Document revision date: 30 March 2001

## Guide to the POSIX Threads Library

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thread attributes object: Object that allows you to specify values for thread attributes when you create a thread.

thread object: Data structure that describes a thread.

thread-safe: Refers to a routine that can be called simultaneously from multiple threads without risk of corruption. Refers to a library that typically consists of routines that do not themselves create or use threads but which can be called safely from applications that use threads.

thread-independent services: Routines in the Threads Library tis interface that support building thread-safe libraries.

thread-specific data: User-specified fields of arbitrary data that can be added to a thread's context.

time slicing: Mechanism that ensures that every thread is allowed time to execute by preempting running threads at fixed intervals.

tis condition variable: Condition variable object that can be created using the Threads Library tis interface routines.

tis mutex: Mutex object that can be created using the Threads Library tis interface routines.

two-level scheduling: Thread scheduling model that schedules user threads onto kernel execution contexts, just as the operating system schedules processes onto the processors of a multiprocessor machine.

upcall: Technique for the operating system kernel to inform the Threads Library that a kernel execution context is available. When a kernel execution context becomes available, the Threads Library scheduler schedules the thread with highest scheduling precedence that is ready to run onto the available kernel execution context.

word tearing: Form of race condition in a multithreaded program where two or more threads independently read the same granule of memory, update different portions of that granule, then independently (that is, asynchronously) store their respective copies of that granule. Can occur due to programmer's inattention to granularity considerations.

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