If your code is only reading from a control block structure and you do not serialize, there is the danger that other code might serialize and update the control block structure in a way that could cause your code to behave incorrectly. I do not know the structure or use of the UCB lookup table (ULUT) as used now in z/OS. But I remember the lookup table scheme in MVT and the queue of UCBs that we used to have in between MVT and z/OS. The other code might change the UCB that you have found and are reading-only, in which case your code needs to withstand the possibility that any or all of the fields may change while you are looking at it. Possibly a UCB might be deleted, in which case even a lookup table can not prevent your code's attempting to accessing freshly FREEMAINed storage. Perhaps even the entire ULUT could be freed and replaced with a whole new ULUT at a different virtual address. Only those who have studied the code that accesses the ULUT can know exactly how safe it is to use the ULUT without first serializing.
Bill Fairchild Programmer Rocket Software 408 Chamberlain Park Lane * Franklin, TN 37069-2526 * USA t: +1.617.614.4503 * e: bfairch...@rocketsoftware.com * w: www.rocketsoftware.com -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of John Gilmore Sent: Tuesday, November 13, 2012 3:38 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: "New" way to do UCB lookups Jim Mulder's point is very well taken indeed. Traversing a dynamic list without serialization on the assumption that since you do not plan to change it no one else will is a mug's game. John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
