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      1 /*
      2  * Copyright 2013 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SkMessageBus_DEFINED
      9 #define SkMessageBus_DEFINED
     10 
     11 #include "SkMutex.h"
     12 #include "SkOnce.h"
     13 #include "SkTArray.h"
     14 #include "SkTDArray.h"
     15 #include "SkTypes.h"
     16 
     17 template <typename Message>
     18 class SkMessageBus : SkNoncopyable {
     19 public:
     20     // Post a message to be received by all Inboxes for this Message type.  Threadsafe.
     21     static void Post(const Message& m);
     22 
     23     class Inbox {
     24     public:
     25         Inbox();
     26         ~Inbox();
     27 
     28         // Overwrite out with all the messages we've received since the last call.  Threadsafe.
     29         void poll(SkTArray<Message>* out);
     30 
     31     private:
     32         SkTArray<Message>  fMessages;
     33         SkMutex            fMessagesMutex;
     34 
     35         friend class SkMessageBus;
     36         void receive(const Message& m);  // SkMessageBus is a friend only to call this.
     37     };
     38 
     39 private:
     40     SkMessageBus();
     41     static SkMessageBus* Get();
     42 
     43     SkTDArray<Inbox*> fInboxes;
     44     SkMutex           fInboxesMutex;
     45 };
     46 
     47 // This must go in a single .cpp file, not some .h, or we risk creating more than one global
     48 // SkMessageBus per type when using shared libraries.  NOTE: at most one per file will compile.
     49 #define DECLARE_SKMESSAGEBUS_MESSAGE(Message)                      \
     50     template <>                                                    \
     51     SkMessageBus<Message>* SkMessageBus<Message>::Get() {          \
     52         static SkOnce once;                                        \
     53         static SkMessageBus<Message>* bus;                         \
     54         once([] { bus = new SkMessageBus<Message>(); });           \
     55         return bus;                                                \
     56     }
     57 
     58 //   ----------------------- Implementation of SkMessageBus::Inbox -----------------------
     59 
     60 template<typename Message>
     61 SkMessageBus<Message>::Inbox::Inbox() {
     62     // Register ourselves with the corresponding message bus.
     63     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     64     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     65     bus->fInboxes.push(this);
     66 }
     67 
     68 template<typename Message>
     69 SkMessageBus<Message>::Inbox::~Inbox() {
     70     // Remove ourselves from the corresponding message bus.
     71     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     72     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     73     // This is a cheaper fInboxes.remove(fInboxes.find(this)) when order doesn't matter.
     74     for (int i = 0; i < bus->fInboxes.count(); i++) {
     75         if (this == bus->fInboxes[i]) {
     76             bus->fInboxes.removeShuffle(i);
     77             break;
     78         }
     79     }
     80 }
     81 
     82 template<typename Message>
     83 void SkMessageBus<Message>::Inbox::receive(const Message& m) {
     84     SkAutoMutexAcquire lock(fMessagesMutex);
     85     fMessages.push_back(m);
     86 }
     87 
     88 template<typename Message>
     89 void SkMessageBus<Message>::Inbox::poll(SkTArray<Message>* messages) {
     90     SkASSERT(messages);
     91     messages->reset();
     92     SkAutoMutexAcquire lock(fMessagesMutex);
     93     fMessages.swap(messages);
     94 }
     95 
     96 //   ----------------------- Implementation of SkMessageBus -----------------------
     97 
     98 template <typename Message>
     99 SkMessageBus<Message>::SkMessageBus() {}
    100 
    101 template <typename Message>
    102 /*static*/ void SkMessageBus<Message>::Post(const Message& m) {
    103     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
    104     SkAutoMutexAcquire lock(bus->fInboxesMutex);
    105     for (int i = 0; i < bus->fInboxes.count(); i++) {
    106         bus->fInboxes[i]->receive(m);
    107     }
    108 }
    109 
    110 #endif  // SkMessageBus_DEFINED
    111