FreeBSD 提供对 GCD 技术的支持

FreeBSD现已支持苹果在Snow Leopard中推出的Grand Central Dispatch技术,该技术旨在优化多核及多处理器环境下的并行处理能力。苹果计划将其GCD技术开源,并已在EuroBSDCon 2009上展示了移植成果。FreeBSD 8.1将内置GCD支持。

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[size=medium]FreeBSD adds support for Snow Leopard's Grand Central Dispatch

By Prince McLean
Published: 05:00 PM EST
[url]http://www.appleinsider.com/articles/09/10/16/freebsd_adds_support_for_snow_leopards_grand_central_dispatch.html[/url]

[b]Apple's Grand Central Dispatch technology, which debuted in Snow Leopard as a mechanism for optimizing parallelism across multiple cores and processors, has now been ported to FreeBSD.[/b]

Apple publicly announced plans to release its GCD technology as open source last month; the FreeBSD team demonstrated its early port of the new feature at EuroBSDCon 2009 in Cambridge, UK just days after Apple's announcement. Out of the box support for GCD is scheduled to appear with the release of FreeBSD 8.1.

The work required to port Apple's GCD event and concurrency framework to other operating systems is more complex than many other higher-level open source packages because GCD requires integration into the kernel (the core component of the operating system which manages processes, memory, and other hardware).

Most Unix-based software is highly portable between Mac OS X, Linux, and BSD, but significant kernel differences between these systems makes porting low-level, kernel-integrated technologies like GCD more work. In particular, Mac OS X uses a unique kernel design based on a hybrid of Mach and BSD. Porting GCD to FreeBSD required adaptations to account for a more conventional kernel environment without a Mach layer, such as using POSIX semaphores instead of Mach semaphores.

FreeBSD's porting efforts should help to make GCD easier to port to other operating systems with conventional Unix or Unix-like kernels, including OpenBSD, NetBSD, Linux, and Solaris.

In addition to kernel support, GCD requires compiler adaptations (a compiler is used to transform human readable source code language into the binary object code of an application). Apple's work on the Clang compiler front end and LLVM (Low Level Virtual Machine, the back end), makes porting this portion of GCD to other operating systems easier. This is particularly the case for FreeBSD, which has been quick to embrace support for Apple's Clang/LLVM open source projects.

The porting of GCD to other operating systems will help broaden the new technology's appeal. MacResearch, a website covering the use of Apple technologies in the scientific research community, observed last month that "with the possibility that Grand Central will become available on other Unix systems, the likelihood that Grand Central will be incorporated into command line tools is greatly increased.”

Significant new outside interest in GCD will also likely result in a wider support base for building parallelism compatible with Apple’s other open technologies, such as OpenCL and the aforementioned Clang/LLVM compiler tools.

[b]FreeBSD and Mac OS X[/b]

FreeBSD is a direct heir of UC Berkeley's "standard distribution" of Unix, which was created first to augment and then to replace AT&T's commercial Unix along with its expensive and closed licensing. NeXT incorporated BSD's operating system technology into its desktop workstations in the late 80s, back when using version 4.3 BSD meant licensing AT&T's Unix as well.

After BSD developers removed the vestiges of AT&T's commercial Unix code in 1991, BSD was released under a permissive license on its own; significant portions were incorporated into a wide variety of operating systems from SVR4 Unix to Windows and in many embedded applications such as network routers and firewalls. The widespread use of BSD Unix, and in particular its high quality networking code, helped to foster smooth interoperability among different vendors' products on the Internet.

In 1992, AT&T sued BSD over copyright and trademark infringement issues that were not resolved until 1994. The legal uncertainties raised by those challenges resulted a vacuum filled by Linux, which first appeared in 1991. That resulted in shifting most open source operating system development from BSD to Linux.

Apple's acquisition of NeXT at the end of 1996 resulted in Mac OS X inheriting a BSD foundation; the company had previously offered a Linux distribution (MkLinux) for its PowerPC Mac users who wanted to run an open, Unix-like environment. While open source development is still centered on Linux, Apple's move to adopt NeXT's operating system technology not only made it the world's largest Unix vendor but also shifted a significant amount of the *nix-world's attention back toward BSD.

[img]http://images.appleinsider.com/osxserver101409-1.png[/img]

Apple has since regularly synced its Mac OS X development roadmap to FreeBSD in its efforts to incorporate open source modernizations into what had been the aging codebase of NeXTSTEP, although the company has also borrowed technologies from other BSDs, Linux, and Sun's OpenSolaris.

The company has also contributed technology back or funded the development of projects that various open source operating systems have incorporated, including Bonjour, Clang/LLVM, CUPS (the Common Unix Printing System), and now of course GCD.[/size]
内容概要:本文档详细介绍了Analog Devices公司生产的AD8436真均方根-直流(RMS-to-DC)转换器的技术细节及其应用场景。AD8436由三个独立模块构成:轨到轨FET输入放大器、高动态范围均方根计算内核和精密轨到轨输出放大器。该器件不仅体积小巧、功耗低,而且具有广泛的输入电压范围和快速响应特性。文档涵盖了AD8436的工作原理、配置选项、外部组件选择(如电容)、增益调节、单电源供电、电流互感器配置、接地故障检测、三相电源监测等方面的内容。此外,还特别强调了PCB设计注意事项和误差源分析,旨在帮助工程师更好地理解和应用这款高性能的RMS-DC转换器。 适合人群:从事模拟电路设计的专业工程师和技术人员,尤其是那些需要精确测量交流电信号均方根值的应用开发者。 使用场景及目标:①用于工业自动化、医疗设备、电力监控等领域,实现对交流电压或电流的精准测量;②适用于手持式数字万用表及其他便携式仪器仪表,提供高效的单电源解决方案;③在电流互感器配置中,用于检测微小的电流变化,保障电气安全;④应用于三相电力系统监控,优化建立时间和转换精度。 其他说明:为了确保最佳性能,文档推荐使用高质量的电容器件,并给出了详细的PCB布局指导。同时提醒用户关注电介质吸收和泄漏电流等因素对测量准确性的影响。
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