iOS'da ko'p ipli dasturlashda global navbat haqida gapiring.

Global Queue (Global Queue) in Grand Central Dispatch (GCD) is a set of predefined system queues accessible to all applications. They are concurrent queues, meaning tasks within them can be executed in parallel on different threads.

Main features:

• Types: Vary according to the level of service quality (QoS - Quality of Service).
• QoS: Determines the priority of task execution, influencing which tasks the system should complete faster.
• Concurrency: Allow multiple tasks to run simultaneously.
• System: Created and managed by the operating system.

Types of global queues (in descending order of priority):

QoS Level	Description
userInteractive	Tasks that directly affect the user interface (animations, events).
userInitiated	Tasks initiated by the user, but not blocking the UI (loading content).
default	Default level without explicit QoS indication.
utility	Tasks requiring time to execute, but not immediately affecting the UI (loading large files).
background	Tasks running in the background, invisible to the user (data synchronization).
unspecified	Rarely used when QoS is not important. Equivalent to default.

Access to global queues:

// Accessing a global queue with a specific QoS level
let userInitiatedQueue = DispatchQueue.global(qos: .userInitiated)

// Accessing the default global queue
let defaultQueue = DispatchQueue.global()

Using global queues to perform tasks:

// Asynchronous execution of a task in a background queue
DispatchQueue.global(qos: .background).async {
    // Long-running code, non-blocking UI
}

// Synchronous execution of a task in the queue (less common for global queues)
DispatchQueue.global(qos: .userInitiated).sync {
    // Code that must be completed before continuing the current thread
}

Important to remember:

• Do not perform tasks that directly affect the user interface in global queues (except userInteractive for very fast operations). Use the main queue (DispatchQueue.main) for UI updates.
• Global queues are intended for parallel execution. The order of task execution may not be guaranteed.
• Using sync in a global queue will block the current thread until the task completes. This can lead to UI blocking if called from the main thread.