lock.assertHeld()

    // If this connection is not accepting new exchanges, we're done.
    if (calls.size >= allocationLimit || noNewExchanges) return false

    // If the non-host fields of the address don't overlap, we're done.
    if (!this.route.address.equalsNonHost(address)) return false

    // If the host exactly matches, we're done: this connection can carry the address.

    try {
      while (currentTask != self) {
        taskRunner.condition.await()
      }
    } finally {
      serialTaskQueue.remove(yieldCompleteTask)
    }

    // If we're yielding until we're exhausted and a task run, keep going until a task doesn't run.
    if (strategy == ResumePriority.AfterOtherTasks && otherTasksStarted) {
      return yieldUntil(strategy, condition)
    }
  }

    val candidate = connectionUser.candidateConnection() ?: return null

    // Make sure this connection is healthy & eligible for new exchanges. If it's no longer needed
    // then we're on the hook to close it.
    val healthy = candidate.isHealthy(connectionUser.doExtensiveHealthChecks())
    var noNewExchangesEvent = false
    val toClose: Socket? =
      candidate.withLock {
        when {

      // Confirm the connection is healthy and return it.
      if (connection.isHealthy(doExtensiveHealthChecks)) return connection

      // In the second synchronized block, release the unhealthy acquired connection. We're also on
      // the hook to close this connection if it's no longer in use.
      val noNewExchangesEvent: Boolean
      val toClose: Socket? =
        connection.withLock {

    while (byteCount > 0L) {
      var toWrite: Int
      this.withLock {
        try {
          while (writeBytesTotal >= writeBytesMaximum) {
            // Before blocking, confirm that the stream we're writing is still open. It's possible
            // that the stream has since been closed (such as if this write timed out.)
            if (!streams.containsKey(streamId)) {
              throw IOException("stream closed")

              if (errorExceptionToDeliver == null &&
                unacknowledgedBytesRead >= connection.okHttpSettings.initialWindowSize / 2
              ) {
                // Flow control: notify the peer that we're ready for more data! Only send a
                // WINDOW_UPDATE if the stream isn't in error.
                connection.writeWindowUpdateLater(id, unacknowledgedBytesRead)

      "FINE: Q10000 starting              : task",
      "FINE: Q10000 finished run in   0 µs: task",
    )
  }

  /** Inspect how many runnables have been enqueued. If none then we're truly sequential. */
  @Test fun singleQueueIsSerial() {
    redQueue.execute("task one", 100.µs) {
      log += "one:run@${taskFaker.nanoTime} parallel=${taskFaker.isParallel}"
    }