Experimental Physics and
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Marty Kraimer wrote: You are correct. This is a really nasty side effect of asynchronous processing. The following assumes a passive record. If a value is written to a record between the two phases of record processing the following is done. The value is written to the record. If the field has pp(TRUE), i.e. process passive, the record will be processed again when the record completes asynchronous processing. Thus can lead to strange side effects. Kay Kasemir and Jeff Hill just told me of one. Assume a bo record has the value 0. Two puts are sent to the record. The first is 1 and the second is 0. If the first asynchronous completion occurs before the second put everything works just like for synchronous records. Two channel access monitors will be issued. The first returns 1. The second returns 0. If the second put occurs before the asynchronous completion from the first, NO ca monitors are issued. The explaination is as follows: The put of 1 occurs: 1 is written to the VAL field The record starts synchronous processsing The put of 0 occurs 0 is written to the record A flag is set requesting that the record be reprocessed The asynchronous completion because of the first put occurs. Record support compares MLST and VAL. Since they are the same because of the second put, no monitor occurs. The record is processed again The record starts asynchronous processing The asynchrononous completion occurs. MLST and VAL are both still 0. Thus no monitors. Thus asynchronous records can lead to strange behavior. See the 3.14 Application Developer's Guide Chaper: Database Locking, Scanning, and Processing Section Guidelines for Asynchronous Records Section: Cached Puts Section putNotify I see no easy solution and perhaps no solution without significent runtime overhead. Marty Kraimer
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ANJ, 10 Aug 2010 |
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