isMainThread
isMainThread (part of Foundation) can be used to check to see if the current Thread is the main thread. In modern Swift concurrency code, prefer @MainActor isolation, which lets the compiler guarantee main-thread execution instead of checking for it at runtime (MainActor.assertIsolated() is available for runtime assertions).
Simple example
import Foundation
print(Thread.isMainThread)
// Output: true
Example with Dispatch
import Foundation
print(Thread.isMainThread) // true
DispatchQueue.global(qos: .background).async {
print(Thread.isMainThread) // false
DispatchQueue.main.async {
print(Thread.isMainThread) // true
}
}
Example with @MainActor function and Dispatch
import Foundation
func someFunction() {
print("1️⃣ On main thread: \(Thread.isMainThread)")
}
@MainActor
func someOtherFunction() {
print("2️⃣ On main thread: \(Thread.isMainThread)")
}
DispatchQueue.global(qos: .background).async {
Task {
someFunction()
await someOtherFunction()
}
}
// Output:
// 1️⃣ On main thread: false
// 2️⃣ On main thread: true
