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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 "SkOncePtr.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     SK_DECLARE_STATIC_ONCE_PTR(SkMessageBus<Message>, bus);        \
     51     template <>                                                    \
     52     SkMessageBus<Message>* SkMessageBus<Message>::Get() {          \
     53         return bus.get([]{ return new SkMessageBus<Message>(); }); \
     54     }
     55 
     56 //   ----------------------- Implementation of SkMessageBus::Inbox -----------------------
     57 
     58 template<typename Message>
     59 SkMessageBus<Message>::Inbox::Inbox() {
     60     // Register ourselves with the corresponding message bus.
     61     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     62     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     63     bus->fInboxes.push(this);
     64 }
     65 
     66 template<typename Message>
     67 SkMessageBus<Message>::Inbox::~Inbox() {
     68     // Remove ourselves from the corresponding message bus.
     69     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     70     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     71     // This is a cheaper fInboxes.remove(fInboxes.find(this)) when order doesn't matter.
     72     for (int i = 0; i < bus->fInboxes.count(); i++) {
     73         if (this == bus->fInboxes[i]) {
     74             bus->fInboxes.removeShuffle(i);
     75             break;
     76         }
     77     }
     78 }
     79 
     80 template<typename Message>
     81 void SkMessageBus<Message>::Inbox::receive(const Message& m) {
     82     SkAutoMutexAcquire lock(fMessagesMutex);
     83     fMessages.push_back(m);
     84 }
     85 
     86 template<typename Message>
     87 void SkMessageBus<Message>::Inbox::poll(SkTArray<Message>* messages) {
     88     SkASSERT(messages);
     89     messages->reset();
     90     SkAutoMutexAcquire lock(fMessagesMutex);
     91     fMessages.swap(messages);
     92 }
     93 
     94 //   ----------------------- Implementation of SkMessageBus -----------------------
     95 
     96 template <typename Message>
     97 SkMessageBus<Message>::SkMessageBus() {}
     98 
     99 template <typename Message>
    100 /*static*/ void SkMessageBus<Message>::Post(const Message& m) {
    101     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
    102     SkAutoMutexAcquire lock(bus->fInboxesMutex);
    103     for (int i = 0; i < bus->fInboxes.count(); i++) {
    104         bus->fInboxes[i]->receive(m);
    105     }
    106 }
    107 
    108 #endif  // SkMessageBus_DEFINED
    109