DosCloseQueue

Description

Ends access to a queue, or deletes a queue.

Syntax

#define INCL_DOSQUEUES
#include <os2.h>

HQUEUE    hq;    /*  The handle of the queue to be closed. */
APIRET    ulrc;  /*  Return Code. */

ulrc = DosCloseQueue(hq);

Parameters

hq (HQUEUE) - input

The handle of the queue to be closed.

This is the handle received from a previous call to DosCreateQueue or DosOpenQueue.

Return Code

ulrc (APIRET) - returns

DosCloseQueue returns one of the following values:

• 0 NO_ERROR
• 337 ERROR_QUE_INVALID_HANDLE

Remarks

DosCloseQueue ends further processing of a queue by the requesting process. The action taken depends on whether the requester is the owner of the queue or a writer of the queue.

For the owner, any outstanding elements are deleted. Other processes that have the queue open will receive the ERROR_QUE_INVALID_HANDLE return code on their next request.

For a writer of the queue, access to the queue is ended, but the queue elements are not deleted.

Example Code

This example creates and opens a queue named "SPECIAL.QUE", writes to it, reads from it, and finally closes it.

 
#define INCL_DOSQUEUES   /* DOS Queue values */
#define INCL_DOSPROCESS  /* DOS thread and process values */
#define INCL_DOSERRORS   /* DOS error values */
#include <os2.h>
#include <stdio.h>
#include <string.h>

int main(VOID) {

   PSZ         szQueueName  = "\\QUEUES\\SPECIAL.QUE";
   HQUEUE      hqSpecialQue = NULLHANDLE; /* Queue handle                   */
   PSZ         DataBuffer   = "";         /* Data buffer for queue data     */
   REQUESTDATA Request      = {0};        /* Reques */
   PID         pidOwner     = 0;
   ULONG       ulDataLen    = 0;          /* Length of data returned        */
   BYTE        ElemPrty     = 0;          /* Priority of element (returned) */
   APIRET      rc           = NO_ERROR;   /* Return code                    */

   rc = DosCreateQueue(&hqSpecialQue,    /* Queue handle                    */
             QUE_FIFO |                  /* First-In First-Out order        */
             QUE_CONVERT_ADDRESS,        /* Convert 16-bit addresses to 32  */
             szQueueName);               /* Name of the queue to create     */
   if (rc!= NO_ERROR) {
      printf ("DosCreateQueue error: return code = %u\n", rc);
      return 1;
   }

   rc = DosOpenQueue (&pidOwner,         /* PID of queue owner              */
                      &hqSpecialQue,     /* Handle for created queue        */
                      szQueueName);      /* Name of the queue to open       */
   if (rc!= NO_ERROR) {
      printf ("DosOpenQueue error: return code = %u\n", rc);
      return 1;
   }

   DataBuffer = "To be, or not to be.  That is the question...";
   rc = DosWriteQueue (hqSpecialQue,        /* Queue to write to           */
                       12345L,              /* Request data                */
                       strlen(DataBuffer),  /* Length of data to write     */
                       DataBuffer,          /* Pointer to data             */
                       0L);              /* Priority (not applicable here) */
   if (rc!= NO_ERROR) {
      printf ("DosWriteQueue error: return code = %u\n", rc);
      return 1;
   }

   DataBuffer = "";                  /* Clear the DataBuffer */
   Request.pid = pidOwner;           /* process ID for the DosReadQueue */
   rc = DosReadQueue (hqSpecialQue,          /* Queue to read from          */
                      &Request,              /* Request data from write     */
                      &ulDataLen,            /* Length of data returned     */
                      (PVOID) &DataBuffer,   /* The data                    */
                      0L,                    /* Remove first element        */
                      DCWW_WAIT,             /* Wait for available data     */
                      &ElemPrty,             /* Priority of data (returned) */
                      0L);             /* Semaphore to use when not waiting */

   if (rc!= NO_ERROR) {
      printf ("DosReadQueue error: return code = %u\n", rc);
      return 1;
   } else {
      printf ("DosReadQueue returns: '%s'\n", DataBuffer);
      printf ("      (Request data = %u)\n", Request.ulData);
   }

   rc = DosCloseQueue(hqSpecialQue);         /* Close the queue */
   if (rc!= NO_ERROR) {
      printf ("DosCloseQueue error: return code = %u\n", rc);
      return 1;
   }

   return NO_ERROR;
}

Related Functions

• DosCreateQueue
• DosOpenQueue
• DosPeekQueue
• DosPurgeQueue
• DosQueryQueue
• DosReadQueue
• DosWriteQueue