Give devsupport networking its own dispatcher and pool (#58094)

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/inspector/DevSupportHttpClient.kt

@@ -11,17 +11,39 @@ package com.facebook.react.devsupport.inspector
 
 import com.facebook.react.modules.network.OkHttpClientProvider
 import java.util.concurrent.TimeUnit
+import okhttp3.ConnectionPool
+import okhttp3.Dispatcher
 import okhttp3.OkHttpClient
 
 /**
- * Shared [OkHttpClient] instances for devsupport networking. Uses a single connection pool and
- * dispatcher across all dev support HTTP and WebSocket usage.
+ * Shared [OkHttpClient] instances for devsupport networking. Configured from the app's client, so a
+ * [com.facebook.react.modules.network.OkHttpClientFactory] override still applies, but with a
+ * connection pool and dispatcher of their own, shared across all dev support HTTP and WebSocket
+ * usage and nothing else.
+ *
+ * The dispatcher must not be the app's. A WebSocket occupies a running-call slot on it for its
+ * whole lifetime — `RealWebSocket.loopReader` runs inside `RealCall.AsyncCall.execute` — and dev
+ * support keeps several open to one host: the packager connection, the inspector, and whatever else
+ * the app connects. OkHttp's default [Dispatcher.maxRequestsPerHost] is 5, so on the app's
+ * dispatcher those sockets throttle, and eventually stall, every other request to the dev server —
+ * including [com.facebook.react.devsupport.BundleDownloader] fetching the bundle itself.
  */
 internal object DevSupportHttpClient {
+  // Enough that the long-lived WebSockets cannot crowd out bundle and asset traffic: the dev
+  // server is the only host this client talks to, so the per-host limit is the effective one.
+  private const val MAX_CONCURRENT_REQUESTS = 32
+
   /** Client for HTTP requests: connect=5s, write=disabled, read=disabled. */
   internal val httpClient: OkHttpClient =
       OkHttpClientProvider.getOkHttpClient()
           .newBuilder()
+          .dispatcher(
+              Dispatcher().apply {
+                maxRequests = MAX_CONCURRENT_REQUESTS
+                maxRequestsPerHost = MAX_CONCURRENT_REQUESTS
+              },
+          )
+          .connectionPool(ConnectionPool())
           .connectTimeout(5, TimeUnit.SECONDS)
           .writeTimeout(0, TimeUnit.MILLISECONDS)
           .readTimeout(0, TimeUnit.MINUTES)