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As I understand there are 3 types of DispatchQueue in swift:
And each one maybe work (asynch or synch)
First question:
Is it main queue working on UI thread only and not working on another thread?
If the answer yes , how DispatchQueue.Main.async not blocking UI thread.
If the answer No , what is the benefit of using DispatchQueue.global as long as DispatchQueue.Main.async work in another thread.
Second question:
what is deference between DispatchQueue.global (async) and DispatchQueue.global (sync) as long as this queue working Concurrent and where to use each one?
Third question:
what is defference between
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Dispatch queues are FIFO queues to which your application can submit tasks in the form of block objects. Dispatch queues execute tasks either serially or concurrently. Work submitted to dispatch queues executes on a pool of threads managed by the system.
The main dispatch queue is a globally available serial queue executing tasks on the application's main thread. As the main thread is used for UI updates it's important to be conscious when executing tasks on this queue.
As I understand there are 3 types of DispatchQueue in swift: Main (serial) (Main Thread) Global (Concurrent) (Background Threads working in parallel) Custom (Concurrent or serial)
There are background threads for heavy tasks. DispatchQueue. global() runs these kind of tasks in background threads. You can tell the queue about how important your task is, so that DispatchQueue can prioritize your task. You can do this by providing Quality-of-Service information.
As I understand:
Queue is not Thread
Main and global queue may work in same thread
Dispatched: means put task in queue
If Global queue dispatched in Main queue as sync , the dispatched task will work on same thread of Main queue and dispatched task added to Global queue , And this task will freezing the thread
If Global queue dispatched in Main queue as async , the dispatched task will work on other thread of Main queue and dispatched task added to Global queue , And this task will not freezing the thread
If Main queue dispatched in Main queue as async , the dispatched task will work on same thread of Main queue
If Main queue dispatched in Main queue as sync will make exception because make deadlock
Dispatch.sync: put task in queue and wait it until finish
Dispatch.async: put task in queue and not wait it until finish (The task may work in same thread or in another thread)
If task dispatched on Global queue and this accord from Main thread then the task will added to Global queue , and new thread will be create and the task will start working immediately in the new thread
If task dispatched on Main queue and this accord from Main thread then the task will added to Main queue , and will not work immediately until older tasks in queue finish working (because Main queue is sequential )
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