From afb9db9033603427eceee4cbc81a4102423a8b09 Mon Sep 17 00:00:00 2001
From: Tristan Colgate <tristan@qubit.com>
Date: Fri, 31 Aug 2018 08:33:25 +0100
Subject: [PATCH] Add detailed Garbage Collection statistics.

This patch adds details stats for the python garbage collector.

- `python_gc_collected_objects`: Histogram of the number of objects collected, by GC generation.
- `python_gc_uncollectable_objects`: Histogram of the number of objects count to be uncollectable, by GC generation.
- `python_gc_duration_seconds`: Histogram of the duration of each GC generation.

Signed-off-by: Tristan Colgate <tristan@qubit.com>
---
 prometheus_client/__init__.py     |  3 ++
 prometheus_client/gc_collector.py | 59 +++++++++++++++++++++++++++++++
 tests/test_gc_collector.py        | 54 ++++++++++++++++++++++++++++
 3 files changed, 116 insertions(+)
 create mode 100644 prometheus_client/gc_collector.py
 create mode 100644 tests/test_gc_collector.py

diff --git a/prometheus_client/__init__.py b/prometheus_client/__init__.py
index 8208d458..3a239353 100644
--- a/prometheus_client/__init__.py
+++ b/prometheus_client/__init__.py
@@ -4,6 +4,7 @@
 from . import exposition
 from . import process_collector
 from . import platform_collector
+from . import gc_collector
 
 __all__ = ['Counter', 'Gauge', 'Summary', 'Histogram', 'Info', 'Enum']
 
@@ -35,6 +36,8 @@
 PlatformCollector = platform_collector.PlatformCollector
 PLATFORM_COLLECTOR = platform_collector.PLATFORM_COLLECTOR
 
+GCCollector = gc_collector.GCCollector
+GC_COLLECTOR = gc_collector.GC_COLLECTOR
 
 if __name__ == '__main__':
     c = Counter('cc', 'A counter')
diff --git a/prometheus_client/gc_collector.py b/prometheus_client/gc_collector.py
new file mode 100644
index 00000000..34efadec
--- /dev/null
+++ b/prometheus_client/gc_collector.py
@@ -0,0 +1,59 @@
+#!/usr/bin/python
+
+from __future__ import unicode_literals
+
+import gc
+import time
+
+from . import core
+
+class GCCollector(object):
+    """Collector for Garbage collection statistics."""
+    def __init__(self, registry=core.REGISTRY, gc=gc):
+        if not hasattr(gc, 'callbacks'):
+            return
+
+        collected = core.Histogram(
+           'python_gc_collected_objects',
+           'Objects collected during gc',
+           ['generation'],
+           buckets=[500, 1000, 5000, 10000, 50000],
+           registry=registry
+        )
+
+        uncollectable = core.Histogram(
+           'python_gc_uncollectable_objects',
+           'Uncollectable object found during GC',
+           ['generation'],
+           buckets=[500, 1000, 5000, 10000, 50000],
+           registry=registry
+        )
+
+        latency = core.Histogram(
+           'python_gc_duration_seconds',
+           'Time spent in garbage collection',
+           ['generation'],
+           registry=registry
+        )
+
+        times = {}
+
+        def _cb(phase, info):
+            gen = info['generation']
+
+            if phase == 'start':
+                times[gen] = time.time()
+
+            if phase == 'stop':
+                delta = time.time() - times[gen]
+                latency.labels(gen).observe(delta)
+                if 'collected' in info:
+                    collected.labels(gen).observe(info['collected'])
+                if 'uncollectable' in info:
+                    uncollectable.labels(gen).observe(info['uncollectable'])
+
+        gc.callbacks.append(_cb)
+
+
+GC_COLLECTOR = GCCollector()
+"""Default GCCollector in default Registry REGISTRY."""
diff --git a/tests/test_gc_collector.py b/tests/test_gc_collector.py
new file mode 100644
index 00000000..573a7dac
--- /dev/null
+++ b/tests/test_gc_collector.py
@@ -0,0 +1,54 @@
+from __future__ import unicode_literals
+
+import unittest
+
+from prometheus_client import CollectorRegistry, GCCollector
+
+
+class TestGCCollector(unittest.TestCase):
+    def setUp(self):
+        self.registry = CollectorRegistry()
+        self.gc = _MockGC()
+
+    def test_working(self):
+        collector = GCCollector(registry=self.registry, gc=self.gc)
+        self.gc.start_gc({'generation': 0})
+        self.gc.stop_gc({'generation': 0, 'collected': 10, 'uncollectable': 2})
+
+        self.assertEqual(1,
+            self.registry.get_sample_value(
+                'python_gc_duration_seconds_count',
+                labels={"generation": "0"}))
+
+        self.assertEqual(1,
+            self.registry.get_sample_value(
+                'python_gc_collected_objects_count',
+                labels={"generation": "0"}))
+
+        self.assertEqual(1,
+            self.registry.get_sample_value(
+                'python_gc_uncollectable_objects_count',
+                labels={"generation": "0"}))
+
+        self.assertEqual(10,
+            self.registry.get_sample_value(
+                'python_gc_collected_objects_sum',
+                labels={"generation": "0"}))
+
+        self.assertEqual(2,
+            self.registry.get_sample_value(
+                'python_gc_uncollectable_objects_sum',
+                labels={"generation": "0"}))
+
+
+class _MockGC(object):
+    def __init__(self):
+        self.callbacks = []
+
+    def start_gc(self, info):
+        for cb in self.callbacks:
+            cb('start', info)
+
+    def stop_gc(self, info):
+        for cb in self.callbacks:
+            cb('stop', info)