Re: NullPointerException when connecting to a database which is shutting down

This was probably spotted and fixed in version 2.35 / 2.40 or even the
snapshot released in July. Please check the code from SVN and see if it
has been fixed.
The current code closes all sessions before closing the session manager.
Fred


On Fri, Sep 1, 2017, at 10:13, Lucas Ventura Carro wrote:
> Hello,
> 
> I use HSQLDB 2.2.9 in a testing environment, where I execute too many
> times restarts of it.> Lastly I have added threads which try to write to database, even when
> is shutdown, so I've faced NullPointerException when the database is
> shutting down, which yeld the database unusable, so is needed to kill
> it and start again.> The log I got is:
> 
>     [Server@9a5a48]: [Thread[main,5,main]]: checkRunning(false)
>     entered>     [Server@9a5a48]: [Thread[main,5,main]]: checkRunning(false) exited>     [Server@9a5a48]: Startup sequence initiated from main() method
>     [Server@9a5a48]: Loaded properties from
>     [/usr/local/hsqldb/trustedx/server.properties]>     [Server@9a5a48]: Initiating startup sequence...
>     [Server@9a5a48]: Server socket opened successfully in 24 ms.
>     [Server@9a5a48]: Database [index=0, id=0, db=file:localdb, alias=]
>     opened sucessfully in 6481 ms.>     [Server@9a5a48]: Startup sequence completed in 6507 ms.
>     [Server@9a5a48]: 2017-08-29 11:56:28.573 HSQLDB server 2.2.9 is
>     online on port 1702>     [Server@9a5a48]: To close normally, connect and execute
>     SHUTDOWN SQL>     [Server@9a5a48]: From command line, use [Ctrl]+[C] to abort
>     abruptly>     Exception in thread "HSQLDB Connection @3600ab"
>     java.lang.NullPointerException>     at org.hsqldb.Session.close(Unknown Source)
>     at org.hsqldb.server.ServerConnection.close(Unknown Source)
>     at org.hsqldb.server.ServerConnection.run(Unknown Source)
>     at java.lang.Thread.run(Thread.java:745)
>     SEVERE SQL Error at '--sql' line 1:
>     "SHUTDOWN"
>     java.lang.NullPointerException java.lang.NullPointerException
>     org.hsqldb.cmdline.SqlTool$SqlToolException
> 
> And each new try to connect to database (even to execute the
> shutdown) writes:> 
>     [Server@9a5a48]: [Thread[HSQLDB Connection @1025dc7,5,HSQLDB
>     Connections @9a5a48]]: database alias= does not exist> 
> In my google searchs I got the already resolved bug #855
> (https://sourceforge.net/p/hsqldb/bugs/855/) and the proposed patch
> #221 (https://sourceforge.net/p/hsqldb/patches/221/) which didn't
> applied to me (I start the database without this property).> 
> After update to 2.3.4, I got the same error.
> 
> So I dig into the code - as this was blocking my automatic tests. When
> I recompiled HSQLDB issued classes with full debug information, the
> stack was:> 
>     Exception in thread "HSQLDB Connection @13dfba4"
>     java.lang.NullPointerException>     at org.hsqldb.Session.close(Session.java:225)
>     at org.hsqldb.server.ServerConnection.close(ServerConnection.java-
>     :228)>     at org.hsqldb.server.ServerConnection.run(ServerConnection.java:1-
>     557)>     at java.lang.Thread.run(Thread.java:745)
> 
> With the affected line being:
> 
>     database.sessionManager.removeSession(this);
> 
> The guilty null was the 'sessionManager' instance, which is nulled
> when database is shutting down.> After adding some syso's to code, I've realized that the problem was
> that 'SessionManager' was creating new sessions **while
> '.closeAllSessions()' was being executed** - classic race condition.> So adding 'synchronized' to '.closeAllSessions()'
> (https://sourceforge.net/p/hsqldb/svn/HEAD/tree/base/tags/2.2.9/src/org/hsqldb/SessionManager.java#l196)
> method didn't caused the issue again.> 
> Seems an issue with shutdown, right?
> 
> Thanks,
> --
> Lucas
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