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
---------------------------
64 bit hardware becomes more and more important for many users.
Add-on tools need to work seamlessly without manual user
configuration, although it is often sufficient to fall back on 32 bit
executables.
The ISABELLE_PLATFORM setting variable refers to the 32 bit version of
the platform, even on 64 bit hardware. Power-tools need to indicate
64 bit support explicitly, via the (optional) ISABELLE_PLATFORM64
setting. 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.
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.