In the current implementation, all of the File Manager calls in Mac OS X call through to the underlying BSD file system. The default behavior of BSD allows for multiple "writers" to a single file. Opening a file for writing does not ensure other processes can not write to the same file. Mac OS X's BSD subsystem does not enforce file read/write privileges in the same way as classic Mac OS. This default behavior allows for one "writer" and multiple "readers" of the file. Usually an fsRdWrPerm error would be returned when other attempts were made to open the file for write access, though attempts to open such a file for read only access would succeed. "Opening a file from classic Mac OS (pre Mac OS X) with fsWrPerm, fsRdWrPerm, or the default fsCurPerm, meant that any other application trying to open that same file with write access would not be able to do so. Why do so many applications fail to provide this security?"
#Apple os x file system how to
"Apple does provide information on how to make sure that open files are not edited while they are open. I think Apple have a man page or technote on this somewhere but it's a big deal if you've ever had your files clobbered by some oaf of a program that doesn't pay attention to Advisory locking :-) If you DO use Mandatory locking you should _always_ check for the existing of advisory locking with flock() *first!*.
#Apple os x file system software
I would caution anyone NOT to use Mandatory locking unless they are sure they have a good reason for doing so as I've had problems porting small apps (even Perl scripts!) written by people who've used Mandatory locking when they shouldn't have, it's not difficult to fix, but it can be a pain to track down.ĭue the previous behaviour of Mac OS's file open behaviour I can forgive old school Mac developers from making this mistake (many have a lot on their plate just moving software to Mac OS X) but for Unix developers I think it's pretty inexcusable to screw up completly (by using fcntl() in appropriately or by not checking for advisory locks with flock()). not even allowing other applications to _read_ the file) - way (not be confused with flocks() ability to simply 'flag' that there is an exlcusive lock). The issues with Mandatory locking are that it's not supported on all operating systems, and that it's ability to give a truly exclusive lock on a file leads to abusive usage by developers locking files in an abusive - overly harsh (i.e. Sorry for shouting, but it can be a big deal :-). Mac OS X developers should note Apple strongly recommend only using Advisory locking and not Mandatory locking. It also gives you a _fully_ exclusive lock on a file, buy blocking read()/write() systems calls - this is both a blessing and a curse and should be used wisely.Īdvisory locking, however, is much more efficent and is widely supported on all Unixes - unlike Mandatory locking which is not (BSD systems tend to support it out of the box, it's an option with Linux, but much more rarely used - vanilla Red Hat or Debian systems tend not to support it IME). The advantage of Mandatory locking is that you can choose to lock parts of a file (and leave other parts of it still open to be written to). X Window System, it does not have the Mac OS X interfaceĪnd thus will not run Mac OS X applications.You can use "Advisory Locking" (flock()) or "Mandatory Locking" (fcntl() - or lockf(), a front end to fcntl()). Although Darwin will run many Unix applications, including the Source, and it is available as a stand-alone operating (apps) developed for iOS are not compatible with Mac OS X, and viceįoundation upon which Mac OS X is based.
Despite their shared origins, applications Handheld devices, and is much more tightly controlled than other IOS: Based on Mac OS X, versions of iOS run on the
For more information, see Apple's Mac OS X Server page. Sharing, QuickTime streaming, NetBoot, and advanced web
Includes a suite of network services, such as a print server, file It is similar to the consumer release of Mac OS X, but also Mac OS X Server: This is Apple's server operating For more information, see Apple's Mac OS X page and Developer page for It is a consumer operating system designed for use Mac OS X: This is the version most Macintosh For the current version's system requirements, seeĬurrently, four Mac OS X-related products are available: Multithreading, and protected memory give Mac OS X improved stabilityĪnd performance. Has much of the look and feel of the former Mac OS,įeatures such as preemptive multitasking, symmetric multiprocessing, Its interface, known asĪqua, is built on a Unix foundation. System for its line of Macintosh computers. Information here may no longer be accurate, and links may no longer be available or reliable. This content has been archived, and is no longer maintained by Indiana University.
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