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
17template <typename Message>
18class SkMessageBus : SkNoncopyable {
19public:
20    // Post a message to be received by Inboxes for this Message type.  Threadsafe.
21    // If id is SK_InvalidUniqueID then it will be sent to all inboxes.
22    // Otherwise it will be sent to the inbox with that id.
23    static void Post(const Message& m, uint32_t destID = SK_InvalidUniqueID);
24
25    class Inbox {
26    public:
27        Inbox(uint32_t uniqueID = SK_InvalidUniqueID);
28        ~Inbox();
29
30        // Overwrite out with all the messages we've received since the last call.  Threadsafe.
31        void poll(SkTArray<Message>* out);
32
33    private:
34        SkTArray<Message>  fMessages;
35        SkMutex            fMessagesMutex;
36        uint32_t           fUniqueID;
37
38        friend class SkMessageBus;
39        void receive(const Message& m);  // SkMessageBus is a friend only to call this.
40    };
41
42private:
43    SkMessageBus();
44    static SkMessageBus* Get();
45
46    SkTDArray<Inbox*> fInboxes;
47    SkMutex           fInboxesMutex;
48};
49
50// This must go in a single .cpp file, not some .h, or we risk creating more than one global
51// SkMessageBus per type when using shared libraries.  NOTE: at most one per file will compile.
52#define DECLARE_SKMESSAGEBUS_MESSAGE(Message)                      \
53    template <>                                                    \
54    SkMessageBus<Message>* SkMessageBus<Message>::Get() {          \
55        static SkOnce once;                                        \
56        static SkMessageBus<Message>* bus;                         \
57        once([] { bus = new SkMessageBus<Message>(); });           \
58        return bus;                                                \
59    }
60
61//   ----------------------- Implementation of SkMessageBus::Inbox -----------------------
62
63template<typename Message>
64SkMessageBus<Message>::Inbox::Inbox(uint32_t uniqueID) : fUniqueID(uniqueID) {
65    // Register ourselves with the corresponding message bus.
66    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
67    SkAutoMutexAcquire lock(bus->fInboxesMutex);
68    bus->fInboxes.push(this);
69}
70
71template<typename Message>
72SkMessageBus<Message>::Inbox::~Inbox() {
73    // Remove ourselves from the corresponding message bus.
74    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
75    SkAutoMutexAcquire lock(bus->fInboxesMutex);
76    // This is a cheaper fInboxes.remove(fInboxes.find(this)) when order doesn't matter.
77    for (int i = 0; i < bus->fInboxes.count(); i++) {
78        if (this == bus->fInboxes[i]) {
79            bus->fInboxes.removeShuffle(i);
80            break;
81        }
82    }
83}
84
85template<typename Message>
86void SkMessageBus<Message>::Inbox::receive(const Message& m) {
87    SkAutoMutexAcquire lock(fMessagesMutex);
88    fMessages.push_back(m);
89}
90
91template<typename Message>
92void SkMessageBus<Message>::Inbox::poll(SkTArray<Message>* messages) {
93    SkASSERT(messages);
94    messages->reset();
95    SkAutoMutexAcquire lock(fMessagesMutex);
96    fMessages.swap(messages);
97}
98
99//   ----------------------- Implementation of SkMessageBus -----------------------
100
101template <typename Message>
102SkMessageBus<Message>::SkMessageBus() {}
103
104template <typename Message>
105/*static*/ void SkMessageBus<Message>::Post(const Message& m, uint32_t destID) {
106    SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
107    SkAutoMutexAcquire lock(bus->fInboxesMutex);
108    for (int i = 0; i < bus->fInboxes.count(); i++) {
109        if (SK_InvalidUniqueID == destID || bus->fInboxes[i]->fUniqueID == destID) {
110            bus->fInboxes[i]->receive(m);
111        }
112    }
113}
114
115#endif  // SkMessageBus_DEFINED
116