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import type { Logger } from '../../logger/definition.ts';
import { OFF_LOGGER } from '../../logger/off-logger.ts';
import { withPrefix } from '../../logger/prefixed-logger.ts';
import { createEventNotifier } from '../../notifier/implementation.ts';
import type { PromiseHolder, PromiseSettledEvent, PromiseTracker } from './definition.ts';
/**
* Creates a new promise tracker for monitoring promises and coordinating async operations.
*
* The tracker maintains an internal set of unsettled promises and provides centralized waiting, real-time event
* notifications, and detailed timing metrics. It's designed for scenarios where you need to coordinate multiple
* unrelated promises or monitor promise performance across different parts of an application.
*
* Each tracker instance is independent and manages its own set of promises. The tracker automatically handles cleanup
* when promises settle and provides comprehensive logging when a logger is configured.
*
* @example Basic tracker creation
*
* ```ts
* import { trackPromises } from 'emitnlog/tracker';
*
* // Create a tracker without logging
* const tracker = trackPromises();
*
* // Track some operations
* const result1 = tracker.track(fetchData(), 'fetch-operation');
* const result2 = tracker.track(() => processData(), 'process-operation');
*
* // Wait for all to complete
* await tracker.wait();
* ```
*
* @example Tracker with logging
*
* ```ts
* import { trackPromises } from 'emitnlog/tracker';
*
* const logger = ;
* const tracker = trackPromises({ logger: new ConsoleLogger('debug') });
*
* // All tracking operations will be logged with 'promise' prefix
* tracker.track(apiCall(), 'api-request');
* // Logs: "promise: tracking a promise with label api-request"
* // Later: "promise: promise with label api-request resolved in 150ms"
* ```
*
* @example Server shutdown coordination
*
* ```ts
* import { trackPromises } from 'emitnlog/tracker';
* import { withTimeout } from 'emitnlog/utils';
*
* const shutdownTracker = trackPromises({ logger: serverLogger });
*
* // Track cleanup operations
* shutdownTracker.track(database.close(), 'db-close');
* shutdownTracker.track(cache.flush(), 'cache-flush');
* shutdownTracker.track(server.close(), 'server-close');
*
* // Wait with timeout for graceful shutdown
* try {
* await withTimeout(shutdownTracker.wait(), 30000);
* console.log('Graceful shutdown completed');
* } catch {
* console.log('Shutdown timeout - forcing exit');
* }
* ```
*
* @example Performance monitoring
*
* ```ts
* import { trackPromises } from 'emitnlog/tracker';
*
* const performanceTracker = trackPromises({ logger: metricsLogger });
*
* // Monitor performance across different operations
* performanceTracker.onSettled((event) => {
* const status = event.rejected ? 'FAILED' : 'SUCCESS';
* metricsCollector.record({ operation: event.label, duration: event.duration, status: status });
* });
*
* // Track various operations
* performanceTracker.track(userService.authenticate(token), 'auth');
* performanceTracker.track(dataService.fetchProfile(userId), 'profile');
* ```
*
* @param options Configuration options for the tracker
* @param options.logger Optional logger for internal tracker operations. If not provided, logging is disabled. The
* logger will be prefixed with 'promise' for easy identification.
* @returns A new PromiseTracker instance
*/
export const trackPromises = (options?: PromiseTrackerOptions): PromiseTracker => {
const promises = new Set<Promise<unknown>>();
const logger = withPrefix(options?.logger ?? OFF_LOGGER, 'promise', { fallbackPrefix: 'emitnlog.promise-tracker' });
const onSettledNotifier = createEventNotifier<PromiseSettledEvent>();
return {
get size() {
return promises.size;
},
onSettled: onSettledNotifier.onEvent,
wait: async () => {
if (!promises.size) {
return;
}
logger.d`waiting for ${promises.size} promises to settle`;
await Promise.allSettled(promises);
},
track: <T>(
first: string | Promise<T> | (() => Promise<T>),
second?: Promise<T> | (() => Promise<T>),
idMap?: Map<string, Promise<unknown>>,
): Promise<T> => {
const label = typeof first === 'string' ? first : undefined;
const promise = typeof first === 'string' ? (second as Promise<T> | (() => Promise<T>)) : first;
if (label && idMap) {
const existing = idMap.get(label);
if (existing) {
logger.d`returning existing promise for label '${label}'`;
return existing as Promise<T>;
}
}
let trackedPromise: Promise<T>;
let start: number;
if (typeof promise === 'function') {
logger.d`tracking a promise supplier${label ? ` with label '${label}'` : ''}`;
start = performance.now();
try {
trackedPromise = promise();
} catch (error) {
// eslint-disable-next-line @typescript-eslint/prefer-promise-reject-errors
trackedPromise = Promise.reject(error);
}
} else {
logger.d`tracking a promise${label ? ` with label '${label}'` : ''}`;
start = performance.now();
trackedPromise = promise;
}
// Completely paranoid...
Iif (!(trackedPromise as { then?: unknown } | undefined)?.then) {
trackedPromise = Promise.resolve(trackedPromise);
}
promises.add(trackedPromise);
const finalPromise = trackedPromise.then(
(result) => {
promises.delete(trackedPromise);
if (label && idMap) {
idMap.delete(label);
}
const duration = performance.now() - start;
logger.d`promise${label ? ` with label '${label}'` : ''} resolved in ${duration}ms`;
const event: Writable<PromiseSettledEvent> = { duration };
if (label !== undefined) {
event.label = label;
}
if (result !== undefined) {
event.result = result;
}
onSettledNotifier.notify(event);
return result;
},
(error: unknown) => {
promises.delete(trackedPromise);
if (label && idMap) {
idMap.delete(label);
}
const duration = performance.now() - start;
logger.d`promise${label ? ` with label '${label}'` : ''} rejected in ${duration}ms`;
const event: Writable<PromiseSettledEvent> = { duration, rejected: true };
if (label !== undefined) {
event.label = label;
}
Eif (error !== undefined) {
event.result = error;
}
onSettledNotifier.notify(event);
throw error;
},
);
if (label && idMap) {
idMap.set(label, finalPromise);
}
return finalPromise;
},
};
};
/**
* Creates a new promise holder for caching async operations and preventing duplicate execution.
*
* The promise holder maintains a cache of ongoing operations identified by unique IDs. When the same operation is
* requested multiple times (same ID), the holder returns the cached promise instead of executing the operation again.
* This is particularly useful for expensive operations like API calls, database queries, or file system operations that
* might be requested simultaneously from different parts of an application.
*
* Each holder instance is independent and manages its own operation cache. The cache is automatically cleaned up when
* operations complete, and comprehensive logging is provided when a logger is configured.
*
* **Key differences from PromiseTracker:**
*
* - **PromiseHolder**: Caches operations by ID to prevent duplicates, ideal for deduplication
* - **PromiseTracker**: Coordinates multiple different operations, ideal for shutdown/monitoring scenarios
*
* @example Basic API call caching
*
* ```ts
* import { holdPromises } from 'emitnlog/tracker';
*
* const apiHolder = holdPromises();
*
* // Multiple simultaneous requests for the same user
* const getUserData = (userId: string) => {
* return apiHolder.track(`user-${userId}`, () => fetchUserFromAPI(userId));
* };
*
* // All these calls will share the same promise/result
* const [user1, user2, user3] = await Promise.all([getUserData('123'), getUserData('123'), getUserData('123')]);
* // Only one API call was made
* ```
*
* @example Database query deduplication with logging
*
* ```ts
* import { holdPromises } from 'emitnlog/tracker';
* import { ConsoleLogger } from 'emitnlog/logger';
*
* const queryHolder = holdPromises({ logger: new ConsoleLogger('debug') });
*
* // Cache expensive queries
* const getProductById = (id: number) => {
* return queryHolder.track(`product-${id}`, async () => {
* console.log(`Executing query for product ${id}`);
* return await db.query('SELECT * FROM products WHERE id = ?', [id]);
* });
* };
*
* // Multiple components requesting the same product
* const product = await getProductById(456);
* const sameProduct = await getProductById(456); // Uses cached result, no duplicate query
* ```
*
* @example Configuration loading with graceful degradation
*
* ```ts
* import { holdPromises } from 'emitnlog/tracker';
* import { withTimeout } from 'emitnlog/utils';
*
* const configHolder = holdPromises({ logger: appLogger });
*
* const loadConfig = (environment: string) => {
* return configHolder.track(`config-${environment}`, async () => {
* try {
* // Try to load from remote first
* return await withTimeout(fetchRemoteConfig(environment), 5000);
* } catch (error) {
* appLogger.w`Failed to load remote config, using local fallback: ${error}`;
* return loadLocalConfig(environment);
* }
* });
* };
*
* // Multiple services requesting config simultaneously
* const [config1, config2] = await Promise.all([loadConfig('production'), loadConfig('production')]);
* // Only one config load attempt (remote + fallback if needed)
* ```
*
* @example File processing with monitoring
*
* ```ts
* import { holdPromises } from 'emitnlog/tracker';
*
* const fileHolder = holdPromises({ logger: fileLogger });
*
* // Monitor file processing performance
* fileHolder.onSettled((event) => {
* const status = event.rejected ? 'FAILED' : 'SUCCESS';
* console.log(`File ${event.label}: ${event.duration}ms - ${status}`);
* });
*
* const processFile = (filename: string) => {
* return fileHolder.track(`file-${filename}`, async () => {
* const content = await fs.readFile(filename, 'utf8');
* return await processLargeFile(content);
* });
* };
*
* // Multiple requests for the same file processing
* const [result1, result2] = await Promise.all([
* processFile('data.json'),
* processFile('data.json'), // Cached - no duplicate file processing
* ]);
* ```
*
* @example Cache inspection and conditional logic
*
* ```ts
* import { holdPromises } from 'emitnlog/tracker';
*
* const operationHolder = holdPromises();
*
* const performExpensiveOperation = async (id: string) => {
* if (operationHolder.has(id)) {
* console.log(`Operation ${id} already in progress...`);
* } else {
* console.log(`Starting operation ${id}...`);
* }
*
* return operationHolder.track(id, () => expensiveAsyncOperation());
* };
*
* // Start operation
* performExpensiveOperation('task-1');
* // Will show "already in progress" message
* performExpensiveOperation('task-1');
* ```
*
* @param options Configuration options for the holder
* @param options.logger Optional logger for internal operations. If not provided, logging is disabled. The logger will
* be prefixed with 'promise' for easy identification of holder-related logs.
* @returns A new PromiseHolder instance
*/
export const holdPromises = (options?: PromiseTrackerOptions): PromiseHolder => {
const idMap = new Map<string, Promise<unknown>>();
const tracker = trackPromises(options);
return {
get size() {
return idMap.size;
},
onSettled: tracker.onSettled,
wait: tracker.wait,
has: (id: string) => idMap.has(id),
track: <T>(id: string, supplier: () => Promise<T>): Promise<T> =>
(
tracker.track as (
id: string,
promise: Promise<T> | (() => Promise<T>),
idMap: Map<string, Promise<unknown>>,
) => Promise<T>
)(id, supplier, idMap),
};
};
type PromiseTrackerOptions = { readonly logger?: Logger };
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