Add distribution context manager and decorator (#581)

Adding a new decorator for distribution

A decorator or context manager that will measure the distribution of a
function's/context's run time using custom metric DISTRIBUTION.

E.g. of usage follows:

    @statsd.distributed('user.query.time', sample_rate=0.5)
    def get_user(user_id):
        # Do what you need to ...
        pass

    # Is equivalent to ...
    with statsd.distributed('user.query.time', sample_rate=0.5):
        # Do what you need to ...
        pass

    # Is equivalent to ...
    start = time.time()
    try:
        get_user(user_id)
    finally:
        statsd.distribution('user.query.time', time.time() - start)

datadog/dogstatsd/base.py

@@ -16,7 +16,10 @@
 from threading import Lock
 
 # datadog
-from datadog.dogstatsd.context import TimedContextManagerDecorator
+from datadog.dogstatsd.context import (
+    TimedContextManagerDecorator,
+    DistributedContextManagerDecorator,
+)
 from datadog.dogstatsd.route import get_default_route
 from datadog.util.compat import text
 from datadog.util.format import normalize_tags
@@ -375,6 +378,34 @@ def get_user(user_id):
         """
         return TimedContextManagerDecorator(self, metric, tags, sample_rate, use_ms)
 
+    def distributed(self, metric=None, tags=None, sample_rate=None, use_ms=None):
+        """
+        A decorator or context manager that will measure the distribution of a
+        function's/context's run time using custom metric distribution.
+        Optionally specify a list of tags or a sample rate. If the metric is not
+        defined as a decorator, the module name and function name will be used.
+        The metric is required as a context manager.
+        ::
+
+            @statsd.distributed('user.query.time', sample_rate=0.5)
+            def get_user(user_id):
+                # Do what you need to ...
+                pass
+
+            # Is equivalent to ...
+            with statsd.distributed('user.query.time', sample_rate=0.5):
+                # Do what you need to ...
+                pass
+
+            # Is equivalent to ...
+            start = time.time()
+            try:
+                get_user(user_id)
+            finally:
+                statsd.distribution('user.query.time', time.time() - start)
+        """
+        return DistributedContextManagerDecorator(self, metric, tags, sample_rate, use_ms)
+
     def set(self, metric, value, tags=None, sample_rate=None):
         """
         Sample a set value.

datadog/dogstatsd/context.py

@@ -17,6 +17,7 @@ class TimedContextManagerDecorator(object):
     """
     def __init__(self, statsd, metric=None, tags=None, sample_rate=1, use_ms=None):
         self.statsd = statsd
+        self.timing_func = statsd.timing
         self.metric = metric
         self.tags = tags
         self.sample_rate = sample_rate
@@ -60,11 +61,21 @@ def _send(self, start):
         elapsed = time() - start
         use_ms = self.use_ms if self.use_ms is not None else self.statsd.use_ms
         elapsed = int(round(1000 * elapsed)) if use_ms else elapsed
-        self.statsd.timing(self.metric, elapsed, self.tags, self.sample_rate)
+        self.timing_func(self.metric, elapsed, self.tags, self.sample_rate)
         self.elapsed = elapsed
 
     def start(self):
         self.__enter__()
 
     def stop(self):
         self.__exit__(None, None, None)
+
+
+class DistributedContextManagerDecorator(TimedContextManagerDecorator):
+    """
+    A context manager and a decorator which will report the elapsed time in
+    the context OR in a function call using the custom distribution metric.
+    """
+    def __init__(self, statsd, metric=None, tags=None, sample_rate=1, use_ms=None):
+        super(DistributedContextManagerDecorator, self).__init__(statsd, metric, tags, sample_rate, use_ms)
+        self.timing_func = statsd.distribution

tests/unit/dogstatsd/test_statsd.py

@@ -379,6 +379,50 @@ def test_socket_overflown(self):
             c = [call("Socket send would block: Socket error, dropping the packet")]
             mock_log.warning.assert_has_calls(c * 2)
 
+    def test_distributed(self):
+        """
+        Measure the distribution of a function's run time using distribution custom metric.
+        """
+        # In seconds
+        @self.statsd.distributed('distributed.test')
+        def func(a, b, c=1, d=1):
+            """docstring"""
+            time.sleep(0.5)
+            return (a, b, c, d)
+
+        assert_equal('func', func.__name__)
+        assert_equal('docstring', func.__doc__)
+
+        result = func(1, 2, d=3)
+        # Assert it handles args and kwargs correctly.
+        assert_equal(result, (1, 2, 1, 3))
+
+        packet = self.recv(2).split("\n")[0] # ignore telemetry packet
+        name_value, type_ = packet.split('|')
+        name, value = name_value.split(':')
+
+        assert_equal('d', type_)
+        assert_equal('distributed.test', name)
+        self.assert_almost_equal(0.5, float(value), 0.1)
+
+        # Repeat, force timer value in milliseconds
+        @self.statsd.distributed('distributed.test', use_ms=True)
+        def func(a, b, c=1, d=1):
+            """docstring"""
+            time.sleep(0.5)
+            return (a, b, c, d)
+
+        func(1, 2, d=3)
+
+        packet = self.recv(2).split("\n")[0] # ignore telemetry packet
+        name_value, type_ = packet.split('|')
+        name, value = name_value.split(':')
+
+        assert_equal('d', type_)
+        assert_equal('distributed.test', name)
+        self.assert_almost_equal(500, float(value), 100)
+
+
     def test_timed(self):
         """
         Measure the distribution of a function's run time.