[Vm-dev] VM Semaphores and external native threads

[David T. Lewis]

On Wed, Nov 08, 2017 at 10:56:50PM -0300, Ronie Salgado wrote:
>  
> Hi,
> 
> I started to make an IDE like tool in Pharo, and I have an external library
> for handling some asynchronous events generated in a separate thread, which
> I am putting in a queue that I am polling each 200 ms from a Pharo image.
> Currently I am using this library for handling pipes of external process
> (GDB with the machine interface), and next I am going to add support for
> inotify.
> 
> I know that I can remove this polling each 200 ms by implementing a
> mechanism for registering multiples event handlers that are called by
> ioProcessEvents. The SDL2DisplayPlugin registers an event handler in this
> places, which asks SDL2 for the presence of events and it signals VM
> Semaphore. However, since in this case I have control of the code in the
> external thread, I would like to just signal the VM Semaphore in this
> external thread to avoid this polling. So here is my question:
> 
> Is signaling a VM Semaphore thread safe? In case it is not, how much work
> would require to make it thread safe.
> 
> Best regards,
> Ronie

Do you mean #signalSemaphoreWithWindex: which signals a Smalltalk semaphore
from the VM or plugin? My expectation is that this is intended to be called
from the main interpreter thread, and would not be thread safe with respect
to calling it from other threads running in the VM. I expect that you would
need to synchronize access to signalSemaphoreWithIndex: in order to make this
work.

Dave