src/servers/media/Queue.cpp

   1 /*
   2  * Copyright 2002, Marcus Overhagen. All rights reserved.
   3  * Distributed under the terms of the MIT License.
   4  */
   5
   6
   7 /*!     This is a simple multi thread save queue.
   8
   9         One thread calls AddItem() to add items, and when it is finished doing
  10         so, it calls Terminate(). Another thread calls RemoveItem() to remove
  11         items from the queue. RemoveItem() blocks when no items are available.
  12         As soon as Terminate() is called and the queue is empty, RemoveItem()
  13         returns NULL.
  14 */
  15
  16
  17 #include "Queue.h"
  18
  19 #include <Autolock.h>
  20 #include <OS.h>
  21
  22
  23 Queue::Queue()
  24         :
  25         BLocker("queue locker"),
  26         fSem(create_sem(0, "queue sem"))
  27 {
  28 }
  29
  30
  31 Queue::~Queue()
  32 {
  33         if (fSem >= 0)
  34                 delete_sem(fSem);
  35 }
  36
  37
  38 status_t
  39 Queue::Terminate()
  40 {
  41         BAutolock _(this);
  42
  43         if (fSem < 0)
  44                 return B_ERROR;
  45
  46         delete_sem(fSem);
  47         fSem = -1;
  48         return B_OK;
  49 }
  50
  51
  52 status_t
  53 Queue::AddItem(void* item)
  54 {
  55         BAutolock _(this);
  56
  57         if (fSem < 0)
  58                 return B_ERROR;
  59
  60         if (!fList.AddItem(item))
  61                 return B_NO_MEMORY;
  62
  63         release_sem(fSem);
  64         return B_OK;
  65 }
  66
  67
  68 void*
  69 Queue::RemoveItem()
  70 {
  71         // if the semaphore is deleted by Terminate(),
  72         // this will no longer block
  73         while (acquire_sem(fSem) == B_INTERRUPTED)
  74                 ;
  75
  76         BAutolock _(this);
  77
  78         // if the list is empty, which can only happen after
  79         // Terminate() was called, item will be NULL
  80         return fList.RemoveItem((int32)0);
  81 }