Patch #428326: New class threading.Timer.

Doc/lib/libthreading.tex

@@ -82,6 +82,10 @@ semaphore is released too many times it's a sign of a bug.  If not given,
 A class that represents a thread of control.  This class can be safely subclassed in a limited fashion.
 \end{classdesc*}
 
+\begin{classdesc*}{Timer}{}
+A thread that executes a function after a specified interval has passed.
+\end{classdesc*}
+
 Detailed interfaces for the objects are documented below.  
 
 The design of this module is loosely based on Java's threading model.
@@ -595,3 +599,35 @@ The initial value is inherited from the creating thread.
 The entire Python program exits when no active non-daemon
 threads are left.
 \end{methoddesc}
+
+
+\subsection{Timer Objects \label{timer-objects}}
+
+This class represents an action that should be run only after a certain amount
+of time has passed --- a timer. \class{Timer} is a subclass of \class{Thread} and
+as such also functions as an example of creating custom threads.
+
+Timers are started, as with threads, by calling their \method{start()} method. The
+timer can be stopped (before its action has begun) by calling the
+\method{cancel()} method. The interval the timer will wait before executing
+its action may not be exactly the same as the interval specified by the
+user.
+
+For example:
+\begin{verbatim}
+def hello():
+    print "hello, world"
+
+t = Timer(30.0, hello)
+t.start() # after 30 seconds, "hello, world" will be printed
+\end{verbatim}
+
+\begin{classdesc}{Timer}{interval, function, args=[], kwargs=\{\}}
+Create a timer that will run \var{function} with arguments \var{args} and 
+keyword arguments \var{kwargs}, after \var{interval} seconds have passed.
+\end{classdesc}
+
+\begin{methoddesc}{cancel}{}
+Stop the timer, and cancel the execution of the timer's action. This will only
+work if the timer is still in its waiting stage.
+\end{methoddesc}

Lib/threading.py

@@ -331,7 +331,6 @@ class _Event(_Verbose):
             self.__cond.wait(timeout)
         self.__cond.release()
 
-
 # Helper to generate new thread names
 _counter = 0
 def _newname(template="Thread-%d"):
@@ -483,6 +482,36 @@ class Thread(_Verbose):
         assert not self.__started, "cannot set daemon status of active thread"
         self.__daemonic = daemonic
 
+# The timer class was contributed by Itamar Shtull-Trauring
+
+def Timer(*args, **kwargs):
+    return _Timer(*args, **kwargs)
+
+class _Timer(Thread):
+    """Call a function after a specified number of seconds:
+    
+    t = Timer(30.0, f, args=[], kwargs={})
+    t.start()
+    t.cancel() # stop the timer's action if it's still waiting
+    """
+    
+    def __init__(self, interval, function, args=[], kwargs={}):
+        Thread.__init__(self)
+        self.interval = interval
+        self.function = function
+        self.args = args
+        self.kwargs = kwargs
+        self.finished = Event()
+    
+    def cancel(self):
+        """Stop the timer if it hasn't finished yet"""
+        self.finished.set()
+    
+    def run(self):
+        self.finished.wait(self.interval)
+        if not self.finished.isSet():
+            self.function(*self.args, **self.kwargs)
+        self.finished.set()
 
 # Special thread class to represent the main thread
 # This is garbage collected through an exit handler

Misc/NEWS

@@ -81,6 +81,9 @@ Core
 
 Library
 
+- Asynchronous timeout actions are available through the new class
+  threading.Timer.
+
 - math.log and math.log10 now return sensible results for even huge
   long arguments.  For example, math.log10(10 ** 10000) ~= 10000.0.