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watch.js
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watch.js
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// @ts-check
import { PromiseWatcherI } from '@agoric/base-zone';
import { getVowPayload, basicE } from './vow-utils.js';
const { apply } = Reflect;
/**
* @import { PromiseWatcher, Zone } from '@agoric/base-zone';
* @import { ERef, EVow, IsRetryableReason, Vow, VowKit, VowResolver, Watcher } from './types.js';
*/
/**
* @param {Zone} zone
*/
const makeWatchNextStep =
zone =>
/**
* If the specimen is a vow, obtain a fresh shortened promise from it,
* otherwise coerce the non-vow specimen to a promise. Then, associate a
* (usually durable) watcher object with the promise.
*
* @param {any} specimen
* @param {PromiseWatcher} promiseWatcher
*/
(specimen, promiseWatcher) => {
let promise;
const payload = getVowPayload(specimen);
if (payload) {
promise = basicE(payload.vowV0).shorten();
} else {
promise = basicE.resolve(specimen);
}
zone.watchPromise(promise, promiseWatcher);
};
/**
* @param {VowResolver | undefined} resolver
* @param {Watcher<unknown, unknown, unknown> | undefined} watcher
* @param {keyof Required<Watcher>} wcb
* @param {unknown} value
* @param {unknown[]} [watcherArgs]
*/
const settle = (resolver, watcher, wcb, value, watcherArgs = []) => {
try {
let chainedValue = value;
const w = watcher && watcher[wcb];
if (w) {
chainedValue = apply(w, watcher, [value, ...watcherArgs]);
} else if (wcb === 'onRejected') {
throw value;
}
resolver && resolver.resolve(chainedValue);
} catch (e) {
if (resolver) {
resolver.reject(e);
} else {
// for host's unhandled rejection handler to catch
throw e;
}
}
};
/**
* @param {Zone} zone
* @param {IsRetryableReason} isRetryableReason
* @param {ReturnType<typeof makeWatchNextStep>} watchNextStep
*/
const preparePromiseWatcher = (zone, isRetryableReason, watchNextStep) => {
// We use an ephemeral WeakSet for the previously seen vows in a watch operation
// While watch is durable, it suffices to detect the cycle in a single incarnation
/** @type {WeakMap<PromiseWatcher, WeakSet<any>>} */
const watcherSeenPayloads = new WeakMap();
/** @param {PromiseWatcher} watcher */
const getSeenPayloads = watcher => {
let seenPayloads = watcherSeenPayloads.get(watcher);
if (!seenPayloads) {
seenPayloads = new WeakSet();
watcherSeenPayloads.set(watcher, seenPayloads);
}
return seenPayloads;
};
return zone.exoClass(
'PromiseWatcher',
PromiseWatcherI,
/**
* @template [T=any]
* @template [TResult1=T]
* @template [TResult2=never]
* @param {VowResolver<TResult1 | TResult2>} resolver
* @param {Watcher<T, TResult1, TResult2>} [watcher]
* @param {unknown[]} [watcherArgs]
*/
(resolver, watcher, watcherArgs) => {
const state = {
vow: /** @type {unknown} */ (undefined),
priorRetryValue: /** @type {any} */ (undefined),
resolver,
watcher,
watcherArgs: harden(watcherArgs),
};
return /** @type {Partial<typeof state>} */ (state);
},
{
/** @type {Required<PromiseWatcher>['onFulfilled']} */
onFulfilled(value) {
const { watcher, watcherArgs, resolver } = this.state;
const payload = getVowPayload(value);
if (payload) {
const seenPayloads = getSeenPayloads(this.self);
// TODO: rely on endowed helper to get storable cap from payload
if (seenPayloads.has(payload.vowV0)) {
return this.self.onRejected(Error('Vow resolution cycle detected'));
}
seenPayloads.add(payload.vowV0);
// We've been shortened, so reflect our state accordingly, and go again.
this.state.vow = value;
watchNextStep(value, this.self);
return;
}
watcherSeenPayloads.delete(this.self);
this.state.priorRetryValue = undefined;
this.state.watcher = undefined;
this.state.resolver = undefined;
settle(resolver, watcher, 'onFulfilled', value, watcherArgs);
},
/** @type {Required<PromiseWatcher>['onRejected']} */
onRejected(reason) {
const { vow, watcher, watcherArgs, resolver, priorRetryValue } =
this.state;
if (vow) {
const retryValue = isRetryableReason(reason, priorRetryValue);
if (retryValue) {
// Retry the same specimen.
this.state.priorRetryValue = retryValue;
watchNextStep(vow, this.self);
return;
}
}
watcherSeenPayloads.delete(this.self);
this.state.priorRetryValue = undefined;
this.state.resolver = undefined;
this.state.watcher = undefined;
settle(resolver, watcher, 'onRejected', reason, watcherArgs);
},
},
);
};
/**
* @param {Zone} zone
* @param {() => VowKit<any>} makeVowKit
* @param {(reason: any, lastValue: any) => any} [isRetryableReason]
*/
export const prepareWatch = (
zone,
makeVowKit,
isRetryableReason = (_reason, _lastValue) => undefined,
) => {
const watchNextStep = makeWatchNextStep(zone);
const makePromiseWatcher = preparePromiseWatcher(
zone,
isRetryableReason,
watchNextStep,
);
/**
* @template [T=any]
* @template [TResult1=T]
* @template [TResult2=never]
* @template {any[]} [C=any[]] watcher args
* @param {EVow<T>} specimenP
* @param {Watcher<T, TResult1, TResult2, C>} [watcher]
* @param {C} watcherArgs
*/
const watch = (specimenP, watcher, ...watcherArgs) => {
/** @typedef {Exclude<TResult1, void> | Exclude<TResult2, void>} Voidless */
/** @typedef {Voidless extends never ? TResult1 : Voidless} Narrowest */
/** @type {VowKit<Narrowest>} */
const { resolver, vow } = makeVowKit();
// Create a promise watcher to track vows, retrying upon rejection as
// controlled by `isRetryableReason`.
const promiseWatcher = makePromiseWatcher(resolver, watcher, watcherArgs);
// Coerce the specimen to a promise, and start the watcher cycle.
zone.watchPromise(basicE.resolve(specimenP), promiseWatcher);
return vow;
};
harden(watch);
return watch;
};
harden(prepareWatch);
/** @typedef {ReturnType<typeof prepareWatch>} Watch */