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@mxinden mxinden commented Oct 14, 2022

Follow up to #103. See also #102.

nox and others added 4 commits October 14, 2022 10:25
The method should not overwrite an existing key after it obtains the write lock.

Consider the following scenario with `Family<LabelSet, Gauge>` used by threads A and B:

1. A and B both call `family.get_or_insert(&label_set)`
2. A and B both acquire read lock and finds no key
3. A gets write lock and inserts a new gauge with value 0
4. A increments returned gauge to 1
5. B gets write lock and inserts a new gauge with value 0
6. B increments returned gauge to 1
7. A decrements gauge back to 0
8. B decrements gauge which now overflows to `u64::MAX`

Signed-off-by: Anthony Ramine <[email protected]>
@mxinden mxinden merged commit a32d413 into prometheus:master Oct 14, 2022
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2 participants