code: public final boolean cancel(@NonNull final String tag, final boolean mayInterrupt) {
          final Integer id = mTaggedRequests.get(tag);
          //noinspection SimplifiableIfStatement
          if (id != null) {
              return cancel(id, mayInterrupt);
          } else {
              return false;
          }
      }
docs: Cancels operation launch by its tag. May not physically kill the background thread, but it is
  guaranteed that the result of the operation will not be delivered to any ServiceConnector.
  
  @param tag          a pre-cache key of the operation launch that should be cancelled
  @param mayInterrupt {@code true} if threads executing operations task should be interrupted;
  otherwise, in-progress tasks are allowed to complete
  @return {@code false} if the task could not be cancelled, typically because it has already
  completed normally or there is no running operation with a given tag; {@code true} otherwise
  @see #invoke(ChronosOperation, boolean)
  @see #invoke(ChronosOperation, String, boolean)
  @see #cancel(int, boolean)
  @see Chronos#cancelAll(boolean)