Multithreading in Swift allows the CPU to produce and run many threads simultaneously. A CPU typically does one operation at a time. However, by using multithreading in Swift, we might be able to let the CPU switch between various tasks so that they can run at the same time.
The user is unaware of the change because the thread switches happen quickly. The UI thread in iOS is a typical example, as the application consistently maintains its User interface even when the CPU is highly occupied with other tasks.
The UI in iOS has its own thread. The user interface doesn't change when we perform a complex task.
The main thread is the only one that every application has. In the hierarchy of threads, this is the thread that has the most power and can assign tasks to other threads. Multithreading in Swift is the process by which the main thread assigns tasks to different background threads. Multithreading in Swift aims to increase application performance by concurrently scheduling tasks on many threads.
Even though time-slicing allows for concurrency on single-core processors, multithreading in Swift and concurrency gained popularity after multi-core machines were introduced in the 1950s. Multi-core processors, as opposed to single-core processors, let us execute numerous threads concurrently without the context switching required for time-slicing. By not employing this feature of running many threads, we are effectively not making the best use of the available resources, which leads to weak performance.
GCD
We don't really interface with threads when using multithreading in Swift while developing an iOS application. This is a result of the GCD handling it in the background. We only need to define the tasks that must be run; GCD will control which threads will execute which jobs. GCD operates on a system level and is more knowledgeable about the system's resources, how to best use them, and how to arrange our activities for the best performance.
Grand-Central-Dispatch, or GCD, is an API used to carry out the closures of the worker pools. It follows First-In-First-Out (FIFO) order.
The application submits the tasks that the CPU will carry out as blocks to the dispatch queue. The system-provided thread pool is used to execute this block. The dispatch queue's jobs are all carried out either concurrently or sequentially. However, the dispatch queue always keeps the tasks in FIFO order.
This framework makes running programs concurrently on multi-core systems easier by sending a job to the system's dispatch queues.
DispatchQueue
The main queue provided by the GCD is a globally available serial queue that executes tasks on the application’s main thread.
⭐You should be careful when executing jobs on this queue because the main thread is used to update the user interface. You do not want to block the main thread.
To block the main thread, though, what does that mean🥴?
Does the user experience suffer🤯?
As we already know, the main thread is used to update the user interface. That activity uses a lot of resources. Since most devices carry out this function several times per second, even a delay of a few hundredths of a second can affect how smooth our user interface will be. If we run unnecessary processes on the main thread, it won't be possible for our application to have enough resources to draw the UI again every second.
To prevent this, GCD also offers us several global queues, also referred to as background queues, which are used to execute tasks that shouldn't be done on the main thread, i.e., anything that isn't a UI update!
To make the application faster and more responsive, we can use GCD to run the application threads and present the information to the user.
For example, If you are parsing a big JSON file that takes 12 - 15 seconds to be fully parsed, then you can run a thread that can show some activity indicator to the users so that they can assume that some tasks are being processed.
The process of multithreading in Swift allows the CPU to produce and run multiple threads simultaneously. A CPU typically does one operation at a time.
What is GCD in iOS Swift?
A low-level API called Grand Central Dispatch (GCD)in IOS Swift is used to manage concurrent operations. It can increase the responsiveness of your program by pushing computationally intensive operations into the background.
What is the main difference between GCD and NSOperationQueue in iOS?
GCD is a low-level C-based API that communicates directly with the system's Unix level. NSOperation and NSOperationQueue are, however, high-level Objective-C classes.
Is iOS single-threaded?
In iOS, each process is made up of one or more threads. Each represents a single path of execution through the application's code. Every application begins with a single thread that executes the main operation.
Conclusion
In this article, we discussed IOS multithreading in Swift. We also discussed GCD, Grand Central Dispatch API, starting with understanding the multithreading.
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