*  **There is no longer a global singleton connection pool.** In OkHttp 2.x,
    all `OkHttpClient` instances shared a common connection pool by default.
    In OkHttp 3.x, each new `OkHttpClient` gets its own private connection pool.
    Applications should avoid creating many connection pools as doing so
    prevents connection reuse. Each connection pool holds its own set of

  private fun waitForConnectionShutdown(connection: RealConnection?) {
    if (connection!!.isHealthy(false)) {
      Thread.sleep(100L)
    }
    if (connection.isHealthy(false)) {
      Thread.sleep(2000L)
    }
    if (connection.isHealthy(false)) {
      throw TimeoutException("connection didn't shutdown within timeout")
    }
  }

  /**

    return null
  }

  override fun connectionReleased(connection: Connection) {
  }

  override fun connectionConnectionAcquired(connection: RealConnection) {
  }

  override fun connectionConnectionReleased(connection: RealConnection) {
  }

  override fun connectionConnectionClosed(connection: RealConnection) {
  }

  override fun noNewExchanges(connection: RealConnection) {
  }

     * automatically send ping frames until either the connection fails or it is closed. This keeps
     * the connection alive and may detect connectivity failures.
     *
     * If the server does not respond to each ping with a pong within `interval`, this client will
     * assume that connectivity has been lost. When this happens on a web socket the connection is

   * HTTP/2 can have both stream timeouts (due to a problem with a single stream) and connection
   * timeouts (due to a problem with the transport). When a stream times out we don't know whether
   * the problem impacts just one stream or the entire connection.
   *
   * To differentiate the two cases we ping the server when a stream times out. If the overall
   * connection is fine the ping will receive a pong; otherwise it won't.
   *

    if (pooled3 != null) return pooled3.connection

    connection.withLock {
      connectionPool.put(connection)
      user.acquireConnectionNoEvents(connection)
    }

    user.connectionAcquired(connection)
    user.connectionConnectionAcquired(connection)
    return connection
  }

  override fun trackFailure(
    call: RealCall,
    e: IOException?,

A **Manager** is used to manage all incoming and outgoing connections to a server.

On startup all remote servers must be specified. 
From that individual connections will be spawned to each remote server, 
or incoming requests will be hooked up to the appropriate connection.

To get a connection to a specific server, use `Manager.Connection(host)` to get a connection to the specified host.
From this connection individual requests can be made.

import okhttp3.internal.ws.RealWebSocket
import okio.BufferedSink
import okio.BufferedSource

/**
 * A connection to a remote web server capable of carrying 1 or more concurrent streams.
 *
 * Connections are shared in a connection pool. Accesses to the connection's state must be guarded
 * by holding a lock on the connection.
 */
class RealConnection(
  val taskRunner: TaskRunner,
  val connectionPool: RealConnectionPool,

  }

  @Test
  fun staleConnectionNotReusedForNonIdempotentRequest() {
    // Capture the connection so that we can later make it stale.
    var connection: RealConnection? = null
    client =
      client.newBuilder()
        .addNetworkInterceptor(
          Interceptor { chain ->
            connection = chain.connection() as RealConnection
            chain.proceed(chain.request())
          },
        )

  /**
   * Half close connection (InputStream for client) after reading the request but before
   * writing the response. Use this to simulate late connection pool failures.
   */
  object HalfCloseAfterRequest : SocketPolicy

  /** Close connection after reading half of the request body (if present). */
  object DisconnectDuringRequestBody : SocketPolicy

  /** Close connection after writing half of the response body (if present). */