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HP OpenVMS Systemsask the wizard |
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The Question is: My question is about disabling ASTs (with SYS$SETAST) in a multithreaded (DEC Threads ie. posix) application linked with both upcalls and kernel threads enabled. I am confused about how the threads scheduler issues upcalls. Are upcalls issued as ASTs? If so, does disabling ASTs mean no upcalls? I have a specific API that is intended to be used in both multithreaded and single threaded environments. The API has routines to read and to update blocks of shared data. The read routines simply call tis_read_lock to lock the data for read access whil e the update routines first disable ASTs by calling SYS$SETAST, then call tis_write_lock. I am concerned that if disabling ASTs also blocks thread scheduler upcalls, will other threads not get scheduled in a timely fashon if a thread that has disabled AS Ts is waiting to aquire a lock? Thanks, Rob The Answer is : For information on mixing ASTs and threads and for various discussions of same, please see topics including (2790), (3072) and (6099), and the pointers in these topics. Related topics include (1661), (2681), (4647), (6984), (7383), and (8938), among other topics. Also please see the lock manager, as this can provide synchronization. In this application, the OpenVMS Wizard would seriously consider the use of RMS with global buffers enabled, as this approach provides all needed synchronization for threading and AST-based operations, fully manages the per-system data cache, and the synchronization is fully distributed across a cluster. (You might start out with what appears to be a more light-weight implementation, but may find that you will eventually find yourself re-implementing what RMS and the file system -- and global buffers -- already provide for you, and particularly should you need to implement additional requirements and distributed synchronization.)
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