Intel Threading Building Blocks

Safety in the Presence of Concurrency

When code is written in such a way that it cannot be run in parallel without the concurrency causing problems, it is said not to be thread-safe. Even with the abstraction that Threading Building Blocks offers, the concept of thread safety is essential. You need to understand how to build a program that is thread-safe, which essentially means that each function can be invoked by more than one thread at the same time.

Single-threaded programs contain only one flow of control, so their parts need not be reentrant or thread-safe. In multithreaded programs, the same functions and the same resources may be utilized concurrently by several flows of control. Code written for multithreaded programs must therefore be reentrant and thread-safe.

Any function that maintains a persistent state between invocations requires careful writing to ensure it is thread-safe. In general, functions should be written to have no side effects so that concurrent use is not an issue. In cases where global side effects—which might range from setting a single variable to creating or deleting a file—do need to occur, the programmer must be careful to call for mutual exclusion, ensuring that only one thread at a time can execute the code that has the side effect, and that other threads are excluded from that section of code.

Be sure to use thread-safe libraries. All the libraries you use should be reviewed to make sure they are thread-safe. The C++ library has some functions inherited ...