Add MutuallyExclusive publisher

1 files changed, 58 insertions, 0 deletions

diff --git a/ios/MullvadVPN/MutuallyExclusive.swift b/ios/MullvadVPN/MutuallyExclusive.swift
new file mode 100644
index 0000000000..cb3803805a
--- /dev/null
+++ b/ios/MullvadVPN/MutuallyExclusive.swift
@@ -0,0 +1,58 @@
+//
+//  MutuallyExclusive.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 24/10/2019.
+//  Copyright © 2019 Amagicom AB. All rights reserved.
+//
+
+import Combine
+import Foundation
+
+extension Publishers {
+
+    /// A publisher that blocks the given DispatchQueue until the produced publisher reported the
+    /// completion.
+    final class MutuallyExclusive<PublisherType, Context>: Publisher where PublisherType: Publisher, Context: Scheduler {
+
+        typealias Output = PublisherType.Output
+        typealias Failure = PublisherType.Failure
+
+        typealias MakePublisherBlock = () -> PublisherType
+
+        private let exclusivityQueue: Context
+        private let executionQueue: Context
+
+        private let createPublisher: MakePublisherBlock
+
+        init(exclusivityQueue: Context, executionQueue: Context, createPublisher: @escaping MakePublisherBlock) {
+            self.exclusivityQueue = exclusivityQueue
+            self.executionQueue = executionQueue
+            self.createPublisher = createPublisher
+        }
+
+        func receive<S>(subscriber: S) where S : Subscriber, S.Failure == Failure, S.Input == Output {
+            exclusivityQueue.schedule {
+                let sema = DispatchSemaphore(value: 0)
+                let releaseLock = {
+                    _ = sema.signal()
+                }
+
+                self.executionQueue.schedule {
+                    self.createPublisher()
+                        .handleEvents(receiveCompletion: { _ in
+                            releaseLock()
+                        }, receiveCancel: {
+                            releaseLock()
+                        })
+                        .subscribe(subscriber)
+                }
+
+                sema.wait()
+            }
+        }
+    }
+
+}
+
+typealias MutuallyExclusive = Publishers.MutuallyExclusive