Pthreads

Pthreads, or POSIX threads, is a standardized API for writing multi-threaded programs in C, C++, and other languages on POSIX-compliant systems. Defined by POSIX.1c (IEEE Std 1003.1c), it specifies interfaces for creating and managing threads, synchronizing their execution, and handling thread-local data.

Core facilities include thread lifecycle: pthread_create, pthread_exit, pthread_join, pthread_cancel, and attributes via pthread_attr_t controlling detach state, stack size, scheduling, and guard size. Synchronization primitives: mutexes (pthread_mutex_t) with lock/unlock; condition variables (pthread_cond_t) for signaling; reader-writer locks (pthread_rwlock_t); barriers (pthread_barrier_t) for group synchronization; and thread-specific data keys (pthread_key_create, pthread_getspecific, pthread_setspecific).

Additional features include thread-local storage, cancellation handling (pthread_setcancelstate, pthread_cancel, and cleanup handlers via pthread_cleanup_push/pthread_cleanup_pop), and scheduling control through pthread_setschedparam and scheduling policies (SCHED_FIFO, SCHED_RR, SCHED_OTHER). The API also provides thread attributes for detach state (joinable or detached) and various stack-related parameters, enabling fine-grained control over thread behavior.

Portability and usage: pthreads is supported on most UNIX-like systems, including Linux, BSD variants, and macOS, where the library is typically provided as part of the system C library. Windows environments achieve POSIX threading behavior through compatibility libraries such as pthreads-w32 or in POSIX-compatibility layers like Cygwin. While the standard promotes portability, exact semantics and performance can vary between implementations. Pthreads remains a foundational API for building scalable servers, parallel compute tasks, and responsive applications on POSIX platforms.