Re: finally caught an error on crash

Albrecht Dreß <[email protected]> Tue, 05 May 2020 22:01:30 +0200
Newsgroups	gmane.comp.gnome.apps.balsa
Message-ID	<[email protected]>
Am 04.05.20 23:01 schrieb(en) Jack via balsa-list:
> This continues to happen at a low, but still annoying frequency.  The line number in the error is now 247, having been 249 for a while, presumably just due to other edits to that file.  As I can remember, it happens after either deleting message(s) from the inbox, and/or moving message(s) to different mailboxes, in case that points to any possibilities.

Hmmm, the error message (failed assertion msgno <= mbox->msgno_2_msg_info->len) “smells” like a corrupted GPtrArray; maybe caused by a race between two threads, when messages are moved and/or deleted.  I'm not really familiar with the mailbox code (Peter? Pawel? Are you?), so this is a wild guess, though.  The failing function seems to be message_info_from_msgno() which is called in several places; do you have a backtrace from a crash?

> Given the recent changes (in the cleanup-logging branch) I'm wondering if I might just for my own use add some additional debug statements, either in the function where the g-assert fails, or else before the calls to that function.

As running in gdb is not always feasible, this may actually be helpful.  Just add g_debug() statements…

> Any quick pointers (or even just a pointer to an example line or two) would be helpful, and also advice on which debug domain to use (or even to set for current testing) or how  to go about adding a new domain.

If you use the new branch, the log domain is set to (line 50) to

#define G_LOG_DOMAIN "mbox-mbox"

so running balsa by calling

G_MESSAGES_DEBUG=mbox-mbox /path/to/balsa

would print /only/ messages from this domain.

It might also be helpful (given that my assumption of a race condition is true) to add debug messages to libbalsa/mailbox.c, namely in libbalsa_lock_mailbox() and libbalsa_unlock_mailbox() (and probably more), like

g_debug("%s: mbox %s", __func__, libbalsa_mailbox_get_name(mailbox));

That file didn't have its own log domain – which is bad, I just pushed a tiny change to the branch setting it to

#define G_LOG_DOMAIN "mailbox"

The above call should now read

G_MESSAGES_DEBUG="mailbox mbox-mbox" /path/to/balsa

Finding the source of a race (which, again, is just a guess) is always /very/ difficult, and adding debug messages may actually change the internal timing of the application, effectively hiding the bug…

Hope this helps,
Albrecht.

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