I will need to look at this closer. Skimming through the
implementation, it seems to me that the Runtime::loadLibrary0 does not
need to be synchronized. ClassLoader::loadLibrary0 should ensure that
a native library of a given name is loaded and registered only once.
Can you explain why you think ClassLoader::findLibrary needs to be
called with a lock?
Mandy
On 9/27/19 9:37 AM, Anton Kozlov wrote:
Hi,
I think that JDK-8194653 [0] affects jdk/jdk and it doesn't specific to
FileSystems.getDefault.
I'm starting a new thread/bug as the original issue marked as resolved ([3])
Ryan, thanks for investigation and providing a test [1]!
But the test fails in the same way if the FileSystems.getDefault replaced with
anything that calls System.loadLibrary in an initializer. For jdk/jdk it may be
jdk.net.ExtendedSocketOptions.SO_FLOW_SLA and the issue will arise.
I don't think it's possible to provide a general fix for that. We are unable to
prevent a user to take the Runtime's monitor and do initialization and
loadLibrary, which make a room for deadlock. Taking the lock is incorrect
action at first. We can only prevent doing that by accident.
From the original deadlock report [2], initialization and loadLibrary under
the monitor caused not by java.* code, but class loader's findLibrary
(sun.misc.ExtClassLoader to be specific). A workaround for ExtClassLoader is
possible, to ensure all necessary classes are inited before findLibrary called,
i.e. in the constructor. But then we should require the same for any custom
class loader. Chances that it would be implemented correctly are not high since
even ExtClassLoader is flawed.
I propose to call a ClassLoader.findLibrary with Runtime's monitor unlocked:
http://cr.openjdk.java.net/~akozlov/8231584/webrev.00
Thanks,
Anton
[0]: https://bugs.openjdk.java.net/browse/JDK-8194653
[1]:
https://mail.openjdk.java.net/pipermail/core-libs-dev/2019-April/059811.html
[2]:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-January/050819.html
[3]: https://bugs.openjdk.java.net/browse/JDK-8231584
