Nonblocking check for mutex

[segadora]

We are working with a queue system. If one mutex is already used, I would like it to be possible to put the job back on the queue. Like

Mutex::check(....)->then(If the mutex is free)->fail(If the mutex is not free)

[mvorisek]

I like this feature and I am gonna to implement it like JavaScript does - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then

Mutex::check(...)
    ->then(
        $checkTrueFx,
        (optional) $checkFalseFx
    )