Hi Sean,
The intent with using Object is to avoid introducing unnecessary new
classes, which increases memory and disk footprint (granted only a
little but it all adds up).
Further I don't see how this is any different to seeing a bunch of
records that all indicate java.util.concurrent.locks.ReentrantLock as
the type of the lock. It is the instance that is important, not the type
(or not just the type). You can't expect a unique type name for each
object used for locking.
My 2c.
David Holmes
Sean Chou said the following on 03/09/11 15:07:
Hi,
I found there are code pieces using java.lang.Object as a lock type. It
appears as follow:
*//example
...
private Object lock = new Object();
...
public void foo() {
synchronized(lock) { ... }
...
//end of example*
This will give some confusing results when using tools like JLM to
analyze
synchronization contention, because tools usually use class name of the lock
instance to indicate the lock. Here is an example from JLM:
*
**//example2
%MISS GETS NONREC SLOW REC TIER2 TIER3 %UTIL AVER-HTM MON-NAME
100 562 562 562 0 0 0 0 3377 [32C7C768] java/lang/Object@9559CA00 (Object)
100 562 562 562 0 0 0 0 3160 [32C7C3D0] java/lang/Object@951DA530 (Object)
// <= which lock is this one representing?
100 560 560 560 0 0 0 0 3155 [37B4E854] java/lang/Object@94BA1C00 (Object)
100 58 58 58 0 0 0 0 3100 [355D3AB8]
org/apache/derby/impl/services/daemon/BasicDaemon@9DE5B348 (Object)
100 28 28 28 0 0 0 0 3892 [355D401C]
com/ibm/ws/sib/msgstore/persistence/lock/DBLockManagerThread@9F6E5D18(Object)
//end of example2*
The first three lines indicate three locks of type java.lang.Object, and
it is impossible to distinguish them.
If these locks are changed to a named type as follows,
//example3
*...
private class InterruptLock {}
private Object lock = new InterruptLock();
...
public void foo() {
synchronized(lock) { ... } }
...*
//end of example3
Exaple2 would be like this:
//example4
*%MISS GETS NONREC SLOW REC TIER2 TIER3 %UTIL AVER-HTM MON-NAME
0 0 0 0 0 0 0 0 0 [36047598]
com/ibm/ws/sib/msgstore/list/ReadWriteLock@A1CA04C8 (Object)
0 0 0 0 0 0 0 0 0 [360475F4]
sun/nio/ch/PollSelectorImpl$InterruptLock@A7C06F58 (Object) // <= we get
the lock name after modification
0 0 0 0 0 0 0 0 0 [36047650]
com/ibm/ws/objectpool/ObjectPoolImpl@9FCAA5F8(Object)
*
//end of example4
There are several classes found containing these pieces of code:
*src/share/classes/java/lang/SecurityManager.java
src/share/classes/java/lang/reflect/Proxy.java
src/solaris/classes/java/lang/UNIXProcess.java.solaris
src/solaris/classes/sun/nio/ch/PollSelectorImpl.java*
It will bring some enhancement to performance tools if these modification
can
be applied. Any comments?
