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Old 05-08-2008, 01:10 AM   #1
ruj.sabya
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Registered: Mar 2007
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Question Implementing shared/exclusive locking (readers/writer) lock


Hi,
I am using semaphore to implement Single Writer Multiple Readers (Reader / writer) lock.
The problem is that semaphores are critical resources in linux systems, and there is a limit on the number of semaphores

that you can create.
So, after creating some semaphores, sometimes my application exceeds this limit, and I get an error like 'No space left on

device.'.

I have to reboot the system sometimes, to release the semaphores, if my application is terminated abruptly!

How should I implement readers/writers lock using something else than semaphore, which is scalable?

I don't need reader/writer locks across multiple processes. I just need to use them in multiple threads of my application,

which is a single process.
But I want a very scalable solution, say I want 500 locks through out my application daemon's lifetime.

I read in the link below that postgres also suffered the same problem, but there it is recommended that the limit should be

increased, which I don't want users to do.
http://www2.units.it/~nircdc/doc/pos...resources.html

Sabyasachi.

Last edited by ruj.sabya; 05-08-2008 at 01:14 AM.
 
Old 05-08-2008, 03:23 AM   #2
chrism01
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Semaphores are a memory flag, should have nothing to do with disk space (afaik)
 
Old 05-08-2008, 05:21 AM   #3
ruj.sabya
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Registered: Mar 2007
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That is the error you get when you exceed the limit.
That is: ENOSPC (errno 28).
 
  


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