What happens if you call the global DispatchQueue?

The global DispatchQueue in iOS is a system queue provided by GCD (Grand Central Dispatch) that manages the execution of tasks on background or main threads.

If you call (for example, invoke the async or sync method) on the global queue, the task will be placed in the queue for execution with a certain priority (QoS). Global queues are concurrent, meaning multiple tasks can run in parallel depending on available resources.

Example:

DispatchQueue.global(qos: .background).async {
    // This code will run on a background thread
    print("Background task")
}

If you simply call the global queue without adding a task, nothing will happen — the queue itself does not execute code; it only manages the tasks placed into it.

Thus, calling the global queue means scheduling an asynchronous or synchronous task on system threads with a specified priority.