OR-5286 Timers:: Using DispatchQueue

[crazymanish]

Context

• Close ticket: [w33(13august-19august)] Timers: Using DispatchQueue #50

In this PR

• Before the Dispatch framework was available, developers relied on RunLoop to asynchronously perform tasks and implement concurrency.
• Timer (NSTimer in Objective-C) could be used to create repeating and non-repeating timers.
• Then Dispatch arrived and with it, DispatchSourceTimer.

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• Using RunLoop
• The main thread and any thread you create, preferably using the Thread class, can have its own RunLoop.
• It is always better, to use the main RunLoop that runs the main thread of your application. RunLoop.main
• RunLoop class is not thread-safe. means You should only call RunLoop methods for the run loop of the current thread.
• RunLoop defines several methods which are relatively low-level, and the only one benefit that lets you create cancellable timers

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• Using the Timer class
• Timer is the oldest timer that was available on the original Mac OS X, long before it was renamed “macOS.”
• It has always been tricky to use because of its delegation pattern and tight relationship with RunLoop.
• Combine brings a modern variant you can directly use as a publisher without all the setup boilerplate.

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• Using DispatchQueue
• You can use a dispatch queue to generate timer events.
• While the Dispatch framework has a DispatchTimerSource event source, Combine surprisingly doesn’t provide a timer interface to it. Instead, you’re going to use an alternative method to generate timer events in your queue.