README.win32

The collector has at various times been compiled under Windows 95 and 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 C++ Builder, with Watcom C, with EMX,
and with the Digital Mars compiler (DMC).

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.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.

A toy editor (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
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, type
"nmake -f NT_MAKEFILE cpu=i386 disable_threads=1 enable_static=1 nodebug=1"
to build the release variant of the collector as a static library without
threads support.

In order to use the C++ interface, the client code should include gc_cpp.h
and/or gc_allocator.h.

[See above for gctest.]

If you would prefer a VC++ .NET project file, ask Hans Boehm.  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.

GNU Tools
---------

The collector should be buildable under Cygwin with the
"./configure; make check" machinery.

MinGW builds (including for x64) are available both directly (on a Windows
host) and via cross-compilation, e.g.
"./configure --host=i686-pc-mingw32; make check"

By default, configure instructs make to build the collector as a DLL (shared
library), adding -D GC_DLL to CFLAGS.

Parallel marker is enabled by default; it could be disabled by
"--disable-parallel-mark" option.

Memory unmapping could be turned off by "--disable-munmap" option.

Borland Tools
-------------

For Borland tools, use `cmake -G "Borland Makefiles"`.  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.)

Digital Mars compiler
---------------------

Same as MS Visual C++ but might require
-DAO_OLD_STYLE_INTERLOCKED_COMPARE_EXCHANGE option to compile with the
parallel marker enabled.

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

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

The collector has been tested with Watcom C 10.6, 11.0 and OpenWatcom 2.0.
It runs under Win32 and win32s, and even under DOS 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 supported (except for MSDOS and OS/2).

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 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.

The alternate way to compile the collector is to use cmake build system:
    cmake -G "Watcom WMake" .
    cmake --build .

Special note for OpenWatcom users: the C (unlike the C++) compiler (of the
latest stable release, not sure for older ones) doesn't force pointer global
variables (i.e. not struct fields, not sure for locals) to be aligned unless
optimizing for speed (e.g., "-ot" option is set); the "-zp" option (or align
pragma) only controls alignment for structs; I don't know whether it's a bug or
a feature (see an old report of same kind -
http://bugzilla.openwatcom.org/show_bug.cgi?id=664), so You are warned.

Incremental Collection
----------------------

There is some support for incremental collection.  By default, the
collector chooses between explicit page protection, and 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
-------

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_threads_discovery() 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.

To build the collector as a dynamic library which handles threads similarly
to other platforms, type "nmake -f NT_MAKEFILE".  If automatic tracking of
threads attached to the collector DLL (i.e. support of both kinds of thread
tracking) is needed then delete "-DTHREAD_LOCAL_ALLOC" from NT_MAKEFILE
manually before the build.

The incremental collection is supported only if it is enabled before any
additional threads are created.

Threads are also supported in static library builds with Microsoft tools
(e.g., NT_MAKEFILE), as well as with the CMake and GNU tools.  The collector
must be built with GC_THREADS defined (this is the default in NT_MAKEFILE,
CMakeLists.txt and configure).

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, the
standard pthread_create/exit calls could be used 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 (in the
C runtime) 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 thread before other GC calls.

We strongly advise against using the TerminateThread() Windows 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 MinGW pthreads-win32 (or other non-Cygwin pthreads
implementation for Windows), use Makefile.direct and explicitly set
GC_WIN32_PTHREADS (or pass --enable-threads=pthreads to configure).
Use -DPTW32_STATIC_LIB for the static threads library.

The alternate (better) way to build the library is to use CMake script;
please see README.cmake for the details.