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* Unified Gatekeeper - Concurrency & Cache Management
*
* Centralized system for:
* 1. Compile slot allocation (semaphore-based)
* 2. Cache Read-Write locking (multiple readers, single writer)
* 3. TTL-based deadlock prevention (auto-release after timeout)
* 4. Priority queuing (system checks prioritized over regular tasks)
* 5. Event-driven architecture (eliminates polling overhead)
*
* Replaces the previous dual-gatekeeper pattern with atomic, deadlock-safe operations.
* Performance: O(1) event notification instead of O(n) polling overhead.
*/
import { Logger } from "@shared/logger";
import { config, getCompileMaxConcurrent } from "../config";
import { cpus } from "node:os";
import { EventEmitter } from "node:events";
// Priority levels for task queuing
export enum TaskPriority {
HIGH = 0, // System health checks, cleanup, user interactions
NORMAL = 1, // Regular compilations
LOW = 2, // Background work
}
interface CacheLockEntry {
key: string;
lockType: "read" | "write";
acquiredAt: number;
expiresAt: number;
owner: string;
}
interface CompileSlotEntry {
priority: TaskPriority;
acquiredAt: number;
expiresAt: number;
owner: string;
}
interface QueuedTask {
priority: TaskPriority;
resolver: (release: () => void) => void;
ownerId: string;
owner: string;
createdAt: number;
}
/**
* Calculate adaptive concurrency based on CPU count
* Formula: max(1, cpuCount - 1)
* Examples:
* 2-core (RasPi): max(1, 2-1) = 1
* 4-core desktop: max(1, 4-1) = 3
* 8-core workstation: max(1, 8-1) = 7
* 16-core server: max(1, 16-1) = 15
*/
function calculateOptimalConcurrency(): number {
try {
const numCores = cpus().length;
return Math.max(1, numCores - 1);
} catch {
return 4; // Fallback default
}
}
export class UnifiedGatekeeper extends EventEmitter {
private readonly maxCompileConcurrent: number;
private availableSlots: number;
private readonly activeSlots: Map<string, CompileSlotEntry> = new Map();
private compileQueue: QueuedTask[] = [];
// Cache locks: key -> [lock entries]
private readonly cacheLocks: Map<string, CacheLockEntry[]> = new Map();
// Lock monitoring
private lockCheckInterval: NodeJS.Timeout | null = null;
private readonly lockTTL = config.timeouts.gatekeeperLockTTLMs;
private readonly checkIntervalMs = config.timeouts.gatekeeperLockCheckIntervalMs;
// Queue size limit to prevent unbounded memory growth under extreme load
private readonly maxQueueSize = config.compilation.gatekeeperMaxQueueSize;
private readonly logger = new Logger("UnifiedGatekeeper");
// Statistics
private stats = {
totalCompileSlotRequests: 0,
totalCacheLockRequests: 0,
expiredLocks: 0,
deadlocksAvoided: 0,
};
constructor(maxConcurrent?: number) {
super();
// Allow unlimited event listeners for high-contention scenarios (200+ waiters)
this.setMaxListeners(0);
// In worker threads, disable gatekeeper since the worker pool controls concurrency
const isWorkerThread = process.env.COMPILE_GATEKEEPER_DISABLED === "true";
if (isWorkerThread) {
this.maxCompileConcurrent = Infinity;
this.availableSlots = Infinity;
this.logger.info("UnifiedGatekeeper in worker thread (pool-controlled)");
} else {
// Priority 1: Explicit env override
// Priority 2: Constructor parameter
// Priority 3: CPU-adaptive calculation
if (maxConcurrent) {
this.maxCompileConcurrent = maxConcurrent;
} else {
this.maxCompileConcurrent = getCompileMaxConcurrent() || calculateOptimalConcurrency();
}
this.availableSlots = this.maxCompileConcurrent;
const numCores = cpus().length;
this.logger.info(
`UnifiedGatekeeper initialized: max ${this.maxCompileConcurrent} concurrent compiles ` +
`(${numCores} CPU cores detected, formula: max(1, cores-1))`,
);
}
// Start periodic lock expiration check
this.startLockMonitoring();
}
/**
* Acquire a compile slot with HIGH priority (for user-initiated simulations)
* Ensures interactive tasks get prompt access
*/
async acquireCompileSlotHighPriority(owner: string = "simulation-start", onQueued?: () => void): Promise<() => void> {
return this.acquireCompileSlot(TaskPriority.HIGH, config.timeouts.compileGatekeeperAcquireMs, owner, onQueued);
}
/**
* Acquire a compile slot (internal method used by all priorities)
*/
async acquireCompileSlot(
priority: TaskPriority = TaskPriority.NORMAL,
timeoutMs: number = config.timeouts.compileGatekeeperAcquireMs,
owner: string = "unknown",
onQueued?: () => void,
): Promise<() => void> {
this.stats.totalCompileSlotRequests++;
const ownerId = `${owner}-${Date.now()}-${crypto.randomUUID()}`;
return new Promise((resolve, reject) => {
let timeoutHandle: NodeJS.Timeout | null = null;
const grant = () => {
Eif (timeoutHandle) clearTimeout(timeoutHandle);
const expiresAt = Date.now() + this.lockTTL;
const entry: CompileSlotEntry = {
priority,
acquiredAt: Date.now(),
expiresAt,
owner: ownerId,
};
this.activeSlots.set(ownerId, entry);
this.availableSlots--;
this.logger.debug(
`✓ Compile slot acquired by ${owner} (available: ${this.availableSlots}, active: ${this.activeSlots.size})`,
);
// Return release function bound to this owner
resolve(this.createReleaseFunction(ownerId, "compile"));
};
// Set immediate timeout for this acquire attempt (not just queue timeout)
timeoutHandle = setTimeout(() => {
const idx = this.compileQueue.findIndex(t => t.ownerId === ownerId);
if (idx >= 0) {
this.compileQueue.splice(idx, 1);
}
this.activeSlots.delete(ownerId);
reject(new Error(`Compile slot acquire timeout after ${timeoutMs}ms for ${owner}`));
}, timeoutMs);
if (this.availableSlots > 0) {
// Fast path: slot available
grant();
} else {
// Slow path: queue the request with timeout
onQueued?.();
const queuedTask: QueuedTask = {
priority,
resolver: (release) => {
const expiresAt = Date.now() + this.lockTTL;
const entry: CompileSlotEntry = {
priority,
acquiredAt: Date.now(),
expiresAt,
owner: ownerId,
};
this.activeSlots.set(ownerId, entry);
this.availableSlots--;
resolve(release);
},
ownerId,
owner,
createdAt: Date.now(),
};
// Reject if queue is full to prevent unbounded memory growth
if (this.compileQueue.length >= this.maxQueueSize) {
reject(new Error(
`Compile queue full (${this.maxQueueSize} pending). ` +
`Try again later. Active: ${this.activeSlots.size}, Queued: ${this.compileQueue.length}`,
));
return;
}
// Priority-aware insertion (O(n) instead of O(n log n) full sort)
let insertIdx = this.compileQueue.length;
for (let i = 0; i < this.compileQueue.length; i++) {
if (queuedTask.priority < this.compileQueue[i].priority) {
insertIdx = i;
break;
}
}
this.compileQueue.splice(insertIdx, 0, queuedTask);
this.logger.debug(
`⏳ Compile slot queued for ${owner} (queue: ${this.compileQueue.length}, active: ${this.activeSlots.size})`,
);
// Timeout handling
const timeoutHandle = setTimeout(() => {
const idx = this.compileQueue.indexOf(queuedTask);
Iif (idx >= 0) {
this.compileQueue.splice(idx, 1);
reject(new Error(`Compile slot timeout after ${timeoutMs}ms for ${owner}`));
}
}, timeoutMs);
// Wrap resolver to clear timeout on success
const originalResolver = queuedTask.resolver;
queuedTask.resolver = (release) => {
clearTimeout(timeoutHandle);
originalResolver(release);
};
}
});
}
/**
* Clean up timeout and event listener after a cache lock is acquired or timed out.
*/
private _cleanupLockWaiter(
key: string,
timeoutHandle: NodeJS.Timeout | null,
eventListener: (() => void) | null,
): void {
if (timeoutHandle) clearTimeout(timeoutHandle);
if (eventListener) this.off(`cache_lock_released:${key}`, eventListener);
}
/**
* Acquire a cache lock (read or write)
* Read locks: multiple readers allowed
* Write locks: exclusive, no other locks allowed
* Uses event-driven approach - no polling overhead
*/
async acquireCacheLock(
key: string,
lockType: "read" | "write" = "read",
timeoutMs: number = config.timeouts.compileGatekeeperAcquireMs,
owner: string = "unknown",
): Promise<() => Promise<void>> {
this.stats.totalCacheLockRequests++;
const ownerId = `${owner}-${Date.now()}-${crypto.randomUUID()}`;
return new Promise((resolve, reject) => {
let timeoutHandle: NodeJS.Timeout | null = null;
let eventListener: (() => void) | null = null;
const tryAcquire = (): boolean => {
const locks = this.cacheLocks.get(key) || [];
const now = Date.now();
// Filter out expired locks
const activeLocks = locks.filter(l => l.expiresAt > now);
if (lockType === "read") {
// Read lock: allowed if no write locks exist
const hasWriteLock = activeLocks.some(l => l.lockType === "write");
if (!hasWriteLock) {
const entry: CacheLockEntry = {
key,
lockType: "read",
acquiredAt: now,
expiresAt: now + this.lockTTL,
owner: ownerId,
};
activeLocks.push(entry);
this.cacheLocks.set(key, activeLocks);
this.logger.debug(`✓ Read lock acquired for ${key} by ${owner}`);
this._cleanupLockWaiter(key, timeoutHandle, eventListener);
resolve(this.createCacheLockReleaser(key, ownerId));
return true;
}
} else if (activeLocks.length === 0) {
// Write lock: exclusive, no other locks allowed
const entry: CacheLockEntry = {
key,
lockType: "write",
acquiredAt: now,
expiresAt: now + this.lockTTL,
owner: ownerId,
};
this.cacheLocks.set(key, [entry]);
this.logger.debug(`✓ Write lock acquired for ${key} by ${owner}`);
this._cleanupLockWaiter(key, timeoutHandle, eventListener);
resolve(this.createCacheLockReleaser(key, ownerId));
return true;
}
return false;
};
// Try immediate acquisition
if (tryAcquire()) {
return;
}
// Set up event-driven waiting (no polling)
const eventName = `cache_lock_released:${key}`;
eventListener = () => {
tryAcquire(); // Event fires when lock might be available
};
this.on(eventName, eventListener);
// Timeout handling with cleanup
timeoutHandle = setTimeout(() => {
Eif (eventListener) {
this.off(eventName, eventListener);
}
reject(new Error(`Cache lock timeout (${lockType}) for ${key} after ${timeoutMs}ms`));
}, timeoutMs);
});
}
/**
* Grant the next task from the compile queue a slot.
* Called after a slot is released to wake up a waiting requester.
*/
private _grantNextQueuedSlot(): void {
if (this.compileQueue.length === 0) return;
const task = this.compileQueue.shift();
Iif (!task) return;
try {
task.resolver(this.createReleaseFunction(task.ownerId, "compile"));
} catch (err) {
this.logger.error(
`Failed to grant queued slot to ${task.owner}: ${err instanceof Error ? err.message : String(err)}`,
);
// Slot remains available (already incremented above), try next task
if (this.compileQueue.length > 0) {
const next = this.compileQueue.shift();
if (!next) return;
try {
next.resolver(this.createReleaseFunction(next.ownerId, "compile"));
} catch {
// Silently drop — slot stays available
}
}
}
}
/**
* Release a compile slot
* Emits event for monitoring and triggers next queued task
*/
private createReleaseFunction(ownerId: string, type: "compile" | "cache"): () => void {
return () => {
Eif (type === "compile") {
const entry = this.activeSlots.get(ownerId);
if (entry) {
this.activeSlots.delete(ownerId);
this.availableSlots++;
this.logger.debug(
`✓ Compile slot released (available: ${this.availableSlots}, active: ${this.activeSlots.size})`,
);
this.emit("slot_released");
this._grantNextQueuedSlot();
}
}
};
}
/**
* Create a cache lock releaser function
* Emits event to wake up waiting tasks (event-driven, no polling)
*/
private createCacheLockReleaser(key: string, ownerId: string): () => Promise<void> {
return async () => {
const locks = this.cacheLocks.get(key);
Eif (locks) {
const filteredLocks = locks.filter(l => l.owner !== ownerId);
if (filteredLocks.length === 0) {
this.cacheLocks.delete(key);
} else {
this.cacheLocks.set(key, filteredLocks);
}
this.logger.debug(`✓ Lock released for ${key}`);
// Emit event to wake up waiting tasks (O(1) notification instead of polling)
this.emit(`cache_lock_released:${key}`);
}
};
}
/**
* Monitor for expired locks and clean them up automatically
* Prevents deadlocks caused by crashed processes
* Emits events to wake up waiting tasks
*/
private startLockMonitoring(): void {
Iif (this.lockCheckInterval) {
return;
}
this.lockCheckInterval = setInterval(() => {
const now = Date.now();
let expiredCount = 0;
const releasedKeys = new Set<string>();
// Check compile slots
for (const [ownerId, slot] of this.activeSlots.entries()) {
Iif (slot.expiresAt < now) {
this.activeSlots.delete(ownerId);
this.availableSlots++;
expiredCount++;
this.logger.warn(`⚠ Compile slot TTL expired for ${slot.owner}, auto-releasing`);
// Emit event to wake up queued tasks
this.emit("slot_released");
}
}
// Check cache locks
for (const [key, locks] of this.cacheLocks.entries()) {
const activeLocks = locks.filter(l => l.expiresAt > now);
const expiredInKey = locks.length - activeLocks.length;
expiredCount += expiredInKey;
if (activeLocks.length === 0) {
this.cacheLocks.delete(key);
} else {
this.cacheLocks.set(key, activeLocks);
}
if (expiredInKey > 0) {
this.logger.warn(`⚠ ${expiredInKey} cache lock(s) TTL expired for ${key}, auto-releasing`);
releasedKeys.add(key);
}
}
// Emit events for all released cache locks (O(1) per key)
for (const key of releasedKeys) {
this.emit(`cache_lock_released:${key}`);
}
Iif (expiredCount > 0) {
this.stats.expiredLocks += expiredCount;
this.stats.deadlocksAvoided++;
}
}, this.checkIntervalMs);
}
/**
* Gracefully stop lock monitoring and cleanup event listeners
*/
stopLockMonitoring(): void {
if (this.lockCheckInterval) {
clearInterval(this.lockCheckInterval);
this.lockCheckInterval = null;
}
// Remove all event listeners to prevent memory leaks
this.removeAllListeners();
}
/**
* Get current gatekeeper statistics for monitoring
*/
getStats() {
return {
maxConcurrentCompiles: this.maxCompileConcurrent,
availableSlots: this.availableSlots,
activeCompiles: this.activeSlots.size,
queuedCompiles: this.compileQueue.length,
activeCacheLocks: this.cacheLocks.size,
totalCompileRequests: this.stats.totalCompileSlotRequests,
totalCacheLockRequests: this.stats.totalCacheLockRequests,
expiredLocks: this.stats.expiredLocks,
deadlocksAvoided: this.stats.deadlocksAvoided,
};
}
/**
* Gracefully drain all queues and wait for completion
*/
async drain(): Promise<void> {
return new Promise((resolve) => {
const checkEmpty = () => {
if (
this.activeSlots.size === 0 &&
this.compileQueue.length === 0 &&
this.cacheLocks.size === 0
) {
resolve();
} else {
setTimeout(checkEmpty, 100);
}
};
checkEmpty();
});
}
/**
* Reset gatekeeper state (for testing)
* Removes all event listeners to prevent memory leaks
*/
reset(): void {
this.activeSlots.clear();
this.compileQueue = [];
this.cacheLocks.clear();
this.availableSlots = this.maxCompileConcurrent;
this.stats = {
totalCompileSlotRequests: 0,
totalCacheLockRequests: 0,
expiredLocks: 0,
deadlocksAvoided: 0,
};
// Remove all event listeners to prevent memory leaks
this.removeAllListeners();
this.logger.info("UnifiedGatekeeper reset");
}
}
/**
* Global singleton instance
*/
let unifiedGatekeeperInstance: UnifiedGatekeeper | null = null;
export function getUnifiedGatekeeper(maxConcurrent?: number): UnifiedGatekeeper {
unifiedGatekeeperInstance ??= new UnifiedGatekeeper(maxConcurrent);
return unifiedGatekeeperInstance;
}
export function resetUnifiedGatekeeper(): void {
const instance = unifiedGatekeeperInstance;
if (instance) {
instance.stopLockMonitoring();
}
unifiedGatekeeperInstance = null;
}
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