[Boost-bugs] [Boost C++ Libraries] #3377: interlocked pointer exchanges cause warnings with mingw64

Subject: [Boost-bugs] [Boost C++ Libraries] #3377: interlocked pointer exchanges cause warnings with mingw64
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-08-31 21:35:18

#3377: interlocked pointer exchanges cause warnings with mingw64
--------------------------+-------------------------------------------------
 Reporter:  anonymous     |       Owner:         
     Type:  Bugs          |      Status:  new    
Milestone:  Boost 1.41.0  |   Component:  None   
  Version:  Boost 1.39.0  |    Severity:  Problem
 Keywords:                |  
--------------------------+-------------------------------------------------
 With a gcc build targeting Win64 (specifically
 http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Release%20for%20GCC%204.4.0

 /mingw-w64_x86-64_linux64-4.4.0-1.tar.bz2/download), I'm seeing warnings
 like this:

 /home/martind/work/unicorn/include/x86_64_mingw32w64/boost/thread/win32/interlocked_read.hpp:
 In function 'void boost::detail::interlocked_write_release(void*
 volatile*, void*)':
 /home/martind/work/unicorn/include/x86_64_mingw32w64/boost/thread/win32/interlocked_read.hpp:71:
 error: cast from 'void*' to 'long int' loses precision
 ...
 /home/martind/work/unicorn/include/x86_64_mingw32w64/boost/thread/win32/basic_timed_mutex.hpp:
 In member function 'void* boost::detail::basic_timed_mutex::get_event()':
 /home/martind/work/unicorn/include/x86_64_mingw32w64/boost/thread/win32/basic_timed_mutex.hpp:152:
 error: cast from 'void*' to 'long int' loses precision
 cc1plus: warnings being treated as errors

 The warnings come from the casts here in boost/detail/interlocked.hpp:

 # define BOOST_INTERLOCKED_COMPARE_EXCHANGE_POINTER(dest,exchange,compare)
 \
     ((void*)BOOST_INTERLOCKED_COMPARE_EXCHANGE((long
 volatile*)(dest),(long)(exchange),(long)(compare)))
 # define BOOST_INTERLOCKED_EXCHANGE_POINTER(dest,exchange) \
     ((void*)BOOST_INTERLOCKED_EXCHANGE((long
 volatile*)(dest),(long)(exchange)))

 On Win64, I see that sizeof(long) == 4 but sizeof(void*) == 8, so the
 compiler is right to warn.  Elsewhere in this file,
 InterlockedCompareExchangePointer and InterlockedExchangePointer are
 conditionally used to implement these macros.  Comments I found elsewhere
 suggested that this is done conditionally because these functions aren't
 available in very old platform SDKs and, indeed, MSDN says that they only
 became available with Windows 2000.  Perhaps Win64 can be assumed to have
 these functions available, as is assumed earlier in the file when
 compiling with MSVC.  gcc for Win64 is a relatively new development
 without wide deployment, which could explain why the branch that handles
 __CYGWIN__ etc doesn't yet cope.

 In the attached patch, I've used the same condition for detecting Win64 as
 used in the MSVC part of the file.  That means that I've changed the
 behavior for IA64 as well as AMD64, despite having no means to test IA64.

 I see interlocked.hpp is used by interprocess, smart_ptr and thread but
 I'm not sure which Component it "belongs" to, so I've left that set to
 None.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3377>
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