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Refactor channel connectivity to avoid multiple spin loops (#380)
The current Swift implementation of the gRPC channel's connectivity observer spins up a new ConnectivityObserver instance which then starts a new "spin loop" thread and continually runs, observing changes to the underlying gRPC Core channel's connectivity and piping those back through a callback closure. This means that there's a new spin loop spun up for each observer for each channel. We can avoid having to spin up multiple spin loops for each observer (keeping only 0 or 1 per channel) by allowing a single ConnectivityObserver instance to pipe changes back to multiple callbacks.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,96 @@ | ||
| /* | ||
| * Copyright 2016, gRPC Authors All rights reserved. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| #if SWIFT_PACKAGE | ||
| import CgRPC | ||
| import Dispatch | ||
| #endif | ||
| import Foundation | ||
|
|
||
| extension Channel { | ||
| /// Provides an interface for observing the connectivity of a given channel. | ||
| final class ConnectivityObserver { | ||
| private let mutex = Mutex() | ||
| private let completionQueue: CompletionQueue | ||
| private let underlyingChannel: UnsafeMutableRawPointer | ||
| private let underlyingCompletionQueue: UnsafeMutableRawPointer | ||
| private var callbacks = [(ConnectivityState) -> Void]() | ||
| private var hasBeenShutdown = false | ||
|
|
||
| init(underlyingChannel: UnsafeMutableRawPointer) { | ||
| self.underlyingChannel = underlyingChannel | ||
| self.underlyingCompletionQueue = cgrpc_completion_queue_create_for_next() | ||
| self.completionQueue = CompletionQueue(underlyingCompletionQueue: self.underlyingCompletionQueue, | ||
| name: "Connectivity State") | ||
| self.run() | ||
| } | ||
|
|
||
| deinit { | ||
| self.shutdown() | ||
| } | ||
|
|
||
| func addConnectivityObserver(callback: @escaping (ConnectivityState) -> Void) { | ||
| self.mutex.synchronize { | ||
| self.callbacks.append(callback) | ||
| } | ||
| } | ||
|
|
||
| func shutdown() { | ||
| self.mutex.synchronize { | ||
| guard !self.hasBeenShutdown else { return } | ||
|
|
||
| self.hasBeenShutdown = true | ||
| self.completionQueue.shutdown() | ||
| } | ||
| } | ||
|
|
||
| // MARK: - Private | ||
|
|
||
| private func run() { | ||
| let spinloopThreadQueue = DispatchQueue(label: "SwiftGRPC.ConnectivityObserver.run.spinloopThread") | ||
| var lastState = ConnectivityState(cgrpc_channel_check_connectivity_state(self.underlyingChannel, 0)) | ||
| spinloopThreadQueue.async { | ||
| while (self.mutex.synchronize { !self.hasBeenShutdown }) { | ||
| guard let underlyingState = lastState.underlyingState else { return } | ||
|
|
||
| let deadline: TimeInterval = 0.2 | ||
| cgrpc_channel_watch_connectivity_state(self.underlyingChannel, self.underlyingCompletionQueue, | ||
| underlyingState, deadline, nil) | ||
|
|
||
| let event = self.completionQueue.wait(timeout: deadline) | ||
| guard (self.mutex.synchronize { !self.hasBeenShutdown }) else { | ||
| return | ||
| } | ||
|
|
||
| switch event.type { | ||
| case .complete: | ||
| let newState = ConnectivityState(cgrpc_channel_check_connectivity_state(self.underlyingChannel, 0)) | ||
| guard newState != lastState else { continue } | ||
|
|
||
| let callbacks = self.mutex.synchronize { Array(self.callbacks) } | ||
| lastState = newState | ||
| callbacks.forEach { callback in callback(newState) } | ||
|
|
||
| case .queueShutdown: | ||
| return | ||
|
|
||
| default: | ||
| continue | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
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