714450 - Slow SQL statement recording accesses a hashtable from multiple threads simultaneously causing badness

Status: RESOLVED FIXED

(Toolkit :: Telemetry, defect)

Description

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

http://hg.mozilla.org/mozilla-central/rev/fd47a1e23039#l8.248

Comment 1

[Vladan Djeric (:vladan)]

(In reply to Kyle Huey [:khuey] ([e-mail]) from comment #0)
> http://hg.mozilla.org/mozilla-central/rev/fd47a1e23039#l8.248

Hmm, the mTrackedDBs hash table is a whitelist initialized when Telemetry is initialized and then only ever read afterwards (at least until destruction anyway). Is there an issue with multiple threads reading from an immutable nsTHashtable without synchronization?

Comment 2

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

As we discussed on IRC, the hashtable needs to be marked as immutable with PL_DHashMarkTableImmutable.  The best way to do this is probably to expose a MarkImmutable() function on nsTHashtable that calls PL_DHashMarkTableImmutable on the underlying table and then call MarkImmutable when you finish setting up the table.

Comment 3

[Vladan Djeric (:vladan)]

Attachment: Mark the DB whitelist in Telemetry immutable after it is initialized

Comment 4

[Vladan Djeric (:vladan)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/b18d407e2321

Comment 5

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/b18d407e2321

Comment 6

[Alex Keybl [:akeybl]]

Is the user pain significant enough, and the patch low-risk enough, to land on Beta? If so, please nominate for Beta 11 approval.

Comment 7

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

The bug that caused this was backed out of 11, so there's nothing to do there.