Drop incorrect use of reentrant locks (#1076)

This fixes a correctness bug introduced in
0014e97 resulting in lost updates
during some scenarios.

The code being locked is not reentrant safe. It's preferable to deadlock
in these situations instead of silently loosing updates for example.

Signed-off-by: Przemysław Suliga <mail@suligap.net>

Author: suligap

prometheus_client/metrics.py

@@ -1,5 +1,5 @@
 import os
-from threading import RLock
+from threading import Lock
 import time
 import types
 from typing import (
@@ -120,7 +120,7 @@ def __init__(self: T,
 
         if self._is_parent():
             # Prepare the fields needed for child metrics.
-            self._lock = RLock()
+            self._lock = Lock()
             self._metrics: Dict[Sequence[str], T] = {}
 
         if self._is_observable():
@@ -673,7 +673,7 @@ class Info(MetricWrapperBase):
 
     def _metric_init(self):
         self._labelname_set = set(self._labelnames)
-        self._lock = RLock()
+        self._lock = Lock()
         self._value = {}
 
     def info(self, val: Dict[str, str]) -> None:
@@ -735,7 +735,7 @@ def __init__(self,
 
     def _metric_init(self) -> None:
         self._value = 0
-        self._lock = RLock()
+        self._lock = Lock()
 
     def state(self, state: str) -> None:
         """Set enum metric state."""

prometheus_client/registry.py

@@ -1,6 +1,6 @@
 from abc import ABC, abstractmethod
 import copy
-from threading import RLock
+from threading import Lock
 from typing import Dict, Iterable, List, Optional
 
 from .metrics_core import Metric
@@ -30,7 +30,7 @@ def __init__(self, auto_describe: bool = False, target_info: Optional[Dict[str,
         self._collector_to_names: Dict[Collector, List[str]] = {}
         self._names_to_collectors: Dict[str, Collector] = {}
         self._auto_describe = auto_describe
-        self._lock = RLock()
+        self._lock = Lock()
         self._target_info: Optional[Dict[str, str]] = {}
         self.set_target_info(target_info)
 

prometheus_client/values.py

@@ -1,5 +1,5 @@
 import os
-from threading import RLock
+from threading import Lock
 import warnings
 
 from .mmap_dict import mmap_key, MmapedDict
@@ -13,7 +13,7 @@ class MutexValue:
     def __init__(self, typ, metric_name, name, labelnames, labelvalues, help_text, **kwargs):
         self._value = 0.0
         self._exemplar = None
-        self._lock = RLock()
+        self._lock = Lock()
 
     def inc(self, amount):
         with self._lock:
@@ -50,7 +50,7 @@ def MultiProcessValue(process_identifier=os.getpid):
     # Use a single global lock when in multi-processing mode
     # as we presume this means there is no threading going on.
     # This avoids the need to also have mutexes in __MmapDict.
-    lock = RLock()
+    lock = Lock()
 
     class MmapedValue:
         """A float protected by a mutex backed by a per-process mmaped file."""

tests/test_core.py

@@ -19,14 +19,6 @@
 )
 
 
-def is_locked(lock):
-    "Tries to obtain a lock, returns True on success, False on failure."
-    locked = lock.acquire(blocking=False)
-    if locked:
-        lock.release()
-    return not locked
-
-
 def assert_not_observable(fn, *args, **kwargs):
     """
     Assert that a function call falls with a ValueError exception containing
@@ -1012,7 +1004,7 @@ def test_restricted_registry_does_not_yield_while_locked(self):
         m = Metric('target', 'Target metadata', 'info')
         m.samples = [Sample('target_info', {'foo': 'bar'}, 1)]
         for _ in registry.restricted_registry(['target_info', 's_sum']).collect():
-            self.assertFalse(is_locked(registry._lock))
+            self.assertFalse(registry._lock.locked())
 
 
 if __name__ == '__main__':