[Boost-bugs] [Boost C++ Libraries] #5108: shared memory object temporary name bug, Mac OSX 10.6.6

Subject: [Boost-bugs] [Boost C++ Libraries] #5108: shared memory object temporary name bug, Mac OSX 10.6.6
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-01-22 03:36:33

#5108: shared memory object temporary name bug, Mac OSX 10.6.6
------------------------------------+---------------------------------------
 Reporter:  david.ibbitson@…        |       Owner:  igaztanaga  
     Type:  Bugs                    |      Status:  new         
Milestone:  To Be Determined        |   Component:  interprocess
  Version:  Boost 1.45.0            |    Severity:  Problem     
 Keywords:  shared memory object    |  
------------------------------------+---------------------------------------
 There is a problem with creating a shared memory object in a 64 bit
 application and trying to open it in a 32 bit application. The problem
 seems to stem from the following snippet of code, found in the function
 get_bootstamp defined on line 50 of the file tmp_dir_helpers.hpp.

 {{{
    std::size_t char_counter = 0;
    long fields[2] = { result.tv_sec, result.tv_usec };
    for(std::size_t field = 0; field != 2; ++field){
       for(std::size_t i = 0; i != sizeof(long); ++i){
          const char *ptr = (const char *)&fields[field];
          bootstamp_str[char_counter++] = Characters[(ptr[i]&0xF0)>>4];
          bootstamp_str[char_counter++] = Characters[(ptr[i]&0x0F)];
       }
    }
 }}}

 On my system sizeof(long) = 4 under a 32 bit application, and sizeof(long)
 = 8 on a 64 bit application. Hence the generated temporary filename stored
 in bootstamp_str is of differing lengths under a 32 bit app and a 64 bit
 app respectively.  Hence, I was seeing the error "file or directory does
 not exist" when trying to open a named shared memory object.

 The fix (cross platform?) seems to be to use the type "long long" because
 sizeof(long long) = 8 under 32 and 64 bit application.

 {{{
    std::size_t char_counter = 0;
    long long fields[2] = { result.tv_sec, result.tv_usec };
    for(std::size_t field = 0; field != 2; ++field){
       for(std::size_t i = 0; i != sizeof(long long); ++i){
          const char *ptr = (const char *)&fields[field];
          bootstamp_str[char_counter++] = Characters[(ptr[i]&0xF0)>>4];
          bootstamp_str[char_counter++] = Characters[(ptr[i]&0x0F)];
       }
    }
 }}}

 Making this change fixed this problem for me.
 Hope this helps!

 David

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5108>
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