[Boost-bugs] [Boost C++ Libraries] #7793: Not needed code for mapped files in windows

Subject: [Boost-bugs] [Boost C++ Libraries] #7793: Not needed code for mapped files in windows
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-12-13 23:40:11

#7793: Not needed code for mapped files in windows
----------------------------------+-----------------------------------------
 Reporter:  lodos@…               |       Owner:  igaztanaga  
     Type:  Tasks                 |      Status:  new         
Milestone:  To Be Determined      |   Component:  interprocess
  Version:  Boost 1.52.0          |    Severity:  Optimization
 Keywords:  mapped file grow      |  
----------------------------------+-----------------------------------------
 The exchange below took place on the boost developer list, it describes
 the request. Thank you.

 > > > When you grow a managed mapped file, the current
 > > > implementation fills all the new space with zeroes. This is less
 > > > efficient than just resizing the file. The comments in the code
 > > > implies there is a reason, so what is  it?
 > >

 > > Interprocess tries to simulate as much as possible POSIX guarantees.
 > > truncate() POSIX system call guarantees that "If the file is
 > extended,
 > > the extended area appears as if it were zero-filled". In windows,
 > > SetFileValidData/SetEndOfFile does not zero-fill the extended size so
 > > Interprocess needs to write it.

 > Given that the mapped file content is not part of the library
 > interface, and the only expected user of the mapped file is the library
 > itself, why waste time in Windows? Seems to me that a requirement that
 > files should be identical is too strong, as long as they work and
 > perhaps don't affect platform portability. File portability between
 > platforms should be warranted? What about platforms with different
 > endianness?

 I need to investigate it, but I tried to support similar behaviour for
 internal file-handling functions. I'll need to think it again. Please fill
 a ticket so this doesn't get lost when reviewing pending issues.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7793>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.