Macro dispatch_or_permit 

macro_rules! dispatch_or_permit {
    ($semaphore:expr, $closure:expr) => { ... };
}

Attempt to dispatch a blocking operation, or otherwise obtain a permit and run on thread, returning the result of the closure.

This helper macro is intended for use in the context of an async block or function. It first attempts to dispatch the closure via dispatch_rx() and await. If a dispatch pool is not registered on the current thread, it instead obtains a permit via blocking_permit_future() and awaits. If the tokio-threaded feature is enabled, it will then run the closure via BlockingPermit::run(). Otherwise it will run the closure directly.

Usage

The closure should return a Result<T, E> where From<Canceled> is implemented for type E. The return type of the closure may be annotated as necessary. The closure may also be a move closure.

async {
    dispatch_or_permit!(&semaphore, move || { /*.. blocking code..*/ });
}