Proactive SkPixelRef invalidation

src/core/SkMessageBus.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkMessageBus_DEFINED
+#define SkMessageBus_DEFINED
+
+#include "SkOnce.h"
+#include "SkTDArray.h"
+#include "SkThread.h"
+#include "SkTypes.h"
+
+template <typename Message>
+class SkMessageBus : SkNoncopyable {
+public:
+    // Post a message to be received by all Inboxes for this Message type.  Threadsafe.
+    static void Post(const Message& m);
+
+    class Inbox {
+    public:
+        Inbox();
+        ~Inbox();
+
+        // Overwrite out with all the messages we've received since the last call.  Threadsafe.
+        void poll(SkTDArray<Message>* out);
+
+    private:
+        SkTDArray<Message> fMessages;
+        SkMutex            fMessagesMutex;
+
+        friend class SkMessageBus;
+        void receive(const Message& m);  // SkMessageBus is a friend only to call this.
+    };
+
+private:
+    SkMessageBus();
+    static SkMessageBus* Get();
+    static void New(SkMessageBus**);
+
+    SkTDArray<Inbox*> fInboxes;
+    SkMutex           fInboxesMutex;
+};
+
+//   ----------------------- Implementation of SkMessageBus::Inbox -----------------------
+
+template<typename Message>
+SkMessageBus<Message>::Inbox::Inbox() {
+    // Register ourselves with the corresponding message bus.
+    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
+    SkAutoMutexAcquire lock(bus->fInboxesMutex);
+    bus->fInboxes.push(this);
+}
+
+template<typename Message>
+SkMessageBus<Message>::Inbox::~Inbox() {
+    // Remove ourselves from the corresponding message bus.
+    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
+    SkAutoMutexAcquire lock(bus->fInboxesMutex);
+    // This is a cheaper fInboxes.remove(fInboxes.find(this)) when order doesn't matter.
+    for (int i = 0; i < bus->fInboxes.count(); i++) {
+        if (this == bus->fInboxes[i]) {
+            bus->fInboxes.removeShuffle(i);
+            break;
+        }
+    }
+}
+
+template<typename Message>
+void SkMessageBus<Message>::Inbox::receive(const Message& m) {
+    SkAutoMutexAcquire lock(fMessagesMutex);
+    fMessages.push(m);
+}
+
+template<typename Message>
+void SkMessageBus<Message>::Inbox::poll(SkTDArray<Message>* messages) {
+    SkASSERT(NULL != messages);
+    messages->reset();
+    SkAutoMutexAcquire lock(fMessagesMutex);
+    messages->swap(fMessages);
+}
+
+//   ----------------------- Implementation of SkMessageBus -----------------------
+
+template <typename Message>
+SkMessageBus<Message>::SkMessageBus() {}
+
+template <typename Message>
+/*static*/ void SkMessageBus<Message>::New(SkMessageBus<Message>** bus) {
+    *bus = new SkMessageBus<Message>();
+}
+
+template <typename Message>
+/*static*/ SkMessageBus<Message>* SkMessageBus<Message>::Get() {
+    // The first time this method is called, create the singleton bus for this message type.
+    static SkMessageBus<Message>* bus = NULL;
+    SK_DECLARE_STATIC_ONCE(once);
+    SkOnce(&once, &New, &bus);
+
+    SkASSERT(bus != NULL);
+    return bus;
+}
+
+template <typename Message>
+/*static*/ void SkMessageBus<Message>::Post(const Message& m) {
+    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
+    SkAutoMutexAcquire lock(bus->fInboxesMutex);
+    for (int i = 0; i < bus->fInboxes.count(); i++) {
+        bus->fInboxes[i]->receive(m);
+    }
+}
+
+#endif  // SkMessageBus_DEFINED