lostluck commented on code in PR #33763:
URL: https://github.com/apache/beam/pull/33763#discussion_r1931051241
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sdks/go/pkg/beam/runners/prism/internal/engine/strategy.go:
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@@ -23,16 +23,351 @@ import (
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/typex"
)
+// This file is intended to consolidate handling of WindowingStrategy and
trigger
+// logic independantly from the bulk of the ElementManager.
+//
+// Triggers by their nature only apply to Aggregation transforms, in
particular:
+// GroupByKeys and CoGroupByKeys are aggregations.
+// Triggers also affect downstream side inputs. That is, a side input consumer
+// is vaccuously an aggregation.
+//
+// Triggers are PerKey+PerWindow, and they may or may not use state per
trigger.
+//
+// The unique state per trigger is the trickiest bit to handle. In principle
+// it could just be handled by the existing state system, which might be
+// sufficient, but it's not prepared for unique tagging per trigger itself.
+// It would also add additional overhead since state is kept as the serialized
+// bytes, instead of in a manipulatable form.
+//
+// Instead, each key+window state cell contains a trigger specific state map,
+// handled via pointer equality from the trigger itself.
+
// WinStrat configures the windowing strategy for the stage, based on the
// stage's input PCollection.
type WinStrat struct {
AllowedLateness time.Duration // Used to extend duration
}
+// EarliestCompletion marks when we can close a window.
func (ws WinStrat) EarliestCompletion(w typex.Window) mtime.Time {
return w.MaxTimestamp().Add(ws.AllowedLateness)
}
func (ws WinStrat) String() string {
return fmt.Sprintf("WinStrat[AllowedLateness:%v]", ws.AllowedLateness)
}
+
+// triggerInput represents a Key + window + stage's trigger conditions.
+type triggerInput struct {
+ newElementCount int // The number of new elements since the last
check.
+ endOfWindowReached bool // Whether or not the end of the window has
been reached.
+}
+
+// Trigger represents a trigger for a windowing strategy. A trigger
determines when
+// to fire a window based on the arrival of elements and the passage of time.
+//
+// See https://s.apache.org/beam-triggers for a more detailed look at triggers.
+type Trigger interface {
+ // IsReady determines if the trigger is ready to fire based on the
current state.
+ isReady(input triggerInput, state *StateData) bool
+ reset(state *StateData)
+
+ // TODO merging triggers and state for merging windows
+}
+
+// triggerState retains additional state for a given trigger execution.
+// Each trigger is responsible for maintaining it's own state as needed.
+type triggerState struct {
+ // finished indicates if the trigger has already fired or not.
+ finished bool
+ // extra is where additional data can be stored.
+ extra any
+}
+
+// TriggerNever is never ready.
+// There will only be an ON_TIME output and a final output at window
expiration.
+type TriggerNever struct{}
+
+func (*TriggerNever) isReady(triggerInput, *StateData) bool {
+ return false
+}
+
+func (t *TriggerNever) reset(state *StateData) {}
+
+// TriggerAlways is always ready.
+// There will be an output for every element, and a final output at window
expiration.
+// Equivalent to TriggerRepeatedly {TriggerElementCount{1}}
+type TriggerAlways struct{}
+
+func (*TriggerAlways) isReady(triggerInput, *StateData) bool {
+ return true
+}
+
+func (t *TriggerAlways) reset(state *StateData) {}
+
+// TriggerAfterAll is ready when all subTriggers are ready.
+// There will be an output when all subTriggers are ready.
+// Logically, an "AND" trigger.
+type TriggerAfterAll struct {
+ SubTriggers []Trigger
+}
+
+func (t *TriggerAfterAll) isReady(input triggerInput, state *StateData) bool {
+ ts := state.getTriggerState(t)
+ if ts.finished {
+ return false
+ }
+ // Track fired states.
+ if ts.extra == nil {
+ ts.extra = map[Trigger]bool{}
+ }
+ isFinished := ts.extra.(map[Trigger]bool)
+ for _, t := range t.SubTriggers {
+ // Don't re-evaluate.
+ if isFinished[t] {
+ continue
+ }
+ if t.isReady(input, state) {
+ isFinished[t] = true
+ }
+ }
+ ready := len(isFinished) == len(t.SubTriggers)
+ if ready {
+ ts.finished = true
+ }
+ state.setTriggerState(t, ts)
+ return ready
+}
+
+func (t *TriggerAfterAll) reset(state *StateData) {
+ for _, sub := range t.SubTriggers {
+ sub.reset(state)
+ }
+ delete(state.Trigger, t)
+}
+
+// TriggerAfterAny is ready the first time any of the subTriggers are ready.
+// Logically, an "OR" trigger.
+type TriggerAfterAny struct {
+ SubTriggers []Trigger
+}
+
+func (t *TriggerAfterAny) isReady(input triggerInput, state *StateData) bool {
+ ts := state.getTriggerState(t)
+ if ts.finished {
+ return false
+ }
+ anyReady := false
+ for _, t := range t.SubTriggers {
+ anyReady = t.isReady(input, state)
+ if anyReady {
+ break
+ }
+ }
+ if anyReady {
+ ts.finished = true
+ for _, sub := range t.SubTriggers {
+ // clear any subtrigger state, as we're fireing anyway.
+ sub.reset(state)
+ }
+ }
+ state.setTriggerState(t, ts)
+ return anyReady
+}
+
+func (t *TriggerAfterAny) reset(state *StateData) {
+ for _, sub := range t.SubTriggers {
+ sub.reset(state)
+ }
+ delete(state.Trigger, t)
+}
+
+// TriggerAfterEach processes each trigger before executing the next.
+// Starting with the first subtrigger, ready when the _current_ subtrigger
+// is ready. After output, advances the current trigger by one.
+type TriggerAfterEach struct {
+ SubTriggers []Trigger
+}
+
+func (t *TriggerAfterEach) isReady(input triggerInput, state *StateData) bool {
+ ts := state.getTriggerState(t)
+ if ts.finished {
+ return false
+ }
+ // Use extra for the current trigger index.
+ if ts.extra == nil {
+ ts.extra = int(0)
+ }
+ current := ts.extra.(int)
+ ready := false
+ if t.SubTriggers[current].isReady(input, state) {
+ current++
+ ready = true
+ }
+ if current >= len(t.SubTriggers) {
+ ts.finished = true
+ }
+ ts.extra = current
+ state.setTriggerState(t, ts)
+ return ready
+}
+
+func (t *TriggerAfterEach) reset(state *StateData) {
+ for _, sub := range t.SubTriggers {
+ sub.reset(state)
+ }
+ delete(state.Trigger, t)
+}
+
+// TriggerElementCount triggers when there have been at least the required
number
+// of elements have arrived.
+type TriggerElementCount struct {
+ ElementCount int
+}
+
+func (t *TriggerElementCount) isReady(input triggerInput, state *StateData)
bool {
+ ts := state.getTriggerState(t)
+ if ts.finished {
+ return false
+ }
+
+ if ts.extra == nil {
+ ts.extra = int(0)
+ }
+ count := ts.extra.(int) + input.newElementCount
+ ts.extra = count
+ ready := count >= t.ElementCount
+ if ready {
+ ts.finished = true
+ }
+ state.setTriggerState(t, ts)
Review Comment:
It is necessary since triggerState is passed by value and not by pointer at
present. It gains more reasonable zero value semantics, since we don't have to
do both a single value initialization, *and* any extra value initialization. It
also makes the state handling explicit.
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