/src/grpc-swift/Sources/GRPC/ClientCalls/LazyEventLoopPromise.swift
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1 | | /* |
2 | | * Copyright 2020, gRPC Authors All rights reserved. |
3 | | * |
4 | | * Licensed under the Apache License, Version 2.0 (the "License"); |
5 | | * you may not use this file except in compliance with the License. |
6 | | * You may obtain a copy of the License at |
7 | | * |
8 | | * http://www.apache.org/licenses/LICENSE-2.0 |
9 | | * |
10 | | * Unless required by applicable law or agreed to in writing, software |
11 | | * distributed under the License is distributed on an "AS IS" BASIS, |
12 | | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
13 | | * See the License for the specific language governing permissions and |
14 | | * limitations under the License. |
15 | | */ |
16 | | import NIOConcurrencyHelpers |
17 | | import NIOCore |
18 | | |
19 | | extension EventLoop { |
20 | 0 | internal func makeLazyPromise<Value>(of: Value.Type = Value.self) -> LazyEventLoopPromise<Value> { |
21 | 0 | return LazyEventLoopPromise(on: self) |
22 | 0 | } |
23 | | } |
24 | | |
25 | | /// A `LazyEventLoopPromise` is similar to an `EventLoopPromise` except that the underlying |
26 | | /// `EventLoopPromise` promise is only created if it is required. That is, when the future result |
27 | | /// has been requested and the promise has not yet been completed. |
28 | | /// |
29 | | /// Note that all methods **must** be called from its `eventLoop`. |
30 | | internal struct LazyEventLoopPromise<Value> { |
31 | | private enum State { |
32 | | // No future has been requested, no result has been delivered. |
33 | | case idle |
34 | | |
35 | | // No future has been requested, but this result have been delivered. |
36 | | case resolvedResult(Result<Value, Error>) |
37 | | |
38 | | // A future has been request; the promise may or may not contain a result. |
39 | | case unresolvedPromise(EventLoopPromise<Value>) |
40 | | |
41 | | // A future was requested, it's also been resolved. |
42 | | case resolvedFuture(EventLoopFuture<Value>) |
43 | | } |
44 | | |
45 | | private var state: State |
46 | | private let eventLoop: EventLoop |
47 | | |
48 | 0 | fileprivate init(on eventLoop: EventLoop) { |
49 | 0 | self.state = .idle |
50 | 0 | self.eventLoop = eventLoop |
51 | 0 | } |
52 | | |
53 | | /// Get the future result of this promise. |
54 | 0 | internal mutating func getFutureResult() -> EventLoopFuture<Value> { |
55 | 0 | self.eventLoop.preconditionInEventLoop() |
56 | 0 |
|
57 | 0 | switch self.state { |
58 | 0 | case .idle: |
59 | 0 | let promise = self.eventLoop.makePromise(of: Value.self) |
60 | 0 | self.state = .unresolvedPromise(promise) |
61 | 0 | return promise.futureResult |
62 | 0 |
|
63 | 0 | case let .resolvedResult(result): |
64 | 0 | let future: EventLoopFuture<Value> |
65 | 0 | switch result { |
66 | 0 | case let .success(value): |
67 | 0 | future = self.eventLoop.makeSucceededFuture(value) |
68 | 0 | case let .failure(error): |
69 | 0 | future = self.eventLoop.makeFailedFuture(error) |
70 | 0 | } |
71 | 0 | self.state = .resolvedFuture(future) |
72 | 0 | return future |
73 | 0 |
|
74 | 0 | case let .unresolvedPromise(promise): |
75 | 0 | return promise.futureResult |
76 | 0 |
|
77 | 0 | case let .resolvedFuture(future): |
78 | 0 | return future |
79 | 0 | } |
80 | 0 | } |
81 | | |
82 | | /// Succeed the promise with the given value. |
83 | 0 | internal mutating func succeed(_ value: Value) { |
84 | 0 | self.completeWith(.success(value)) |
85 | 0 | } |
86 | | |
87 | | /// Fail the promise with the given error. |
88 | 0 | internal mutating func fail(_ error: Error) { |
89 | 0 | self.completeWith(.failure(error)) |
90 | 0 | } |
91 | | |
92 | | /// Complete the promise with the given result. |
93 | 0 | internal mutating func completeWith(_ result: Result<Value, Error>) { |
94 | 0 | self.eventLoop.preconditionInEventLoop() |
95 | 0 |
|
96 | 0 | switch self.state { |
97 | 0 | case .idle: |
98 | 0 | self.state = .resolvedResult(result) |
99 | 0 |
|
100 | 0 | case let .unresolvedPromise(promise): |
101 | 0 | promise.completeWith(result) |
102 | 0 | self.state = .resolvedFuture(promise.futureResult) |
103 | 0 |
|
104 | 0 | case .resolvedResult, .resolvedFuture: |
105 | 0 | () |
106 | 0 | } |
107 | 0 | } |
108 | | } |