We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
message_filters: Incorporate python approximate time synchronizer
https://github.com/ros-perception/image_pipeline/issues/76


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `utilities/message_filters/src/message_filters/__init__.py`
Content:
```
1 # Copyright (c) 2009, Willow Garage, Inc.
2 # All rights reserved.
3 #
4 # Redistribution and use in source and binary forms, with or without
5 # modification, are permitted provided that the following conditions are met:
6 #
7 #     * Redistributions of source code must retain the above copyright
8 #       notice, this list of conditions and the following disclaimer.
9 #     * Redistributions in binary form must reproduce the above copyright
10 #       notice, this list of conditions and the following disclaimer in the
11 #       documentation and/or other materials provided with the distribution.
12 #     * Neither the name of the Willow Garage, Inc. nor the names of its
13 #       contributors may be used to endorse or promote products derived from
14 #       this software without specific prior written permission.
15 #
16 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 # ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
20 # LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 # CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 # SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 # INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 # CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 # POSSIBILITY OF SUCH DAMAGE.
27 
28 """
29 Message Filter Objects
30 ======================
31 """
32 
33 import threading
34 import rospy
35 
36 class SimpleFilter:
37 
38     def __init__(self):
39         self.callbacks = {}
40 
41     def registerCallback(self, cb, *args):
42         """
43         Register a callback function `cb` to be called when this filter
44         has output.
45         The filter calls the function ``cb`` with a filter-dependent list of arguments,
46         followed by the call-supplied arguments ``args``.
47         """
48 
49         conn = len(self.callbacks)
50         self.callbacks[conn] = (cb, args)
51         return conn
52 
53     def signalMessage(self, *msg):
54         for (cb, args) in self.callbacks.values():
55             cb(*(msg + args))
56 
57 class Subscriber(SimpleFilter):
58     
59     """
60     ROS subscription filter.  Identical arguments as :class:`rospy.Subscriber`.
61 
62     This class acts as a highest-level filter, simply passing messages
63     from a ROS subscription through to the filters which have connected
64     to it.
65     """
66     def __init__(self, *args, **kwargs):
67         SimpleFilter.__init__(self)
68         self.topic = args[0]
69         kwargs['callback'] = self.callback
70         self.sub = rospy.Subscriber(*args, **kwargs)
71 
72     def callback(self, msg):
73         self.signalMessage(msg)
74 
75     def getTopic(self):
76         return self.topic
77 
78 class Cache(SimpleFilter):
79 
80     """
81     Stores a time history of messages.
82 
83     Given a stream of messages, the most recent ``cache_size`` messages
84     are cached in a ring buffer, from which time intervals of the cache
85     can then be retrieved by the client.
86     """
87 
88     def __init__(self, f, cache_size = 1):
89         SimpleFilter.__init__(self)
90         self.connectInput(f)
91         self.cache_size = cache_size
92 
93     def connectInput(self, f):
94         self.incoming_connection = f.registerCallback(self.add)
95 
96     def add(self, msg):
97         # Add msg to cache... XXX TODO
98 
99         self.signalMessage(msg)
100 
101 class TimeSynchronizer(SimpleFilter):
102 
103     """
104     Synchronizes messages by their timestamps.
105 
106     :class:`TimeSynchronizer` synchronizes incoming message filters by the
107     timestamps contained in their messages' headers. TimeSynchronizer
108     listens on multiple input message filters ``fs``, and invokes the callback
109     when it has a collection of messages with matching timestamps.
110 
111     The signature of the callback function is::
112 
113         def callback(msg1, ... msgN):
114 
115     where N is the number of input message filters, and each message is
116     the output of the corresponding filter in ``fs``.
117     The required ``queue size`` parameter specifies how many sets of
118     messages it should store from each input filter (by timestamp)
119     while waiting for messages to arrive and complete their "set".
120     """
121 
122     def __init__(self, fs, queue_size):
123         SimpleFilter.__init__(self)
124         self.connectInput(fs)
125         self.queue_size = queue_size
126         self.lock = threading.Lock()
127 
128     def connectInput(self, fs):
129         self.queues = [{} for f in fs]
130         self.input_connections = [f.registerCallback(self.add, q) for (f, q) in zip(fs, self.queues)]
131 
132     def add(self, msg, my_queue):
133         self.lock.acquire()
134         my_queue[msg.header.stamp] = msg
135         while len(my_queue) > self.queue_size:
136             del my_queue[min(my_queue)]
137         # common is the set of timestamps that occur in all queues
138         common = reduce(set.intersection, [set(q) for q in self.queues])
139         for t in sorted(common):
140             # msgs is list of msgs (one from each queue) with stamp t
141             msgs = [q[t] for q in self.queues]
142             self.signalMessage(*msgs)
143             for q in self.queues:
144                 del q[t]
145         self.lock.release()
146
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/utilities/message_filters/src/message_filters/__init__.py b/utilities/message_filters/src/message_filters/__init__.py
--- a/utilities/message_filters/src/message_filters/__init__.py
+++ b/utilities/message_filters/src/message_filters/__init__.py
@@ -30,6 +30,7 @@
 ======================
 """
 
+import itertools
 import threading
 import rospy
 
@@ -143,3 +144,33 @@
             for q in self.queues:
                 del q[t]
         self.lock.release()
+
+class ApproximateTimeSynchronizer(TimeSynchronizer):
+
+    """
+    Approximately synchronizes messages by their timestamps.
+
+    :class:`ApproximateTimeSynchronizer` synchronizes incoming message filters by the
+    timestamps contained in their messages' headers. The API is the same as TimeSynchronizer
+    except for an extra `slop` parameter in the constructor that defines the delay (in seconds)
+    with which messages can be synchronized
+    """
+
+    def __init__(self, fs, queue_size, slop):
+        TimeSynchronizer.__init__(self, fs, queue_size)
+        self.slop = rospy.Duration.from_sec(slop)
+
+    def add(self, msg, my_queue):
+        self.lock.acquire()
+        my_queue[msg.header.stamp] = msg
+        while len(my_queue) > self.queue_size:
+            del my_queue[min(my_queue)]
+        for vv in itertools.product(*[list(q.keys()) for q in self.queues]):
+            qt = list(zip(self.queues, vv))
+            if ( ((max(vv) - min(vv)) < self.slop) and
+                (len([1 for q,t in qt if t not in q]) == 0) ):
+                msgs = [q[t] for q,t in qt]
+                self.signalMessage(*msgs)
+                for q,t in qt:
+                    del q[t]
+        self.lock.release()

{"golden_diff": "diff --git a/utilities/message_filters/src/message_filters/__init__.py b/utilities/message_filters/src/message_filters/__init__.py\n--- a/utilities/message_filters/src/message_filters/__init__.py\n+++ b/utilities/message_filters/src/message_filters/__init__.py\n@@ -30,6 +30,7 @@\n ======================\n \"\"\"\n \n+import itertools\n import threading\n import rospy\n \n@@ -143,3 +144,33 @@\n             for q in self.queues:\n                 del q[t]\n         self.lock.release()\n+\n+class ApproximateTimeSynchronizer(TimeSynchronizer):\n+\n+    \"\"\"\n+    Approximately synchronizes messages by their timestamps.\n+\n+    :class:`ApproximateTimeSynchronizer` synchronizes incoming message filters by the\n+    timestamps contained in their messages' headers. The API is the same as TimeSynchronizer\n+    except for an extra `slop` parameter in the constructor that defines the delay (in seconds)\n+    with which messages can be synchronized\n+    \"\"\"\n+\n+    def __init__(self, fs, queue_size, slop):\n+        TimeSynchronizer.__init__(self, fs, queue_size)\n+        self.slop = rospy.Duration.from_sec(slop)\n+\n+    def add(self, msg, my_queue):\n+        self.lock.acquire()\n+        my_queue[msg.header.stamp] = msg\n+        while len(my_queue) > self.queue_size:\n+            del my_queue[min(my_queue)]\n+        for vv in itertools.product(*[list(q.keys()) for q in self.queues]):\n+            qt = list(zip(self.queues, vv))\n+            if ( ((max(vv) - min(vv)) < self.slop) and\n+                (len([1 for q,t in qt if t not in q]) == 0) ):\n+                msgs = [q[t] for q,t in qt]\n+                self.signalMessage(*msgs)\n+                for q,t in qt:\n+                    del q[t]\n+        self.lock.release()\n", "issue": "message_filters: Incorporate python approximate time synchronizer\nhttps://github.com/ros-perception/image_pipeline/issues/76\n\n", "before_files": [{"content": "# Copyright (c) 2009, Willow Garage, Inc.\n# All rights reserved.\n#\n# Redistribution and use in source and binary forms, with or without\n# modification, are permitted provided that the following conditions are met:\n#\n#     * Redistributions of source code must retain the above copyright\n#       notice, this list of conditions and the following disclaimer.\n#     * Redistributions in binary form must reproduce the above copyright\n#       notice, this list of conditions and the following disclaimer in the\n#       documentation and/or other materials provided with the distribution.\n#     * Neither the name of the Willow Garage, Inc. nor the names of its\n#       contributors may be used to endorse or promote products derived from\n#       this software without specific prior written permission.\n#\n# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS \"AS IS\"\n# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE\n# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE\n# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR\n# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF\n# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS\n# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN\n# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)\n# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE\n# POSSIBILITY OF SUCH DAMAGE.\n\n\"\"\"\nMessage Filter Objects\n======================\n\"\"\"\n\nimport threading\nimport rospy\n\nclass SimpleFilter:\n\n    def __init__(self):\n        self.callbacks = {}\n\n    def registerCallback(self, cb, *args):\n        \"\"\"\n        Register a callback function `cb` to be called when this filter\n        has output.\n        The filter calls the function ``cb`` with a filter-dependent list of arguments,\n        followed by the call-supplied arguments ``args``.\n        \"\"\"\n\n        conn = len(self.callbacks)\n        self.callbacks[conn] = (cb, args)\n        return conn\n\n    def signalMessage(self, *msg):\n        for (cb, args) in self.callbacks.values():\n            cb(*(msg + args))\n\nclass Subscriber(SimpleFilter):\n    \n    \"\"\"\n    ROS subscription filter.  Identical arguments as :class:`rospy.Subscriber`.\n\n    This class acts as a highest-level filter, simply passing messages\n    from a ROS subscription through to the filters which have connected\n    to it.\n    \"\"\"\n    def __init__(self, *args, **kwargs):\n        SimpleFilter.__init__(self)\n        self.topic = args[0]\n        kwargs['callback'] = self.callback\n        self.sub = rospy.Subscriber(*args, **kwargs)\n\n    def callback(self, msg):\n        self.signalMessage(msg)\n\n    def getTopic(self):\n        return self.topic\n\nclass Cache(SimpleFilter):\n\n    \"\"\"\n    Stores a time history of messages.\n\n    Given a stream of messages, the most recent ``cache_size`` messages\n    are cached in a ring buffer, from which time intervals of the cache\n    can then be retrieved by the client.\n    \"\"\"\n\n    def __init__(self, f, cache_size = 1):\n        SimpleFilter.__init__(self)\n        self.connectInput(f)\n        self.cache_size = cache_size\n\n    def connectInput(self, f):\n        self.incoming_connection = f.registerCallback(self.add)\n\n    def add(self, msg):\n        # Add msg to cache... XXX TODO\n\n        self.signalMessage(msg)\n\nclass TimeSynchronizer(SimpleFilter):\n\n    \"\"\"\n    Synchronizes messages by their timestamps.\n\n    :class:`TimeSynchronizer` synchronizes incoming message filters by the\n    timestamps contained in their messages' headers. TimeSynchronizer\n    listens on multiple input message filters ``fs``, and invokes the callback\n    when it has a collection of messages with matching timestamps.\n\n    The signature of the callback function is::\n\n        def callback(msg1, ... msgN):\n\n    where N is the number of input message filters, and each message is\n    the output of the corresponding filter in ``fs``.\n    The required ``queue size`` parameter specifies how many sets of\n    messages it should store from each input filter (by timestamp)\n    while waiting for messages to arrive and complete their \"set\".\n    \"\"\"\n\n    def __init__(self, fs, queue_size):\n        SimpleFilter.__init__(self)\n        self.connectInput(fs)\n        self.queue_size = queue_size\n        self.lock = threading.Lock()\n\n    def connectInput(self, fs):\n        self.queues = [{} for f in fs]\n        self.input_connections = [f.registerCallback(self.add, q) for (f, q) in zip(fs, self.queues)]\n\n    def add(self, msg, my_queue):\n        self.lock.acquire()\n        my_queue[msg.header.stamp] = msg\n        while len(my_queue) > self.queue_size:\n            del my_queue[min(my_queue)]\n        # common is the set of timestamps that occur in all queues\n        common = reduce(set.intersection, [set(q) for q in self.queues])\n        for t in sorted(common):\n            # msgs is list of msgs (one from each queue) with stamp t\n            msgs = [q[t] for q in self.queues]\n            self.signalMessage(*msgs)\n            for q in self.queues:\n                del q[t]\n        self.lock.release()\n", "path": "utilities/message_filters/src/message_filters/__init__.py"}], "after_files": [{"content": "# Copyright (c) 2009, Willow Garage, Inc.\n# All rights reserved.\n#\n# Redistribution and use in source and binary forms, with or without\n# modification, are permitted provided that the following conditions are met:\n#\n#     * Redistributions of source code must retain the above copyright\n#       notice, this list of conditions and the following disclaimer.\n#     * Redistributions in binary form must reproduce the above copyright\n#       notice, this list of conditions and the following disclaimer in the\n#       documentation and/or other materials provided with the distribution.\n#     * Neither the name of the Willow Garage, Inc. nor the names of its\n#       contributors may be used to endorse or promote products derived from\n#       this software without specific prior written permission.\n#\n# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS \"AS IS\"\n# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE\n# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE\n# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR\n# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF\n# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS\n# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN\n# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)\n# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE\n# POSSIBILITY OF SUCH DAMAGE.\n\n\"\"\"\nMessage Filter Objects\n======================\n\"\"\"\n\nimport itertools\nimport threading\nimport rospy\n\nclass SimpleFilter:\n\n    def __init__(self):\n        self.callbacks = {}\n\n    def registerCallback(self, cb, *args):\n        \"\"\"\n        Register a callback function `cb` to be called when this filter\n        has output.\n        The filter calls the function ``cb`` with a filter-dependent list of arguments,\n        followed by the call-supplied arguments ``args``.\n        \"\"\"\n\n        conn = len(self.callbacks)\n        self.callbacks[conn] = (cb, args)\n        return conn\n\n    def signalMessage(self, *msg):\n        for (cb, args) in self.callbacks.values():\n            cb(*(msg + args))\n\nclass Subscriber(SimpleFilter):\n    \n    \"\"\"\n    ROS subscription filter.  Identical arguments as :class:`rospy.Subscriber`.\n\n    This class acts as a highest-level filter, simply passing messages\n    from a ROS subscription through to the filters which have connected\n    to it.\n    \"\"\"\n    def __init__(self, *args, **kwargs):\n        SimpleFilter.__init__(self)\n        self.topic = args[0]\n        kwargs['callback'] = self.callback\n        self.sub = rospy.Subscriber(*args, **kwargs)\n\n    def callback(self, msg):\n        self.signalMessage(msg)\n\n    def getTopic(self):\n        return self.topic\n\nclass Cache(SimpleFilter):\n\n    \"\"\"\n    Stores a time history of messages.\n\n    Given a stream of messages, the most recent ``cache_size`` messages\n    are cached in a ring buffer, from which time intervals of the cache\n    can then be retrieved by the client.\n    \"\"\"\n\n    def __init__(self, f, cache_size = 1):\n        SimpleFilter.__init__(self)\n        self.connectInput(f)\n        self.cache_size = cache_size\n\n    def connectInput(self, f):\n        self.incoming_connection = f.registerCallback(self.add)\n\n    def add(self, msg):\n        # Add msg to cache... XXX TODO\n\n        self.signalMessage(msg)\n\nclass TimeSynchronizer(SimpleFilter):\n\n    \"\"\"\n    Synchronizes messages by their timestamps.\n\n    :class:`TimeSynchronizer` synchronizes incoming message filters by the\n    timestamps contained in their messages' headers. TimeSynchronizer\n    listens on multiple input message filters ``fs``, and invokes the callback\n    when it has a collection of messages with matching timestamps.\n\n    The signature of the callback function is::\n\n        def callback(msg1, ... msgN):\n\n    where N is the number of input message filters, and each message is\n    the output of the corresponding filter in ``fs``.\n    The required ``queue size`` parameter specifies how many sets of\n    messages it should store from each input filter (by timestamp)\n    while waiting for messages to arrive and complete their \"set\".\n    \"\"\"\n\n    def __init__(self, fs, queue_size):\n        SimpleFilter.__init__(self)\n        self.connectInput(fs)\n        self.queue_size = queue_size\n        self.lock = threading.Lock()\n\n    def connectInput(self, fs):\n        self.queues = [{} for f in fs]\n        self.input_connections = [f.registerCallback(self.add, q) for (f, q) in zip(fs, self.queues)]\n\n    def add(self, msg, my_queue):\n        self.lock.acquire()\n        my_queue[msg.header.stamp] = msg\n        while len(my_queue) > self.queue_size:\n            del my_queue[min(my_queue)]\n        # common is the set of timestamps that occur in all queues\n        common = reduce(set.intersection, [set(q) for q in self.queues])\n        for t in sorted(common):\n            # msgs is list of msgs (one from each queue) with stamp t\n            msgs = [q[t] for q in self.queues]\n            self.signalMessage(*msgs)\n            for q in self.queues:\n                del q[t]\n        self.lock.release()\n\nclass ApproximateTimeSynchronizer(TimeSynchronizer):\n\n    \"\"\"\n    Approximately synchronizes messages by their timestamps.\n\n    :class:`ApproximateTimeSynchronizer` synchronizes incoming message filters by the\n    timestamps contained in their messages' headers. The API is the same as TimeSynchronizer\n    except for an extra `slop` parameter in the constructor that defines the delay (in seconds)\n    with which messages can be synchronized\n    \"\"\"\n\n    def __init__(self, fs, queue_size, slop):\n        TimeSynchronizer.__init__(self, fs, queue_size)\n        self.slop = rospy.Duration.from_sec(slop)\n\n    def add(self, msg, my_queue):\n        self.lock.acquire()\n        my_queue[msg.header.stamp] = msg\n        while len(my_queue) > self.queue_size:\n            del my_queue[min(my_queue)]\n        for vv in itertools.product(*[list(q.keys()) for q in self.queues]):\n            qt = list(zip(self.queues, vv))\n            if ( ((max(vv) - min(vv)) < self.slop) and\n                (len([1 for q,t in qt if t not in q]) == 0) ):\n                msgs = [q[t] for q,t in qt]\n                self.signalMessage(*msgs)\n                for q,t in qt:\n                    del q[t]\n        self.lock.release()\n", "path": "utilities/message_filters/src/message_filters/__init__.py"}]}