[GHC] #4363: openFile sharing permissions are inconsistent across platforms

[GHC]

#4363: openFile sharing permissions are inconsistent across platforms
---------------------------------+------------------------------------------
    Reporter:  jystic            |       Owner:                             
        Type:  bug               |      Status:  new                        
    Priority:  high              |   Milestone:  7.6.1                      
   Component:  libraries/base    |     Version:  6.12.3                     
    Keywords:                    |          Os:  Windows                    
Architecture:  Unknown/Multiple  |     Failure:  Incorrect result at runtime
  Difficulty:                    |    Testcase:                             
   Blockedby:                    |    Blocking:                             
     Related:                    |  
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Comment(by jystic):

 I've read through the mailing list archives and I can understand where
 Duncan is coming from. The lazy IO problem certainly complicates matters.

 Would it be feasible to implementing in-process locking on Windows?

 It seems to me like that would be a solution which is good enough to solve
 this specific problem. Sure it would be great to offer a more advanced
 file API in the long term, but it could be a while before the community
 comes to a consensus on the right design.

 I see that the POSIX file locking code uses the device and inode as a
 unique identifier for files. Unfortunately, Windows doesn't return
 sensible information for st_ino when using fstat. You can however get a
 similar thing using GetFileInformationByHandle.

 Here's an example I just tested out using gcc on Windows.

 {{{

 #include <stdio.h>
 #include <share.h>
 #include <fcntl.h>
 #include <windows.h>

 int main()
 {
     const wchar_t *file = L"file.txt";

     int fd;
     HANDLE h;

     BY_HANDLE_FILE_INFORMATION info;
     long long inode;
     int device;

     /* assuming file already exists */
     fd = _wsopen(file, O_RDWR | _O_NOINHERIT, _SH_DENYWR, 0);

     /* convert file descriptor to windows handle */
     h = (HANDLE)_get_osfhandle(fd);

     if (GetFileInformationByHandle(h, &info))
     {
         device = info.dwVolumeSerialNumber;
         inode  = info.nFileIndexLow | ((long long)info.nFileIndexHigh <<
 32);

         printf("device: %x\n", device);
         printf("inode: %I64x\n", inode);
     }

     return 0;
 }

 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4363#comment:11>
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