我发现串行队列将使用多个线程来运行异步代码。这是操场上的测试代码。
import Foundation
let q = DispatchQueue(label: "test")
q.async {
print("hi \(Thread.current)")
}
q.async {
print("hi \(Thread.current)")
}
q.async {
print("hi \(Thread.current)")
}
q.async {
print("hi \(Thread.current)")
}
q.async {
print("hi \(Thread.current)")
}
当我反复执行操场时,有时会出现这样的输出。据我了解,串行队列应该只使用一个线程,但日志显示它使用了 2 个线程。我真的很困惑。什么是正确的行为?
hi <NSThread: 0x7fc26a467b90>{number = 2, name = (null)}
hi <NSThread: 0x7fc26a467b90>{number = 2, name = (null)}
hi <NSThread: 0x7fc26a467b90>{number = 2, name = (null)}
hi <NSThread: 0x7fc26a467b90>{number = 2, name = (null)}
hi <NSThread: 0x7fc26b1003e0>{number = 3, name = (null)}