kaijaytu commented on code in PR #1114:
URL: https://github.com/apache/yunikorn-core/pull/1114#discussion_r3695388996
##########
pkg/scheduler/objects/application.go:
##########
@@ -2162,6 +2164,18 @@ func (sa *Application) executeTerminatedCallback() {
}
}
+func (sa *Application) SetReservationReleasedCallback(callback func(released
int)) {
+ sa.Lock()
+ defer sa.Unlock()
+ sa.reservationReleasedCallback = callback
+}
+
+func (sa *Application) executeReservationReleasedCallback(released int) {
+ if released > 0 && sa.reservationReleasedCallback != nil {
+ go sa.reservationReleasedCallback(released)
Review Comment:
The goroutine is necessary to prevent a deadlock. Here's what I checked:
1. `decReservationCount` requires `pc.Lock()` (partition write lock):
- partition.go L1793-1796
2. `timeoutPlaceholderProcessing` holds `sa.Lock()` (application write lock)
for its entire duration:
- application.go L407-409: `sa.Lock()` with `defer sa.Unlock()`
3. The reverse lock order exists in `AddApplication`:
- partition.go L346: `pc.Lock()` with `defer pc.Unlock()`
- partition.go L404: calls `app.SetTerminatedCallback()` while still
holding `pc.Lock()`
- application.go L2153-2156: `SetTerminatedCallback` internally takes
`sa.Lock()`
- So: `pc.Lock()` -> `sa.Lock()`
4. If the callback were synchronous, `timeoutPlaceholderProcessing` would
create:
- `sa.Lock()` -> `pc.Lock()` (via callback -> `decReservationCount`)
This is a classic lock-ordering inversion:
- Thread A (AddApplication): pc.Lock() -> sa.Lock()
- Thread B (timeoutPlaceholderProcessing): sa.Lock() -> pc.Lock()
The partition struct comment (partition.go L71-80) explicitly documents this
constraint:
> "The partition write lock must not be held while manipulating an
application... If the partition write lock is held while manipulating an
application a deadlock could occur."
The `go` keyword breaks the nesting so `pc.Lock()` is never acquired while
`sa.Lock()` is held. This is the same reason `executeTerminatedCallback`
(application.go L2159-2161) uses `go` for `moveTerminatedApp`, which also takes
`pc.Lock()`.
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