<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <link rel="STYLESHEET" href="lib.css" type='text/css' /> <link rel="SHORTCUT ICON" href="../icons/pyfav.gif" /> <link rel='start' href='../index.html' title='Python Documentation Index' /> <link rel="first" href="lib.html" title='Python Library Reference' /> <link rel='contents' href='contents.html' title="Contents" /> <link rel='index' href='genindex.html' title='Index' /> <link rel='last' href='about.html' title='About this document...' /> <link rel='help' href='about.html' title='About this document...' /> <LINK rel="next" href="thread-objects.html"> <LINK rel="prev" href="semaphore-objects.html"> <LINK rel="parent" href="module-threading.html"> <LINK rel="next" href="thread-objects.html"> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <meta name='aesop' content='information' /> <META name="description" content="Event Objects "> <META name="keywords" content="lib"> <META name="resource-type" content="document"> <META name="distribution" content="global"> <title>7.5.5 Event Objects </title> </head> <body> <DIV CLASS="navigation"> <div id='top-navigation-panel'> <table align="center" width="100%" cellpadding="0" cellspacing="2"> <tr> <td class='online-navigation'><a rel="prev" title="7.5.4.1 Semaphore Example" href="semaphore-examples.html"><img src='../icons/previous.png' border='0' height='32' alt='Previous Page' width='32' /></A></td> <td class='online-navigation'><a rel="parent" title="7.5 threading " href="module-threading.html"><img src='../icons/up.png' border='0' height='32' alt='Up One Level' width='32' /></A></td> <td class='online-navigation'><a rel="next" title="7.5.6 Thread Objects" href="thread-objects.html"><img src='../icons/next.png' border='0' height='32' alt='Next Page' width='32' /></A></td> <td align="center" width="100%">Python Library Reference</td> <td class='online-navigation'><a rel="contents" title="Table of Contents" href="contents.html"><img src='../icons/contents.png' border='0' height='32' alt='Contents' width='32' /></A></td> <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' border='0' height='32' alt='Module Index' width='32' /></a></td> <td class='online-navigation'><a rel="index" title="Index" href="genindex.html"><img src='../icons/index.png' border='0' height='32' alt='Index' width='32' /></A></td> </tr></table> <div class='online-navigation'> <b class="navlabel">Previous:</b> <a class="sectref" rel="prev" href="semaphore-examples.html">7.5.4.1 Semaphore Example</A> <b class="navlabel">Up:</b> <a class="sectref" rel="parent" href="module-threading.html">7.5 threading </A> <b class="navlabel">Next:</b> <a class="sectref" rel="next" href="thread-objects.html">7.5.6 Thread Objects</A> </div> <hr /></div> </DIV> <!--End of Navigation Panel--> <H2><A NAME="SECTION009550000000000000000"><!--x--></A><A NAME="event-objects"><!--z--></A> <BR> 7.5.5 Event Objects </H2> <P> This is one of the simplest mechanisms for communication between threads: one thread signals an event and other threads wait for it. <P> An event object manages an internal flag that can be set to true with the <tt class="method">set()</tt> method and reset to false with the <tt class="method">clear()</tt> method. The <tt class="method">wait()</tt> method blocks until the flag is true. <P> <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-2537' class="class">Event</tt></b>(</nobr></td> <td>)</td></tr></table></dt> <dd> The internal flag is initially false. </dl> <P> <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> <td><nobr><b><tt id='l2h-2538' class="method">isSet</tt></b>(</nobr></td> <td>)</td></tr></table></dt> <dd> Return true if and only if the internal flag is true. </dl> <P> <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> <td><nobr><b><tt id='l2h-2539' class="method">set</tt></b>(</nobr></td> <td>)</td></tr></table></dt> <dd> Set the internal flag to true. All threads waiting for it to become true are awakened. Threads that call <tt class="method">wait()</tt> once the flag is true will not block at all. </dl> <P> <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> <td><nobr><b><tt id='l2h-2540' class="method">clear</tt></b>(</nobr></td> <td>)</td></tr></table></dt> <dd> Reset the internal flag to false. Subsequently, threads calling <tt class="method">wait()</tt> will block until <tt class="method">set()</tt> is called to set the internal flag to true again. </dl> <P> <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> <td><nobr><b><tt id='l2h-2541' class="method">wait</tt></b>(</nobr></td> <td><big>[</big><var>timeout</var><big>]</big>)</td></tr></table></dt> <dd> Block until the internal flag is true. If the internal flag is true on entry, return immediately. Otherwise, block until another thread calls <tt class="method">set()</tt> to set the flag to true, or until the optional timeout occurs. <P> When the timeout argument is present and not <code>None</code>, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof). </dl> <P> <DIV CLASS="navigation"> <div class='online-navigation'><hr /> <table align="center" width="100%" cellpadding="0" cellspacing="2"> <tr> <td class='online-navigation'><a rel="prev" title="7.5.4.1 Semaphore Example" rel="prev" title="7.5.4.1 Semaphore Example" href="semaphore-examples.html"><img src='../icons/previous.png' border='0' height='32' alt='Previous Page' width='32' /></A></td> <td class='online-navigation'><a rel="parent" title="7.5 threading " rel="parent" title="7.5 threading " href="module-threading.html"><img src='../icons/up.png' border='0' height='32' alt='Up One Level' width='32' /></A></td> <td class='online-navigation'><a rel="next" title="7.5.6 Thread Objects" rel="next" title="7.5.6 Thread Objects" href="thread-objects.html"><img src='../icons/next.png' border='0' height='32' alt='Next Page' width='32' /></A></td> <td align="center" width="100%">Python Library Reference</td> <td class='online-navigation'><a rel="contents" title="Table of Contents" rel="contents" title="Table of Contents" href="contents.html"><img src='../icons/contents.png' border='0' height='32' alt='Contents' width='32' /></A></td> <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' border='0' height='32' alt='Module Index' width='32' /></a></td> <td class='online-navigation'><a rel="index" title="Index" rel="index" title="Index" href="genindex.html"><img src='../icons/index.png' border='0' height='32' alt='Index' width='32' /></A></td> </tr></table> <div class='online-navigation'> <b class="navlabel">Previous:</b> <a class="sectref" rel="prev" href="semaphore-examples.html">7.5.4.1 Semaphore Example</A> <b class="navlabel">Up:</b> <a class="sectref" rel="parent" href="module-threading.html">7.5 threading </A> <b class="navlabel">Next:</b> <a class="sectref" rel="next" href="thread-objects.html">7.5.6 Thread Objects</A> </div> </div> <hr /> <span class="release-info">Release 2.3.4, documentation updated on May 20, 2004.</span> </DIV> <!--End of Navigation Panel--> <ADDRESS> See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. </ADDRESS> </BODY> </HTML>
