Allow user to specify enqueue DispatchQueue to fix multi-thread enqueue crash (#403)

Author: Lucas Nelaupe

Sources/SwiftQueue/JobBuilder.swift

@@ -184,7 +184,6 @@ public final class JobBuilder {
             assert(JSONSerialization.isValidJSONObject(info.params))
             info.constraints.append(PersisterConstraint(serializer: manager.params.serializer, persister: manager.params.persister))
         }
-
         manager.enqueue(info: info)
     }
 

Sources/SwiftQueue/SwiftQueueManager.swift

@@ -63,6 +63,16 @@ public final class SwiftQueueManager {
     /// Schedule a job to the queue
     /// TODO Need to remove this method
     public func enqueue(info: JobInfo) {
+        if let thread = params.enqueueThread {
+            thread.sync(flags: .barrier) {
+                enqueueInMainThread(info: info)
+            }
+        } else {
+            enqueueInMainThread(info: info)
+        }
+    }
+
+    private func enqueueInMainThread(info: JobInfo) {
         let queue = getQueue(queueName: info.queueName)
         let job = queue.createHandler(type: info.type, params: info.params)
         let constraints = info.constraints
@@ -167,14 +177,17 @@ internal struct SqManagerParams {
 
     var initInBackground: Bool
 
+    var enqueueThread: DispatchQueue?
+
     init(jobCreator: JobCreator,
          queueCreator: QueueCreator,
          persister: JobPersister = UserDefaultsPersister(),
          serializer: JobInfoSerializer = DecodableSerializer(maker: DefaultConstraintMaker()),
          logger: SwiftQueueLogger = NoLogger.shared,
          listener: JobListener? = nil,
          initInBackground: Bool = false,
-         dispatchQueue: DispatchQueue = DispatchQueue.global(qos: DispatchQoS.QoSClass.utility)
+         dispatchQueue: DispatchQueue = DispatchQueue.global(qos: DispatchQoS.QoSClass.utility),
+         enqueueThread: DispatchQueue? = nil
     ) {
         self.jobCreator = jobCreator
         self.queueCreator = queueCreator
@@ -184,6 +197,7 @@ internal struct SqManagerParams {
         self.listener = listener
         self.initInBackground = initInBackground
         self.dispatchQueue = dispatchQueue
+        self.enqueueThread = enqueueThread
     }
 
 }
@@ -242,6 +256,14 @@ public final class SwiftQueueManagerBuilder {
         return self
     }
 
+    /// Use a single DispatchQueue to enqueue jobs
+    /// This can solve crashes when calling 'enqueue' in a multi-thread environment
+    public func set(enqueueDispatcher: DispatchQueue) -> Self {
+        params.enqueueThread = enqueueDispatcher
+        return self
+    }
+
+
     /// Get an instance of `SwiftQueueManager`
     public func build() -> SwiftQueueManager {
         return SwiftQueueManager(params: params, isSuspended: isSuspended)

Tests/SwiftQueueTests/SwiftQueueManagerTests.swift

@@ -305,4 +305,29 @@ class SwiftQueueManagerTests: XCTestCase {
         job.assertError(queueError: .canceled)
     }
 
+    func testConcurrentScheduling() {
+        let (type, job) = (UUID().uuidString, TestJob())
+        let creator = TestCreator([type: job])
+        let persister = PersisterTracker(key: UUID().uuidString)
+        let manager = SwiftQueueManagerBuilder(creator: creator)
+                .set(isSuspended: true)
+                .set(enqueueDispatcher: .main)
+                .set(persister: persister).build()
+
+
+        let concurrentQueue = DispatchQueue(label: "com.test.concurrent", attributes: .concurrent)
+        for _ in 0..<10 {
+            concurrentQueue.async {
+                JobBuilder(type: type).parallel(queueName: UUID().uuidString).schedule(manager: manager)
+            }
+        }
+
+        for _ in 0..<10 {
+            DispatchQueue(label: "com.test.concurrent", attributes: .concurrent).async {
+                JobBuilder(type: type).parallel(queueName: UUID().uuidString).schedule(manager: manager)
+            }
+        }
+
+    }
+
 }