This is a common idiom for limiting concurrency.
</p>

<p>
This program starts a goroutine for every entry in the work list, but the
goroutines coordinate using the <code>limit</code> channel to ensure
that at most three are running work functions at a time.
</p>

<pre>
var limit = make(chan int, 3)

func main() {
	for _, w := range work {
		go func(w func()) {
			limit &lt;- 1
			w()
			&lt;-limit

	if err != nil {
		t.Fatalf("got error: %v", err)
	}

	if len(results) != 3 {
		t.Errorf("Three users should be found, instead found %d", len(results))
	}
}

func TestGenericsUpsert(t *testing.T) {
	ctx := context.Background()
	lang := Language{Code: "upsert", Name: "Upsert"}

   * size (the final list may be smaller). For example, partitioning a list containing {@code [a, b,
   * c, d, e]} with a partition size of 3 yields {@code [[a, b, c], [d, e]]} -- an outer list
   * containing two inner lists of three and two elements, all in the original order.
   *
   * <p>The outer list is unmodifiable, but reflects the latest state of the source list. The inner

   * size (the final list may be smaller). For example, partitioning a list containing {@code [a, b,
   * c, d, e]} with a partition size of 3 yields {@code [[a, b, c], [d, e]]} -- an outer list
   * containing two inner lists of three and two elements, all in the original order.
   *
   * <p>The outer list is unmodifiable, but reflects the latest state of the source list. The inner

   *
   * <ul>
   *   <li>When a {@code ListenableFuture} listener is registered to run under {@code
   *       directExecutor}, the listener can execute in any of three possible threads:
   *       <ol>
   *         <li>When a thread attaches a listener to a {@code ListenableFuture} that's already
   *             complete, the listener runs immediately in that thread.

    Ordering<Number> unusedC = objects.compound(numbers);

    Ordering<Integer> unusedD = numbers.compound(integers);
    Ordering<Integer> unusedE = integers.compound(numbers);

    // This works with three levels too (IDEA falsely reports errors as noted
    // below. Both javac and eclipse handle these cases correctly.)

    Ordering<Number> unusedF = numbers.compound(objects).compound(objects); // bad IDEA

    Ordering<Number> unusedC = objects.compound(numbers);

    Ordering<Integer> unusedD = numbers.compound(integers);
    Ordering<Integer> unusedE = integers.compound(numbers);

    // This works with three levels too (IDEA falsely reports errors as noted
    // below. Both javac and eclipse handle these cases correctly.)

    Ordering<Number> unusedF = numbers.compound(objects).compound(objects); // bad IDEA

    return ImmutableList.copyOf(SORTED_NUMBER_NAMES.subList(i, j));
  }

  private static final ImmutableList<String> NUMBER_NAMES =
      ImmutableList.of("one", "two", "three", "four", "five", "six", "seven");

  private static final ImmutableList<String> SORTED_NUMBER_NAMES =
      Ordering.<String>natural().immutableSortedCopy(NUMBER_NAMES);

  /**
   * Returns {@code true} if this instance falls within the range (as defined by <a
   * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html">the HTTP Accept header</a>) given
   * by the argument according to three criteria:
   *
   * <ol>
   *   <li>The type of the argument is the wildcard or equal to the type of this instance.
   *   <li>The subtype of the argument is the wildcard or equal to the subtype of this instance.

 *  Breaking: Rename `RecordedRequest.path` to `RecordedRequest.target`. (This property is
    _sometimes_ a path, but it can also be a path and query, or a full URL.)

 *  Breaking: Decompose the `RecordedRequest.requestLine` into three properties, `method`, `target`,
    and `version`. This better suits HTTP/2 where the request line had to be synthesized from
    component headers.