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Open File Locking and Mac OS X?
ArcticMyst asks: "In Mac OS X the responsibility of locking open files has moved from the operating system to individual applications. With the exception of Apple's most recent release of AppleWorks, I have not been able to find many applications written for Mac OS X that will lock a network resident file when it is opened. Not marking a file as locked allows more than one user to have a file open, then edit and save back to the original file. Even most of Apple's own applications fail to do this. Apple does provide information on how to make sure that open files are not edited while they are open. Why do so many applications fail to provide this security?"
This doesn't actually lock the file for exclusive access, it just sets a status. Anyone who checks the status will see that it is locked for exclusive access, but will not be 'locked' out from accessing it. I think it's in the flock man pages. Is this correct?
People seem to be interpreting this to mean that Mac OS X applications will never use file locking unless the programmer explicitly requests it. This may have been true prior to 10.2 (Jaguar), but is no longer the case. The tech note is a little bit sketchy on this point, but it was written before the release of Jaguar.
Applications that open files with calls to the standard Mac frameworks will use locking. A Carbon app that locks in OS 9 will still lock when running under a recent version of OS X.
Until this [major] oversight was fixed, workarounds were required in application code. This is no longer the case.
Only applications that use open() directly need to take extra steps to lock files. This is the way it's done in the Unix world, and Apple has chosen the correct implementation by not forcing the standard open() call to lock.
Mark