[zeromq-dev] Thread Safe sockets

[john skaller]

> A mutex works fine with a 0mq socket so adding one to the socket itself would also work. I just don't think it would perform well plus everyone would have to pay that price even if they didn't need it. Yuck.

I have implemented (but not tested) thread safe sockets, available in Pull request.

YMMV. Perhaps it should go in a branch or not get pulled at all.

One function is added to the C API:

	zmq_init_thread_safe (nthreads)

If this function is used, all C API socket functions on any socket spawned by that
context will be wrapped in a mutex.

There is no semantic impact on any existing C or C++ code. 
Calls internal to ZMQ C++ code base are not affected.

Cost, memory, everyone pays: one bool in context and one bool and one mutex in socket.
Cost, speed, everyone pays: currently two tests in every C API socket call.
Could be reduced to one at he expense of duplicating the C++ method call.

There is no way to selectively turn on or off socket thread safety from the C API.

BUGS: I deliberately used a "set" method to allow the C++ constructor arguments
to remain unchanged: attempting to provide minimal interference to any
existing ZMQ core C++ code.

This required exposing a "set" method on the sockets.
It is NOT safe to call that method, but I can't protect it or the C API wouldn't
be able to access it. This should be fixed if the patch proves useful.

I have no real input on its utility. It may help in some bindings such as Java.
It may also be useful in "utilities" where functionality and rapid prototyping
are more important than performance.


--
john skaller
skaller at users.sourceforge.net