jack1/doc/porting.dox

/*
 * This file documents the process of porting JACK to new platforms.
 * It is part of the JACK reference manual, built using doxygen.
 */

/**

@page porting-guide Porting JACK

The @ref index is designed to be portable to any system supporting the
relevant POSIX and C language standards.  It currently works with
GNU/Linux and Mac OS X on several different processor architectures.
This document describes the steps needed to port JACK to another
platform, and the methods used to provide portability.

  - @ref portrequirements
  - @ref portoverview
  - @ref portopsys
  - @ref portcpu
  - @ref portissues

@section portrequirements Requirements

  - Each platform should build directly from CVS or from a tarball
  using the GNU @c ./configure tools.  Platform-specific toolsets can
  by used for development, but the GNU tools should at least work for
  basic distribution and configuration.

  - For long-term maintainability we want to minimize the use of
  conditional compilation in source files.

  - We should provide generic versions of all system-dependent
  headers, so platforms need only provide those they modify.

  - In some cases, operating system-specific information must be able
  to override processor-specific data.

@section portoverview Overview

JACK relies on two types of platform-specific headers:

  - @ref portopsys
  - @ref portcpu

OS-specific headers take precedence over CPU-specific headers.

The JACK @c configure.host script and its system-dependent header
directories were adapted from the @c libstdc++-v3 component of the GNU
Compiler Collective, <http://gcc.gnu.org>.


@section portlang C Language Dependencies

JACK is written to conform with C99, as defined in International
Standard ISO/IEC 9899:1999.  Because many existing compilers do not
fully support this standard, some new features should be avoided for
portablility reasons.  For example, variables should not be declared
in the middle of a compound statement, because many compilers still
cannot handle that language extension.


@section portopsys Operating System Dependencies

JACK is written for a POSIX environment compliant with IEEE Std
1003.1-2001, ISO/IEC 9945:2003, including the POSIX Threads Extension
(1003.1c-1995) and the Realtime and Realtime Threads feature groups.
When some needed POSIX feature is missing on a platform, the preferred
solution is to provide a substitute, as with the @c fakepoll.c
implementation for Mac OS X.

Whenever possible, OS dependencies should be auto-detected by @c
configure.  Sometimes they can be isolated in OS-specific header
files, found in subdirectories of @c config/os and referenced with a
@c <sysdeps/xxx.h> name.

If conditional compilation must be used in mainline
platform-independent code, avoid using the system name.  Instead, @c
\#define a descriptive name in @c <config.h>, and test it like this:

@code
  \#ifdef JACK_USE_MACH_THREADS
          allocate_mach_serverport(engine, client);
          client->running = FALSE;
  \#endif
@endcode

Be sure to place any generic implementation alternative in the @c
\#else or use an @c \#ifndef, so no other code needs to know your
conditional labels.

@section portcpu Processor Dependencies

JACK uses some low-level machine operations for thread-safe updates to
shared memory.  A low-level implementation of @c <sysdeps/atomicity.h>
is provided for every target processor architecture.  There is also a
generic implementation using POSIX spin locks, but that is not a good
enough solution for serious use.

The GCC package provides versions that work on most modern hardware.
We've tried to keep things as close to the original as possible, while
removing a bunch of os-specific files that didn't seem relevant.  A
primary goal has been to avoid changing the CPU-dependent @c
<sysdeps/atomicity.h> headers.

The relevant GCC documentation provides some helpful background,
especially the @c atomicity.h discussion at
<http://gcc.gnu.org/onlinedocs/porting/Thread-safety.html>.


@section portissues Issues Not Addressed

  - Cross-compilation has not been tested, or even thought through in
  much detail.  The @a host is the system on which JACK will run.
  This may differ from the @a build system doing the compilation.
  These are selected using the standard @c ./configure options @c
  --host and @c --build.  Usually, @c ./config.guess can print the
  appropriate canonical name for any system on which it runs.

  - Platform-specific build tools like Apple's Project Builder are not
  well-supported.

*/