}

    fun flowControlListener(flowControlListener: FlowControlListener) =
      apply {
        this.flowControlListener = flowControlListener
      }

    fun build(): Http2Connection {
      return Http2Connection(this)
    }
  }

  /**
   * Methods in this class must not lock FrameWriter. If a method needs to write a frame, create an
   * async task to do so.
   */

    val http2Connection =
      Http2Connection.Builder(client = true, taskRunner)
        .socket(socket, route.address.url.host, source, sink)
        .listener(this)
        .pingIntervalMillis(pingIntervalMillis)
        .flowControlListener(flowControlListener)
        .build()
    this.http2Connection = http2Connection

    val connection = routePlanner.plans.first().connection
    val http2Connection = connectHttp2(peer, connection, 5)
    setPolicy(pool, address, ConnectionPool.AddressPolicy(5))
    assertThat(pool.connectionCount()).isEqualTo(1)

    // Decrease the connection's max so that another connection is needed
    updateMaxConcurrentStreams(http2Connection, 4)
    assertThat(pool.connectionCount()).isEqualTo(2)

  private fun connect(
    peer: MockHttp2Peer,
    pushObserver: PushObserver = IGNORE,
    listener: Http2Connection.Listener = Http2Connection.Listener.REFUSE_INCOMING_STREAMS,
  ): Http2Connection {
    val connection =
      Http2Connection.Builder(true, TaskRunner.INSTANCE)
        .socket(peer.openSocket())
        .pushObserver(pushObserver)
        .listener(listener)
        .build()

Lokhttp3/internal/http2/Http2Connection$ReaderRunnable$settings$1;
Lokhttp3/internal/http2/Http2Connection$ReaderRunnable;
Lokhttp3/internal/http2/Http2Connection$pushDataLater$1;
Lokhttp3/internal/http2/Http2Connection$pushHeadersLater$1;
Lokhttp3/internal/http2/Http2Connection$pushRequestLater$2;
Lokhttp3/internal/http2/Http2Connection$pushResetLater$1;
Lokhttp3/internal/http2/Http2Connection$sendDegradedPingLater$2;

/** Encode requests and responses using HTTP/2 frames. */
class Http2ExchangeCodec(
  client: OkHttpClient,
  override val carrier: Carrier,
  private val chain: RealInterceptorChain,
  private val http2Connection: Http2Connection,
) : ExchangeCodec {
  @Volatile private var stream: Http2Stream? = null

  private val protocol: Protocol =
    if (Protocol.H2_PRIOR_KNOWLEDGE in client.protocols) {
      Protocol.H2_PRIOR_KNOWLEDGE

import kotlin.concurrent.withLock
import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.InvocationKind
import kotlin.contracts.contract
import okhttp3.Dispatcher
import okhttp3.internal.http2.Http2Connection
import okhttp3.internal.http2.Http2Stream
import okhttp3.internal.http2.Http2Writer

/**
 * Centralisation of central locks according to docs/contribute/concurrency.md
 */
internal object Locks {

import okhttp3.Protocol
import okhttp3.Protocol.Companion.get
import okhttp3.internal.closeQuietly
import okhttp3.internal.concurrent.TaskRunner
import okhttp3.internal.http2.Header
import okhttp3.internal.http2.Http2Connection
import okhttp3.internal.http2.Http2Stream
import okhttp3.internal.platform.Platform
import okhttp3.tls.internal.TlsUtil.localhost
import okio.buffer
import okio.source

              override fun writeTo(sink: BufferedSink) {
                sink.write(postBytes) // push bytes into the stream's buffer
                sink.flush() // Http2Connection.writeData subject to write window
                sink.close() // Http2Connection.writeData empty frame
              }
            },
        ),
      )
    val response = call.execute()
    assertThat(response.body.string()).isEqualTo("ABCDE")

### Locks

We have 3 different things that we synchronize on.

#### Http2Connection

This lock guards internal state of each connection. This lock is never held for blocking operations. That means that we acquire the lock, read or write a few fields and release the lock. No I/O and no application-layer callbacks.