VxWorks任务优先级抢占调度

/* includes */
#include "vxWorks.h"
#include "taskLib.h"
#include "kernelLib.h"
#include "sysLib.h"

 

/* function prototypes */
void taskOne(void);
void taskTwo(void);
void taskThree(void);

 

/* globals */
#define ITER1 100
#define ITER2 10
#define HIGH 100 /* high priority */
#define MID 101 /* medium priority */
#define LOW 102 /* low priority */
#define LONG_TIME 0xFFFFFFL

 

void sched(void) /* function to create the two tasks */
{
    int taskIdOne, taskIdTwo, taskIdThree;
    printf("\n\n\n\n\n");
   
    /* spawn the three tasks */
    if ((taskIdOne = taskSpawn("task1", LOW, 0x100, 20000, (FUNCPTR)taskOne, 0, 0,
                            0, 0, 0, 0, 0, 0, 0, 0)) == ERROR)
        printf("taskSpawn taskOne failed\n");
   
    if ((taskIdTwo = taskSpawn("task2", MID, 0x100, 20000, (FUNCPTR)taskTwo, 0, 0,
                            0, 0, 0, 0, 0, 0, 0, 0)) == ERROR)
        printf("taskSpawn taskTwo failed\n");
   
    if ((taskIdThree = taskSpawn("task3", HIGH, 0x100, 20000, (FUNCPTR)taskThree,
                                0, 0, 0, 0, 0, 0, 0, 0, 0, 0)) == ERROR)
        printf("taskSpawn taskThree failed\n");
}

 

void taskOne(void)
{
    unsigned int i, j;
    for (i = 0; i < ITER1; i++)
    {
        /* log messages */
        for (j = 0; j < ITER2; j++)
            printf("task1\n");
   
        /* allow time for context switch */
        for (j = 0; j < LONG_TIME; j++)
            ;
    }
}

 

void taskTwo(void)
{
    unsigned int i, j;
    for (i = 0; i < ITER1; i++)
    {
        /* log messages */
        for (j = 0; j < ITER2; j++)
            printf("task2\n");
       
        /* allow time for context switch */
        for (j = 0; j < LONG_TIME; j++)
            ;
    }
}

 

void taskThree(void)
{
    unsigned int i, j;
    for (i = 0; i < ITER1; i++)
    {
        /* log messages */
        for (j = 0; j < ITER2; j++)
            printf("task3\n");
       
        /* allow time for context switch */
        for (j = 0; j < LONG_TIME; j++)
            ;
    }
}

  程序的运行结果为：先输出ITER1* ITER2个“task3”，再输出ITER1* ITER2个“task2”，最后输出ITER1* ITER2个“task1”。这是因为task1、task2、task3的优先级顺序是“task3－task2－task1”，故在task3执行完（或被阻塞、挂起）前，task2得不到执行；同理，在在task2执行完（或被阻塞、挂起）前，task1也得不到执行。