OTHER模式.我已经多次看到thread2被thread1抢占了.

有人可以帮助我找到问题吗？

解决方法 您可能有效的这些sysctl设置,它们是默认值：

kernel.sched_rt_period_us = 1000000kernel.sched_rt_runtime_us = 950000

这意味着允许实时线程每1秒钟仅占95％.

另见：Can’t provoke Priority Inversion in C++

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