#### Per-Connection Locks

Each connection has its own lock. The connections in the pool are all in a `ConcurrentLinkedQueue`. Due to data races, iterators of this queue may return removed connections. Callers must check the connection's `noNewExchanges` property before using connections from the pool.

The connection lock is never held while doing I/O (even closing a socket) to prevent contention.

  abstract void setCountCheckReturnValue(E element, int count);

  /**
   * Call the {@code setCount()} method under test, but do not check its return value. Callers
   * should use this method over {@link #setCountCheckReturnValue(Object, int)} when they expect
   * {@code setCount()} to throw an exception, as checking the return value could produce an

   *     the {@link ExecutionException} thrown by {@code input.get()} or, if {@code get()} throws a
   *     different kind of exception, that exception itself. To avoid hiding bugs and other
   *     unrecoverable errors, callers should prefer more specific types, avoiding {@code
   *     Throwable.class} in particular.
   * @param fallback the {@link Function} to be called if {@code input} fails with the expected

    }

    /**
     * Sets the level and returns this.
     *
     * This was deprecated in OkHttp 4.0 in favor of the [level] val. In OkHttp 4.3 it is
     * un-deprecated because Java callers can't chain when assigning Kotlin vals. (The getter remains
     * deprecated).
     */
    fun setLevel(level: Level) =
      apply {
        this.level = level
      }

    @JvmName("-deprecated_level")

  public final @Nullable V getOrDefault(@Nullable Object key, @Nullable V defaultValue) {
    /*
     * Even though it's weird to pass a defaultValue that is null, some callers do so. Those who
     * pass a literal "null" should probably just use `get`, but I would expect other callers to
     * pass an expression that *might* be null. This could happen with:
     *
     * - a `getFooOrDefault(@Nullable Foo defaultValue)` method that returns

   * Internal constructor. Users should use {@link PairedStatsAccumulator#snapshot}.
   *
   * <p>To ensure that the created instance obeys its contract, the parameters should satisfy the
   * following constraints. This is the callers responsibility and is not enforced here.
   *
   * <ul>
   *   <li>Both {@code xStats} and {@code yStats} must have the same {@code count}.
   *   <li>If that {@code count} is 1, {@code sumOfProductsOfDeltas} must be exactly 0.0.

  public final @Nullable V getOrDefault(@Nullable Object key, @Nullable V defaultValue) {
    /*
     * Even though it's weird to pass a defaultValue that is null, some callers do so. Those who
     * pass a literal "null" should probably just use `get`, but I would expect other callers to
     * pass an expression that *might* be null. This could happen with:
     *
     * - a `getFooOrDefault(@Nullable Foo defaultValue)` method that returns

  /*
   * The following methods are safe to call as long as both of the following hold:
   *
   * - allocArrays() has been called. Callers can confirm this by checking needsAllocArrays().
   *
   * - The map has not switched to delegating to a java.util implementation to mitigate hash
   *   flooding. Callers can confirm this by null-checking delegateOrNull().
   *

      return ImmutableSortedSet.orderedBy(STRING_REVERSED).add(elements).build();
    }

    /*
     * While the current implementation returns `this`, that's not something we mean to guarantee.
     * Callers of TestContainerGenerator.order need to be prepared for implementations to return a new
     * collection.
     */
    @SuppressWarnings("CanIgnoreReturnValueSuggester")
    @Override

                            if (log.isDebugEnabled()) {
                                log.debug("Transport still in use, no idle timeout " + this);
                            }
                            // notify, so that callers with timed-out requests can handle them
                            for (final Response response : this.response_map.values()) {
                                synchronized (response) {