Investigate dumper crash in sub marks_delete

[eksopl]

The dumpers often die inside the marks_delete function. Usually line 88, with:

Thread 21 terminated abnormally: Invalid value for shared scalar at ./board-dump.pl line 88.

Most likely a race condition where a thread's info is deleted while another thread is in the middle of marking posts as deleted, but I'm having troubles reproducing.

(Imported from issue 24 @ Google Code)

[eksopl]

Gzip and I-M-S make this race condition almost impossible to happen, I've been running a dumper for a week or so and it hasn't crashed once.

I would like to reproduce this before attempting a fix, but I may have to attempt a blind fix instead. It's either that or trying to trigger it with something like dummynet or whatever.

[nstepien]

It's either that or trying to trigger it with something like dummynet or whatever.

You could try to trigger it by running the dumper without the GZIP and IMS fixes.

[eksopl]

Even like that, it takes far too long to trigger the race condition.

[voh]

Is this in any way related to the issue where the dumper will suddenly spit 4chan's header html at me then proceed to spam uninitialized value warnings? I've been getting that quite frequently lately.

[eksopl]

Nope. When it happens again, post a new issue with the output you get.

[eksopl]

Well, this is definitely fixed now, considering I rewrote half of the dumper's body.

Obviously, I must have introduced 20 other bugs in the process, but at least this long standing one is finally gone.