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graph.ts
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/**
* @license
* Copyright Google LLC All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
// Required as the signals library is in a separate package, so we need to explicitly ensure the
// global `ngDevMode` type is defined.
declare const ngDevMode: boolean|undefined;
/**
* The currently active consumer `ReactiveNode`, if running code in a reactive context.
*
* Change this via `setActiveConsumer`.
*/
let activeConsumer: ReactiveNode|null = null;
let inNotificationPhase = false;
type Version = number&{__brand: 'Version'};
/**
* Global epoch counter. Incremented whenever a source signal is set.
*/
let epoch: Version = 1 as Version;
/**
* Symbol used to tell `Signal`s apart from other functions.
*
* This can be used to auto-unwrap signals in various cases, or to auto-wrap non-signal values.
*/
export const SIGNAL = /* @__PURE__ */ Symbol('SIGNAL');
export function setActiveConsumer(consumer: ReactiveNode|null): ReactiveNode|null {
const prev = activeConsumer;
activeConsumer = consumer;
return prev;
}
export function getActiveConsumer(): ReactiveNode|null {
return activeConsumer;
}
export function isInNotificationPhase(): boolean {
return inNotificationPhase;
}
export interface Reactive {
[SIGNAL]: ReactiveNode;
}
export function isReactive(value: unknown): value is Reactive {
return (value as Partial<Reactive>)[SIGNAL] !== undefined;
}
export const REACTIVE_NODE: ReactiveNode = {
version: 0 as Version,
lastCleanEpoch: 0 as Version,
dirty: false,
producerNode: undefined,
producerLastReadVersion: undefined,
producerIndexOfThis: undefined,
nextProducerIndex: 0,
liveConsumerNode: undefined,
liveConsumerIndexOfThis: undefined,
consumerAllowSignalWrites: false,
consumerIsAlwaysLive: false,
producerMustRecompute: () => false,
producerRecomputeValue: () => {},
consumerMarkedDirty: () => {},
consumerOnSignalRead: () => {},
};
/**
* A producer and/or consumer which participates in the reactive graph.
*
* Producer `ReactiveNode`s which are accessed when a consumer `ReactiveNode` is the
* `activeConsumer` are tracked as dependencies of that consumer.
*
* Certain consumers are also tracked as "live" consumers and create edges in the other direction,
* from producer to consumer. These edges are used to propagate change notifications when a
* producer's value is updated.
*
* A `ReactiveNode` may be both a producer and consumer.
*/
export interface ReactiveNode {
/**
* Version of the value that this node produces.
*
* This is incremented whenever a new value is produced by this node which is not equal to the
* previous value (by whatever definition of equality is in use).
*/
version: Version;
/**
* Epoch at which this node is verified to be clean.
*
* This allows skipping of some polling operations in the case where no signals have been set
* since this node was last read.
*/
lastCleanEpoch: Version;
/**
* Whether this node (in its consumer capacity) is dirty.
*
* Only live consumers become dirty, when receiving a change notification from a dependency
* producer.
*/
dirty: boolean;
/**
* Producers which are dependencies of this consumer.
*
* Uses the same indices as the `producerLastReadVersion` and `producerIndexOfThis` arrays.
*/
producerNode: ReactiveNode[]|undefined;
/**
* `Version` of the value last read by a given producer.
*
* Uses the same indices as the `producerNode` and `producerIndexOfThis` arrays.
*/
producerLastReadVersion: Version[]|undefined;
/**
* Index of `this` (consumer) in each producer's `liveConsumers` array.
*
* This value is only meaningful if this node is live (`liveConsumers.length > 0`). Otherwise
* these indices are stale.
*
* Uses the same indices as the `producerNode` and `producerLastReadVersion` arrays.
*/
producerIndexOfThis: number[]|undefined;
/**
* Index into the producer arrays that the next dependency of this node as a consumer will use.
*
* This index is zeroed before this node as a consumer begins executing. When a producer is read,
* it gets inserted into the producers arrays at this index. There may be an existing dependency
* in this location which may or may not match the incoming producer, depending on whether the
* same producers were read in the same order as the last computation.
*/
nextProducerIndex: number;
/**
* Array of consumers of this producer that are "live" (they require push notifications).
*
* `liveConsumerNode.length` is effectively our reference count for this node.
*/
liveConsumerNode: ReactiveNode[]|undefined;
/**
* Index of `this` (producer) in each consumer's `producerNode` array.
*
* Uses the same indices as the `liveConsumerNode` array.
*/
liveConsumerIndexOfThis: number[]|undefined;
/**
* Whether writes to signals are allowed when this consumer is the `activeConsumer`.
*
* This is used to enforce guardrails such as preventing writes to writable signals in the
* computation function of computed signals, which is supposed to be pure.
*/
consumerAllowSignalWrites: boolean;
readonly consumerIsAlwaysLive: boolean;
/**
* Tracks whether producers need to recompute their value independently of the reactive graph (for
* example, if no initial value has been computed).
*/
producerMustRecompute(node: unknown): boolean;
producerRecomputeValue(node: unknown): void;
consumerMarkedDirty(node: unknown): void;
/**
* Called when a signal is read within this consumer.
*/
consumerOnSignalRead(node: unknown): void;
}
interface ConsumerNode extends ReactiveNode {
producerNode: NonNullable<ReactiveNode['producerNode']>;
producerIndexOfThis: NonNullable<ReactiveNode['producerIndexOfThis']>;
producerLastReadVersion: NonNullable<ReactiveNode['producerLastReadVersion']>;
}
interface ProducerNode extends ReactiveNode {
liveConsumerNode: NonNullable<ReactiveNode['liveConsumerNode']>;
liveConsumerIndexOfThis: NonNullable<ReactiveNode['liveConsumerIndexOfThis']>;
}
/**
* Called by implementations when a producer's signal is read.
*/
export function producerAccessed(node: ReactiveNode): void {
if (inNotificationPhase) {
throw new Error(
typeof ngDevMode !== 'undefined' && ngDevMode ?
`Assertion error: signal read during notification phase` :
'');
}
if (activeConsumer === null) {
// Accessed outside of a reactive context, so nothing to record.
return;
}
activeConsumer.consumerOnSignalRead(node);
// This producer is the `idx`th dependency of `activeConsumer`.
const idx = activeConsumer.nextProducerIndex++;
assertConsumerNode(activeConsumer);
if (idx < activeConsumer.producerNode.length && activeConsumer.producerNode[idx] !== node) {
// There's been a change in producers since the last execution of `activeConsumer`.
// `activeConsumer.producerNode[idx]` holds a stale dependency which will be be removed and
// replaced with `this`.
//
// If `activeConsumer` isn't live, then this is a no-op, since we can replace the producer in
// `activeConsumer.producerNode` directly. However, if `activeConsumer` is live, then we need
// to remove it from the stale producer's `liveConsumer`s.
if (consumerIsLive(activeConsumer)) {
const staleProducer = activeConsumer.producerNode[idx];
producerRemoveLiveConsumerAtIndex(staleProducer, activeConsumer.producerIndexOfThis[idx]);
// At this point, the only record of `staleProducer` is the reference at
// `activeConsumer.producerNode[idx]` which will be overwritten below.
}
}
if (activeConsumer.producerNode[idx] !== node) {
// We're a new dependency of the consumer (at `idx`).
activeConsumer.producerNode[idx] = node;
// If the active consumer is live, then add it as a live consumer. If not, then use 0 as a
// placeholder value.
activeConsumer.producerIndexOfThis[idx] =
consumerIsLive(activeConsumer) ? producerAddLiveConsumer(node, activeConsumer, idx) : 0;
}
activeConsumer.producerLastReadVersion[idx] = node.version;
}
/**
* Increment the global epoch counter.
*
* Called by source producers (that is, not computeds) whenever their values change.
*/
export function producerIncrementEpoch(): void {
epoch++;
}
/**
* Ensure this producer's `version` is up-to-date.
*/
export function producerUpdateValueVersion(node: ReactiveNode): void {
if (consumerIsLive(node) && !node.dirty) {
// A live consumer will be marked dirty by producers, so a clean state means that its version
// is guaranteed to be up-to-date.
return;
}
if (!node.dirty && node.lastCleanEpoch === epoch) {
// Even non-live consumers can skip polling if they previously found themselves to be clean at
// the current epoch, since their dependencies could not possibly have changed (such a change
// would've increased the epoch).
return;
}
if (!node.producerMustRecompute(node) && !consumerPollProducersForChange(node)) {
// None of our producers report a change since the last time they were read, so no
// recomputation of our value is necessary, and we can consider ourselves clean.
node.dirty = false;
node.lastCleanEpoch = epoch;
return;
}
node.producerRecomputeValue(node);
// After recomputing the value, we're no longer dirty.
node.dirty = false;
node.lastCleanEpoch = epoch;
}
/**
* Propagate a dirty notification to live consumers of this producer.
*/
export function producerNotifyConsumers(node: ReactiveNode): void {
if (node.liveConsumerNode === undefined) {
return;
}
// Prevent signal reads when we're updating the graph
const prev = inNotificationPhase;
inNotificationPhase = true;
try {
for (const consumer of node.liveConsumerNode) {
if (!consumer.dirty) {
consumerMarkDirty(consumer);
}
}
} finally {
inNotificationPhase = prev;
}
}
/**
* Whether this `ReactiveNode` in its producer capacity is currently allowed to initiate updates,
* based on the current consumer context.
*/
export function producerUpdatesAllowed(): boolean {
return activeConsumer?.consumerAllowSignalWrites !== false;
}
export function consumerMarkDirty(node: ReactiveNode): void {
node.dirty = true;
producerNotifyConsumers(node);
node.consumerMarkedDirty?.(node);
}
/**
* Prepare this consumer to run a computation in its reactive context.
*
* Must be called by subclasses which represent reactive computations, before those computations
* begin.
*/
export function consumerBeforeComputation(node: ReactiveNode|null): ReactiveNode|null {
node && (node.nextProducerIndex = 0);
return setActiveConsumer(node);
}
/**
* Finalize this consumer's state after a reactive computation has run.
*
* Must be called by subclasses which represent reactive computations, after those computations
* have finished.
*/
export function consumerAfterComputation(
node: ReactiveNode|null, prevConsumer: ReactiveNode|null): void {
setActiveConsumer(prevConsumer);
if (!node || node.producerNode === undefined || node.producerIndexOfThis === undefined ||
node.producerLastReadVersion === undefined) {
return;
}
if (consumerIsLive(node)) {
// For live consumers, we need to remove the producer -> consumer edge for any stale producers
// which weren't dependencies after the recomputation.
for (let i = node.nextProducerIndex; i < node.producerNode.length; i++) {
producerRemoveLiveConsumerAtIndex(node.producerNode[i], node.producerIndexOfThis[i]);
}
}
// Truncate the producer tracking arrays.
// Perf note: this is essentially truncating the length to `node.nextProducerIndex`, but
// benchmarking has shown that individual pop operations are faster.
while (node.producerNode.length > node.nextProducerIndex) {
node.producerNode.pop();
node.producerLastReadVersion.pop();
node.producerIndexOfThis.pop();
}
}
/**
* Determine whether this consumer has any dependencies which have changed since the last time
* they were read.
*/
export function consumerPollProducersForChange(node: ReactiveNode): boolean {
assertConsumerNode(node);
// Poll producers for change.
for (let i = 0; i < node.producerNode.length; i++) {
const producer = node.producerNode[i];
const seenVersion = node.producerLastReadVersion[i];
// First check the versions. A mismatch means that the producer's value is known to have
// changed since the last time we read it.
if (seenVersion !== producer.version) {
return true;
}
// The producer's version is the same as the last time we read it, but it might itself be
// stale. Force the producer to recompute its version (calculating a new value if necessary).
producerUpdateValueVersion(producer);
// Now when we do this check, `producer.version` is guaranteed to be up to date, so if the
// versions still match then it has not changed since the last time we read it.
if (seenVersion !== producer.version) {
return true;
}
}
return false;
}
/**
* Disconnect this consumer from the graph.
*/
export function consumerDestroy(node: ReactiveNode): void {
assertConsumerNode(node);
if (consumerIsLive(node)) {
// Drop all connections from the graph to this node.
for (let i = 0; i < node.producerNode.length; i++) {
producerRemoveLiveConsumerAtIndex(node.producerNode[i], node.producerIndexOfThis[i]);
}
}
// Truncate all the arrays to drop all connection from this node to the graph.
node.producerNode.length = node.producerLastReadVersion.length = node.producerIndexOfThis.length =
0;
if (node.liveConsumerNode) {
node.liveConsumerNode.length = node.liveConsumerIndexOfThis!.length = 0;
}
}
/**
* Add `consumer` as a live consumer of this node.
*
* Note that this operation is potentially transitive. If this node becomes live, then it becomes
* a live consumer of all of its current producers.
*/
function producerAddLiveConsumer(
node: ReactiveNode, consumer: ReactiveNode, indexOfThis: number): number {
assertProducerNode(node);
assertConsumerNode(node);
if (node.liveConsumerNode.length === 0) {
// When going from 0 to 1 live consumers, we become a live consumer to our producers.
for (let i = 0; i < node.producerNode.length; i++) {
node.producerIndexOfThis[i] = producerAddLiveConsumer(node.producerNode[i], node, i);
}
}
node.liveConsumerIndexOfThis.push(indexOfThis);
return node.liveConsumerNode.push(consumer) - 1;
}
/**
* Remove the live consumer at `idx`.
*/
function producerRemoveLiveConsumerAtIndex(node: ReactiveNode, idx: number): void {
assertProducerNode(node);
assertConsumerNode(node);
if (typeof ngDevMode !== 'undefined' && ngDevMode && idx >= node.liveConsumerNode.length) {
throw new Error(`Assertion error: active consumer index ${idx} is out of bounds of ${
node.liveConsumerNode.length} consumers)`);
}
if (node.liveConsumerNode.length === 1) {
// When removing the last live consumer, we will no longer be live. We need to remove
// ourselves from our producers' tracking (which may cause consumer-producers to lose
// liveness as well).
for (let i = 0; i < node.producerNode.length; i++) {
producerRemoveLiveConsumerAtIndex(node.producerNode[i], node.producerIndexOfThis[i]);
}
}
// Move the last value of `liveConsumers` into `idx`. Note that if there's only a single
// live consumer, this is a no-op.
const lastIdx = node.liveConsumerNode.length - 1;
node.liveConsumerNode[idx] = node.liveConsumerNode[lastIdx];
node.liveConsumerIndexOfThis[idx] = node.liveConsumerIndexOfThis[lastIdx];
// Truncate the array.
node.liveConsumerNode.length--;
node.liveConsumerIndexOfThis.length--;
// If the index is still valid, then we need to fix the index pointer from the producer to this
// consumer, and update it from `lastIdx` to `idx` (accounting for the move above).
if (idx < node.liveConsumerNode.length) {
const idxProducer = node.liveConsumerIndexOfThis[idx];
const consumer = node.liveConsumerNode[idx];
assertConsumerNode(consumer);
consumer.producerIndexOfThis[idxProducer] = idx;
}
}
function consumerIsLive(node: ReactiveNode): boolean {
return node.consumerIsAlwaysLive || (node?.liveConsumerNode?.length ?? 0) > 0;
}
function assertConsumerNode(node: ReactiveNode): asserts node is ConsumerNode {
node.producerNode ??= [];
node.producerIndexOfThis ??= [];
node.producerLastReadVersion ??= [];
}
function assertProducerNode(node: ReactiveNode): asserts node is ProducerNode {
node.liveConsumerNode ??= [];
node.liveConsumerIndexOfThis ??= [];
}