Q:

How to pass a parameter to a block executed asynchronously in Swift? 

In addition to function dispatch_async, that submits a block for asynchronous execution, iOS provides another function dispatch_async_f to submit a function with a single parameter for asynchronous execution. 
in Swift, I can call dispatch_async as DispatchQueue.global().async {}, but I did not find any way to call dispatch_async_f. 
So, how do I pass a parameter to a block executed asynchronously? 

A:

dispatch_async_f() can be used in C code, which has no blocks or closures. 
In Swift you simply pass a closure, and the closure calls the function:
DispatchQueue.global().async {
    let theParameter = ...
    theFunction(theParameter)
}

The closure can also capture values when created:
let theParameter = ...
DispatchQueue.global().async {
    theFunction(theParameter)
}

