Returns the thread that has invoked <code>syncExec</code>
or null if no such runnable is currently being invoked by
the user-interface thread.
<p>
Note: If a runnable invoked by asyncExec is currently
running, this method will return null.
</p>
@return the receiver's sync-interface thread
@exception SWTException <ul>
<li>ERROR_DEVICE_DISPOSED - if the receiver has been disposed</li>
</ul>
Returns the thread that has invoked <code>syncExec</code> or null if no such runnable is currently being invoked by the user-interface thread. <p> Note: If a runnable invoked by asyncExec is currently running, this method will return null. </p>
@return the receiver's sync-interface thread
@exception SWTException <ul> <li>ERROR_DEVICE_DISPOSED - if the receiver has been disposed</li> </ul>