Unsafe: removing the monitorEnter/monitorExit/tryMonitorEnter methods (original) (raw)

David Holmes david.holmes at oracle.com
Tue Mar 4 03:51:52 UTC 2014

On 3/03/2014 10:57 PM, David M. Lloyd wrote:

On 02/27/2014 06:38 AM, David Holmes wrote:

On 27/02/2014 9:12 PM, Stephen Colebourne wrote:

On 26 February 2014 20:54, Martin Buchholz <martinrb at google.com> wrote:

It does seem that being able to tell whether a java object monitor is currently locked is useful for debugging and monitoring - there should be a way to do that.

Perhaps it would be useful to be able to expose a java object monitor as an instance of Lock? Lock lk = Lock.ofMonitor(object) if (lk.tryLock()) { ... } Such a method feels like it would be a useful missing link between synchronized and locks. I don't think this is workable. Exposing a monitor as Lock would allow you to break the guarantees/requirements involving balanced-locking for monitors. The JNI APIs also allow this, do they not?

No:

http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/functions.html#wp5252

"Native code must not use MonitorExit to exit a monitor entered through a synchronized method or a monitorenter Java virtual machine instruction."

The above isn't enforced as with most JNI usage rules.

David

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