gecko-dev/xpcom/threads/nsEventQueue.h

93 lines
2.7 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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/ReentrantMonitor.h"
#include "nsIRunnable.h"
// A threadsafe FIFO event queue...
class nsEventQueue
{
typedef mozilla::ReentrantMonitor ReentrantMonitor;
public:
nsEventQueue();
~nsEventQueue();
// This method adds a new event to the pending event queue. The event object
// is AddRef'd if this method succeeds. This method returns true if the
// event was stored in the event queue, and it returns false if it could
// not allocate sufficient memory.
bool PutEvent(nsIRunnable *event);
// 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 mayWait, nsIRunnable **event);
// This method returns true if there is a pending event.
bool HasPendingEvent() {
return GetEvent(false, nullptr);
}
// This method returns the next pending event or null.
bool GetPendingEvent(nsIRunnable **runnable) {
return GetEvent(false, runnable);
}
// This method waits for and returns the next pending event.
bool WaitPendingEvent(nsIRunnable **runnable) {
return GetEvent(true, runnable);
}
// Expose the event queue's monitor for "power users"
ReentrantMonitor& GetReentrantMonitor() {
return mReentrantMonitor;
}
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 *>(calloc(1, sizeof(Page)));
}
static void FreePage(Page *p) {
free(p);
}
ReentrantMonitor mReentrantMonitor;
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
};
#endif // nsEventQueue_h__