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HP OpenVMS Systemsask the wizard |
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The Question is:
Dear Sir,
I did asked a question about the benefit of
multithread programming on sigle CPU and the answer
is "it depends" so I would like to know some more
if talk about only VMS , does it support
full function of multithread such as
it allows computational threads to execute
while I/O threads are waiting for I/Os to
complete or not. Regard that my task is
suitable for multithread programming.
I run VMS 7.1 on Alpha 2100 , DEC 5.6.
I think I still stuck with the question
that I still gain benefit from the multithread
on single CPU or not if I use VMS.
Regards
Seng
The Answer is : You've reached a different Wizard this time, but you are going to get pretty much the same answer, I'm afraid. Whether or not your application will gain benefits from using multiple threads when running on only one CPU depends mostly on the application, and only slightly on the implementation of the threads services. Part of it depends on how you define "benefits". As the other Wizard indicated, using threads can simplify your application's implementation, either by making the code itself simpler or by making its operation easier to understand. Likewise, if you rely on threads instead of asynchronous programming, your code is likely to be much more portale. These "benefits" are applicable regardless of which operating system you are running on and regardless of how many processors you have. In terms of seeing a performance benefit, using threads on a single CPU system is only likely to help your application if it is able to perform compute activity in one thread while one or more other threads are waiting for I/O (or some other blocking activity). In your specific case, running on VMS V7.1, you may need to use the /THREADS qualifier when you link your application, in order to see any significant benefit. This qualifier enables the kernel support for threads, which causes all system calls (e.g., I/O blocks) to be thread-synchronous. (Without it, threads are run on a strict timeslice model, and if a thread makes a blocking system call, then it will block the entire process for the duration of its timeslice; furthermore, if the blocking thread has the highest priority, it will be scheduled to run again for the next timeslice, and the process will remain blocked.)
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