readme.win32

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The collector has at various times been compiled under Windows 95 & later, NT,
and XP, with the original Microsoft SDK, with Visual C++ 2.0, 4.0, and 6, with
the GNU win32 tools, with Borland 4.5,  with Watcom C, and recently
with the Digital Mars compiler.  It is likely that some of these have been
broken in the meantime.  Patches are appreciated.

For historical reasons,
the collector test program "gctest" is linked as a GUI application,
but does not open any windows.  Its output normally appears in the file
"gctest.exe.log".  It may be started from the file manager.  The hour glass
cursor may appear as long as it's running.  If it is started from the
command line, it will usually run in the background.  Wait a few
minutes (a few seconds on a modern machine) before you check the output.
You should see either a failure indication or a "Collector appears to
work" message.

The cord test program has not been ported (but should port
easily).  A toy editor (cord/de.exe) based on cords (heavyweight
strings represented as trees) has been ported and is included.
It runs fine under either win32 or win32S.  It serves as an example
of a true Windows application, except that it was written by a
nonexpert Windows programmer.  (There are some peculiarities
in the way files are displayed.  The <cr> is displayed explicitly
for standard DOS text files.  As in the UNIX version, control
characters are displayed explicitly, but in this case as red text.
This may be suboptimal for some tastes and/or sets of default
window colors.)

In general -DREDIRECT_MALLOC is unlikely to work unless the
application is completely statically linked.

The collector normally allocates memory from the OS with VirtualAlloc.
This appears to cause problems under Windows NT and Windows 2000 (but
not Windows 95/98) if the memory is later passed to CreateDIBitmap.
To work around this problem, build the collector with -DUSE_GLOBAL_ALLOC.
This is currently incompatible with -DUSE_MUNMAP.  (Thanks to Jonathan
Clark for tracking this down.  There's some chance this may be fixed
in 6.1alpha4, since we now separate heap sections with an unused page.)

[Threads and incremental collection are discussed near the end, below.]

Microsoft Tools
---------------
For Microsoft development tools, rename NT_MAKEFILE as
MAKEFILE.  (Make sure that the CPU environment variable is defined
to be i386.)  In order to use the gc_cpp.h C++ interface, all
client code should include gc_cpp.h.

For historical reasons,
the collector test program "gctest" is linked as a GUI application,
but does not open any windows.  Its output appears in the file
"gc.log".  It may be started from the file manager.  The hour glass
cursor may appear as long as it's running.  If it is started from the
command line, it will usually run in the background.  Wait a few
minutes (a few seconds on a modern machine) before you check the output.
You should see either a failure indication or a "Collector appears to
work" message.

If you would prefer a VC++.NET project file, ask [e-mail].  One has
been contributed, but it seems to contain some absolute paths etc., so
it can presumably only be a starting point, and is not in the standard
distribution.  It is unclear (to me, Hans Boehm) whether it is feasible to
change that.

Clients may need to define GC_NOT_DLL before including gc.h, if the
collector was built as a static library (as it normally is in the
absence of thread support).

GNU Tools
---------
The collector should be buildable under Cygwin with either the old standard
Makefile, or possibly with the "configure --diable-shared;make" machinery.
(For the latter use --enable-threads=posix for thread support.) The major issue
here seems to be that dynamic library support is not currently enabled for
Cygwin.  (This is probably fixable without a great deal of difficulty by
reusing the standard WIN32 code.  But it requires some tweaking.)  As a result
of this, "configure; make; make check" currently does not completely succeed,
though the static library appears to be OK when used only from the main
programs, and correspondingly the Makefile.direct self tests succeed.

Mingw32 builds are not regularly tested, and may or may not work.
The following paragraph is probably obsolete:

For GNU-win32, use the regular makefile, possibly after uncommenting
the line "include Makefile.DLLs".  The latter should be necessary only
if you want to package the collector as a DLL.
[Is the following sentence obsolete? -HB] The GNU-win32 port is
believed to work only for b18, not b19, probably due to linker changes
in b19.  This is probably fixable with a different definition of
DATASTART and DATAEND in gcconfig.h.

Borland Tools
-------------
[Rarely tested.]
For Borland tools, use BCC_MAKEFILE.  Note that
Borland's compiler defaults to 1 byte alignment in structures (-a1),
whereas Visual C++ appears to default to 8 byte alignment (/Zp8).
The garbage collector in its default configuration EXPECTS AT
LEAST 4 BYTE ALIGNMENT.  Thus the BORLAND DEFAULT MUST
BE OVERRIDDEN.  (In my opinion, it should usually be anyway.
I expect that -a1 introduces major performance penalties on a
486 or Pentium.)  Note that this changes structure layouts.  (As a last
resort, gcconfig.h can be changed to allow 1 byte alignment.  But
this has significant negative performance implications.)
The Makefile is set up to assume Borland 4.5.  If you have another
version, change the line near the top.  By default, it does not
require the assembler.  If you do have the assembler, I recommend
removing the -DUSE_GENERIC.


Watcom compiler
---------------

Ivan V. Demakov's README for the Watcom port:

The collector has been compiled with Watcom C 10.6 and 11.0.
It runs under win32, win32s, and even under msdos with dos4gw
dos-extender. It should also run under OS/2, though this isn't
tested. Under win32 the collector can be built either as dll
or as static library.

Note that all compilations were done under Windows 95 or NT.
For unknown reason compiling under Windows 3.11 for NT (one
attempt has been made) leads to broken executables.

Incremental collection is not supported.

cord is not ported.

Before compiling you may need to edit WCC_MAKEFILE to set target
platform, library type (dynamic or static), calling conventions, and
optimization options.

To compile the collector and testing programs use the command:
    wmake -f WCC_MAKEFILE

All programs using gc should be compiled with 4-byte alignment.
For further explanations on this see comments about Borland.

If the gc is compiled as dll, the macro ``GC_DLL'' should be defined before
including "gc.h" (for example, with -DGC_DLL compiler option). It's
important, otherwise resulting programs will not run.

Ivan Demakov (email: [e-mail])

Incremental Collection
----------------------
There is some support for incremental collection.  By default, the
collector chooses between explicit page protection, anf GetWriteWatch-based
write tracking automatically, depending on the platform.

The former is slow and interacts poorly with a debugger.
Pages are protected.  Protection faults are caught by a handler
installed at the bottom of the handler
stack.  Whenever possible, I recommend adding a call to
GC_enable_incremental at the last possible moment, after most
debugging is complete.  No system
calls are wrapped by the collector itself.  It may be necessary
to wrap ReadFile calls that use a buffer in the heap, so that the
call does not encounter a protection fault while it's running.
(As usual, none of this is an issue unless GC_enable_incremental
is called.)

Note that incremental collection is disabled with -DSMALL_CONFIG.

Threads
-------

This version of the collector by default handles threads similarly
to other platforms.  James Clark's code which tracks threads attached
to the collector DLL still exists, but requires that both
- the collector is built in a DLL with GC_DLL defined, and
- GC_use_DllMain() is called before GC initialization, which
  in turn must happen before creating additional threads.
We generally recommend avoiding this if possible, since it seems to
be less than 100% reliable.

Use NT_THREADS_MAKEFILE (a.k.a gc.mak) instead of NT_MAKEFILE
to build a version that supports both kinds of thread tracking.
To build the garbage collector
test with VC++ from the command line, use

nmake /F ".\gc.mak" CFG="gctest - Win32 Release"

This requires that the subdirectory gctest\Release exist.
The test program and DLL will reside in the Release directory.

This version currently supports incremental collection only if it is
enabled before any additional threads are created.

Since 6.3alpha2, threads are also better supported in static library builds
with Microsoft tools (use NT_STATIC_THREADS_MAKEFILE) and with the GNU
tools.  In all cases,the collector must be built with GC_WIN32_THREADS
defined, even if the Cygwin pthreads interface is used.
(NT_STATIC_THREADS_MAKEFILE does this implicitly.  Under Cygwin,
./configure --enable-threads=posix defines GC_WIN32_THREADS.)

For the normal, non-dll-based thread tracking to work properly,
threads should be created with GC_CreateThread or GC_beginthreadex,
and exit normally or call GC_endthreadex or GC_ExitThread.  (For
Cygwin, use standard pthread calls instead.)  As in the pthread
case, including gc.h will redefine CreateThread, _beginthreadex,
_endthreadex, and ExitThread to call the GC_ versions instead.

Note that, as usual, GC_CreateThread tends to introduce resource leaks
that are avoided by GC_beginthreadex.  There is currently no equivalent of
_beginthread, and it should not be used.

GC_INIT should be called from the main executable before other GC calls.

We strongly advise against using the TerminateThread() win32 API call,
especially with the garbage collector.  Any use is likely to provoke a
crash in the GC, since it makes it impossible for the collector to
correctly track threads.

To build the collector for Mingw32 Pthreads, use Makefile.direct and
explicitly set GC_WIN32_PTHREADS.  Use -DPTW32_STATIC_LIB for the static
threads library.  Note that the DEBUG_WIN32_PTHREADS support in
win32_threads.c is currently broken and looking for someone to debug it.
(This information and the port came from Romano Paolo Tenca).