Contribution: Lock Contention Profiler for HotSpot

Markus Gronlund markus.gronlund at
Tue Nov 8 14:14:12 UTC 2016

Hi Peter,

Thanks for your offer to contribute this work to the OpenJDK.

You will most likely need to follow the Java Enhancement Proposal (JEP) process for this work:

Please see the following link for the JEP process description:


-----Original Message-----
From: Peter Hofer [mailto:peter.hofer at] 
Sent: den 4 november 2016 11:01
To: hotspot-dev at
Cc: David Gnedt; Andreas Schoergenhumer
Subject: Contribution: Lock Contention Profiler for HotSpot

Hello everyone,

we are researchers at the University of Linz and have worked on a lock contention profiler that is built into HotSpot. We would like to contribute this work to the OpenJDK community.

Our profiler records an event when a thread fails to acquire a contended lock and also when a thread releases a contended lock. It further efficiently records the stack traces where these events occur. We devised a versatile visualization tool that analyzes the recorded events and determines when and where threads _cause_ contention by holding a contended lock. The visualization tool can show the contention by stack trace, by lock, by lock class, by thread, and by any combination of those aspects.

We described our profiler in more detail in a research paper at ICPE 2016. [1] In our evaluation, we found that the overhead is typically below 10% for common multi-threaded Java benchmarks. Please find a free download of the paper on our website:

I contribute this work on behalf of Dynatrace Austria (the sponsor of this research), my colleagues David Gnedt and Andreas Schoergenhumer, and myself. The necessary OCAs have already been submitted.

We provide two patches:

Patch 1. A patch for OpenJDK 8u102-b14 with the profiler that we described and evaluated in our paper, plus minor improvements. It records events for Java intrinsic locks (monitors) and for java.util.concurrent locks (ReentrantLock and ReentrantReadWriteLock). 
We support only Linux on 64-bit x86 hardware.

> /

Patch 2. A patch for OpenJDK 9+140 with a profiler for VM-internal native locks only. We consider this to be useful for HotSpot developers to find locking bottlenecks in HotSpot itself. We tested this patch only on Linux on 64-bit x86 hardware, but it should require few changes for other platforms.

> spot_jdk9%2b140/ 
> _jdk-9%2b140/

With both patches, the profiler is enabled with -XX:+EnableEventTracing. 
By default, an uncompressed event trace is written to file "output.trc".

More detailed usage information and a download of the corresponding visualization tool is available on our website,

Kind regards,
  Peter Hofer

Peter Hofer
Christian Doppler Laboratory on Monitoring and Evolution of Very-Large-Scale Software Systems / Institute for System Software University of Linz

[1] Peter Hofer, David Gnedt, Andreas Schoergenhumer, Hanspeter 
Moessenboeck. Efficient Tracing and Versatile Analysis of Lock 
Contention in Java Applications on the Virtual Machine Level. 
Proceedings of the 7th ACM/SPEC International Conference on Performance 
Engineering (ICPE’16), Delft, Netherlands, 2016.

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