DosQueryQueue

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Queries the number of elements in a queue.

Syntax

DosQueryQueue(hq, pcbEntries)

Parameters

hq (HQUEUE) - input 
The handle of the queue to be queried.
pcbEntries (PULONG) - output 
A pointer to the number of elements in the queue.
ulrc (APIRET) - returns
Return Code.
DosQueryQueue returns one of the following values:
0 NO_ERROR
337 ERROR_QUE_INVALID_HANDLE

Remarks

DosQueryQueue returns the number of elements that are currently in a queue. This function can be used by the server process and its threads, as well as by any client processes that have gained access to the queue by issuing DosOpenQueue.

If the server process closes the queue before this request is made, ERROR_QUE_INVALID_HANDLE is returned.

Example Code

This example shows how to create, write, query, and close a queue.

#define INCL_DOSQUEUES   /* DOS Queue values */
#define INCL_DOSERRORS   /* DOS Error values */
#include <os2.h>
#include <stdio.h>
#include <string.h>

#define QUE_NAME "\\QUEUES\\PANDAWRITE\\LOCALQUEUE"

int main(VOID) {

   HQUEUE QueueHandle = NULLHANDLE;  /* Queue handle                   */
   CHAR   *DataBuffer = "";          /* Data to write to queue         */
   ULONG  ulNumElems  = 0L;          /* Number of elements on queue    */
   APIRET rc          = NO_ERROR;    /* Return code                    */

   rc = DosCreateQueue(&QueueHandle, /* Queue handle                   */
           QUE_LIFO |                /* Last In, First Out ordering    */
           QUE_CONVERT_ADDRESS,      /* Do 16-bit to 32-bit conversion */
           QUE_NAME);                /* Name of the queue              */
   if (rc!= NO_ERROR) {
      printf ("DosCreateQueue error: return code = %u\n", rc);
      return 1;
   }

   DataBuffer = "Element 1 of 2";
   rc = DosWriteQueue (QueueHandle, 100L, strlen(DataBuffer),
                       (PVOID)DataBuffer, 0L);
   if (rc!= NO_ERROR) {
      printf ("DosWriteQueue error: return code = %u\n", rc);
      return 1;
   }

   rc = DosQueryQueue (QueueHandle, &ulNumElems);
   if (rc != NO_ERROR) {
      printf ("DosQueryQueue error: return code = %u\n", rc);
      return 1;
   } else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }

   DataBuffer = "Element 2 of 2";
   rc = DosWriteQueue (QueueHandle, 200L, strlen(DataBuffer),
                       (PVOID)DataBuffer, 0L);
   if (rc!= NO_ERROR) {
      printf ("DosWriteQueue error: return code = %u\n", rc);
      return 1;
   }

   rc = DosQueryQueue (QueueHandle, &ulNumElems);
   if (rc != NO_ERROR) {
      printf ("DosQueryQueue error: return code = %u\n", rc);
      return 1;
   } else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }
   rc = DosPurgeQueue (QueueHandle);
   if (rc != NO_ERROR) {
      printf ("DosPurgeQueue error: return code = %u\n", rc);
      return 1;        }

   rc = DosQueryQueue (QueueHandle, &ulNumElems);
   if (rc != NO_ERROR) {
      printf ("DosQueryQueue error: return code = %u\n", rc);
      return 1;
   } else { printf ("DosQueryQueue: %u elements\n", ulNumElems); }

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

   return NO_ERROR;
}

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