Odd issue with std::map and thread safety

Question

This isn't so much of a problem now as I've implemented my own collection but still a little curious on this one.

I've got a singleton which provides access to various common components, it holds instances of these components with thread ID's so each thread should (and does, I checked) have it's own instance of the component such as an Oracle database access library.

When running the system (which is a C++ library being called by a C# application) with multiple incoming requests everything seems to run fine for a while but then it crashes out with an AccessViolation exception. Stepping through the debugger the problem appears to be when one thread finishes and clears out it's session information (held in a std::map object) the session information held in a separate collection instance for the other thread also appears to be cleared out.

Is this something anyone else has encountered or knows about? I've tried having a look around but can't find anything about this kind of problem.

Cheers

Answer 1

Standard C++ containers do not concern themselves with thread safety much. Your code sounds like it is modifying the map instance from two different threads or modifying the map in one thread and reading from it in another. That is obviously wrong. Use some locking primitives to synchronize the access between the threads.

Answer 2

如果您想要的只是每个线程的单独对象，则可能需要看一下boost::thread_specific_ptr 。

Answer 3

How do you manage giving each thread its own session information? Somewhere under there you have classes managing the lifetimes of these objects, and this is where it appears to be going wrong.