xpcom/threads/nsEventQueue.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "nsEventQueue.h"
   8 #include "nsAutoPtr.h"
   9 #include "prlog.h"
  10 #include "nsThreadUtils.h"
  11 #include "prthread.h"
  12 #include "mozilla/ChaosMode.h"
  13
  14 using namespace mozilla;
  15
  16 #ifdef PR_LOGGING
  17 static PRLogModuleInfo*
  18 GetLog()
  19 {
  20   static PRLogModuleInfo* sLog;
  21   if (!sLog) {
  22     sLog = PR_NewLogModule("nsEventQueue");
  23   }
  24   return sLog;
  25 }
  26 #endif
  27 #ifdef LOG
  28 #undef LOG
  29 #endif
  30 #define LOG(args) PR_LOG(GetLog(), PR_LOG_DEBUG, args)
  31
  32 nsEventQueue::nsEventQueue()
  33   : mReentrantMonitor("nsEventQueue.mReentrantMonitor")
  34   , mHead(nullptr)
  35   , mTail(nullptr)
  36   , mOffsetHead(0)
  37   , mOffsetTail(0)
  38 {
  39 }
  40
  41 nsEventQueue::~nsEventQueue()
  42 {
  43   // It'd be nice to be able to assert that no one else is holding the monitor,
  44   // but NSPR doesn't really expose APIs for it.
  45   NS_ASSERTION(IsEmpty(),
  46                "Non-empty event queue being destroyed; events being leaked.");
  47
  48   if (mHead) {
  49     FreePage(mHead);
  50   }
  51 }
  52
  53 bool
  54 nsEventQueue::GetEvent(bool aMayWait, nsIRunnable** aResult)
  55 {
  56   {
  57     ReentrantMonitorAutoEnter mon(mReentrantMonitor);
  58
  59     while (IsEmpty()) {
  60       if (!aMayWait) {
  61         if (aResult) {
  62           *aResult = nullptr;
  63         }
  64         return false;
  65       }
  66       LOG(("EVENTQ(%p): wait begin\n", this));
  67       mon.Wait();
  68       LOG(("EVENTQ(%p): wait end\n", this));
  69     }
  70
  71     if (aResult) {
  72       *aResult = mHead->mEvents[mOffsetHead++];
  73
  74       // Check if mHead points to empty Page
  75       if (mOffsetHead == EVENTS_PER_PAGE) {
  76         Page* dead = mHead;
  77         mHead = mHead->mNext;
  78         FreePage(dead);
  79         mOffsetHead = 0;
  80       }
  81     }
  82   }
  83
  84   return true;
  85 }
  86
  87 void
  88 nsEventQueue::PutEvent(nsIRunnable* aRunnable)
  89 {
  90   // Avoid calling AddRef+Release while holding our monitor.
  91   nsRefPtr<nsIRunnable> event(aRunnable);
  92
  93   if (ChaosMode::isActive()) {
  94     // With probability 0.5, yield so other threads have a chance to
  95     // dispatch events to this queue first.
  96     if (ChaosMode::randomUint32LessThan(2)) {
  97       PR_Sleep(PR_INTERVAL_NO_WAIT);
  98     }
  99   }
 100
 101   ReentrantMonitorAutoEnter mon(mReentrantMonitor);
 102
 103   if (!mHead) {
 104     mHead = NewPage();
 105     MOZ_ASSERT(mHead);
 106
 107     mTail = mHead;
 108     mOffsetHead = 0;
 109     mOffsetTail = 0;
 110   } else if (mOffsetTail == EVENTS_PER_PAGE) {
 111     Page* page = NewPage();
 112     MOZ_ASSERT(page);
 113
 114     mTail->mNext = page;
 115     mTail = page;
 116     mOffsetTail = 0;
 117   }
 118
 119   event.swap(mTail->mEvents[mOffsetTail]);
 120   ++mOffsetTail;
 121   LOG(("EVENTQ(%p): notify\n", this));
 122   mon.NotifyAll();
 123 }