c - linux 实时调度任务时出现运行时错误？

Question

#define _POSIX_C_SOURCE 200809L
#define _XOPEN_SOURCE   500

#include <sched.h>  /* for sched_setsched */
#include <unistd.h> /* for usleep */
#include <time.h>   /* for clock_gettime */
#include <string.h> /* for memset */
#include <stdio.h>

#define MS_to_US(x) ((x)*1000)

void TASK1()
{
    printf("hi \n");
}

void TASK2()
{
    printf("hi2 \n");
}

void TASK3()
{
    printf("hi3 \n");
}

useconds_t delta_t_us(struct timespec const *a, struct timespec const *b)
{
    time_t const delta_sec  = b->tv_sec  - a->tv_sec;
    long   const delta_nsec = b->tv_nsec - a->tv_nsec;

    /* this might actually overflow for "long" time intervalls"
     * should be safe for a delta_t < 2ms though */
    return delta_sec * 1000000 + delta_nsec / 1000;
}

void rastertask()
{
    struct sched_param sparm;
    memset(&sparm, 0, sizeof(sparm));
    sparm.sched_priority = 10; /* 0 = lowest, 99 = highest */

    sched_setscheduler(
        0 /* pid, 0 ==> this process */,
        SCHED_RR /* policy */,
        &sparm);

    unsigned int n_loop;
    for(n_loop=0;;n_loop++) {
        struct timespec ts_start, ts_end;
        clock_gettime(CLOCK_REALTIME, &ts_start);

        TASK1(); /* gets called every 2ms */
        if( (n_loop % 5) == 0) {
            TASK2(); /* get called every 5 * 2ms = 10ms */
        }
        if( (n_loop % 50) == 0) {
            TASK2(); /* get called every 50 * 2ms = 100ms */
        }

        if( (n_loop % 250) == 0 ) {
            /* reset loop counter when smallest common
             * multiple of timing grid has been reached */
            n_loop = 0;
        }

        clock_gettime(CLOCK_REALTIME, &ts_end);
        useconds_t const tasks_execution_time = delta_t_us(&ts_start, &ts_end);

        if( tasks_execution_time >= MS_to_US(2) ) {
            /* report an error that tasks took longer than 2ms to execute */
        }

        /* wait for 2ms - task_execution_time so that tasks get called in
         * a close 2ms timing grid */
        usleep( MS_to_US(2) - tasks_execution_time );
    }
}

int main()
{
    rastertask();
    return 1;
}

我创建了一个调度程序，用于每 2ms(毫秒)、10ms 和 100ms 调度一次任务。上面的代码正在编译并且正在运行。运行一定时间后，调度程序将停止执行任务。调度程序每 2ms、10 和 100ms 调用三个任务。任务正在打印 hi、hi1 和 hi3

问题:为什么上面的代码没有打印 hi3 100ms ？为什么它会在一段时间后停止？

Answer 1

问题1)TASK3 未执行，因为您没有调用它。 TASK2 在两个 if 语句之后调用

问题2)if (tasks_execution_time 大于 2ms: MS_to_US(2) -tasks_execution_time 将为负数，usleep 将等待很长时间。我建议在 usleep 之前使用“else”，因为 if 已经在检查这一点。