1 files changed, 123 insertions, 0 deletions
diff --git a/xpcom/threads/nsEventQueue.h b/xpcom/threads/nsEventQueue.h
new file mode 100644
index 000000000..23b55e63d
--- /dev/null
+++ b/xpcom/threads/nsEventQueue.h
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsEventQueue_h__
+#define nsEventQueue_h__
+
+#include <stdlib.h>
+#include "mozilla/CondVar.h"
+#include "mozilla/Mutex.h"
+#include "nsIRunnable.h"
+#include "nsCOMPtr.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/UniquePtr.h"
+
+class nsThreadPool;
+
+// A threadsafe FIFO event queue...
+class nsEventQueue
+{
+public:
+  typedef mozilla::MutexAutoLock MutexAutoLock;
+
+  enum EventQueueType
+  {
+    eNormalQueue,
+    eSharedCondVarQueue
+  };
+
+  nsEventQueue(mozilla::CondVar& aCondVar, EventQueueType aType);
+  ~nsEventQueue();
+
+  // This method adds a new event to the pending event queue.  The queue holds
+  // a strong reference to the event after this method returns.  This method
+  // cannot fail.
+  void PutEvent(nsIRunnable* aEvent, MutexAutoLock& aProofOfLock);
+  void PutEvent(already_AddRefed<nsIRunnable>&& aEvent,
+                MutexAutoLock& aProofOfLock);
+
+  // This method gets an event from the event queue.  If mayWait is true, then
+  // the method will block the calling thread until an event is available.  If
+  // the event is null, then the method returns immediately indicating whether
+  // or not an event is pending.  When the resulting event is non-null, the
+  // caller is responsible for releasing the event object.  This method does
+  // not alter the reference count of the resulting event.
+  bool GetEvent(bool aMayWait, nsIRunnable** aEvent,
+                MutexAutoLock& aProofOfLock);
+
+  // This method returns true if there is a pending event.
+  bool HasPendingEvent(MutexAutoLock& aProofOfLock)
+  {
+    return GetEvent(false, nullptr, aProofOfLock);
+  }
+
+  // This method returns the next pending event or null.
+  bool GetPendingEvent(nsIRunnable** aRunnable, MutexAutoLock& aProofOfLock)
+  {
+    return GetEvent(false, aRunnable, aProofOfLock);
+  }
+
+  size_t Count(MutexAutoLock&) const;
+
+private:
+  bool IsEmpty()
+  {
+    return !mHead || (mHead == mTail && mOffsetHead == mOffsetTail);
+  }
+
+  enum
+  {
+    EVENTS_PER_PAGE = 255
+  };
+
+  // Page objects are linked together to form a simple deque.
+
+  struct Page
+  {
+    struct Page* mNext;
+    nsIRunnable* mEvents[EVENTS_PER_PAGE];
+  };
+
+  static_assert((sizeof(Page) & (sizeof(Page) - 1)) == 0,
+                "sizeof(Page) should be a power of two to avoid heap slop.");
+
+  static Page* NewPage()
+  {
+    return static_cast<Page*>(moz_xcalloc(1, sizeof(Page)));
+  }
+
+  static void FreePage(Page* aPage)
+  {
+    free(aPage);
+  }
+
+  Page* mHead;
+  Page* mTail;
+
+  uint16_t mOffsetHead;  // offset into mHead where next item is removed
+  uint16_t mOffsetTail;  // offset into mTail where next item is added
+  mozilla::CondVar& mEventsAvailable;
+
+  EventQueueType mType;
+
+  // These methods are made available to nsThreadPool as a hack, since
+  // nsThreadPool needs to have its threads sleep for fixed amounts of
+  // time as well as being able to wake up all threads when thread
+  // limits change.
+  friend class nsThreadPool;
+  void Wait(PRIntervalTime aInterval)
+  {
+    MOZ_ASSERT(mType == eNormalQueue);
+    mEventsAvailable.Wait(aInterval);
+  }
+  void NotifyAll()
+  {
+    MOZ_ASSERT(mType == eNormalQueue);
+    mEventsAvailable.NotifyAll();
+  }
+};
+
+#endif  // nsEventQueue_h__