1 // Copyright 2016 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef MOJO_EDK_SYSTEM_PORTS_MESSAGE_QUEUE_H_
6 #define MOJO_EDK_SYSTEM_PORTS_MESSAGE_QUEUE_H_
7 
8 #include <stdint.h>
9 
10 #include <deque>
11 #include <functional>
12 #include <limits>
13 #include <vector>
14 
15 #include "base/macros.h"
16 #include "mojo/edk/system/ports/message.h"
17 
18 namespace mojo {
19 namespace edk {
20 namespace ports {
21 
22 const uint64_t kInitialSequenceNum = 1;
23 const uint64_t kInvalidSequenceNum = std::numeric_limits<uint64_t>::max();
24 
25 // An incoming message queue for a port. MessageQueue keeps track of the highest
26 // known sequence number and can indicate whether the next sequential message is
27 // available. Thus the queue enforces message ordering for the consumer without
28 // enforcing it for the producer (see AcceptMessage() below.)
29 class MessageQueue {
30  public:
31   explicit MessageQueue();
32   explicit MessageQueue(uint64_t next_sequence_num);
33   ~MessageQueue();
34 
set_signalable(bool value)35   void set_signalable(bool value) { signalable_ = value; }
36 
next_sequence_num()37   uint64_t next_sequence_num() const { return next_sequence_num_; }
38 
39   bool HasNextMessage() const;
40 
41   // Gives ownership of the message. The selector may be null.
42   void GetNextMessageIf(std::function<bool(const Message&)> selector,
43                         ScopedMessage* message);
44 
45   // Takes ownership of the message. Note: Messages are ordered, so while we
46   // have added a message to the queue, we may still be waiting on a message
47   // ahead of this one before we can let any of the messages be returned by
48   // GetNextMessage.
49   //
50   // Furthermore, once has_next_message is set to true, it will remain false
51   // until GetNextMessage is called enough times to return a null message.
52   // In other words, has_next_message acts like an edge trigger.
53   //
54   void AcceptMessage(ScopedMessage message, bool* has_next_message);
55 
56   // Returns all of the ports referenced by messages in this message queue.
57   void GetReferencedPorts(std::deque<PortName>* ports);
58 
59  private:
60   std::vector<ScopedMessage> heap_;
61   uint64_t next_sequence_num_;
62   bool signalable_ = true;
63 
64   DISALLOW_COPY_AND_ASSIGN(MessageQueue);
65 };
66 
67 }  // namespace ports
68 }  // namespace edk
69 }  // namespace mojo
70 
71 #endif  // MOJO_EDK_SYSTEM_PORTS_MESSAGE_QUEUE_H_
72