[ts] add first problem - limited connection pool

source/routes/index.ts

@@ -1,15 +1,17 @@
 import type { FastifyInstance, FastifyPluginAsync } from 'fastify'
-import cpu from './cpu.ts'
-import io from './io.ts'
-import mem from './mem.ts'
-import ping from './ping.ts'
+import cpu from './load/cpu.ts'
+import io from './load/io.ts'
+import mem from './load/mem.ts'
+import ping from './load/ping.ts'
+import limitedConnectionsPool from './problems/connectionsPool.ts'
 
 // eslint-disable-next-line jsdoc/require-jsdoc
 const routes: FastifyPluginAsync = async (fastify: FastifyInstance) => {
   void fastify.register(ping)
   void fastify.register(cpu)
   void fastify.register(mem)
   void fastify.register(io)
+  void fastify.register(limitedConnectionsPool)
 }
 
 export default routes

source/routes/problems/connectionsPool.ts

@@ -0,0 +1,57 @@
+import type { FastifyPluginAsync } from 'fastify'
+import { delayResponse } from '~/simulate/load.ts'
+
+const MAX_CONCURRENT_CONNECTIONS = 5
+
+class ConnectionsPool {
+  private readonly maxConnections: number
+  private currentConnections: number
+  private readonly queue: Array<(value: string) => void>
+
+  constructor(maxConnections: number) {
+    this.maxConnections = maxConnections
+    this.currentConnections = 0
+    this.queue = []
+  }
+
+  async acquire(): Promise<void> {
+    if (this.currentConnections < this.maxConnections) {
+      this.currentConnections++
+      await Promise.resolve()
+      return
+    }
+
+    await new Promise((resolve) => {
+      this.queue.push(resolve)
+    })
+  }
+
+  release(): void {
+    this.currentConnections--
+    if (this.queue.length > 0) {
+      const next = this.queue.shift()
+      if (next) {
+        this.currentConnections++
+        next('work')
+      }
+    }
+  }
+}
+
+const pool = new ConnectionsPool(MAX_CONCURRENT_CONNECTIONS)
+
+// eslint-disable-next-line jsdoc/require-jsdoc
+export const limitedConnectionsPool: FastifyPluginAsync = async (fastify) => {
+  fastify.get<{ Params: { ms: string } }>('/problems/limited-connections/pool/:ms', async (request) => {
+    try {
+      await pool.acquire()
+
+      // Simulate some work
+      return await delayResponse(Number.parseInt(request.params.ms, 10))
+    } finally {
+      pool.release()
+    }
+  })
+}
+
+export default limitedConnectionsPool

source/simulate/load.ts

@@ -1,7 +1,7 @@
 import fs from 'node:fs/promises'
 import os from 'node:os'
 import path from 'node:path'
-import { parseSize } from '../utils/parseSize.ts'
+import { parseSize } from '~/utils/parseSize.ts'
 
 const MAX_DELAY = 5000
 const memoryLeaks: unknown[] = []