What will happen if a synchronous call to itself is made in the main thread, and why will this lead to a deadlock?

If a synchronous call to itself is made in the main thread of an iOS application, for example, via DispatchQueue.main.sync, it will lead to a deadlock.

Why does this happen:

• The main thread is already busy executing the current code.
• During a synchronous call, it tries to execute a block of code that should be placed in the main thread's queue.
• But the main thread cannot process this block until it finishes the current one, and the current one is waiting for the synchronous call to complete.

As a result, a situation occurs where the thread waits for itself, and execution stops forever.

Example in Swift:

DispatchQueue.main.sync {
    // This code attempts to execute synchronously on the main thread,
    // but if the call is made from the main thread, it will cause a deadlock
}