Pthreads

In computing, POSIX Threads, commonly known as pthreads (after its header ), is an execution model that exists independently from a programming language, as well as a parallel execution model. It allows a program to control multiple different flows of work that overlap in time. Each flow of work is referred to as a thread, and creation and control over these flows is achieved by making calls to the POSIX Threads API. POSIX Threads is an API defined by the Institute of Electrical and Electronics Engineers (IEEE) standard POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995). Implementations of the API are available on many Unix-like POSIX-conformant operating systems such as FreeBSD, NetBSD, OpenBSD, Linux, macOS, Android, Solaris, Redox, QNX, and AUTOSAR Adaptive, typically bundled as a library libpthread. DR-DOS and Microsoft Windows implementations also exist: within the SFU/SUA subsystem which provides a native implementation of a number of POSIX APIs, and also within third-party packages such as pthreads-w32, which implements pthreads on top of existing Windows API.

In computing, POSIX Threads, commonly known as pthreads (after its header ), is an execution model that exists independently from a programming language, as well as a parallel execution model. It allows a program to control multiple different flows of work that overlap in time. Each flow of work is referred to as a thread, and creation and control over these flows is achieved by making calls to the POSIX Threads API. POSIX Threads is an API defined by the Institute of Electrical and Electronics Engineers (IEEE) standard POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995). Implementations of the API are available on many Unix-like POSIX-conformant operating systems such as FreeBSD, NetBSD, OpenBSD, Linux, macOS, Android, Solaris, Redox, QNX, and AUTOSAR Adaptive, typically bundled as a library libpthread. DR-DOS and Microsoft Windows implementations also exist: within the SFU/SUA subsystem which provides a native implementation of a number of POSIX APIs, and also within third-party packages such as pthreads-w32, which implements pthreads on top of existing Windows API. ==Contents== pthreads defines a set of C programming language types, functions and constants. It is implemented with a pthread.h header and a thread library. There are around 100 threads procedures, all prefixed pthread_ and they can be categorized into five groups: Thread management – creating, joining threads etc. Mutexes Condition variables Synchronization between threads using read write locks and barriers Spinlocks The POSIX semaphore API works with POSIX threads but is not part of the threads standard, having been defined in the POSIX.1b, Real-time extensions (IEEE Std 1003.1b-1993) standard. Consequently, the semaphore procedures are prefixed by sem_ instead of pthread_ . ==Example== An example illustrating the use of pthreads in C: include include include include include define NUM_THREADS 5 void* perform_work(void* arguments){ int index = *((int*)arguments); int sleep_time = 1 + rand() % NUM_THREADS; printf("Thread %d: Started.\n", index); printf("Thread %d: Will be sleeping for %d seconds.\n", index, sleep_time); sleep(sleep_time); printf("Thread %d: Ended.\n", index); return NULL; } int main(void) { pthread_t threads[NUM_THREADS]; int thread_args[NUM_THREADS]; int result_code; //create all threads one by one for (int i = 0; i This program creates five threads, each executing the function perform_work that prints the unique number of this thread to standard output. If a programmer wanted the threads to communicate with each other, this would require defining a variable outside of the scope of any of the functions, making it a global variable. This program can be compiled using the gcc compiler with the following command: gcc pthreads_demo.c -pthread -o pthreads_demo Here is one of the many possible outputs from running this program. In main: Creating thread 0. In main: Creating thread 1. In main: Creating thread 2. In main: Creating thread 3. Thread 0: Started. In main: Creating thread 4. Thread 3: Started. Thread 2: Started. Thread 0: Will be sleeping for 3 seconds. Thread 1: Started. Thread 1: Will be sleeping for 5 seconds. Thread 2: Will be sleeping for 4 seconds. Thread 4: Started. Thread 4: Will be sleeping for 1 seconds. In main: All threads are created. Thread 3: Will be sleeping for 4 seconds. Thread 4: Ended. Thread 0: Ended. In main: Thread 0 has ended. Thread 2: Ended. Thread 3: Ended. Thread 1: Ended. In main: Thread 1 has ended. In main: Thread 2 has ended. In main: Thread 3 has ended. In main: Thread 4 has ended. Main program has ended. ==See also== Runtime system OpenMP Cilk/Cilk Plus Threading Building Blocks (TBB) Native POSIX Thread Library (NPTL) DCEThreads clone (Linux system call) Spurious wakeup Thread-local storage GNU Portable Threads Grand Central Dispatch (Apple's thread library) State Threads, an event driven approach to threading ==References== ==Further reading==

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