Admin/PLATFORMS

updated platform information;

Some notes on multi-platform support of Isabelle
================================================

Preamble
--------

The general programming model is that of a stylized ML + Scala + POSIX
environment, with hardly any system specific code in user-space tools
and packages.

The basic Isabelle system infrastructure provides some facilities to
make this work, e.g. see the ML structures File and Path, or functions
like Isabelle_System.bash.  The settings environment also provides
some means for portability, e.g. jvm_path to keep the impression that
Java on Windows/Cygwin adheres to Isabelle/POSIX standards (inside the
JVM itself there are many Windows-specific things, though).

When producing add-on tools, it is important to stay within this clean
room of Isabelle, and refrain from overly ambitious system hacking.
The existing Isabelle scripts follow a certain style that might look
odd at first sight, but it reflects long years of experience in
getting system plumbing right (which is quite hard).


Supported platforms
-------------------

The following hardware and operating system platforms are officially
supported by the Isabelle distribution (and bundled tools), with the
following reference versions (which have been selected to be neither
too old nor too new):

  x86-linux         Ubuntu 10.04 LTS
  x86-darwin        Mac OS Leopard (macbroy30)
                    Mac OS Snow Leopard (macbroy2)
                    Mac OS Lion (macbroy6)
  x86-cygwin        Cygwin 1.7 (vmbroy9)

  x86_64-linux      Ubuntu 10.04 LTS
  x86_64-darwin     Mac OS Leopard (macbroy30)
                    Mac OS Snow Leopard (macbroy2)
                    Mac OS Lion (macbroy6)

All of the above platforms are 100% supported by Isabelle -- end-users
should not have to care about the differences (at least in theory).
There are also some additional platforms where Poly/ML also happens to
work, but they are *not* covered by the official Isabelle
distribution:

  ppc-darwin
  sparc-solaris
  x86-solaris
  x86-bsd

There are increasing problems to make contributing components of
Isabelle work on such fringe platforms.  Note that x86-bsd is silently
treated like x86-linux -- this works if certain Linux compatibility
packages are installed on BSD.


32 bit vs. 64 bit platforms
---------------------------

Most users already have 64 bit hardware, and many of them are running
a 64 bit operating system.  Native 64 bit support for ML and Scala/JVM
is increasingly important for big Isabelle applications, but 32 bit is
often the default to get started.  Add-on executables need to work
seamlessly without manual user configuration, either as native 64 bit
executables or in 32 bit mode on a 64 bit platform.

The ISABELLE_PLATFORM setting variable refers to the 32 bit version of
the platform, even on 64 bit hardware.  Tools need to indicate 64 bit
support explicitly via the (optional) ISABELLE_PLATFORM64 setting, if
this is really required.  The following bash expression prefers the 64
bit platform, if that is available:

  "${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM}"

Note that ML and JVM may have a different idea of the platform,
depending on the respective binaries that are actually run.  The
"uname" Unix tool usually only tells about its own executable format,
not the underlying platform.


Dependable system tools
-----------------------

The following portable system tools can be taken for granted:

* GNU bash as uniform shell on all platforms.  The POSIX "standard"
  shell /bin/sh is *not* appropriate, because there are too many
  non-standard implementations of it.

* Perl as largely portable system programming language.  In some
  situations Python may serve as an alternative, but it usually
  performs not as well in addressing various delicate details of
  operating system concepts (processes, signals, sockets etc.).

* Scala with Java Runtime 1.6.  The Isabelle/Scala layer irons out
  many oddities and portability issues of the Java platform.


Known problems
--------------

* Mac OS: If MacPorts is installed there is some danger that
  accidental references to its shared libraries are created
  (e.g. libgmp).  Use otool -L to check if compiled binaries also work
  without MacPorts.

* Mac OS: If MacPorts is installed and its version of Perl takes
  precedence over /usr/bin/perl in the PATH, then the end-user needs
  to take care of installing extra modules, e.g. for HTTP support.
  Such add-ons are usually included in Apple's /usr/bin/perl by
  default.

* The Java runtime has its own idea about the underlying platform,
  e.g. on a 64 bit machine Isabelle/ML could be x86-linux, but the JVM
  could be x86_64-linux.  This affects Java native libraries in
  particular -- which cause extra portability problems and can make
  the JVM crash anyway.

  In Isabelle/Scala isabelle.Platform.jvm_platform identifies the JVM
  platform.  Since there can be many different Java installations on
  the same machine, which can also be run with different options,
  reliable JVM platform identification works from inside the running
  JVM only.