The OP originally stated that he had two STC processes that updated the same z/Unix file at the same time and wanted to prevent this. Are two STC's both considered z/Unix processes under the same kernel when they are running on the same LPAR? If so, ISTM that locking and unlocking the file around the write code will work as a mechanism to prevent simultaneous writes.
But what about two STC's running on different LPAR's in the same sysplex? Does z/Unix file locking work across LPAR's, or only within the same LPAR? Just curious. ISTR that simultaneous writes to a common file are classically solved in most unix systems by implementing a daemon process that is the only process allowed to write to the file, and other processes send messages to the daemon to accomplish the write function, like the syslog daemon for system messages. The new question is whether Java on z/Unix provides access to any file locking mechanism at all, as the OP also just said it was a Java application and he wants to share the file among tasks of the *same* program. That would argue that using whatever the Java equivalent of the C flockfile function is would be the solution to use. But can z/Unix Java do that? Or does he have to write a JNI function to be called from his z/Unix Java code to implement a file lock? Or should he just implement a third process/task under the same program for the file writes and have both of the other tasks just send messages to the write process? Peter -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Walt Farrell Sent: Friday, April 20, 2012 8:27 AM To: [email protected] Subject: Re: USS File Integrity On Fri, 20 Apr 2012 11:18:45 +0800, David Crayford <[email protected]> wrote: >Of course, fcntl() can be used to implement byte-range-locking. So in >theory you could use it to implement >row-level locking in a dictionary library. ENQ is not that granular. ENQ is as granular as the application wants to make it, depending on how clever the application programmer is at encoding information into the RNAME the application will use. The key point about UNIX files, though, is that all the locking is advisory, and controlled by the applications that use the file. If they all implement the same locking mechanism (whatever that may be), the locking will work. If they don't, it won't work. -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
