On Mon, Apr 8, 2019 at 11:23:16 UTC+2 Brian Dickens wrote:
> On Mon, Apr 8, 2019 at 3:40 AM <[email protected]> wrote:
>
> > I really cannot believe that it is not possible to compile such
> > a simple interactive program with emcc.
>
> Believe it. :-)
>
> The JavaScript hosts like Node.js and browsers weren't designed for
synchronous I/O. In a browser you can use Window.prompt() and
alert()...both of which are too annoying to be practical. But other than
that you won't see any I/O or impacts of DOM manipulations. JavaScript
programmers have just learned to live with it.
>
> For I/O to process you have to yield to the main loop...which means your C
code can't still be running (on the main thread) when it does. The only
options for C code that wants to do synchronous I/O while remaining on the
stack are if that code is running on a worker thread, ...
I looked at the worker_threads provided by node.js.
When a worker thread is started it can get some workerData from
the main thread. A worker_thread can also send something back to
the main thread via a parentPort. To receive the message from the
worker_thread the main thread uses something like
worker.on('message', (msg) => { console.log(msg); });
and then terminates. The message from the worker_thread is then
handled in this callback. I have found also examples where the
worker_thread registers some callback and terminates itself to
receive a message from the main thread. It seems that this works
like anything else in JavaScript: asynchronous
What I am missing is: The worker thread should be able to wait
for a message (without callback and terminating the worker_thread)
and to continue after the message has been received. It is
important that no termination of the thread is necessary and
that the program can continue after the "wait" statement.
A not so elegant solution would be possible, when there is the
possibility to poll, if a message has been sent. In this case
the worker_thread could poll for a message (possibly with some
sleep in between).
I can understand that the main thread works asynchronous and
never waits for something. But for worker_threads this could
be different.
I was thinking to start a worker_thread with the main program
and the main thread would only handle events and sending them
to the worker_thread. To do this the worker_thread must be
able to work synchronous (wait for messages from the main thread).
Is this possible?
Regards,
Thomas Mertes
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