Unsafe: removing the monitorEnter/monitorExit/tryMonitorEnter methods

[Peter Levart]

On 02/27/2014 08:29 AM, Peter Levart wrote:
> On 02/26/2014 09:54 PM, Martin Buchholz wrote:
>> I don't recall having added this particular wart
>> to test/java/lang/ProcessBuilder/Basic.java, and history suggests that
>> others did that.
>>
>> 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.
>
> Thread.holdsLock(Object) ?

Ah, you meant to query from some other thread, right?

Peter

>
> Regards, Peter
>
>>
>>
>> On Wed, Feb 26, 2014 at 7:12 AM, Paul Sandoz <paul.sandoz at oracle.com> 
>> wrote:
>>
>>> Hi,
>>>
>>> Out of all the methods on Unsafe i think the
>>> monitorEnter/monitorExit/tryMonitorEnter are the least used and are 
>>> very
>>> strong candidates for removal.
>>>
>>> 99% of use-cases are supported by classes in the
>>> java.util.concurrent.locks package.
>>>
>>>
>>> Within the JDK itself it is only used in one JDK test file
>>> test/java/lang/ProcessBuilder/Basic.java:
>>>
>>>                      while (unsafe.tryMonitorEnter(s)) {
>>>                          unsafe.monitorExit(s);
>>>                          Thread.sleep(1);
>>>                      }
>>>
>>> for a test verifying an EOF is received on pending reads and it is 
>>> polling
>>> to check when the process builder acquires the lock before 
>>> destroying the
>>> process, presumably to avoid some sort of race condition that 
>>> occasionally
>>> causes the test to fail.
>>>
>>> I believe this test as been through a number of rounds, i stared at 
>>> things
>>> for a bit, but cannot quickly work out a replacement; i lack the 
>>> knowledge
>>> on this area.
>>>
>>>
>>> Outside of the JDK i can only find one usage of monitorExit/Enter
>>> (according to grep code) in JBoss modules, and i believe this is 
>>> only used
>>> on Java 1.6 to work around some limitations in class loading that were
>>> fixed in 1.7.
>>>
>>>
>>> Given such very limited use i propose to remove these methods after 
>>> having
>>> worked out a fix for ProcessBuilder/Basic.java test.
>>>
>>> Paul.
>>>
>