shared memory object temporary name bug, Mac OSX 10.6.6

[david.ibbitson@…]

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

[David Ibbitson <david.ibbitson@…>]

It looks like ticket #4251 is related if not the same issue.

[david.ibbitson@…]

Program demonstrating Leopard sysctl bug.

[david.ibbitson@…]

Another update. It appears that on Leopard the sysctl function periodically returns an invalid timeval struct under a 64 bit build. In particular the microsecond field is occasionally incorrect. See the attached file for a sample program that shows the issue.

[Ion Gaztañaga]

Disabled bootstamp in Boost 1.47. This means that shared memory/queues will go to /tmp if it exists. If /tmp is not cleared on reboot shared memory will survive to reboots, but this behaviour is allowed by POSIX. Using bootstamps to detect reboots is doing more harm than good.