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1 | // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- |
2 | /* | |
3 | * This file is open source software, licensed to you under the terms | |
4 | * of the Apache License, Version 2.0 (the "License"). See the NOTICE file | |
5 | * distributed with this work for additional information regarding copyright | |
6 | * ownership. You may not use this file except in compliance with the License. | |
7 | * | |
8 | * You may obtain a copy of the License at | |
9 | * | |
10 | * http://www.apache.org/licenses/LICENSE-2.0 | |
11 | * | |
12 | * Unless required by applicable law or agreed to in writing, | |
13 | * software distributed under the License is distributed on an | |
14 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
15 | * KIND, either express or implied. See the License for the | |
16 | * specific language governing permissions and limitations | |
17 | * under the License. | |
18 | */ | |
19 | /* | |
20 | * Copyright (C) 2014 Cloudius Systems, Ltd. | |
21 | */ | |
7c673cae FG |
22 | |
23 | #ifndef CEPH_MSG_STREAM_H_ | |
24 | #define CEPH_MSG_STREAM_H_ | |
25 | ||
26 | #include <exception> | |
27 | #include <cassert> | |
28 | ||
29 | // A stream<> is the producer side. It may call produce() as long | |
30 | // as the returned from the previous invocation is ready. | |
31 | // To signify no more data is available, call close(). | |
32 | // | |
33 | // A subscription<> is the consumer side. It is created by a call | |
34 | // to stream::listen(). Calling subscription::start(), | |
35 | // which registers the data processing callback, starts processing | |
36 | // events. It may register for end-of-stream notifications by | |
37 | // return the when_done() future, which also delivers error | |
38 | // events (as exceptions). | |
39 | // | |
40 | // The consumer can pause generation of new data by returning | |
41 | // positive integer; when it becomes ready, the producer | |
42 | // will resume processing. | |
43 | ||
44 | template <typename... T> | |
45 | class subscription; | |
46 | ||
47 | template <typename... T> | |
48 | class stream { | |
49 | subscription<T...>* _sub = nullptr; | |
50 | int done; | |
51 | bool ready; | |
52 | public: | |
53 | using next_fn = std::function<int (T...)>; | |
54 | stream() = default; | |
55 | stream(const stream&) = delete; | |
56 | stream(stream&&) = delete; | |
57 | ~stream() { | |
58 | if (_sub) { | |
59 | _sub->_stream = nullptr; | |
60 | } | |
61 | } | |
62 | ||
63 | void operator=(const stream&) = delete; | |
64 | void operator=(stream&&) = delete; | |
65 | ||
66 | // Returns a subscription that reads value from this | |
67 | // stream. | |
68 | subscription<T...> listen() { | |
69 | return subscription<T...>(this); | |
70 | } | |
71 | ||
72 | // Returns a subscription that reads value from this | |
73 | // stream, and also sets up the listen function. | |
74 | subscription<T...> listen(next_fn next) { | |
75 | auto sub = subscription<T...>(this); | |
76 | sub.start(std::move(next)); | |
77 | return sub; | |
78 | } | |
79 | ||
80 | // Becomes ready when the listener is ready to accept | |
81 | // values. Call only once, when beginning to produce | |
82 | // values. | |
83 | bool started() { | |
84 | return ready; | |
85 | } | |
86 | ||
87 | // Produce a value. Call only after started(), and after | |
88 | // a previous produce() is ready. | |
89 | int produce(T... data) { | |
90 | return _sub->_next(std::move(data)...); | |
91 | } | |
92 | ||
93 | // End the stream. Call only after started(), and after | |
94 | // a previous produce() is ready. No functions may be called | |
95 | // after this. | |
96 | void close() { | |
97 | done = 1; | |
98 | } | |
99 | ||
100 | // Signal an error. Call only after started(), and after | |
101 | // a previous produce() is ready. No functions may be called | |
102 | // after this. | |
103 | void set_exception(int error) { | |
104 | done = error; | |
105 | } | |
106 | private: | |
107 | void start(); | |
108 | friend class subscription<T...>; | |
109 | }; | |
110 | ||
111 | template <typename... T> | |
112 | class subscription { | |
113 | public: | |
114 | using next_fn = typename stream<T...>::next_fn; | |
115 | private: | |
116 | stream<T...>* _stream; | |
117 | next_fn _next; | |
118 | private: | |
119 | explicit subscription(stream<T...>* s): _stream(s) { | |
11fdf7f2 | 120 | ceph_assert(!_stream->_sub); |
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121 | _stream->_sub = this; |
122 | } | |
123 | ||
124 | public: | |
125 | subscription(subscription&& x) | |
126 | : _stream(x._stream), _next(std::move(x._next)) { | |
127 | x._stream = nullptr; | |
128 | if (_stream) { | |
129 | _stream->_sub = this; | |
130 | } | |
131 | } | |
132 | ~subscription() { | |
133 | if (_stream) { | |
134 | _stream->_sub = nullptr; | |
135 | } | |
136 | } | |
137 | ||
138 | /// \brief Start receiving events from the stream. | |
139 | /// | |
140 | /// \param next Callback to call for each event | |
141 | void start(std::function<int (T...)> next) { | |
142 | _next = std::move(next); | |
143 | _stream->ready = true; | |
144 | } | |
145 | ||
146 | // Becomes ready when the stream is empty, or when an error | |
147 | // happens (in that case, an exception is held). | |
148 | int done() { | |
149 | return _stream->done; | |
150 | } | |
151 | ||
152 | friend class stream<T...>; | |
153 | }; | |
154 | ||
155 | #endif /* CEPH_MSG_STREAM_H_ */ |