RFR: 8087322: Implement a Semaphore utility class (original) (raw)

Stefan Karlsson stefan.karlsson at oracle.com
Fri Jun 12 15:21:08 UTC 2015

Hi all,

Please review this patch to create a Semaphore utility class. I need this class to implementing faster GC thread synchronization [1].

http://cr.openjdk.java.net/~stefank/8087322/webrev.00/ https://bugs.openjdk.java.net/browse/JDK-8087322

Some of our platforms already implement a Semaphore class, but those classes are hidden inside os_.cpp. I've moved the class declaration to semaphore.hpp, but the implementation is left in the os_.hpp. I considered creating semaphore_.cpp files, but I ended up having to restructure too much code and I wanted to focus on the feature in [1] instead. Should I create a RFE to move the semaphore implementations?

There seems to be another opportunity to cleanup the code. If we take os_linux.cpp, as an example, the code uses both the existing Semaphore class and the global ::sem_wait and ::sem_post functions. We might want to consider unifying that code.

Since HotSpot is built on platforms that I don't have access to and can't test, I've added the IMPLEMENTS_SEMAPHORE_CLASS define. So, that I can detect if the the current platform implements the Semaphore class, and choose what synchronization primitive to use by the GC.

The os_bsd.cpp file has support for "non-apple BSD", but I've only tested this patch with OS X.

This patch has been tested in JPRT and our nightly testing together with the patches in [1]. The patch also contains a few unit tests in semaphore.cpp.

Thanks, StefanK

[1] http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2015-June/013829.html

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