POSIX defines read and write locks. A write lock is exclusive and a
read lock inhibits a write lock from occurring. Any number of
processes/threads can have a read lock but as long as one read lock is
in place a write lock cannot be established. When a write lock is set
no read or write locks can complete.
Andrew Teirney wrote:
Jay Sprenkle wrote
Sorry, Accidently hit send before I was finished. This documentation
needs
to be updated
so it makes sense. Making up this conceptual 'shared lock' thing
instead of
explaining how
the locking mechanism really works is not helpful. A 'shared lock' in
reality is just opening
the disk file that makes up the database without locking. Any number of
other processes
can read the file. You can't acquire a shared lock, you just don't
acquire a
write lock.
Perhaps i have misread something along the way, but when it comes to a
SHARED lock its actually obtaining a advisory read lock on the file?
Several documents that i have seen regarding posix advisory locks
indicate that there is such a thing, and that they can prevent a write
lock from be taken.
CU,
Andrew
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