On Tue, 2008-08-26 at 11:12 -0700, David Blevins wrote: > On Aug 26, 2008, at 5:23 AM, Martin Vysny wrote: > > > Many thanks for clarifying on how the locks works! One more question, > > just to be 100% sure :) . Recently I studied the java memory model a > > bit > > (there is beautiful FAQ located at [1]) and I'd like to ask: > > > > Let's assume that the execution exited some method m1 protected by > > Lock.READ (or Lock.WRITE) and is about to enter some method m2 (in the > > same Singleton bean) protected by Lock.WRITE. Is any operation invoked > > in method m1 guaranteed to "happen-before" any operation invoked in > > method m2? > > Those details are better described on this page: > > http://cwiki.apache.org/OPENEJBx30/singleton-beans.html > > I've slightly tweaked it to make the connection with ReadWriteLock > stronger and to explicitly mention we use a ReentrantReadWriteLock. > Hopefully people will follow those links. > > Here are a couple quotes from those docs that answer your questions a > little more specifically: > > All ReadWriteLock implementations must guarantee that the > memory synchronization effects of writeLock operations (as > specified in the Lock interface) also hold with respect to the > associated readLock. That is, a thread successfully acquiring > the read lock will see all updates made upon previous release > of the write lock. > > -- > http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/locks/ReadWriteLock.html > > Reentrancy also allows downgrading from the write lock to a > read lock, by acquiring the write lock, then the read lock and > then releasing the write lock. However, upgrading from a read > lock to the write lock is not possible. > > -- > http://java.sun.com/j2se/1.5.0/docs/api/java/util/concurrent/locks/ReentrantReadWriteLock.html > > > We could probably quote some of those two javadocs if there were one > or two really critical things we think people should know above all > else. If you have any thoughts on that regard that'd be great. > > -David >
Thanks David, the documentation now answers my question very clearly. I think you could explicitly quote this sentence: "That is, a thread successfully acquiring the read lock will see all updates made upon previous release of the write lock." - it sums an answer to the question very nicely and simply. However, I have no other questions, the documentation is perfect, thanks :) Sincerely Martin
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