Re: RFR: 8145083: Use semaphore instead of mutex for synchronization of Unified Logging configuration

[Marcus Larsson]

Thanks for reviewing, David!

On 2015-12-17 06:34, David Holmes wrote:

Looks good!

Thanks,
David

On 16/12/2015 1:12 AM, Marcus Larsson wrote:

Hey Markus,

On 2015-12-15 11:58, Markus Gronlund wrote:

Hi Marcus,

Looks good!

One minor thing that you don't need to fix if you don't want to:

I would use:

class ConfigurationLock {
...

   debug_only(static bool current_thread_has_lock();)

};

to declare the this function in the class, then I would move the
definition outside of it (since it's sits inside ASSERT macros).

#ifdef ASSERT
   bool ConfigurationLock::current_thread_has_lock() {
     return _locking_thread_id == os::current_thread_id();
   }
#endif


I just find it easier to read the class declaration without the macros
inside of the class declaration (and since this is debug code, there
is no real use of defining inline). As I said, you don’t need to fix
this and to post another webrev.

I think it's worth another round. :)

New webrev:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.04/

Incremental:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.03-04/

Thanks,
Marcus

Good work!

/Markus



-----Original Message-----
From: Marcus Larsson
Sent: den 15 december 2015 11:25
To: serviceability-dev@openjdk.java.net
Cc: hotspot-runtime-...@openjdk.java.net
Subject: Re: RFR: 8145083: Use semaphore instead of mutex for
synchronization of Unified Logging configuration

Hi,

New webrev:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.03/

Incremental:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.02-03/

ConfigurationLocker renamed to ConfigurationLock to avoid confusion
with the MutexLocker family of classes.
Semaphore and locking thread id moved into the ConfigurationLock;
added a function to check if current thread has the lock when asserts
are enabled.

Regards,
Marcus


On 2015-12-14 16:30, Marcus Larsson wrote:

Hi again,

Made some changes to the patch after feedback from Markus Grönlund.
The ConfigurationLocker and the semaphore have been moved out of the
LogConfiguration.hpp and into the .cpp instead. The lock is only used
internally by the LogConfiguration so this makes sense. It simplifies
the LogConfiguration interface and hides the details of the locking
under the hood.

New webrev:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.02/

Incremental:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.01-02/

Thanks,
Marcus

On 2015-12-14 15:53, Marcus Larsson wrote:

Hi,

New webrev:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.01/

Incremental:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.00-01/

Changes:
* Introduced the ConfigurationLocker class for automatic wait/signal
in constructor/destructor just like a MutexLocker.
* Added an assert to verify that the "lock" is held by the current
thread when calling configure_output.
* Made the config-string functions in LogOutput protected and
LogConfiguration a friend of LogOutput to prevent incorrect usage of
these functions. These functions should typically only be used inside
configure_output, which now ensures that the lock is held.

Thanks,
Marcus


On 2015-12-14 11:13, Marcus Larsson wrote:

Hi,

Please review the following patch to use a semaphore instead of a
mutex for the synchronization of log configuration. Using a mutex
requires some parts of the VM to be initialized, whereas the
semaphores can be used right from the start. This simplifies the
code and allows very early log configuration without special cases
for early configuration vs reconfiguration after VM init.

Webrev:
http://cr.openjdk.java.net/~mlarsson/8145083/webrev.00/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8145083

Thanks,
Marcus