What is a Dispatch queue?

Dispatch Queue is a lightweight object that submits tasks for asynchronous or synchronous execution in GCD (Grand Central Dispatch).

Types of queues:

1. Serial: Executes tasks strictly in order, one after another.
2. Concurrent: Executes tasks simultaneously (as allowed by the system and available CPU cores).

Ways to obtain queues:

• Main Queue: A serial queue associated with the main thread of the application (UI).

  let mainQueue = DispatchQueue.main
  

• Global Concurrent Queues: Provided by the system with different quality of service (QoS) priorities.

  let userInitiatedQueue = DispatchQueue.global(qos: .userInitiated)
  

• Custom Queues: Can be serial or concurrent.

  let customSerialQueue = DispatchQueue(label: "com.example.mySerialQueue")
  let customConcurrentQueue = DispatchQueue(label: "com.example.myConcurrentQueue", attributes: .concurrent)
  

Submitting tasks:

• async: Adds a task to the queue for asynchronous execution, not blocking the current thread.

  customSerialQueue.async {
      // Asynchronous task
  }
  

• sync: Adds a task to the queue for synchronous execution, blocking the current thread until the task completes.

  customSerialQueue.sync {
      // Synchronous task
  }
  

  Use sync with caution, especially on the main queue, to avoid deadlocks.

Applications:

• Executing background tasks without blocking the UI.
• Managing access to shared resources (serial queues are used for synchronization).
• Parallelizing computations.