Hi Pavel,

I'm looking at PosixSharedMemory again since I have to write a Master student proposal and I think this could be a good topic. I'm not really expert on SharedMemory, so I'm going to share what I have in mind, we can discuss about it, you could also co-supervise the student indirectly (though officially the supervisor has to be VUB staff).

Implementation-wise, I was thinking what could be interesting are:
- Making PosixSharedMemory compatible with TaskIt so from you image you can create a SharedMemory buffer, spawn another image+VM and attach it to the shared memory to have multiple threads working on the shared section.
- Add the #at:if:put: primitive, which write into the shared memory using compare and swap instruction for efficient thread-safe access.
- Add on SharedMemory all the primitives to read/write native types to the buffer (int64, double, etc.) with CAS and non CAS instructions.
- Maybe add APIs to read/write objects through Fuel to pass them by copy, though this looks difficult in some cases.
- Implement a lock system or a semaphore system on top of the CAS��
- implement lock-free and lock-full algorithm using CAS and non CAS instructions (I think a first try would be parallelSort on a 1Gb buffer of int32 with 4 native threads)

What do you think ? Do you have ideas ? Are you interested ? Do you thing having a student on this would be nice ?

The master thesis proposal has to include a research question. I am not sure what other languages do regarding shared memory.It's not clear so far what the research question is.

Best,

On Mon, Feb 12, 2018 at 10:33 AM, Pavel Krivanek <pavel.krivanek@gmail.com> wrote:
Hi,

among other less interesting things, I spent some time on existing
PosixSharedMemory project. It is a UFFI binding for the LibC methods
that provide support for the memory allocation between several
separate processes. I significantly improved the performance by
implementing the block access. Writing of 10MB byte array takes about
1 millisecond, reading of it from other image took me about 4
milliseconds. While serialization with Fuel is very fast, it opens
interesting possibilities.
To have a shared memory without synchronization tools is not very
useful so I wrote a basic UFFI interface for the POSIX named
semaphores. They are quite easy to use and work nicely with Pharo. The
VM can all wait on the semaphore or it can check the status of it
periodically in an image thread. It has two small disadvantages. It
requires to dynamically link the next library (pthread) and they must
be cleaned manually. I plan to look at System V alternative in future.
Now we should write a nice framework for inter-image communication on
top of it or/and adopt Seamless for it ;-)

Cheers,
-- Pavel




--