The following message is a courtesy copy of an article that has been posted to alt.folklore.computers,bit.listserv.ibm-man as well.
Anne & Lynn Wheeler <[EMAIL PROTECTED]> writes: > A.6 Multiprogramming and Multiprocessing Examples > http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/DZ9ZR003/A.6?SHELF=DZ9ZBK03&DT=20040504121320 > > from above: > > When two or more programs sharing common storage locations are being > executed concurrently in a multiprogramming or multiprocessing > environment, one program may, for example, set a flag bit in the > common-storage area for testing by another program. It should be noted > that the instructions AND (NI or NC), EXCLUSIVE OR (XI or XC), and OR > (OI or OC) could be used to set flag bits in a multiprogramming > environment; but the same instructions may cause program logic errors > in a multiprocessing configuration where two or more CPUs can fetch, > modify, and store data in the same storage locations simultaneously. > > Subtopics: > > * A.6.1 Example of a Program Failure Using OR Immediate > * A.6.2 Conditional Swapping Instructions (CS, CDS) > * A.6.3 Bypassing Post and Wait > * A.6.4 Lock/Unlock > * A.6.5 Free-Pool Manipulation > * A.6.6 PERFORM LOCKED OPERATION (PLO) > > ... snip ... re: http://www.garlic.com/~lynn/2006s.html#53 Is the teaching of non-reentrant HLASM coding practices ever defensible? ... as to having people well versed with "A.6.1" problems ... there was a rumor in the late 70s that the hardware engineers were approached by MVS group to make the immediate instructions atomic on multiprocessor machines. MVS was moving kernel from the old-style os/360 single global kernel/supervisor lock to higher degrees of kernel parallelism and were having a devil of a time converting all the non-atomic immediate instruction coding for parallel operation. ... having re-entrant programming supporting multiple concurrent operation ... including supporting multiple concurrent operation in same address space (aka threading/multitasking) ... for highly parallel operation. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
