This single header file C90 library provides a portable collection of synchronization primitives for use in multithreaded programming. The following primitives are provided:

• cds_sync_futex_t -- A futex (fast userspace mutex), guaranteed to stay in userspace code unless a thread must be put to sleep or awakened.
• cds_sync_fusem_t -- A fast userspace semaphore, guaranteed to stay in userspace code unless a thread must be put to sleep or awakened.
• cds_sync_monitor_t -- A monitor, which bundles a condition variable and its associated mutex.
• cds_sync_eventcount_t -- An event count which lets callers safely avoid waiting unless there's actually no work to do.
• cds_sync_monsem_t -- A monitored semaphore, which builds on the basic semaphore by allowing a master thread to wait for the semaphore to have a certain positive non-zero value.
• cds_sync_barrier_t -- Lets users specify a barrier that all threads must reach before any thread can proceed.

• Identical API on all supported platforms. The following platforms are tested regularly:
  • Microsoft Windows 7
    • Visual Studio 2010
    • Visual Studio 2012
    • Visual Studio 2013
  • Linux Mint
    • LLVM/Clang 3.5
    • gcc 4.8.4
  • Apple OSX
    • Apple LLVM/Clang 6.1.0
• No (mandatory) external dependencies. Only standard C library functions are used, and even those can be overriden with custom implementations through #defines if desired.
• Dirt-simple integration. Just a single header file to include in your project.
• Public domain license terms.

• Sean Barrett: master of single-header C libraries.
• Charles Bloom: poster of sync primitives; ranter.
• Allen B. Downey: author of The Little Book of Semaphores.