On Wed, 30 May 2012 17:00:43 +0100, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 5/30/12 5:32 AM, Regan Heath wrote:
On Wed, 30 May 2012 10:21:00 +0100, deadalnix <deadal...@gmail.com>
wrote:
You don't want to synchronize on ANY object. You want to synchronize
on explicit mutexes.
+1 .. this is the key point/issue.
TDPL's design only allows for entire synchronized classes (not separate
synchronized and unsynchronized methods), which pair mutexes with the
data they protect. This is more restrictive than exposing mutexes, but
in a good way. We use such a library artifact in C++ at Facebook all the
time, to great success.
Can you call pass them to a synchronized statement? i.e.
TDPLStyleSynchClass a = new TDPLStyleSynchClass();
synchronized(a) {
}
.. because, if you can, then you're exposing the mutex. If you can't, how
do you do the above with these classes? By explicitly calling a lock() or
tryLock() method? (do they implement a known interface?)
People shouldn't create designs that have synchronized classes referring
to one another naively. Designing with mutexes (explicit or implicit)
will always create the possibility of deadlock, so examples how that
could happen are easy to come across.
True. But in my Example 1 the classes could be "entire" synchronized
classes, and they do not refer to each other naively. Instead, two
threads have shared access to them and in each case they explicitly
acquire one mutex (via a synchronized() statement), but implicitly acquire
another (by calling a method). It's the implicit acquisition which makes
the bug hard to see and easy to do accidentally.
TDPL improves on deadlocks by introducing synchronized statements with
more than one argument, see 13.15.
Is there anywhere I can see this online? (for free :p)
The implicit mutexes used by synchronized classes are recursive.
:) why would you want anything else.
R
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