bpo-34054: multiprocessing uses time.monotonic() (GH-8118)

The multiprocessing module now uses the monotonic clock
time.monotonic() instead of the system clock time.time() to implement
timeouts.

Lib/multiprocessing/connection.py

@@ -57,10 +57,10 @@ if sys.platform == 'win32':
 
 
 def _init_timeout(timeout=CONNECTION_TIMEOUT):
-    return time.time() + timeout
+    return time.monotonic() + timeout
 
 def _check_timeout(t):
-    return time.time() > t
+    return time.monotonic() > t
 
 #
 #
@@ -914,7 +914,7 @@ else:
                 selector.register(obj, selectors.EVENT_READ)
 
             if timeout is not None:
-                deadline = time.time() + timeout
+                deadline = time.monotonic() + timeout
 
             while True:
                 ready = selector.select(timeout)
@@ -922,7 +922,7 @@ else:
                     return [key.fileobj for (key, events) in ready]
                 else:
                     if timeout is not None:
-                        timeout = deadline - time.time()
+                        timeout = deadline - time.monotonic()
                         if timeout < 0:
                             return ready
 

Lib/multiprocessing/managers.py

@@ -18,8 +18,8 @@ import sys
 import threading
 import array
 import queue
+import time
 
-from time import time as _time
 from traceback import format_exc
 
 from . import connection
@@ -1045,13 +1045,13 @@ class ConditionProxy(AcquirerProxy):
         if result:
             return result
         if timeout is not None:
-            endtime = _time() + timeout
+            endtime = time.monotonic() + timeout
         else:
             endtime = None
             waittime = None
         while not result:
             if endtime is not None:
-                waittime = endtime - _time()
+                waittime = endtime - time.monotonic()
                 if waittime <= 0:
                     break
             self.wait(waittime)

Lib/multiprocessing/queues.py

@@ -95,12 +95,12 @@ class Queue(object):
             self._sem.release()
         else:
             if block:
-                deadline = time.time() + timeout
+                deadline = time.monotonic() + timeout
             if not self._rlock.acquire(block, timeout):
                 raise Empty
             try:
                 if block:
-                    timeout = deadline - time.time()
+                    timeout = deadline - time.monotonic()
                     if not self._poll(timeout):
                         raise Empty
                 elif not self._poll():

Lib/multiprocessing/synchronize.py

@@ -15,8 +15,7 @@ import threading
 import sys
 import tempfile
 import _multiprocessing
-
-from time import time as _time
+import time
 
 from . import context
 from . import process
@@ -302,13 +301,13 @@ class Condition(object):
         if result:
             return result
         if timeout is not None:
-            endtime = _time() + timeout
+            endtime = time.monotonic() + timeout
         else:
             endtime = None
             waittime = None
         while not result:
             if endtime is not None:
-                waittime = endtime - _time()
+                waittime = endtime - time.monotonic()
                 if waittime <= 0:
                     break
             self.wait(waittime)

Misc/NEWS.d/next/Library/2018-07-05-18-37-05.bpo-34054.nWRS6M.rst

@@ -0,0 +1,3 @@
+The multiprocessing module now uses the monotonic clock
+:func:`time.monotonic` instead of the system clock :func:`time.time` to
+implement timeout.