I have not found the post you mention. Based on https://mercure.iro.umontreal.ca/pipermail/gambit-list/2014-February/007441...., I understood it was a work in progress... If you remember the thread, it would be great.

Has anyone faced a similar situation regarding asynchronous callbacks? Do you have any suggestion about handling that situation (maybe a different approach than the one I proposed)?

Thank you!

Regards, Francisco

On Mon, Mar 31, 2014 at 3:18 AM, Mikael mikael.rcv@gmail.com wrote:

It is possible to have more than one GVM in one OS process, please see Marc's posting from the spring of 2012 I believe it was, with code attachment.

When you get this going please share your experience.

2014-03-30 23:02 GMT+02:00 Francisco fjvallarino@gmail.com:

...

Hi,

I'm doing some tests using SDL2 (via Scheme Spheres bindings), and I'm having an issue related to multithreading. I want to generate audio procedurally, so what I need basically is access to an audio buffer that I can write on. SDL2 provides access to this buffer using a callback mechanism, which periodically invokes a provided function that is responsible for filling the buffer. This function is invoked in a separate thread of the main event loop. I implemented this callback function using c-define, but it eventually leads to a segmentation fault.

I understand that this is not possible using a single VM (based on [1]), but I have recently seen some discussion regarding multiple VMs on a single process [2]. Is this functionality available for testing? I know that for the moment it is considered alpha, but it could help for doing some preliminary tests. I intend to have the main program running on a Gambit VM, and for audio processing implement a C callback which will in turn invoke a function on a different Gambit VM (both created when the program starts, probably on a simple C initialization program). These VMs would communicate via message passing/sockets/etc.

For the moment I have the audio processing logic implemented in pure C, but I'd rather use Scheme for (almost) everything. This issue also arises in other asynchronous calls, for instance suspend/resume events on mobile platforms (Android specifically). I know that using multiple processes is an option on desktop versions, but I don't think I can create separate processes on Android.

Thank you!

Regards, Francisco

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Marc,

Thank you for the example! This will definitely allow me to run multiple threads to separate UI from audio processing.

I will try to dig a bit deeper to understand how the VMs work. One of the things I need to do is invoking a function on a specific VM (to generate audio I need to register a C callback that is invoked on a thread that is not controlled my me). My plan is having a standard VM running the main program and have another "idle" VM that will only be invoked by the C callback function. This way I should avoid corruption of the main VM stack. This idle VM would receive the information it needs from an in process message queue or a socket. If I can find the way of invoking the function on the right VM, I think my problem would be solved.

Thank you!

Regards, Francisco

On Sat, Apr 5, 2014 at 12:17 PM, Marc Feeley feeley@iro.umontreal.cawrote:

On Apr 1, 2014, at 10:06 AM, Francisco fjvallarino@gmail.com wrote:

...

I have not found the post you mention. Based on

https://mercure.iro.umontreal.ca/pipermail/gambit-list/2014-February/007441...., I understood it was a work in progress... If you remember the thread, it would be great.

Here is an example that uses the multiple VM support. I've tested it on OS X only, but it should be portable to other OSes.

You first have to build Gambit with

./configure --enable-multiple-vms
make

And then

cd multiple-vm-example
make

then

telnet localhost 12345

to connect to the VM that is created.

There are still issues with the multiple VM support, notably the VMs share a single console, which means there are race conditions if you try to read/write things to the console from different VMs. This is why the example code runs one of the VMs on a network connection (which is probably what you want to do anyway in practice).

Marc