Date: Mon, 20 Jul 2009 01:06:53 -0400 (EDT) From: Benjamin Kaduk <kaduk@MIT.EDU> To: freebsd-hackers@freebsd.org Subject: add missing content to locking.9 ? Message-ID: <alpine.GSO.1.10.0907200106100.17043@multics.mit.edu>
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Hi all, In trying to track down an unrelated issue, I happened to note that locking.9 needed a bit of help. They easy changes went into docs/136918, but I am less confident about my reading of the posix semaphore code. Would anyone care to comment on the following?: --- locking.9 2009-07-20 00:34:46.000000000 -0400 +++ locking.9.new 2009-07-20 00:31:27.000000000 -0400 @@ -215,6 +215,11 @@ a turnstile, its priority can propagate to the thread that holds the lock, helping to avoid a deadlock situation. .Ss Semaphores +.Tn POSIX +semaphores provide a wait channel in the filesystem namespace +whereby different threads can communicate with each other (by waiting +on the semaphore, and waking up the thread(s) waiting on that semaphore). +They are currently implemented on top of condition variables. .Ss Condition variables Condition variables are used in conjunction with mutexes to wait for conditions to occur. It should also be noted that there remains a comment "I don't know what the downsides are but I'm sure someone will fill in this part" regarding lockmgr locks ... I am not up for reading the code enough to comment, tonight, though. Thanks, Ben Kaduk
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