Scalability problem with Pthread Read/Write Locks

Johan De Taeye
Sun Oct 23 12:45:00 GMT 2005

My multi-threaded application is creating a lot of
pthread_rwlock objects to protect access to my objects.
I am noticing that this doesn't scale up well. As the number
of active objects being created/changed/deleted increases
into the thousands, the runtime performance degrades very

When investigating the problem I noticed from the source code
in the files winsup/cygwin/thread.h and
winsup/cygwin/ that a static double-linked list
(called rwlocks) is used to keep track of all rwlocks present
in the process. Removal of an element in the list is O(n) and
explains the behavior of my application.

When compiling under Linux no such scalability problems are
found. (I believe the pthreads implementation there doesn't
need to  keep track of the active rwlocks)

Finally the question: Could/should the =list= data structure
be replaced with a =set= to provide better scalability?
Or, is my application design simply not right and is creating
a large number of rwlocks not a wise choice? 



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