C ++ async uses thread pool when creating for macOS with Xcode?

Question

Using standard development tools and compilers for the platform [1], std::async generate a new OS thread for each background job or use a thread pool or some system based on theft of work tasks?

• Xcode, Clang / LLVM

Answer 1

An application built with a standard platform toolchain (Xcode / Clang) does not use a thread pool. The stack base of a task launched with std::async contains calls to std :: thread and pthread.

On exit, each job calls pthread_exit() to kill the thread executing it.

Xcode 8.3.3 also uses the OS thread for every job launched with std::async when creating for iOS (tested on the original target of iPad version 9.7).

Answer 2

Currently, the main standard implementation does not use thread pools for std::async . Despite this notion that an implementation can do this, it will be extremely difficult to implement in practice, and I do not foresee it in the near future.