Possible VM deadlock due to FileSystems.getDefault and System.loadLibrary interplay (original) (raw)

David Holmes david.holmes at oracle.com
Thu Jan 4 01:35:53 UTC 2018

On 4/01/2018 3:13 AM, Vitaly Davidovich wrote:

On Wed, Jan 3, 2018 at 12:00 PM, Alan Bateman <Alan.Bateman at oracle.com> wrote:

The stack trace looks like JDK 8 or older. The initialization has changed quite a bit in JDK 9+ and would be interesting to see if you can duplicate it there. Yes - it's 8u152 as I mentioned in the follow-up email (sorry, should've mentioned that initially). Trying this on JDK9 is a bit tricky as the code (and its dependencies) in question isn't easily runnable on 9 without quite a bit of work. Do you agree with the deadlock assessment though? That's what it looks like to me but wanted to make sure I'm not missing anything.

You're not missing anything. It's a class initialization related "deadlock".

Thread A has called FileSystems.getDefault() which is doing of DefaultFileSystemHolder, which in turn leads to Runtime.loadLibrary0 which needs to lock the Runtime instance.

Thread B is already doing a loadLibrary and holds the Runtime lock, the loadLibrary code then needs to do FileSystems.getDefault() which has to load and initialize DefaultFileSystemHolder, but that initialization is already in progress so internally the thread does a wait().

So Thread B is waiting for Thread A to finish initialization, but holds the monitor lock that Thread A needs to finish the initialization. Deadlock.

AFAICS this will still be possible in 9/10/11

Cheers, David

Thanks Alan

-Alan

On 03/01/2018 16:56, Vitaly Davidovich wrote: Hi all, Consider the following stacktraces of the main app thread and a background thread: "main" #1 prio=5 osprio=0 tid=0x0000000001bfd000 nid=0x1958 waiting for monitor entry [0x00002b98ceba3000] java.lang.Thread.State: BLOCKED (on object monitor) at java.lang.Runtime.loadLibrary0(Runtime.java:862) - waiting to lock <0x00000007bf834b20> (a java.lang.Runtime) at java.lang.System.loadLibrary(System.java:1122) at sun.nio.fs.UnixNativeDispatcher$1.run( UnixNativeDispatcher.java:573) at sun.nio.fs.UnixNativeDispatcher$1.run( UnixNativeDispatcher.java:571) at java.security.AccessController.doPrivileged(Native Method) at sun.nio.fs.UnixNativeDispatcher.( UnixNativeDispatcher.java:571) at sun.nio.fs.UnixFileSystem.(UnixFileSystem.java:67) at sun.nio.fs.LinuxFileSystem.<_ _init>(LinuxFileSystem.java:39) at sun.nio.fs.LinuxFileSystemProvider.newFileSystem( LinuxFileSystemProvider.java:46) at sun.nio.fs.LinuxFileSystemProvider.newFileSystem( LinuxFileSystemProvider.java:39) at sun.nio.fs.UnixFileSystemProvider.( UnixFileSystemProvider.java:56) at sun.nio.fs.LinuxFileSystemProvider. (LinuxFileSystemProvider.java:41) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorA ccessorImpl.newInstance( NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorI mpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor. newInstance(Constructor.java:423) at java.lang.Class.newInstance(Class.java:442) at sun.nio.fs.DefaultFileSystemProvider.createProvider( DefaultFileSystemProvider.java:48) at sun.nio.fs.DefaultFileSystemProvider.create( DefaultFileSystemProvider.java:63) at java.nio.file.FileSystems$DefaultFileSystemHolder. getDefaultProvider(FileSystems.java:108) at java.nio.file.FileSystems$DefaultFileSystemHolder. access$000(FileSystems.java:89) at java.nio.file.FileSystems$Defa ultFileSystemHolder$1.run( FileSystems.java:98) at java.nio.file.FileSystems$Defa ultFileSystemHolder$1.run( FileSystems.java:96) at java.security.AccessController.doPrivileged(Native Method) at java.nio.file.FileSystems$DefaultFileSystemHolder. defaultFileSystem(FileSystems.java:96) at java.nio.file.FileSystems$DefaultFileSystemHolder.<_ _clinit>(FileSystems.java:90) at java.nio.file.FileSystems.getD efault(FileSystems.java: 176) at java.nio.file.Paths.get(Paths.java:84) at .ServiceLoader. setup(ServiceLoader.java:446) at .MetadataAdminLoader.main( MetadataAdminLoader.java:52)

"shardDbExecutor-0-pool-0" #33 prio=5 osprio=0 tid=0x0000000001ebf000 nid=0x1d01 in Object.wait() [0x00002b991f941000] java.lang.Thread.State: RUNNABLE at java.nio.file.FileSystems.getD efault(FileSystems.java: 176) at java.nio.file.Paths.get(Paths.java:138) at sun.misc.Launcher$ExtClassLoader.findLibrary( Launcher.java:224) at java.lang.ClassLoader.loadLibr ary(ClassLoader.java:1830) at java.lang.Runtime.loadLibrary0(Runtime.java:870) - locked <0x00000007bf834b20> (a java.lang.Runtime) at java.lang.System.loadLibrary(System.java:1122) at sun.security.ec.SunEC$1.run(SunEC.java:60) at sun.security.ec.SunEC$1.run(SunEC.java:58) at java.security.AccessController.doPrivileged(Native Method) at sun.security.ec.SunEC.(SunEC.java:58) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorA ccessorImpl.newInstance( NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorI mpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor. newInstance(Constructor.java:423) at java.lang.Class.newInstance(Class.java:442) at sun.security.jca.ProviderConfig$2.run( ProviderConfig.java:221) at sun.security.jca.ProviderConfig$2.run( ProviderConfig.java:206) at java.security.AccessController.doPrivileged(Native Method) at sun.security.jca.ProviderConfig.doLoadProvider( ProviderConfig.java:206) at sun.security.jca.ProviderConfig.getProvider( ProviderConfig.java:187) - locked <0x00000007bea03f48> (a sun.security.jca. ProviderConfig) at sun.security.jca.ProviderList. getProvider(ProviderList.java:233) at sun.security.jca.ProviderList. getService(ProviderList.java:331) at sun.security.jca.GetInstance. getInstance(GetInstance.java:157) at javax.net.ssl.SSLContext.getIn stance(SSLContext.java:156) at com.microsoft.sqlserver.jdbc. TDSChannel.enableSSL(IOBuffer.java:1658) at com.microsoft.sqlserver.jdbc.SQLServerConnection. connectHelper(SQLServerConnection.java:1976) at com.microsoft.sqlserver.jdbc.S QLServerConnection.login( SQLServerConnection.java:1627) at com.microsoft.sqlserver.jdbc.SQLServerConnection. connectInternal(SQLServerConnection.java:1458) at com.microsoft.sqlserver.jdbc.S QLServerConnection.connect( SQLServerConnection.java:772) at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect( SQLServerDriver.java:1168) at java.sql.DriverManager.getConnection(DriverManager. java:664) at java.sql.DriverManager.getConnection(DriverManager. java:208) at .ConnectionPool.createGoodConnection( ConnectionPool.java:565) at .ConnectionPool.createNewConnection( ConnectionPool.java:519) at .ConnectionPool. getConnection(ConnectionPool.java:407) at .StatementCachingConnectionImpl .setupConnection(StatementCachingConnectionImpl.java:94) at .StatementCachingConnectionImpl.( StatementCachingConnectionImpl.java:54) at .TestConnectionFactories$ FaultInjectingConnection.(TestConnectionFactories.java:90) at .TestConnectionF actories.lambda$static$3( TestConnectionFactories.java:33) at .TestConnectionFactories$$ Lambda$12/1738236591.newConnection(Unknown Source) at .SedaExecutor. setupConnections(SedaExecutor.java:130) at .SedaExecutor$SedaThreadFactory.lambda$ newThread$0(SedaExecutor.java:165) at .SedaExecutor$SedaThreadFactory$$Lambda$22/139 2419022.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) The application intermittently hangs on startup, and the above callstacks are present. It seems like there's a deadlock due to concurrent class loading and default FileSystem initialization (which itself triggers class loading here). I wasn't able to find any existing JBS entries reporting anything similar. Am I seeing this right? Is this a known issue? Thanks

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