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<title>7.5.5 Event Objects
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<H2><A NAME=
"SECTION009550000000000000000"></A><A NAME=
"event-objects"></A>
This is one of the simplest mechanisms for communication between
threads: one thread signals an event and other threads wait for it.
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.
<dl><dt><table cellpadding=
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"0"><tr valign=
"baseline">
<td><nobr><b><span class=
"typelabel">class
</span> <tt id='l2h-
2733' xml:id='l2h-
2733'
class=
"class">Event
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
The internal flag is initially false.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
2734' xml:id='l2h-
2734'
class=
"method">isSet
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
Return true if and only if the internal flag is true.
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
2735' xml:id='l2h-
2735'
class=
"method">set
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
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
<dl><dt><table cellpadding=
"0" cellspacing=
"0"><tr valign=
"baseline">
<td><nobr><b><tt id='l2h-
2736' xml:id='l2h-
2736'
class=
"method">clear
</tt></b>(
</nobr></td>
<td><var></var>)
</td></tr></table></dt>
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.
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<td><nobr><b><tt id='l2h-
2737' xml:id='l2h-
2737'
class=
"method">wait
</tt></b>(
</nobr></td>
<td><var></var><big>[
</big><var>timeout
</var><big>]
</big><var></var>)
</td></tr></table></dt>
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.
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).
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<span class=
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2005.
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