Thread (computing): Difference between revisions

Revision as of 18:33, 1 January 2004

Revision as of 05:38, 2 January 2004

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[[ja:スレッド (コンピュータプログラミング)]] [[pl:Wątek (informatyka)]] [[es:hilo(informática)]] [[de:Thread]]

Many [[programming language]]s, [[operating system]]s, and other [[software development]] environments support what are called "'''threads'''" of [[execution]]. [[Thread]]s are similar to [[computer process|processes]], in that both represent a single [[sequence]] of [[instruction]]s executed in parallel with other sequences, either by [[Computer multitasking|time slicing]] or [[multiprocessing]]. ThisThreads is a way allowsfor a [[computer program|program]] to split itself into two or more simultaneously running [[task]]s.

A common use of threads is having one thread paying attention to the [[graphical user interface]], while others do a long calculation [[Background (computer software)|in the background]].

As a result, the user will experience a responsive [[application]] more readily responds to user's interaction.

Threads are distinguished from traditional multi-tasking [[computer process|processes]] in that processes are typically independent, carry considerable [[state information]], and interact only through system-provided [[inter-process communication]] mechanisms. Multiple threads, on the other hand, typically share the state information of a single process, share [[Computer storage|memory]] and other [[resource]]s directly. On [[operating system]]s that have special facilities for threads, it is typically faster for the system to [[context switch]] between different threads in the same process than to switch between different processes.

Systems like [[Windows NT]] and [[OS/2]] are said to have "cheap" threads and "expensive" processes, while in systems like [[Linux]] there is not so big a difference.

An advantage of a multi-threaded program is that it can operate faster on [[computer system]]s that have multiple [[CPU]]s, or across a [[computer cluster|cluster]] of machines. This is because the threaded naturethreads of the [[algorithm]]sprogram allownaturally truelend simultaneousthemselves andfor independenttruly [[concurrent programming|concurrent]] [[processingexecution]]. In such a case, the [[programmer]] needs to be careful to avoid [[race condition]]s, and other non-intuitive [[behavior]]s. In order for data to be correctly manipulated, threads will often need to [[rendezvous]] in time in order to process the data in the correct order. Threads may also require [[Atomic_(computer_science)|atomic]] operations (often implemented using [[semaphore (programming)|semaphores]]) in order to prevent common data from being simultaneously modified, or read while in the process of being modified. Careless use of such [[primitive]]s can lead to [[deadlock]]s.

Use of threads in [[programming]] often causes a [[state inconsistency]]. A common [[anti-pattern]] is to set a [[global variable]], then invoke [[subprogram]]s that depend on its value. This is known as ''[[accumulate and fire]]''.