Re: async.el: A simple asynchronous framework for Emacs

[John Wiegley]

Just a note, I've generalized async.el a bit further so that I can also have
async-start-process -- which uses a different process that Emacs, but keeps
the rest of the functionality the same.

So, asynchronous invocation of a lambda with callback is the same as before:

    (async-start (lambda () ... in child process ...)
                 (lambda (ret) ... handle return value from lambda ...))

Now I can get the same sort of functionality with other processes too:

    (async-start-process "cp" "/bin/cp"
                         (lambda (proc) ... use proc to get exit code ...)
                         "file1" "file2")

Further, as with `async-start', if the callback function is nil you'll get a
closure that you can inspect when you're ready.  I've also added two new
functions for working with these futures:

    (async-ready FUTURE)    ; returns t if `async-get' would not block
    (async-wait FUTURE)     ; waits for FUTURE to become ready, returns nil
    (async-get FUTURE)

Lastly, you can call `async-get' now even if you did provide a callback, it
will simply always return nil in that case (since the return value went to the
callback).

My motivation for `async-start-process' is that I want dired-async.el to use
native cp/mv/rm if all files are local (file-remote-p == nil).  But I want to
keep the same infrastructure, i.e., the simple-to-specify callbacks for
manipulating the dired buffer once the operation is complete.

Updates are on GitHub.

John