DispatchQueue

class DispatchQueue : DispatchObject


                    
                    
                    once(token:block:)

Executes a block of code, associated with a unique token, only once. The code is thread safe and will only execute the code once even in the presence of multithreaded calls.

Declaration

Swift

public class func once(token: String, block: () -> Void)

Parameters

`token`	A unique reverse DNS style name such as com.vectorform. or a GUID
`block`	Block to execute once