Watchdog thread race condition

[Patrik Dufresne]

Hello

In a Windows VM, I'm experience a race condition in FileLock.run() using version 1.3.174. Basically, when I open a database with the windows computer, the database get properly open, but looking at the threads, I don't see a "H2 File Lock Watchdog" thread.

The problem is always reproducible. In debug mode, I see the thread being called, but it goes straight to "watchdog end". Most likely, called to "locked = true;" was run after the call to "while (locked && filename!=null)".

I don't see how I can fix it from application level. Help please

[Patrik Dufresne]

Looking t the code, this problem probably affect current version too.

https://github.com/h2database/h2database/blob/278e6e8172db9ff393afec415cebe5fbb719ce65/h2/src/main/org/h2/store/FileLock.java#L510

I recommend to fix this issue by replacing this line:

while (locked && fileName != null) {

by:

while (fileName != null) {

When unlocking, the variable "fileName" get set to null in all cases.

[Noel Grandin]

Thanks for the analysis.

Are you perhaps using the FILE_LOCK=SOCKET option?

Because that is the only way I can see what you describe happening.
In the FILE_LOCK=FILE case, we set "locked = true" just before we start the watchdog, so I can't see what you describe
happening.

[Patrik Dufresne]

I'm using FILE_LOCK=FILE.

You are right. In Trunk, locked = true is set before creating the thread. But in version 1.3.174 it's not. Also the changed seams very recent (Oct 2015)

https://github.com/h2database/h2database/commit/e8725b5f8b284aeaa39bf6b4d0e9410c80c946b2

So unless I'm using a beta version 1.4.191, I cannot get this fixed. Any plan to backport this fix to 1.3 branch ?

--

Patrik Dufresne

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[Noel Grandin]

On 2016/02/29 2:30 PM, Patrik Dufresne wrote:
>
> So unless I'm using a beta version 1.4.191, I cannot get this fixed. Any plan to backport this fix to 1.3 branch ?
>

Unlikely. But you can run the 1.4 series with the old engine easily enough, just append MV_STORE=false to your URL.

[Patrik Dufresne]

I've upgrade to 1.4 series. My unit test doesn't show any regression. I've set MV_STORE=FALSE to use the old store.

Thanks for your help.

--

Patrik Dufresne