Item 12: Have realistic expectations about the thread safety of STL containers

The world of standard C++ is rather sheltered and old-fashioned. In this rarefied world, all executables are statically linked. Neither memory-mapped files nor shared memory exist. There are no window systems, no networks, no databases, no other processes. That being the case, you should not be surprised to learn that the Standard says not a word about threading. The first expectation you should have about the thread safety of the STL, then, is that it will vary from implementation to implementation.

Of course, multithreaded programs are common, so most STL vendors strive to make their implementations work well in a threaded environment. Even when they do a good job, however, much of the burden remains on your shoulders, and it’s important to understand why. There’s only so much STL vendors can do to ease your multithreading pain, and you need to know what it is.