What are Threads in Swift?

What is the Thread?

A Thread is a small set of instructions that can be executed independently from the main program. Threads are often used to improve program performance by allowing multiple tasks to be executed at the same time. The Thread has its own stack, registers, and program counters.

Threads share memory address space, and it is possible to communicate between Threads using shared memory space.

How to use it?

You can create a single Thread by the following example:

// Create a new thread and start it
let newThread = Thread { }
newThread.start()

What else can you do?

You can:

• cancel
• exit
• sleep
• etc

You can check the current Thread execution state:

• isExecuting
• isFinished
• isCancelled

You can subclass Thread and override the main() method if you need it.

Caveats

The main problem with Threads is that you must manually manage relationships between them. It can cause testability, readability, and potentially Thread Explosion issues.

What is Thread Explosion?

Thread Explosion occurs when a system has too many running Threads simultaneously. It can cause performance issues such as memory overhead and cost of context switching (CPU cycles).

Tips

You can delegate your work with Threads to Grand Central Dispatch (GCD).

GCD provides an API that manages the number of Threads automatically.

You can also use async/await and Task functionality from Swift 5.5 that helps manage the number of Threads in poll-based factors like system load and the number of available CPUs. If you have a long-running operation, you can call the Task.yield() method and let other tasks in your program make progress on their work.

Thank you for reading!