Support metric help text in multiprocess mode

Issue #211
Add support for storing the metrics help text in the multiprocess map.
The help will come from the first process read, but it should be the
same for all metrics.

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 << 20
 _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):