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* Copyright 2020 Google LLC
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkIDChangeListener_DEFINED
#define SkIDChangeListener_DEFINED
#include "include/core/SkRefCnt.h"
#include "include/private/SkMutex.h"
#include "include/private/SkTDArray.h"
#include <atomic>
* Used to be notified when a gen/unique ID is invalidated, typically to preemptively purge
* associated items from a cache that are no longer reachable. The listener can
* be marked for deregistration if the cached item is remove before the listener is
* triggered. This prevents unbounded listener growth when cache items are routinely
* removed before the gen ID/unique ID is invalidated.
class SkIDChangeListener : public SkRefCnt {
~SkIDChangeListener() override;
virtual void changed() = 0;
* Mark the listener is no longer needed. It should be removed and changed() should not be
* called.
void markShouldDeregister() {, std::memory_order_relaxed); }
/** Indicates whether markShouldDeregister was called. */
bool shouldDeregister() { return fShouldDeregister.load(std::memory_order_acquire); }
/** Manages a list of SkIDChangeListeners. */
class List {
* Add a new listener to the list. It must not already be deregistered. Also clears out
* previously deregistered listeners.
void add(sk_sp<SkIDChangeListener> listener) SK_EXCLUDES(fMutex);
* The number of registered listeners (including deregisterd listeners that are yet-to-be
* removed.
int count() const SK_EXCLUDES(fMutex);
/** Calls changed() on all listeners that haven't been deregistered and resets the list. */
void changed() SK_EXCLUDES(fMutex);
/** Resets without calling changed() on the listeners. */
void reset() SK_EXCLUDES(fMutex);
mutable SkMutex fMutex;
SkTDArray<SkIDChangeListener*> fListeners SK_GUARDED_BY(fMutex); // pointers are reffed
std::atomic<bool> fShouldDeregister;