[834] in Pthreads mailing list archive
POSIX MUTEX
daemon@ATHENA.MIT.EDU (Manavalan, Anou)
Fri May 28 15:42:29 1999
From: "Manavalan, Anou" <AManavalan@neonsoft.com>
To: "'pthreads@mit.edu'" <pthreads@MIT.EDU>
Date: Fri, 28 May 1999 13:19:55 -0600
Return-Receipt-To: "Manavalan, Anou" <AManavalan@neonsoft.com>
Hi,
I heard that,
POSIX mutexes slow way down on multi-CPU machines.
if "attempting" value is 0
place this process's thread's lock key (LockKey) in "attempting"
value.
if "acquired" value is 0
place LockKey in "acquired" value
if "attempting" value is not LockKey,
We lost.
Set "acquired" value back to 0
Don't touch "attempting" (the other thread will
reset it)
Start over
We win.
Return
We lost.
Set "attempting" value back to 0
Start over.
Sleep a sec,
Start over.
on a multi-CPU machine, though, is that the update of "attempting" by one
thread is not visible to the other thread until this whole process is
complete. The cache on the CPU is not written through to memory quick
enough. Therefor, placing additional checks within showed that the lock
could be simultaneously locked by multiple processes.
Is this true ?
thanks for your time,
-amana
