Bill Fairchild writes: <begin extract> 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. <end extract>
and thus makes my point better than I did. In this OCO period we cannot know. We must therefore assume that accessing a dynamic list, q On 11/13/12, Bill Fairchild <bfairch...@rocketsoftware.com> wrote: > 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 > -- John Gilmore, Ashland, MA 01721 - USA t. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
