Guys,
In the latest 1.4.186 release I see NPE when running simple multithreaded
benchmark:
@Benchmark
@Threads(4)
public void testMethod() throws SQLException {
Connection c = connect.get();
try (Statement s = c.createStatement()) {
s.executeUpdate("create local temporary table t(id int)");
s.executeUpdate("drop table t");
}
}
Caused by: java.lang.NullPointerException
at org.h2.mvstore.db.MVTable.checkDeadlock(MVTable.java:317)
at org.h2.mvstore.db.MVTable.doLock1(MVTable.java:169)
at org.h2.mvstore.db.MVTable.lock(MVTable.java:132)
at org.h2.engine.Database.lockMeta(Database.java:890)
at org.h2.command.ddl.DropTable.executeDrop(DropTable.java:102)
at org.h2.command.ddl.DropTable.update(DropTable.java:114)
at org.h2.command.CommandContainer.update(CommandContainer.java:78)
at org.h2.command.Command.executeUpdate(Command.java:254)
... 15 more
This happens because field MVTable#lockExclusiveSession is nullified
outside of lock in method #unlock but in method #checkDeadlock it is
getting reread after the null check. To fix either assign it to a local var
in #checkDeadlock or don't update outside of the lock in method #unlock.
By the way method #contains on ConcurrentHashMap (see field
MVTable#lockSharedSessions) really means #constainsValue and does iteration
over the whole map, I would recommend either to use #conatinsKey or use
wrapper Collections.newSetFromMap to avoid confusions like that.
Sergi
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