On 5/30/12 10:40 AM, Regan Heath wrote:
On Wed, 30 May 2012 18:16:38 +0100, Andrei Alexandrescu
<[email protected]> wrote:
On 5/30/12 9:43 AM, Regan Heath wrote:
On Wed, 30 May 2012 17:00:43 +0100, Andrei Alexandrescu
<[email protected]> wrote:
On 5/30/12 5:32 AM, Regan Heath wrote:
On Wed, 30 May 2012 10:21:00 +0100, deadalnix <[email protected]>
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) {
}
Yes. Well I recommend acquiring the text! :o)
... because, if you can, then you're exposing the mutex.
No.
For the purposes of this thread, and the anti-pattern/problem we're
discussing, you are.
No. I explained in my previous post that the synchronized statement does
not expose locks. This is not a matter of opinion.
It is the combination of synchronized
classes/methods (implicit locking) and external synchronized statements
(explicit locking) which result in the unexpected, accidental, and hard
to see deadlocks we're talking about here.
You can have deadlocks but with synchronized you can't leak locks or
doubly-unlock them. With free mutexes you have all of the above.
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
Your example 1 should not compile.
o.. k.. I expected you would get my meaning with the simplified example.
Here you are:
[snip]
Runs and deadlocks immediately.
Sure. As I said, synchronized helps with scoping the locks and unlocks,
but not with deadlocks. You can rewrite the example with two bare
mutexes just as well.
Andrei
