Shaul Karl wrote:
>
> I found the last paragraph of subsection 12.1.1 of the "Linux Application
> Development" (3rd edition) contradicting my knowledge. Am I right that it is
> not accurate, or do I missing something essential?
>
> Trying to quote the paragraph without copying the entire subsection, I get:
>
> Although nonblocking I/O allows us to switch easily between file descriptors,
> it has a high price. If it was up to the polling processes then they would
> constantly be running - never blocks. Which inflicts a heavy performance
> penalty on the system as the OS can never put these processes to sleep (try
> running 10 processes like the one that was discussed previously and see how it
> affects system performance).
>
> "the OS can never put these processes to sleep"? - Perhaps in the Windows
> world, but with Linux/Unix?
Quoting the late W. Richard Stevens in "UNIX Network Programming" (2nd
ed, p. 145):
"...The application is continually polling the kernel to see if some
operation is ready. This is often a waste of CPU time..."
So, of course, the book you quoted is accurate.
If you're continually calling the kernel, how could it put your app to
sleep? That's what they invented select/poll for.
Gavrie.
--
Gavrie Philipson
System Administrator
Netmor Applied Modeling Research Ltd.
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