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+The collector has at various times been compiled under Windows 95 & NT,
+with the original Microsoft SDK, with Visual C++ 2.0, 4.0, and 6, with
+the GNU win32 environment, with Borland 4.5, and recently with
+Watcom C. It is likely that some of these have been broken in the
+meantime. Patches are appreciated.
+It runs under both win32s and win32, but with different semantics.
+Under win32, all writable pages outside of the heaps and stack are
+scanned for roots. Thus the collector sees pointers in DLL data
+segments. Under win32s, only the main data segment is scanned.
+(The main data segment should always be scanned. Under some
+versions of win32s, other regions may also be scanned.)
+Thus all accessible objects should be accessible from local variables
+or variables in the main data segment. Alternatively, other data
+segments (e.g. in DLLs) may be registered with the collector by
+calling GC_init() and then GC_register_root_section(a), where
+a is the address of some variable inside the data segment. (Duplicate
+registrations are ignored, but not terribly quickly.)
+(There are two reasons for this. We didn't want to see many 16:16
+pointers. And the VirtualQuery call has different semantics under
+the two systems, and under different versions of win32s.)
+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
+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
+In general -DREDIRECT_MALLOC is unlikely to work unless the
+application is completely statically linked.
+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.
+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).
+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. The GNU-win32 port is
+believed to work only for b18, not b19, probably dues to linker changes
+in b19. This is probably fixable with a different definition of
+DATASTART and DATAEND in gcconfig.h.
+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.
+There is some support for incremental collection. This is
+currently pretty simple-minded. Pages are protected. Protection
+faults are caught by a handler installed at the bottom of the handler
+stack. This is both slow and interacts poorly with a debugger.
+Whenever possible, I recommend adding a call to
+GC_enable_incremental at the last possible moment, after most
+debugging is complete. Unlike the UNIX versions, 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
+Note that incremental collection is disabled with -DSMALL_CONFIG.
+James Clark has contributed the necessary code to support win32 threads.
+Use NT_THREADS_MAKEFILE (a.k.a gc.mak) instead of NT_MAKEFILE
+to build this version. Note that this requires some files whose names
+are more than 8 + 3 characters long. Thus you should unpack the tar file
+so that long file names are preserved. 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 relies on the collector residing in a dll.
+This version currently supports incremental collection only if it is
+enabled before any additional threads are created.
+Version 4.13 attempts to fix some of the earlier problems, but there
+may be other issues. If you need solid support for win32 threads, you
+might check with Geodesic Systems. Their collector must be licensed,
+but they have invested far more time in win32-specific issues.
+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
+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 gc 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: email@example.com)