I am not entirely sure what exactly the threading=multi flag does when building boost. The documentation says:
Causes the produced binaries to be thread-safe. This requires proper
support in the source code itself.
which does not seem to be very specific. Does this mean that the accesses to, for example, boost containers are guarded by mutexes/locks or similar? As the performance of my code is critical, I would like to minimize any unnecessary mutexes etc.
Some more details:
My code is a plug-in DLL which gets loaded into a multi-threaded third-party application. I statically link boost into the DLL (the plug-in is not allowed to have any other dependencies except standard Windows DLLs, so I am forced to do this).
Although, the application is multi-threaded, most of the functions in my DLL are only ever called from a single thread and therefore the accesses to containers need not be guarded. I explicitly guard the the remaining places of my code, which can be called from multiple threads, by using boost::mutex and friends.
I've tried building boost with both threading=multi and threading=single and both seem to work but I'd really like to know what I am doing here.