fix: avoid need to lock state for restart.Pending() #451
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This is based on canonical/snapd#12166 (though the diff was applied more or less manually, as the patch couldn't be applied directly). It includes the name changes to the restart.Handler interface methods.
hpidcock
approved these changes
Jul 17, 2024
| @@ -60,7 +61,7 @@ type restartManagerKey struct{} | |||
| // RestartManager takes care of restart-related state. | |||
| type RestartManager struct { | |||
| state *state.State | |||
| restarting RestartType | |||
| restarting atomic.Int32 // really of type RestartType | |||
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In future we could use an atomic.Pointer[RestartType] instead, although unnecessary heap allocation for such a small type, keeps the type.
| rm := cached.(*RestartManager) | ||
| return rm.restarting != RestartUnset, rm.restarting | ||
| // NOTE: the state does not need to be locked to fetch this information. | ||
| func (rm *RestartManager) Pending() (bool, RestartType) { |
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an "ok" bool is usually the last return value (like error)
e.g.
v, ok := myMap[k]
Since this is existing functionality, I don't mind.
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Yeah, I was actually tempted to get rid of the bool entirely, because it's just b != RestartUnset, which is easy for the caller to do. However, given it has this signature in snapd, I want to keep it as is.
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This change avoids the need to lock/unlock state when fetching
restart.Pending(), avoiding the need for one state lock/unlock on every HTTP request. (We hope to get rid of the other lock/unlock by removing warnings, but that's a separate issue.)Updates #366