SCHED_FIFO线程在Linux中被SCHED_OTHER线程抢占

我已经编写了testing程序来testingSCHED_FIFO 。我了解到SCHED_FIFO不能被SCHED_OTHER线程抢占。但是我不能解释同一个程序运行多次的结果。

 /* 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 thread this 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, NULL, (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->thread_no, data->message,policy); int i=0; /* do the work */ printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self()); for(i=0;i<100;i++) printf("Thread %d says %d \n", data->thread_no,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(), policy, &param); printf("Thread %d says sched policy %d \n", data->thread_no, SCHED_FIFO); pthread_getschedparam(pthread_self(),&policy,&param); printf("Thread %d says %s %d \n", data->thread_no, data->message,policy); int i=0; /* do the work */ printf("Thread %d says %s %d \n", data->thread_no, data->message,(int)pthread_self()); for(i=0;i<100;i++) printf("Thread %d says %d \n", data->thread_no,data->thread_value++); pthread_exit(0); /* exit */ } /* print_message_function ( void *ptr ) */

在多次运行中，我看到SCHED_FIFO被SCHED_OTHER线程抢占，即按照程序，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抢占的地方。

有人能帮我找出问题吗？

你可能有这些sysctl设置有效，这是默认值：

 kernel.sched_rt_period_us = 1000000 kernel.sched_rt_runtime_us = 950000

这意味着实时线程只允许每1秒周期的95％。

另请参阅：不能在C ++中激发优先级反转

此外，无论何时您的线程阻塞IO，也许从printf语句，另一个线程可能被安排。