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From "Mark Miller (JIRA)" <>
Subject [jira] Commented: (LUCENE-1877) Improve IndexWriter javadoc on locking
Date Sun, 30 Aug 2009 21:49:34 GMT


Mark Miller commented on LUCENE-1877:

{quote}This interface follows the completely stupid semantics of System V and IEEE
Std 1003.1-1988 (``POSIX.1'') that require that all locks associated with a
file for a given process are removed when any file descriptor for that file is
closed by that process. This semantic means that applications must be aware
of any files that a subroutine library may access. For example if an
application for updating the password file locks the password file database
while making the update, and then calls getpwname(3) to retrieve a record, the
lock will be lost because getpwname(3) opens, reads, and closes the password
database. The database close will release all locks that the process has
associated with the database, even if the library routine never requested a
lock on the database. Another minor semantic problem with this interface is
that locks are not inherited by a child process created using the fork(2)
function. The flock(2) interface has much more rational last close
semantics and allows locks to be inherited by child processes. Flock(2) is
recommended for applications that want to ensure the integrity of their locks
when using library routines or wish to pass locks to their children... {quote}

I can see how this is not ideal, but I'm not seeing how any of the mentioned issues apply
to our simple lock usage ...

> Improve IndexWriter javadoc on locking
> --------------------------------------
>                 Key: LUCENE-1877
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Javadocs
>            Reporter: Mark Miller
>            Priority: Trivial
>             Fix For: 2.9
> A user requested we add a note in IndexWriter alerting the availability of NativeFSLockFactory
(allowing you to avoid retaining locks on abnormal jvm exit). Seems reasonable to me - we
want users to be able to easily stumble upon this class. The below code looks like a good
spot to add a note - could also improve whats there a bit - opening an IndexWriter does not
necessarily create a lock file - that would depend on the LockFactory used.
> {code}  <p>Opening an <code>IndexWriter</code> creates a lock file
for the directory in use. Trying to open
>   another <code>IndexWriter</code> on the same directory will lead to a
>   {@link LockObtainFailedException}. The {@link LockObtainFailedException}
>   is also thrown if an IndexReader on the same directory is used to delete documents
>   from the index.</p>{code}
> Anyone remember why NativeFSLockFactory is not the default over SimpleFSLockFactory?

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