times for the same *path operation*, for example, multiple dependencies have a common sub-dependency, **FastAPI** will know to call that sub-dependency only once per request.

And it will save the returned value in a <abbr title="A utility/system to store computed/generated values, to reuse them instead of computing them again.">"cache"</abbr> and pass it to all the "dependants" that need it in that specific request, instead of calling the dependency multiple times for the same request....

// An Update function must be set to provide an updated value when needed.
type Cache[T any] struct {
	// updateFn must return an updated value.
	// If an error is returned the cached value is not set.
	// Only one caller will call this function at any time, others will be blocking.
	// The returned value can no longer be modified once returned.
	// Should be set before calling Get().
	updateFn func(ctx context.Context) (T, error)

```

This behavior is consistent across all keys; each key self-documents itself with valid examples.

## Dynamic systems without restarting server

The following sub-systems are dynamic i.e., configuration parameters for each sub-systems can be changed while the server is running without any restarts.

```
api                   manage global HTTP API call specific features, such as throttling, authentication types, etc.

 *
 * @author David Beaumont
 */
@GwtCompatible
final class UrlEscaperTesting {
  /**
   * Helper to assert common expected behaviour of uri escapers. You should call
   * assertBasicUrlEscaper() unless the escaper explicitly does not escape '%'.
   */
  static void assertBasicUrlEscaperExceptPercent(UnicodeEscaper e) {
    // URL escapers should throw null pointer exceptions for null input

       *
       * - In deleteDirectoryContents, the path argument may have no parent. Fortunately, all the
       *   *other* paths we process will be descendants of that. That leaves only the original path
       *   argument for us to consider. And the only place we call pathNotFound is from
       *   throwDeleteFailed, and the other place that we call throwDeleteFailed inside

     */
    ModelBuildingResult build(ModelBuildingRequest request) throws ModelBuildingException;

    /**
     * Builds the effective model by completing the specified interim result which was produced by a previous call to
     * {@link #build(ModelBuildingRequest)} with {@link ModelBuildingRequest#isTwoPhaseBuilding()} being {@code true}.
     * The model building request passed to this method must be the same as the one used for the first phase of the

 *
 * @author David Beaumont
 */
@GwtCompatible
final class UrlEscaperTesting {
  /**
   * Helper to assert common expected behaviour of uri escapers. You should call
   * assertBasicUrlEscaper() unless the escaper explicitly does not escape '%'.
   */
  static void assertBasicUrlEscaperExceptPercent(UnicodeEscaper e) {
    // URL escapers should throw null pointer exceptions for null input

        classes.put(fullyQualifiedClassName, metaData);
    }

    @Override
    public void each(Closure cl) {
        for (Map.Entry<String, T> entry : classes.entrySet()) {
            cl.call(new Object[]{entry.getKey(), entry.getValue()});
        }
    }

    public void each(Action<? super T> action) {
        for (T t : classes.values()) {
            action.execute(t);
        }
    }

                            bufDataStart + dataDisplacement, dataCount );
            bufferIndex += dataCount;
        }

        /* Check to see if the entire transaction has been
         * read. If so call the read methods.
         */

        if( !parametersDone &&
                ( parameterDisplacement + parameterCount ) == totalParameterCount) {
            parametersDone = true;
        }

	if index < dynamicTimeoutLogSize {
		dt.mutex.Lock()
		dt.log[index] = duration

		// We leak entries while we copy
		if entries == dynamicTimeoutLogSize {

			// Make copy on stack in order to call adjust()
			logCopy := [dynamicTimeoutLogSize]time.Duration{}
			copy(logCopy[:], dt.log[:])

			// reset log entries
			atomic.StoreInt64(&dt.entries, 0)
			dt.mutex.Unlock()

			dt.adjust(logCopy)