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064bfd6 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 | /**
* Synchronous state machine for the query lifecycle, compatible with
* React's `useSyncExternalStore`.
*
* Three states:
* idle → no query, safe to dequeue and process
* dispatching → an item was dequeued, async chain hasn't reached onQuery yet
* running → onQuery called tryStart(), query is executing
*
* Transitions:
* idle → dispatching (reserve)
* dispatching → running (tryStart)
* idle → running (tryStart, for direct user submissions)
* running → idle (end / forceEnd)
* dispatching → idle (cancelReservation, when processQueueIfReady fails)
*
* `isActive` returns true for both dispatching and running, preventing
* re-entry from the queue processor during the async gap.
*
* Usage with React:
* const queryGuard = useRef(new QueryGuard()).current
* const isQueryActive = useSyncExternalStore(
* queryGuard.subscribe,
* queryGuard.getSnapshot,
* )
*/
import { createSignal } from './signal.js'
export class QueryGuard {
private _status: 'idle' | 'dispatching' | 'running' = 'idle'
private _generation = 0
private _changed = createSignal()
/**
* Reserve the guard for queue processing. Transitions idle → dispatching.
* Returns false if not idle (another query or dispatch in progress).
*/
reserve(): boolean {
if (this._status !== 'idle') return false
this._status = 'dispatching'
this._notify()
return true
}
/**
* Cancel a reservation when processQueueIfReady had nothing to process.
* Transitions dispatching → idle.
*/
cancelReservation(): void {
if (this._status !== 'dispatching') return
this._status = 'idle'
this._notify()
}
/**
* Start a query. Returns the generation number on success,
* or null if a query is already running (concurrent guard).
* Accepts transitions from both idle (direct user submit)
* and dispatching (queue processor path).
*/
tryStart(): number | null {
if (this._status === 'running') return null
this._status = 'running'
++this._generation
this._notify()
return this._generation
}
/**
* End a query. Returns true if this generation is still current
* (meaning the caller should perform cleanup). Returns false if a
* newer query has started (stale finally block from a cancelled query).
*/
end(generation: number): boolean {
if (this._generation !== generation) return false
if (this._status !== 'running') return false
this._status = 'idle'
this._notify()
return true
}
/**
* Force-end the current query regardless of generation.
* Used by onCancel where any running query should be terminated.
* Increments generation so stale finally blocks from the cancelled
* query's promise rejection will see a mismatch and skip cleanup.
*/
forceEnd(): void {
if (this._status === 'idle') return
this._status = 'idle'
++this._generation
this._notify()
}
/**
* Is the guard active (dispatching or running)?
* Always synchronous — not subject to React state batching delays.
*/
get isActive(): boolean {
return this._status !== 'idle'
}
get generation(): number {
return this._generation
}
// --
// useSyncExternalStore interface
/** Subscribe to state changes. Stable reference — safe as useEffect dep. */
subscribe = this._changed.subscribe
/** Snapshot for useSyncExternalStore. Returns `isActive`. */
getSnapshot = (): boolean => {
return this._status !== 'idle'
}
private _notify(): void {
this._changed.emit()
}
}
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