Implements interrupt-safe transaction log

[palacsint]

When an interrupt happened on a thread during writing the transaction
log, the underlying FileChannel was closed as a result. Any further
use (even from another threads) threw a
java.nio.channels.ClosedChannelException rendering the transaction
manager unusable since the transaction logs were never reopened. This
commit changes this behavior, log file operations reopen the file if
it was closed by an interrupt of another thread.

fixes #45

Commit by Tibor Billes, Miklós Karakó, Balázs Póka

[brettwooldridge]

Unfortunately, by introducing synchronized methods this pull request reverts the disk journal to a sequential write model -- only one thread can write at a time.

To see why this was an issue in 2.1, you can read here.

In 3.0 (SNAPSHOT), the disk journal was re-architected to allow a concurrent write model, with large performance gains. You can read about it here.

Unfortunately, this leaves #45 as yet unresolved, but you now have context if you want to have another go at addressing the issue.

[krokodylowy]

Palacsint, please attach your results of performace tests described on https://github.com/brettwooldridge/bitronix-hp/wiki/Disk-Journal-Improvements page.

Why don't you make simply patch of original code only with reopenFileChannelIfClosed() method?

[palacsint]

@krokodylowy, actually we have abandoned this patch and the idea too for a custom SecurityManager which delays interrupts in our application, so interrupts never reach the FileChannel.

I don't really remember why reopenFileChannelIfClose() alone was not enough but looking at the patch again I guess because of the currentPosition field. Feel free to rewrite the patch and I hope the attached tests will show you the case where it's necessary.

[krokodylowy]

Thanks for response. Can you share your concept of SecurityManager?

ClosedChannelException is serious gap in Bitronix. It can be 'fixed' by better design of user application but CCE still can occur in any moment and can hang enterprise system.