Potential Deadlock Deinit (#36)

* Validate queue before calling stop on deinit

* Add dispatch precondition

Author: dsmurfin

Sources/sACNKit/Receiver/sACNDiscoveryReceiver.swift

@@ -30,12 +30,15 @@ import Foundation
 ///
 /// An E1.31-2018 sACN Receiver which receives universe discovery messages.
 public class sACNDiscoveryReceiver {
-    
+
     // MARK: Socket
-    
+
+    /// A key used to identify the socket delegate queue for the current execution context.
+    private static let socketDelegateQueueSpecificKey = DispatchSpecificKey<Bool>()
+
     /// The Internet Protocol version(s) used by the receiver.
     private let ipMode: sACNIPMode
-    
+
     /// The queue on which socket notifications occur (also used to protect state).
     private let socketDelegateQueue: DispatchQueue
 
@@ -120,6 +123,7 @@ public class sACNDiscoveryReceiver {
         // sockets
         self.ipMode = ipMode
         let socketDelegateQueue = DispatchQueue(label: "com.danielmurfin.sACNKit.discoveryReceiverSocketDelegate")
+        socketDelegateQueue.setSpecific(key: Self.socketDelegateQueueSpecificKey, value: true)
         self.socketDelegateQueue = socketDelegateQueue
         if interfaces.isEmpty {
             let socket = ComponentSocket(type: .receive, ipMode: ipMode, port: UDP.sdtPort, delegateQueue: socketDelegateQueue)
@@ -172,19 +176,29 @@ public class sACNDiscoveryReceiver {
     ///
     /// The receiver will stop listening for sACN Universe Discovery messages.
     public func stop() {
-        socketDelegateQueue.sync {
-            guard _isListening else { return }
-            _isListening = false
-            
-            stopHeartbeat()
-            
-            sockets.forEach { interface, socket in
-                socket.delegate = nil
-                socket.stopListening()
-            }
-            
-            sources = [:]
+        if DispatchQueue.getSpecific(key: Self.socketDelegateQueueSpecificKey) == true {
+            _stop()
+        } else {
+            socketDelegateQueue.sync { _stop() }
+        }
+    }
+
+    /// Performs the stop logic.
+    ///
+    /// Must be called on `socketDelegateQueue`.
+    private func _stop() {
+        dispatchPrecondition(condition: .onQueue(socketDelegateQueue))
+        guard _isListening else { return }
+        _isListening = false
+
+        stopHeartbeat()
+
+        sockets.forEach { interface, socket in
+            socket.delegate = nil
+            socket.stopListening()
         }
+
+        sources = [:]
     }
 
     /// Updates the interfaces on which this receiver listens for sACN Universe Discovery messages.

Sources/sACNKit/Receiver/sACNReceiverRaw.swift

@@ -32,10 +32,13 @@ import Foundation
 public class sACNReceiverRaw {
 
     // MARK: Socket
-    
+
+    /// A key used to identify the socket delegate queue for the current execution context.
+    private static let socketDelegateQueueSpecificKey = DispatchSpecificKey<Bool>()
+
     /// The Internet Protocol version(s) used by the receiver.
     private let ipMode: sACNIPMode
-    
+
     /// The queue on which socket notifications occur (also used to protect state).
     private let socketDelegateQueue: DispatchQueue
 
@@ -170,6 +173,7 @@ public class sACNReceiverRaw {
         // sockets
         self.ipMode = ipMode
         let socketDelegateQueue = DispatchQueue(label: "com.danielmurfin.sACNKit.receiverSocketDelegate-\(universe)")
+        socketDelegateQueue.setSpecific(key: Self.socketDelegateQueueSpecificKey, value: true)
         self.socketDelegateQueue = socketDelegateQueue
         if interfaces.isEmpty {
             let socket = ComponentSocket(type: .receive, ipMode: ipMode, port: UDP.sdtPort, delegateQueue: socketDelegateQueue)
@@ -238,23 +242,33 @@ public class sACNReceiverRaw {
     ///
     /// The receiver will stop listening for sACN Data messages.
     public func stop() {
-        socketDelegateQueue.sync {
-            guard _isListening else { return }
-            self._isListening = false
-            
-            sampleTimer?.cancel()
-            sampleTimer = nil
-            stopHeartbeat()
-            
-            sockets.forEach { interface, socket in
-                socket.delegate = nil
-                socket.stopListening()
-            }
-            
-            sampling = false
-            sources = [:]
+        if DispatchQueue.getSpecific(key: Self.socketDelegateQueueSpecificKey) == true {
+            _stop()
+        } else {
+            socketDelegateQueue.sync { _stop() }
         }
     }
+
+    /// Performs the stop logic.
+    ///
+    /// Must be called on `socketDelegateQueue`.
+    private func _stop() {
+        dispatchPrecondition(condition: .onQueue(socketDelegateQueue))
+        guard _isListening else { return }
+        self._isListening = false
+
+        sampleTimer?.cancel()
+        sampleTimer = nil
+        stopHeartbeat()
+
+        sockets.forEach { interface, socket in
+            socket.delegate = nil
+            socket.stopListening()
+        }
+
+        sampling = false
+        sources = [:]
+    }
 
     /// Updates the interfaces on which this receiver listens for sACN Data messages.
     ///

Sources/sACNKit/Source/sACNSource.swift

@@ -31,12 +31,15 @@ import CocoaAsyncSocket
 final public class sACNSource {
 
     private typealias UniverseData = (universeNumber: UInt16, data: Data)
-    
+
     // MARK: Socket
-    
+
+    /// A key used to identify the socket delegate queue for the current execution context.
+    private static let socketDelegateQueueSpecificKey = DispatchSpecificKey<Bool>()
+
     /// The Internet Protocol version(s) used by the source.
     private let ipMode: sACNIPMode
-    
+
     /// The queue on which socket notifications occur (also used to protect state).
     private let socketDelegateQueue: DispatchQueue
 
@@ -200,6 +203,7 @@ final public class sACNSource {
         // sockets
         self.ipMode = ipMode
         let socketDelegateQueue = DispatchQueue(label: "com.danielmurfin.sACNKit.sourceSocketDelegate")
+        socketDelegateQueue.setSpecific(key: Self.socketDelegateQueueSpecificKey, value: true)
         self.socketDelegateQueue = socketDelegateQueue
         self.socketsShouldTerminate = [:]
         if interfaces.isEmpty {
@@ -285,18 +289,28 @@ final public class sACNSource {
     /// When stopped, this source will no longer transmit sACN messages.
     ///
     public func stop() {
-        socketDelegateQueue.sync {
-            guard _isListening else { return }
-            self._isListening = false
-            
-            // stops heartbeats
-            stopUniverseDiscovery()
-            stopDataTransmit()
-            
-            // stop listening on socket occurs after
-            // final termination is sent
+        if DispatchQueue.getSpecific(key: Self.socketDelegateQueueSpecificKey) == true {
+            _stop()
+        } else {
+            socketDelegateQueue.sync { _stop() }
         }
     }
+
+    /// Performs the stop logic.
+    ///
+    /// Must be called on `socketDelegateQueue`.
+    private func _stop() {
+        dispatchPrecondition(condition: .onQueue(socketDelegateQueue))
+        guard _isListening else { return }
+        self._isListening = false
+
+        // stops heartbeats
+        stopUniverseDiscovery()
+        stopDataTransmit()
+
+        // stop listening on socket occurs after
+        // final termination is sent
+    }
 
     /// Updates the interfaces on which this source transmits for sACN Universe Discovery and Data messages.
     ///