Synchronizing threads with latches, barriers, and semaphores

The thread support library from C++11 includes mutexes and condition variables that enable thread-synchronization to shared resources. A mutex allows only one thread of multiple processes to execute, while other threads that want to access a shared resource are put to sleep. Mutexes can be expensive to use in some scenarios. For this reason, the C++20 standard features several new, simpler synchronization mechanisms: latches, barriers, and semaphores. Although these do not provide new use cases, they are simpler to use and can be more performant because they may internally rely on lock-free mechanisms.

Getting ready

The new C++20 synchronization mechanisms are defined in new headers. You have to include <latch> for std::latch, <barrier>, or std::barrier, and <semaphore> for std::counting_semaphore and std::binary_semaphore.

The code snippets in this recipe will use the following two functions...