/**
* Instances of this class are responsible for managing the
* connection between SWT and the underlying operating
* system. Their most important function is to implement
* the SWT event loop in terms of the platform event model.
* They also provide various methods for accessing information
* about the operating system, and have overall control over
* the operating system resources which SWT allocates.
* <p>
* Applications which are built with SWT will <em>almost always</em>
* require only a single display. In particular, some platforms
* which SWT supports will not allow more than one <em>active</em>
* display. In other words, some platforms do not support
* creating a new display if one already exists that has not been
* sent the <code>dispose()</code> message.
* <p>
* In SWT, the thread which creates a <code>Display</code>
* instance is distinguished as the <em>user-interface thread</em>
* for that display.
* </p>
* The user-interface thread for a particular display has the
* following special attributes:
* <ul>
* <li>
* The event loop for that display must be run from the thread.
* </li>
* <li>
* Some SWT API methods (notably, most of the public methods in
* <code>Widget</code> and its subclasses), may only be called
* from the thread. (To support multi-threaded user-interface
* applications, class <code>Display</code> provides inter-thread
* communication methods which allow threads other than the
* user-interface thread to request that it perform operations
* on their behalf.)
* </li>
* <li>
* The thread is not allowed to construct other
* <code>Display</code>s until that display has been disposed.
* (Note that, this is in addition to the restriction mentioned
* above concerning platform support for multiple displays. Thus,
* the only way to have multiple simultaneously active displays,
* even on platforms which support it, is to have multiple threads.)
* </li>
* </ul>
* Enforcing these attributes allows SWT to be implemented directly
* on the underlying operating system's event model. This has
* numerous benefits including smaller footprint, better use of
* resources, safer memory management, clearer program logic,
* better performance, and fewer overall operating system threads
* required. The down side however, is that care must be taken
* (only) when constructing multi-threaded applications to use the
* inter-thread communication mechanisms which this class provides
* when required.
* </p><p>
* All SWT API methods which may only be called from the user-interface
* thread are distinguished in their documentation by indicating that
* they throw the "<code>ERROR_THREAD_INVALID_ACCESS</code>"
* SWT exception.
* </p>
* <dl>
* <dt><b>Styles:</b></dt>
* <dd>(none)</dd>
* <dt><b>Events:</b></dt>
* <dd>Close, Dispose, OpenDocument, Settings, Skin</dd>
* </dl>
* <p>
* IMPORTANT: This class is <em>not</em> intended to be subclassed.
* </p>
* @see #syncExec
* @see #asyncExec
* @see #wake
* @see #readAndDispatch
* @see #sleep
* @see Device#dispose
* @see <a href="http://www.eclipse.org/swt/snippets/#display">Display snippets</a>
* @see <a href="http://www.eclipse.org/swt/%22%3ESample code and further information</a>
* @noextend This class is not intended to be subclassed by clients.
*/