[jira] [Updated] (QPID-1158) Portability problems with flock on solaris

["Justin Ross (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/QPID-1158?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Justin Ross updated QPID-1158:
------------------------------

    Fix Version/s: 0.6
    
> Portability problems with flock on solaris
> ------------------------------------------
>
>                 Key: QPID-1158
>                 URL: https://issues.apache.org/jira/browse/QPID-1158
>             Project: Qpid
>          Issue Type: Bug
>          Components: C++ Broker
>            Reporter: Alan Conway
>            Assignee: Alan Conway
>             Fix For: 0.6
>
>         Attachments: lockfile-abstraction.patch
>
>
> On Thu, 2008-06-26 at 12:12 +0200, Manuel Teira wrote:
> Hello.
> > After further  investigation and tests, related with the change in 
> > r671604 to drop the file locking strategy in favour of a flock on the 
> > data dir.
> > 
> > Trying to write a similar code, but using lockf, I hit the issue that 
> > the file must be opened using O_RDWR or O_RWONLY, and that's not allowed 
> > for a directory.
> > The same happens trying to use a fcntl call.
> > And unexpectedly, the same for flock. In the solaris manual page:
> > 
> > <snip>
> >      Read permission is required on a file  to  obtain  a  shared
> >      lock,   and  write  permission  is  required  to  obtain  an
> >      exclusive lock.
> > </snip>
> > 
> > But the linux man page claims:
> > 
> > <snip>
> > A shared or exclusive lock can be placed on a file regardless of the 
> > mode in which the file was opened.
> > </snip>
> > 
> > I've searched the web for some BSD system pages, but they don't say 
> > anything about the file mode.
> > 
> > 
> > On the other way, POSIX fcntl specification says, apropos the failure 
> > causes:
> > 
> > [EBADF]
> >     The /fildes/ argument is not a valid open file descriptor, or the
> >     argument /cmd/ is F_SETLK or F_SETLKW, the type of lock, *l_type*,
> >     is a shared lock (F_RDLCK), and /fildes/ is not a valid file
> >     descriptor open for reading, or the type of lock *l_type*, is an
> >     exclusive lock (F_WRLCK), and /fildes/ is not a valid file
> >     descriptor open for writing. 
> > 
> > Posix specs also forces write permissions for lockf:
> > http://www.opengroup.org/onlinepubs/007908799/xsh/lockf.html
> > 
> > 
> > 
> > This leads to solaris not being able to lock directly on a directory, 
> > I'm afraid. Any idea?
> > 
> Yes, we can create (if it doesn't already exist) a lock file in the directory and then use lockf to lock it. There's already code in Daemon.cpp that does exactly this for the PID file. The reason I switched to flock was because crashing or killed brokers were sometimes leaving the lock file behind them, whereas a flock (or lockf)  lock is automatically released when the process exits. 
> We need to
>  - create a qpid::sys::LockFile class that can be re-implemented on different platforms.
>  - use the Daemon.cpp code as the posix implementation.
>  - Replace the locking code in Daemon.cpp and DataDir.cpp with the common sys::LockFile.

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