[Vm-dev] VM Semaphores and external native threads

[Nicolas Cellier]

They proclaim being thread safe and use atomics ops for that purpose
(lock-free)

https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/platforms/Cross/vm/sqExternalSemaphores.c
https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/platforms/Cross/vm/sqAtomicOps.h


2017-11-09 10:13 GMT+01:00 Denis Kudriashov <dionisiydk at gmail.com>:

>
> I am wondering, external semaphores are used in sockets. I suppose that it
> must be thread safe for that case.
>
> 2017-11-09 4:01 GMT+01:00 John McIntosh <johnmci at smalltalkconsulting.com>:
>
>>
>> In the past the semaphore signaling logic was written to be mostly thread
>> safe because I was driving it from a UI thread and we had to queue requests
>> as the VM only processed the queue every N ms. Don’t know where it sits
>> today as it was rewritten.
>>
>> Sent from my iPhone
>>
>> > On Nov 8, 2017, at 18:32, David T. Lewis <lewis at mail.msen.com> wrote:
>> >
>> >
>> >> 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
>> >
>>
>
>
>
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