<p class="rule">
The completion of a single call of <code>f()</code> from <code>once.Do(f)</code>
is synchronized before the return of any call of <code>once.Do(f)</code>.
</p>

<p>
In this program:
</p>

<pre>
var a string
var once sync.Once

func setup() {
	a = "hello, world"
}

func doprint() {
	once.Do(setup)
	print(a)
}

func twoprint() {
	go doprint()

   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
   * write, and twice for each cache loading computation (once prior to loading the new value, and
   * once after loading completes). Much internal cache management is performed at the segment

	"fmt"
	"net/url"
	"os"
	"path/filepath"
	"time"

	mqtt "github.com/eclipse/paho.mqtt.golang"
	"github.com/minio/minio/internal/event"
	"github.com/minio/minio/internal/logger"
	"github.com/minio/minio/internal/once"
	"github.com/minio/minio/internal/store"
	xnet "github.com/minio/pkg/v3/net"
)

const (
	reconnectInterval = 5 * time.Second
	storePrefix       = "minio"
)

// MQTT input constants
const (

    }

    @Test
    void testSetURLStreamHandlerFactory_ThrowsIllegalStateExceptionOnSecondAttempt() {
        // This test ensures that attempting to set the URLStreamHandlerFactory more than once
        // throws an IllegalStateException as per the contract.
        URLStreamHandlerFactory mockFactory1 = mock(URLStreamHandlerFactory.class);
        URLStreamHandlerFactory mockFactory2 = mock(URLStreamHandlerFactory.class);

      throws TimeoutException, ExecutionException {
    SettableFuture<String> future = SettableFuture.create();
    future.set(RESULT);
    /*
     * getUninterruptibly should call the timed get method once with a
     * wait of 0 seconds (and it should succeed, since the result is already
     * available).
     */
    assertThat(getUninterruptibly(future, 0, SECONDS)).isEqualTo(RESULT);
  }

  Just then her head struck against the roof of the hall:  in
fact she was now more than nine feet high, and she at once took
up the little golden key and hurried off to the garden door.

  Poor Alice!  It was as much as she could do, lying down on one
side, to look through into the garden with one eye; but to get
through was more hopeless than ever:  she sat down and began to
cry again.

#   DefaultVersionResolverRequest    - Version resolution results (session/soft, less critical than artifacts)
#   RgavCacheKey                     - BOM import caching (session/soft, typically resolved once)
#   DefaultModelBuilderRequest       - Model building operations (none, ensures fresh dynamic builds)
#   *                                - Fallback for all other requests (request/soft for temporary child request caching)
#

	ctx = context.WithValue(ctx, healthDiskCtxKey{}, &healthDiskCtxValue{lastSuccess: &p.health.lastSuccess})
	si := p.updateStorageMetrics(s, paths...)
	var once sync.Once
	return ctx, func(sz int64, errp *error) {
		p.health.waiting.Add(-1)
		once.Do(func() {
			if errp != nil {
				err := *errp
				if err == nil || errors.Is(err, io.EOF) {
					p.health.logSuccess()
				}
			}
			si(sz, errp)
		})

            new Function<AnEnum, AnEnum>() {
              boolean used = false;

              @Override
              public AnEnum apply(AnEnum ae) {
                checkState(!used, "should not be applied more than once");
                used = true;
                return ae;
              }
            });
    ImmutableMap<AnEnum, AnEnum> copy = immutableEnumMap(map);

  // TODO: replace this with an accessor.
  protected Collection<E> collection;

  @Override
  protected Collection<E> actualContents() {
    return collection;
  }

  // TODO: dispose of this once collection is encapsulated.
  @Override
  @CanIgnoreReturnValue
  protected Collection<E> resetContainer(Collection<E> newContents) {
    collection = super.resetContainer(newContents);
    return collection;
  }