Admin/PLATFORMS

misc tuning and modernization;

Multi-platform support of Isabelle
==================================

Preamble
--------

The general programming model is that of a stylized ML + Scala + POSIX
environment, with as little system-specific code in user-space tools
as possible.

The basic Isabelle system infrastructure provides some facilities to
make this work, e.g. see the ML and Scala modules File and Path, or
functions like Isabelle_System.bash.  The settings environment also
provides some means for portability, e.g. the bash function
"platform_path" to keep the impression that Windows/Cygwin adheres to
Isabelle/POSIX standards, although Poly/ML and the JVM are native on
Windows.

When producing add-on tools, it is important to stay within this clean
room of Isabelle, and refrain from low-level access to the operating
system. The Isabelle environment uses peculiar scripts for GNU bash and
perl to get the plumbing right. This style should be imitated as far as
possible.


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

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

  x86_64-linux      Ubuntu 12.04 LTS

  x86_64-darwin     Mac OS X 10.9 Mavericks (macbroy2 MacPro4,1)
                    Mac OS X 10.10 Yosemite (macbroy31 MacBookPro6,2)
                    Mac OS X 10.11 El Capitan (?)
                    macOS 10.12 Sierra (macbroy30 MacBookPro6,2)

  x86_64-windows    Windows 7
  x86_64-cygwin     Cygwin 2.8 http://isabelle.in.tum.de/cygwin_2017 (x86_64/release)

All of the above platforms are 100% supported by Isabelle -- end-users
should not have to care about the differences (at least in theory).

Fringe platforms like BSD or Solaris are not supported.


64 bit vs. 32 bit platform personality
--------------------------------------

Isabelle requires 64 bit hardware running a 64 bit operating. Windows
and Mac OS X allow x86 executables as well, but for Linux this requires
separate installation of 32 bit shared libraries. The POSIX emulation on
Windows via Cygwin64 is exclusively for x86_64.

ML works both for x86_64 and x86, and the latter is preferred for space
and performance reasons. Java is always for x86_64 on all platforms.

Add-on executables are expected to work without manual user
configuration. Each component settings script needs to determine the
platform details appropriately.


The Isabelle settings environment provides the following variables to
help configuring platform-dependent tools:

  ISABELLE_PLATFORM64  (potentially empty)
  ISABELLE_PLATFORM32  (potentially empty)
  ISABELLE_PLATFORM

The ISABELLE_PLATFORM setting variable prefers the 32 bit personality of
the platform, if possible. Using regular bash notation, tools may
express their preference for 64 bit with a fall-back for 32 bit as
follows:

  "${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}"


There is a second set of settings for native Windows (instead of the
POSIX emulation of Cygwin used before):

  ISABELLE_WINDOWS_PLATFORM64
  ISABELLE_WINDOWS_PLATFORM32
  ISABELLE_WINDOWS_PLATFORM

It can be used like this:

  "${ISABELLE_WINDOWS_PLATFORM:-$ISABELLE_PLATFORM}"

  "${ISABELLE_WINDOWS_PLATFORM64:-${ISABELLE_WINDOWS_PLATFORM32:-${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}}}"


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

The following portable system tools can be taken for granted:

* Scala on top of Java 8.  Isabelle/Scala irons out many oddities and
  portability issues of the Java platform.

* GNU bash as uniform shell on all platforms. The POSIX "standard" shell
  /bin/sh does *not* work -- there are too many non-standard
  implementations of it. On Debian and Ubuntu /bin/sh is actually
  /bin/dash and thus introduces many oddities.

* Perl as largely portable system programming language, with its
  fairly robust support for processes, signals, sockets etc.


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

* Mac OS X: 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 X: 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, which
  affects Java native libraries in particular. In Isabelle/Scala the
  function isabelle.Platform.jvm_platform identifies the JVM platform.
  In the settings environment, ISABELLE_JAVA_PLATFORM provides the same
  information without running the JVM.

* Common Unix tools like /bin/sh, /bin/kill, sed, ulimit are
  notoriously non-portable an should be avoided.

* The traditional "uname" Unix tool only tells about its own executable
  format, not the underlying platform!