Update ConcurrentSequenceExecutor to use AutoReleasingSemaphore (#33)

* Update ConcurrentSequenceExecutor to use AutoReleasingSemaphore

Fixes #29

* Remove debugging code

Author: neakor

Sources/Concurrency/AutoReleasingSemaphore.swift

@@ -38,6 +38,7 @@ public class AutoReleasingSemaphore {
     /// in dispatch_semaphore_wait(_:_:).
     /// - returns: This function returns non-zero if a thread is woken.
     /// Otherwise, zero is returned.
+    @discardableResult
     public func signal() -> Int {
         let newValue = waitingCount.decrementAndGet()
         if newValue < 0 {
@@ -65,6 +66,7 @@ public class AutoReleasingSemaphore {
     /// - parameter timeout: The amount of time in seconds to wait
     /// before returning with failure.
     /// - returns: The waiting result.
+    @discardableResult
     public func wait(timeout: TimeInterval) -> DispatchTimeoutResult {
         waitingCount.incrementAndGet()
         return semaphore.wait(timeout: DispatchTime.now() + timeout)

Sources/Concurrency/Executor/ConcurrentSequenceExecutor.swift

@@ -39,7 +39,7 @@ public class ConcurrentSequenceExecutor: SequenceExecutor {
     public init(name: String, qos: DispatchQoS = .userInitiated, shouldTrackTaskId: Bool = false, maxConcurrentTasks: Int? = nil) {
         taskQueue = DispatchQueue(label: "Executor.taskQueue-\(name)", qos: qos, attributes: .concurrent)
         if let maxConcurrentTasks = maxConcurrentTasks {
-            taskSemaphore = DispatchSemaphore(value: maxConcurrentTasks)
+            taskSemaphore = AutoReleasingSemaphore(value: maxConcurrentTasks)
         } else {
             taskSemaphore = nil
         }
@@ -66,7 +66,7 @@ public class ConcurrentSequenceExecutor: SequenceExecutor {
     // MARK: - Private
 
     private let taskQueue: DispatchQueue
-    private let taskSemaphore: DispatchSemaphore?
+    private let taskSemaphore: AutoReleasingSemaphore?
     private let shouldTrackTaskId: Bool
 
     private func execute<SequenceResultType>(_ task: Task, with sequenceHandle: SynchronizedSequenceExecutionHandle<SequenceResultType>, _ execution: @escaping (Task, Any) -> SequenceExecution<SequenceResultType>) {