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refactor: Ensure writes happen in clock order #469

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merged 1 commit into from
Oct 30, 2024
Merged

refactor: Ensure writes happen in clock order #469

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91 changes: 60 additions & 31 deletions src/library.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,6 @@ export interface Document {
readonly tree: MarkdownTree;
readonly metadata: Readonly<DocumentMetadata>;
readonly storedMetadata: Readonly<DocumentMetadata>;
readonly dirty: boolean;
updateMetadata(updater: (metadata: DocumentMetadata) => boolean): void;
}

Expand Down Expand Up @@ -345,6 +344,27 @@ export class IdbLibrary
new TypedCustomEvent('post-edit-update', {detail: {node, change}}),
);
}

#writeQueue: (() => Promise<void>)[] = [];
#writing = false;
async enqueueWrite(write: () => Promise<void>) {
this.#writeQueue.push(write);
if (this.#writing) return;
this.#writing = true;
while (true) {
const write = cast(this.#writeQueue.pop());
await write();
if (!this.#writeQueue.length) {
this.#writing = false;
return;
}
let preIdle = NaN;
do {
preIdle = this.#writeQueue.length;
await new Promise((resolve) => requestIdleCallback(resolve));
} while (preIdle != this.#writeQueue.length);
}
}
}

class IdbDocument implements Document {
Expand All @@ -369,15 +389,14 @@ class IdbDocument implements Document {
return this.#metadata;
}
readonly tree: MarkdownTree;
dirty = false;
updateMetadata(
updater: (metadata: DocumentMetadata) => boolean,
markDirty = true,
scheduleSave = true,
) {
const newMetadata = structuredClone(this.metadata);
if (!updater(newMetadata)) return;
this.#metadata = newMetadata;
if (markDirty) this.metadataChanged();
if (scheduleSave) this.metadataChanged();
}
get name() {
return (
Expand All @@ -400,7 +419,7 @@ class IdbDocument implements Document {
this.tree.connect();
this.tree.setRoot(this.tree.add<DocumentNode>(root), false);
}
noAwait(this.markDirty());
noAwait(this.scheduleSave());
}
async save() {
const {root, caches} = this.tree.serializeWithCaches();
Expand Down Expand Up @@ -428,7 +447,7 @@ class IdbDocument implements Document {
});
}
private metadataChanged() {
noAwait(this.markDirty());
noAwait(this.scheduleSave());
}
private treeChanged(change: TreeChange) {
if (change === 'edit') {
Expand All @@ -438,34 +457,44 @@ class IdbDocument implements Document {
return true;
}, false);
}
noAwait(this.markDirty());
noAwait(this.scheduleSave());
}
private pendingModifications = 0;
private async markDirty() {
this.dirty = true;
if (this.pendingModifications++) return;
while (true) {
const preSave = this.pendingModifications;
// Save immediately on the fist iteration, may help keep tests fast.
const oldMetadata = this.#storedMetadata;
await this.save();
this.library.dispatchEvent(
new TypedCustomEvent('document-change', {
detail: {document: this, oldMetadata},
}),
);
if (this.pendingModifications === preSave) {
this.pendingModifications = 0;
this.dirty = false;

#pendinSaveOldMetadata: DocumentMetadata | undefined;
#pendingSaveClock: number | undefined;
private async scheduleSave() {
const writeClock = this.#metadata.clock ?? 0;
if (this.#pendingSaveClock === undefined) {
this.#pendinSaveOldMetadata = this.#storedMetadata;
} else {
assert(this.#pendinSaveOldMetadata);
if (writeClock === this.#pendingSaveClock) {
// If the clock has not changed, we can join the scheduled write.
return;
}
// Wait for an idle period with no modifications.
let preIdle = NaN;
do {
preIdle = this.pendingModifications;
// TODO: maybe a timeout is better?
await new Promise((resolve) => requestIdleCallback(resolve));
} while (preIdle != this.pendingModifications);
}
this.#pendingSaveClock = writeClock;
noAwait(
this.library.enqueueWrite(async () => {
if (writeClock !== this.#pendingSaveClock) {
assert(
this.#pendingSaveClock !== undefined &&
this.#pendingSaveClock > writeClock,
);
// A write for a newer clock will supersede this.
return;
}
this.#pendingSaveClock = undefined;
await this.save();
if (this.#pendingSaveClock !== undefined) return;
const oldMetadata = cast(this.#pendinSaveOldMetadata);
this.#pendinSaveOldMetadata = undefined;
this.library.dispatchEvent(
new TypedCustomEvent('document-change', {
detail: {document: this, oldMetadata},
}),
);
}),
);
}
}
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