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Grand Central Dispatch (GCD) is a technology developed by Apple Inc. to optimize application support for systems with multi-core processors and other symmetric multiprocessing systems.〔(Apple Previews Mac OS X Snow Leopard to Developers ), June 9, 2008.〕 It is an implementation of task parallelism based on the thread pool pattern. The fundamental idea is to move the management of the thread pool out of the hands of the developer, and closer to the operating system. The developer injects "work packages" into the pool oblivious of the pool's architecture. This model improves simplicity, portability and performance. GCD was first released with Mac OS X 10.6, and is also available with iOS 4 and above. The name "Grand Central Dispatch" is a reference to Grand Central Terminal. The source code for the library that provides the implementation of GCD's services, libdispatch, was released by Apple under the Apache License on September 10, 2009〔http://libdispatch.macosforge.org/〕 It has been ported〔(GCD libdispatch w/Blocks support working on FreeBSD )〕 to the FreeBSD operating system, starting with FreeBSD 8.1.〔(FreeBSD Quarterly Status Report )〕 MidnightBSD 0.3-CURRENT includes "libdispatch" without blocks support.〔(libdispatch )〕 Linux and Solaris support are provided within the upstream trunk.〔(libdispatch mailing list: "Porting status Linux" ) April 10, 2011〕〔(libdispatch mailing list: "Porting status Solaris x86/64" ) April 10, 2011〕 In order to develop support for Windows, currently two forks exist at (opensource.mlba-team.de ) and (Github ).〔(libdispatch mailing list: "libdispatch for Win32" ) April 22, 2011〕〔(libdispatch mailing list: "Updates regarding the status of libdispatch on Windows" ) May 5, 2011〕 Apple has its own port of libdispatch.dll for Windows shipped with Safari and iTunes, but no SDK is provided. == Design == GCD works by allowing specific tasks in a program that can be run in parallel to be queued up for execution and, depending on availability of processing resources, scheduling them to execute on any of the available processor cores (referred to as "routing" by Apple).〔(【引用サイトリンク】title=WWDC 2008: New in Mac OS X Snow Leopard )〕 A task can be expressed either as a function or as a "block."〔(【引用サイトリンク】url=http://developer.apple.com/mac/library/documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html )〕 Blocks are an extension to the syntax of C, C++, and Objective-C programming languages that encapsulate code and data into a single object in a way similar to a closure.〔 GCD can still be used in environments where blocks are not available. Grand Central Dispatch still uses threads at the low level but abstracts them away from the programmer, who will not need to be concerned with as many details. Tasks in GCD are lightweight to create and queue; Apple states that 15 instructions are required to queue up a work unit in GCD, while creating a traditional thread could easily require several hundred instructions.〔 A task in Grand Central Dispatch can be used either to create a work item that is placed in a queue or assign it to an event source. If a task is assigned to an event source, then a work unit is made from the block or function when the event triggers, and the work unit is placed in an appropriate queue. This is described by Apple as more efficient than creating a thread whose sole purpose is to wait on a single event triggering. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Grand Central Dispatch」の詳細全文を読む スポンサード リンク
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