Introduction to C++ standard library features for multi-threading.

Background

Language Support

C++’s support for concurrency has evolved over time. The language largely predates multi-threaded systems, so older language specs have no built-in support. Most concurrency support was added in C++11. C++14 and C++17 refine these features.

A timeline is roughly:

  • C++98 - no concurrency
  • C++11 - threads, mutexes, locks, conditions, futures/promises
  • C++14 - shared locks
  • C++17 - scoped locks, shared mutexes

Debugging

Debugging multi-threaded systems is notoriously difficult. There are a variety of tools (and languages!) available to help solve these problems at compile time or run time. Here we will add support for one tool, the thread sanitizer. This seems to have begun in clang but is also supported in gcc.

The thread sanitizer is built in to the compiler itself. If enabled, it reports on concurrency bugs as they are encountered at run time. Importantly, tsan only reports on bugs that actually occur, so its report can vary between executions!

Terminology

I attempt to distinguish between data races and API races as referred to by Google.

Getting Started

See Setup.