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sqlitestore: create new connections on new PIDs
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Authored by indygreg on Dec 11 2018, 7:00 PM.

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Summary

If the Mercurial process fork()s, the Python thread ID remains
unchanged. The previous code for returning a SQLite connection would
recycle the existing connection among all children.

Mercurial can fork() when performing working directory updates.
For reasons I don't fully understand, the recycling of even a
read-only SQLite connection was resulting in Python raising a
"DatabaseError: database disk image is malformed" exception. This
message comes from the bowels of SQLite. I suspect there is some
internal client state in the SQLite database somewhere and having
multiple clients race to update it results in badness. Who knows.

This commit teaches the "get a SQLite connection" logic to also
verify the PID matches before returning an existing connection.

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Event Timeline

indygreg created this revision.Dec 11 2018, 7:00 PM
indygreg planned changes to this revision.Dec 11 2018, 7:10 PM

Hold off on reviewing this. I'm still debugging some issues at Mozilla and want to be sure this patch is correct...

indygreg abandoned this revision.Dec 11 2018, 8:55 PM

It turns out we were hitting a bug in an ancient version of SQLite. Upgrading from 3.11 to 3.22 fixed it. I don't think this patch is needed.