/* mutexSemDemo.c -  Demonstrate the usage of the mutual exclusion semaphore  *                   for intertask synchronization and obtaining exclusive  *                   access to a data structure shared among multiple tasks. *//* Copyright 1984-1997 Wind River Systems, Inc. *//*modification history--------------------01c,06nov97,mm  added copyright.01b,16sep97,ram included logLib.h, sysLib.h, stdio.h		 The arguments to logMsg are required arguments(6)		 Since there were fewer than 6 arguments the remaining		 have been filled up with zeros.01a,14jan94,ms   written.*/#include "vxWorks.h"#include "semLib.h"#include "taskLib.h"#include "mutexSemDemo.h"#include "logLib.h"#include "sysLib.h"#include "stdio.h"LOCAL STATUS protectSharedResource ();      /* protect shared data structure */LOCAL STATUS releaseProtectedSharedResource (); /* release protected access */LOCAL STATUS producerTask ();               /* producer task */LOCAL STATUS consumerTask ();               /* consumer task */LOCAL struct shMem shMemResource;           /* shared memory structure */LOCAL SEM_ID mutexSemId;                    /* mutual exclusion semaphore id*/LOCAL BOOL notFinished;                     /* Flag that indicates the                                              * completion *//***************************************************************************** *  mutexSemDemo - Demonstrate the usage of the mutual exclusion semaphore  *                 for intertask synchronization and obtaining exclusive  *                 access to a data structure shared among multiple tasks. * *  DESCRIPTION *  Creates a mutual exclusion semaphore for intertask syncronization  *  between the producerTask and the consumerTask. Both producerTask and *  consumerTask access and manipulate the global shared memory data  *  structure simultaneously. To avoid corruption of the global shared *  memory data structure mutual exclusion semaphores are used.  * *  Spawns the producerTask that produces the message and puts the message *  in the global shared data structure. Spawns the consumerTask that  *  consumes the message from the global shared data structure and *  updates the status field to CONSUMED so that producerTask can put *  the next produced message in the global shared data structure.  *  After consumerTask has consumed all the messages, the mutual exclusion *  semaphore is deleted. * *  RETURNS: OK or ERROR * *  EXAMPLE * *  -> sp mutexSemDemo * */ STATUS mutexSemDemo()    {    notFinished = TRUE;  /* initialize the global flag */     /* Create the mutual exclusion semaphore*/    if ((mutexSemId = semMCreate (SEM_Q_PRIORITY | SEM_DELETE_SAFE                                          | SEM_INVERSION_SAFE)) == NULL)        {        perror ("Error in creating mutual exclusion semaphore");        return (ERROR);        }      /* Spwan the consumerTask task */    if (taskSpawn ("tConsumerTask", CONSUMER_TASK_PRI, 0, TASK_STACK_SIZE,                    (FUNCPTR) consumerTask, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)                    == ERROR)        {        perror ("consumerTask: Error in spawning demoTask");        return (ERROR);        }     /* Spwan the producerTask task */    if (taskSpawn ("tProducerTask", PRODUCER_TASK_PRI, 0, TASK_STACK_SIZE,                    (FUNCPTR) producerTask, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)                    == ERROR)        {        perror ("producerTask: Error in spawning demoTask");        return (ERROR);        }      /* Polling is not recommended. But used for making this demonstration      * simple */    while (notFinished)        taskDelay (sysClkRateGet ());    /* When done delete the mutual exclusion semaphore*/     if (semDelete (mutexSemId) == ERROR)       {       perror ("Error in deleting mutual exclusion semaphore");       return (ERROR);       }      return (OK);     }/***************************************************************************** *  producerTask - produce the message, and write the message to the global  *                 shared data structure by obtaining exclusive access to  *                 that structure which is shared with the consumerTask.  * *  RETURNS: OK or ERROR * */STATUS producerTask ()    {    int count = 0;    int notDone = TRUE;printf("in producerTask\n");    while (notDone)        {        /* Produce NUM_ITEMS, write each of these items to the shared         * global data structure.         */         if (count < NUM_ITEMS)            {            /* Obtain exclusive access to the global shared data structure */            if (protectSharedResource() == ERROR)                return (ERROR);            /* Access and manipulate the global shared data structure */            if (shMemResource.status == CONSUMED)                {                 count++;                shMemResource.tid = taskIdSelf ();                shMemResource.count = count;                shMemResource.status = PRODUCED;                }            /* Release exclusive access to the global shared data structure */            if (releaseProtectedSharedResource () == ERROR)                return (ERROR);            logMsg ("ProducerTask: tid = %#x, producing item = %d\n",                                                        taskIdSelf (), count,0,0,0,0);            taskDelay (sysClkRateGet()/6); /* relingiush the CPU so that                                             * consumerTask can access the                                             * global shared data structure.                                             */            }        else             notDone = FALSE;        }    return (OK);    }/***************************************************************************** *  consumerTask -  consumes the message from the global shared data  *                  structure and updates the status filled to CONSUMED  *                  so that producerTask can put the next produced message  *                  in the global shared data structure.  * *  RETURNS: OK or ERROR * */STATUS consumerTask ()    {    int notDone = TRUE;        printf("in consumerTask\n");    /* Initialize to consumed status */    if (protectSharedResource() == ERROR)        return (ERROR);    shMemResource.status = CONSUMED;    if (releaseProtectedSharedResource () == ERROR)        return (ERROR);    while (notDone)         {        taskDelay (sysClkRateGet()/6);     /* relingiush the CPU so that                                             * producerTask can access the                                             * global shared data structure.                                             */        /* Obtain exclusive access to the global shared data structure */        if (protectSharedResource() == ERROR)            return (ERROR);        /* Access and manipulate the global shared data structure */        if ((shMemResource.status == PRODUCED) && (shMemResource.count > 0))             {            logMsg ("ConsumerTask: Consuming item = %d from tid = %#x\n\n",                shMemResource.count, shMemResource.tid,0,0,0,0);            shMemResource.status = CONSUMED;            }        if (shMemResource.count >= NUM_ITEMS)            notDone = FALSE;        /* Release exclusive access to the global shared data structure */        if (releaseProtectedSharedResource () == ERROR)            return (ERROR);        }    notFinished = FALSE;    return (OK);    }/***************************************************************************** *  protectSharedResource -  Protect access to the shared data structure with  *                           the mutual exclusion  semaphore. * *  RETURNS: OK or ERROR * */LOCAL STATUS protectSharedResource ()    {    if (semTake (mutexSemId, WAIT_FOREVER) == ERROR)        {        perror ("protectSharedResource: Error in semTake");        return (ERROR);        }    else        return (OK);    }/***************************************************************************** *  releaseProtectedSharedResource -  Release the protected access to the  *                                    shared data structure using the mutual  *                                    exclusion semaphore * *  RETURNS: OK or ERROR * */LOCAL STATUS releaseProtectedSharedResource ()    {    if (semGive (mutexSemId) == ERROR)        {        perror ("protectSharedResource: Error in semTake");        return (ERROR);        }    else        return (OK);    }