Agoric Cache

This cache mechanism allows a cache client function to synchronize with a cache backend. Any passable object can be a cache key or a cache value.

Demo

import { makeCache, makeScalarStoreCoordinator } from '@agoric/cache';
import { M } from '@agoric/store';
import { makeScalarBigMapStore } from '@agoric/vat-data';

const store = makeScalarBigMapStore('cache');
const coordinator = makeScalarStoreCoordinator(store);
const cache = makeCache(coordinator);

// Direct value manipulation.
await cache('baz'); // undefined
await cache('baz', 'barbosa'); // 'barbosa'

// Match-and-set.
await cache('baz', 'babaloo', undefined); // 'barbosa'
await cache('baz', 'babaloo', 'barbosa'); // 'babaloo'

// One-time initialization.
await cache('frotz', 'default'); // 'default'
await cache('frotz', 'ignored'); // 'default'

// Update the `'foo'` entry, using its old value (initially `undefined`).
await cache('foo'); // `undefined`
const updater = (oldValue = 'bar') => `${oldValue}1`;
await cache('foo', updater, M.any()); // 'bar1'
await cache('foo', updater, M.any()); // 'bar11'
await cache('foo'); // 'bar11'

// You can also specify a guard pattern for the value to update.  If it
// doesn't match the latest value, then the cache isn't updated.
await cache('foo', updater, 'nomatch'); // 'bar11'
await cache('foo', updater, 'bar11'); // 'bar111'
await cache('foo', updater, 'bar11'); // 'bar111'
await cache('foo'); // 'bar111'

Cache client

The client-side API is normally exposed as a single function named cache. You can create a cache client function by running makeCache(coordinator, follower). If not specified, the default coordinator is just a local in-memory map without persistence.

• the ground state for a cache key value is undefined. It is impossible to distinguish a set value of undefined from an unset key
• cache(key, (oldValue) => ERef<newValue>, guardPattern?): Promise<newValue> - transactionally updates the value of key from a value matched by guardPattern to the results of sanitizing the result of calling the updater function with that value. Retries all three steps (read current value, attempt match, call updater), if the transaction is stale. guardPattern defaults to matching only undefined. Returns the current value after any resulting update.
• cache(key, passable, guardPattern?): Promise<newValue> - same as above with an updater function that ignores arguments and returns passable (e.g., () => passable).

Cache coordinator

The cache coordinator must implement the Coordinator interface, which supports eventual consistency with optimistic updates:

interface Updater {
  /**
   * Calculate the newValue for a given oldValue
   */
  update: (oldValue: Passable) => unknown
}

interface Coordinator {
  /**
   * Read an eventually-consistent value for the specified key.
   */
  getRecentValue: (key: Passable) => Promise<Passable>,
  /**
   * Update a cache value to newValue, but only if guardPattern matches the current value.
   */
  setCacheValue: (key: Passable, newValue: Passable, guardPattern: Pattern) => Promise<Passable>,
  /**
   * Update a cache value via an updater calculation of newValue, but only if guardPattern
   * matches the current value.
   */
  updateCacheValue: (key: Passable, updater: ERef<Updater>, assertedMatch: Matcher) => Promise<Passable>,
}