Grand Central Dispatch (GCD) GCD is a concurrent programming framework first shipped with Mac OS X Snow Leopard. This package is an open source bundling of libdispatch, the core user space library implementing GCD. At the time of writing, support for the BSD kqueue API, and specifically extensions introduced in Mac OS X Snow Leopard and FreeBSD 9-CURRENT, are required to use libdispatch. Other systems are currently unsupported. Configuring and installing libdispatch GCD is built using autoconf, automake, and libtool, and has a number of compile-time configuration options that should be reviewed before starting. An uncustomized install requires: sh autogen.sh ./configure make make install The following configure options may be of general interest: --with-apple-libc-source Specify the path to Apple's Libc package, so that appropriate headers can be found and used. --with-apple-libclosure-source Specify the path to Apple's Libclosure package, so that appropriate headers can be found and used. --with-apple-xnu-source Specify the path to Apple's XNU package, so that appropriate headers can be found and used. --with-blocks-runtime On systems where -fblocks is supported, specify an additional library path in which libBlocksRuntime can be found. This is not required on Mac OS X, where the Blocks runtime is included in libSystem, but is required on FreeBSD. The following options are likely to only be useful when building libdispatch on Mac OS X as a replacement for /usr/lib/system/libdispatch.dylib: --disable-libdispatch-init-constructor Do not tag libdispatch's init routine as __constructor, in which case it must be run manually before libdispatch routines can be called. For the libdispatch library in /usr/lib/system, the init routine is called automatically during process start. --enable-apple-tsd-optimizations Use a non-portable allocation scheme for pthread per-thread data (TSD) keys when building libdispatch for /usr/lib/system on Mac OS X. This should not be used on other OS's, or on Mac OS X when building a stand-alone library. Typical configuration commands The following command lines create the configuration required to build libdispatch for /usr/lib/system on Mac OS X Lion: sh autogen.sh ./configure CFLAGS='-arch x86_64 -arch i386' \ --prefix=/usr --libdir=/usr/lib/system \ --disable-dependency-tracking --disable-static \ --disable-libdispatch-init-constructor \ --enable-apple-tsd-optimizations \ --with-apple-libc-source=/path/to/10.7.0/Libc-763.11 \ --with-apple-libclosure-source=/path/to/10.7.0/libclosure-53 \ --with-apple-xnu-source=/path/to/10.7.0/xnu-1699.22.73 Typical configuration line for FreeBSD 8.x and 9.x to build libdispatch with clang and blocks support: sh autogen.sh ./configure CC=clang --with-blocks-runtime=/usr/local/lib