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 portopsys Operating System Dependencies

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

Whenever possible, OS dependencies should be isolated in OS-specific
header files.  Each target OS may optionally provide a @c
<sysdeps/os_defines.h> header, otherwise @c
conf/os/generic/os_defines.h will be used.  The @c configure.host
script distinguishes OS variations using a case statement based on the
host system's type and version.

Some needed POSIX features may be missing on certain platforms.  If
so, the preferred solution is to provide a substitute, like the @c
fakepoll.c implementation for Mac OS X.

If conditional compilation is required in mainline
platform-independent code, avoid using the system name.  Instead, @c
#define a descriptive name in your @c <sysdeps/os_defines.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 other OS ports are not required to know
your platform's 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.

*/