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