It’s been almost eight years since I first updated Advanced Programming in the UNIX Environment, and already so much has changed.
• Before the second edition was published, The Open Group created a 2004 edition of the Single UNIX Specification, folding in the changes from two sets of corrigenda. In 2008, The Open Group created a new version of the Single UNIX Specification, updating the base definitions, adding new interfaces, and removing obsolete ones. This was called the 2008 version of POSIX.1, which included version 7 of the Base Specification and was published in 2009. In 2010, this was bundled with an updated curses interface and reissued as version 4 of the Single UNIX Specification.
• Versions 10.5, 10.6, and 10.8 of the Mac OS X operating system, running on Intel processors, have been certified to be UNIX® systems by The Open Group.
• Apple Computer discontinued development of Mac OS X for the PowerPC platform. From Release 10.6 (Snow Leopard) onward, new operating system versions are released for the x86 platform only.
• The Solaris operating system was released in open source form to try to compete with the popularity of the open source model followed by FreeBSD, Linux, and Mac OS X. After Oracle Corporation bought Sun Microsystems in 2010, it discontinued the development of OpenSolaris. Instead, the Solaris community formed the Illumos project to continue open source development based on OpenSolaris. For more information, see http://www.illumos.org.
• In 2011, the C standard was updated, but because systems haven’t caught up yet with the changes, we still refer to the 1999 version in this text. Most notably, the platforms used in the second edition have become out-of-date. In this book, the third edition, I cover the following platforms:
1. FreeBSD 8.0, a descendant of the 4.4BSD release from the Computer Systems Research Group at the University of California at Berkeley, running on a 32-bit Intel Pentium processor.
2. Linux 3.2.0 (the Ubuntu 12.04 distribution), a free UNIX-like operating system, running on a 64-bit Intel Core i5 processor.
3. Apple Mac OS X, version 10.6.8 (Darwin 10.8.0) on a 64-bit Intel Core 2 Duo processor. (Darwin is based on FreeBSD and Mach.) I chose to switch to an Intel platform instead of continuing with one based on the PowerPC, because the latest versions of Mac OS X are no longer being ported to the PowerPC platform. The drawback to this choice is that the processors covered are now slanted in favor of Intel. When discussing issues of heterogeneity, it is helpful to have processors with different characteristics, such as byte ordering and integer size.
4. Solaris 10, a derivative of System V Release 4 from Sun Microsystems (now Oracle), running on a 64-bit UltraSPARC IIi processor.
Changes from the Second Edition
One of the biggest changes to the Single UNIX Specification in POSIX.1-2008 is the demotion of the STREAMS-related interfaces to obsolescent status. This is the first step before these interfaces are removed entirely in a future version of the standard. Because of this, I have reluctantly removed the STREAMS content from this edition of the book. This is an unfortunate change, because the STREAMS interfaces provided a nice contrast to the socket interfaces, and in many ways were more flexible. Admittedly, I am not entirely unbiased when it comes to the STREAMS mechanism, but there is no debating the reduced role it is playing in current systems:
• Linux doesn’t include STREAMS in its base system, although packages (LiS and OpenSS7) are available to add this functionality.
• Although Solaris 10 includes STREAMS, Solaris 11 uses a socket implementation that is not built on top of STREAMS.
• Mac OS X doesn’t include support for STREAMS.
• FreeBSD doesn’t include support for STREAMS (and never did). So with the removal of the STREAMS related material, an opportunity exists to replace it with new topics, such as POSIX asynchronous I/O.
In the second edition, the Linux version covered was based on the 2.4 version of the source. In this edition, I have updated the version of Linux to 3.2. One of the largest area of differences between these two versions is the threads subsystem. Between Linux 2.4 and Linux 2.6, the threads implementation was changed to the Native POSIX Thread Library (NPTL). NPTL makes threads on Linux behave more like threads on the other systems.
In total, this edition includes more than 70 new interfaces, including interfaces to handle asynchronous I/O, spin locks, barriers, and POSIX semaphores. Most obsolete interfaces are removed, except for a few ubiquitous ones.