[erlang-patches] win32 memory allocation fix / mmap emulation

Rickard Green <>
Fri Dec 11 23:21:20 CET 2009


Blaine Whittle wrote:
> Björn Gustavsson wrote:
>> My gut feeling, though, is that lying about Windows having MMAP might
>> not be the best way to
>> got, as MMAP could possibly be used in other places in a future
>> version of OTP. So it may be
>> better to change the memory management code to test some other define
>> that covers both the
>> mmap() case and the virtual allocation functions on Windows. (For ease
>> of reviewing, it would
>> be a good idea to put such re-factoring into a separate commit.)
> Ya, I was unsure the best way to handle the defines for that very reason.
> The only files that involved the MMAP change are erl_mseg.h and
> erl_mseg.c.  However any win32 specific should go in win32\erl_win_sys.h
> and win32\sys.c

However, apart from the above, the mmap()/munmap() emulation
implementation is copyright GeNeSys mbH and without any specific license
which makes it hard to include into Erlang/OTP.

The best solution would be to drop the mmap()/munmap() emulation and
just implement mseg_create()/mseg_destroy() (in erl_mseg.c) using
VirtualAlloc()/VirtualFree() (which should be straightforward since they
map onto each other very well). When this have been done, change the
following in erl_mseg.h:

  #  define HAVE_ERTS_MSEG 1
  #  define HAVE_ERTS_MSEG 0


  #if HAVE_MMAP || defined(__WIN32__)
  #  define HAVE_ERTS_MSEG 1
  #  define HAVE_ERTS_MSEG 0

which will make other allocators use mseg_alloc for retrieving raw memory.

Rickard Green, Erlang/OTP, Ericsson AB.

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