Status callbacks

README.md

@@ -18,6 +18,8 @@
 * [Serial and Concurrent Tasks](#serial-and-concurrent-tasks)
 * [GCD Queue Control](#gcd-queue-control)
 * [Extensive Example](#extensive-example)
+* [Callbacks](#callbacks)
+* [Callbacks Example](#callbacks-example)
 * [Credit](#credit)
 * [License](#license)
 
@@ -293,6 +295,48 @@ queue.run { result in
 
 Run the included demo app to see some of these examples above in action.
 
+## Callbacks
+
+You can register closures to receive status updates on the queue after each task executes.
+
+```swift
+typealias ClosureWithTaskQueueStatus = (TaskQueueStatus) -> Void
+```
+
+They will receive a status object:
+
+```swift
+struct TaskQueueStatus {
+  var activeTaskCount: Int
+  var maximumActiveTaskCount: Int
+  var queuedTaskCount: Int
+  var running: Bool
+}
+```
+
+## Callbacks example
+
+```swift
+let queue = TaskQueue()
+
+//
+// Simple sync task, just prints to console
+//
+queue.tasks += {
+    print("====== tasks ======")
+    print("task #1: run")
+}
+
+//
+// Simple callback, just prints to console
+//
+queue.callbacks.append({ (status) in
+  print("task queue status", status)
+})
+
+
+queue.run()
+```
 
 ## Credit
 

Sources/TaskQueue.swift

@@ -14,6 +14,13 @@
 
 import Foundation
 
+public struct TaskQueueStatus {
+  public var activeTaskCount: Int
+  public var maximumActiveTaskCount: Int
+  public var queuedTaskCount: Int
+  public var running: Bool
+}
+
 // MARK: TaskQueue class
 
 open class TaskQueue: CustomStringConvertible {
@@ -23,12 +30,14 @@ open class TaskQueue: CustomStringConvertible {
     //
     public typealias ClosureNoResultNext = () -> Void
     public typealias ClosureWithResultNext = (Any? , @escaping (Any?) -> Void) -> Void
+    public typealias ClosureWithTaskQueueStatus = (TaskQueueStatus) -> Void
 
     //
     // tasks and completions storage
     //
     open var tasks = [ClosureWithResultNext]()
     open lazy var completions = [ClosureNoResultNext]()
+    open var callbacks = [ClosureWithTaskQueueStatus]()
 
     //
     // concurrency
@@ -125,6 +134,13 @@ open class TaskQueue: CustomStringConvertible {
             task!(self.maximumNumberOfActiveTasks > 1 ? nil : result) { nextResult in
                 self.numberOfActiveTasks -= 1
                 self._runNextTask(nextResult)
+                self.callbacks.forEach({ (callback) in
+                  callback(TaskQueueStatus(activeTaskCount: self.numberOfActiveTasks,
+                                           maximumActiveTaskCount: self.maximumNumberOfActiveTasks,
+                                           queuedTaskCount: self.tasks.count,
+                                           running: self.running)
+                  )
+                })
             }
         }