Support metric help text in multiprocess mode

prometheus_client/metrics.py

@@ -275,7 +275,7 @@ def f():
 
     def _metric_init(self) -> None:
         self._value = values.ValueClass(self._type, self._name, self._name + '_total', self._labelnames,
-                                        self._labelvalues)
+                                        self._labelvalues, self._documentation)
         self._created = time.time()
 
     def inc(self, amount: float = 1, exemplar: Optional[Dict[str, str]] = None) -> None:
@@ -377,7 +377,7 @@ def __init__(self,
     def _metric_init(self) -> None:
         self._value = values.ValueClass(
             self._type, self._name, self._name, self._labelnames, self._labelvalues,
-            multiprocess_mode=self._multiprocess_mode
+            self._documentation, multiprocess_mode=self._multiprocess_mode
         )
 
     def inc(self, amount: float = 1) -> None:
@@ -469,8 +469,8 @@ def create_response(request):
 
     def _metric_init(self) -> None:
         self._count = values.ValueClass(self._type, self._name, self._name + '_count', self._labelnames,
-                                        self._labelvalues)
-        self._sum = values.ValueClass(self._type, self._name, self._name + '_sum', self._labelnames, self._labelvalues)
+                                        self._labelvalues, self._documentation)
+        self._sum = values.ValueClass(self._type, self._name, self._name + '_sum', self._labelnames, self._labelvalues, self._documentation)
         self._created = time.time()
 
     def observe(self, amount: float) -> None:
@@ -583,14 +583,15 @@ def _metric_init(self) -> None:
         self._buckets: List[values.ValueClass] = []
         self._created = time.time()
         bucket_labelnames = self._labelnames + ('le',)
-        self._sum = values.ValueClass(self._type, self._name, self._name + '_sum', self._labelnames, self._labelvalues)
+        self._sum = values.ValueClass(self._type, self._name, self._name + '_sum', self._labelnames, self._labelvalues, self._documentation)
         for b in self._upper_bounds:
             self._buckets.append(values.ValueClass(
                 self._type,
                 self._name,
                 self._name + '_bucket',
                 bucket_labelnames,
-                self._labelvalues + (floatToGoString(b),))
+                self._labelvalues + (floatToGoString(b),),
+                self._documentation)
             )
 
     def observe(self, amount: float, exemplar: Optional[Dict[str, str]] = None) -> None:

prometheus_client/mmap_dict.py

@@ -2,6 +2,7 @@
 import mmap
 import os
 import struct
+from typing import List
 
 _INITIAL_MMAP_SIZE = 1 << 16
 _pack_integer_func = struct.Struct(b'i').pack
@@ -137,8 +138,8 @@ def close(self):
             self._f = None
 
 
-def mmap_key(metric_name, name, labelnames, labelvalues):
+def mmap_key(metric_name: str, name: str, labelnames: List[str], labelvalues: List[str], help_text: str) -> str:
     """Format a key for use in the mmap file."""
     # ensure labels are in consistent order for identity
     labels = dict(zip(labelnames, labelvalues))
-    return json.dumps([metric_name, name, labels], sort_keys=True)
+    return json.dumps([metric_name, name, labels, help_text], sort_keys=True)

prometheus_client/multiprocess.py

@@ -15,8 +15,6 @@
 except NameError:  # Python >= 2.5
     FileNotFoundError = IOError
 
-MP_METRIC_HELP = 'Multiprocess metric'
-
 
 class MultiProcessCollector:
     """Collector for files for multi-process mode."""
@@ -53,9 +51,9 @@ def _read_metrics(files):
         def _parse_key(key):
             val = key_cache.get(key)
             if not val:
-                metric_name, name, labels = json.loads(key)
+                metric_name, name, labels, help_text = json.loads(key)
                 labels_key = tuple(sorted(labels.items()))
-                val = key_cache[key] = (metric_name, name, labels, labels_key)
+                val = key_cache[key] = (metric_name, name, labels, labels_key, help_text)
             return val
 
         for f in files:
@@ -71,11 +69,11 @@ def _parse_key(key):
                     continue
                 raise
             for key, value, _ in file_values:
-                metric_name, name, labels, labels_key = _parse_key(key)
+                metric_name, name, labels, labels_key, help_text = _parse_key(key)
 
                 metric = metrics.get(metric_name)
                 if metric is None:
-                    metric = Metric(metric_name, MP_METRIC_HELP, typ)
+                    metric = Metric(metric_name, help_text, typ)
                     metrics[metric_name] = metric
 
                 if typ == 'gauge':

prometheus_client/values.py

@@ -10,7 +10,7 @@ class MutexValue:
 
     _multiprocess = False
 
-    def __init__(self, typ, metric_name, name, labelnames, labelvalues, **kwargs):
+    def __init__(self, typ, metric_name, name, labelnames, labelvalues, help_text, **kwargs):
         self._value = 0.0
         self._exemplar = None
         self._lock = Lock()
@@ -57,8 +57,8 @@ class MmapedValue:
 
         _multiprocess = True
 
-        def __init__(self, typ, metric_name, name, labelnames, labelvalues, multiprocess_mode='', **kwargs):
-            self._params = typ, metric_name, name, labelnames, labelvalues, multiprocess_mode
+        def __init__(self, typ, metric_name, name, labelnames, labelvalues, help_text, multiprocess_mode='', **kwargs):
+            self._params = typ, metric_name, name, labelnames, labelvalues, help_text, multiprocess_mode
             # This deprecation warning can go away in a few releases when removing the compatibility
             if 'prometheus_multiproc_dir' in os.environ and 'PROMETHEUS_MULTIPROC_DIR' not in os.environ:
                 os.environ['PROMETHEUS_MULTIPROC_DIR'] = os.environ['prometheus_multiproc_dir']
@@ -69,7 +69,7 @@ def __init__(self, typ, metric_name, name, labelnames, labelvalues, multiprocess
                 values.append(self)
 
         def __reset(self):
-            typ, metric_name, name, labelnames, labelvalues, multiprocess_mode = self._params
+            typ, metric_name, name, labelnames, labelvalues, help_text, multiprocess_mode = self._params
             if typ == 'gauge':
                 file_prefix = typ + '_' + multiprocess_mode
             else:
@@ -81,7 +81,7 @@ def __reset(self):
 
                 files[file_prefix] = MmapedDict(filename)
             self._file = files[file_prefix]
-            self._key = mmap_key(metric_name, name, labelnames, labelvalues)
+            self._key = mmap_key(metric_name, name, labelnames, labelvalues, help_text)
             self._value = self._file.read_value(self._key)
 
         def __check_for_pid_change(self):

tests/test_multiprocess.py

@@ -281,6 +281,31 @@ def add_label(key, value):
 
         self.assertEqual(metrics['h'].samples, expected_histogram)
 
+    def test_collect_preserves_help(self):
+        pid = 0
+        values.ValueClass = MultiProcessValue(lambda: pid)
+        labels = {i: i for i in 'abcd'}
+
+        c = Counter('c', 'c help', labelnames=labels.keys(), registry=None)
+        g = Gauge('g', 'g help', labelnames=labels.keys(), registry=None)
+        h = Histogram('h', 'h help', labelnames=labels.keys(), registry=None)
+
+        c.labels(**labels).inc(1)
+        g.labels(**labels).set(1)
+        h.labels(**labels).observe(1)
+
+        pid = 1
+
+        c.labels(**labels).inc(1)
+        g.labels(**labels).set(1)
+        h.labels(**labels).observe(5)
+
+        metrics = {m.name: m for m in self.collector.collect()}
+
+        self.assertEqual(metrics['c'].documentation, 'c help')
+        self.assertEqual(metrics['g'].documentation, 'g help')
+        self.assertEqual(metrics['h'].documentation, 'h help')
+
     def test_merge_no_accumulate(self):
         pid = 0
         values.ValueClass = MultiProcessValue(lambda: pid)