From fd3172486554f0b9d9c3d4284daa085ac49ec401 Mon Sep 17 00:00:00 2001
From: crusaderky <crusaderky@gmail.com>
Date: Sat, 23 Apr 2022 01:50:17 +0100
Subject: [PATCH] Add distributed.metrics.monotonic

---
 distributed/metrics.py             | 27 ++++++++++++++++-----------
 distributed/tests/test_metrics.py  | 17 ++++++++++-------
 distributed/tests/test_variable.py |  4 ++--
 3 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/distributed/metrics.py b/distributed/metrics.py
index 0599ab5bfe..d2ac55f15b 100755
--- a/distributed/metrics.py
+++ b/distributed/metrics.py
@@ -1,8 +1,12 @@
+from __future__ import annotations
+
 import collections
-import sys
 import time as timemod
+from collections.abc import Callable
 from functools import wraps
 
+from distributed.compatibility import WINDOWS
+
 _empty_namedtuple = collections.namedtuple("_empty_namedtuple", ())
 
 
@@ -36,15 +40,15 @@ def wrapper():  # pragma: no cover
 
 
 class _WindowsTime:
-    """
-    Combine time.time() and time.perf_counter() to get an absolute clock
-    with fine resolution.
+    """Combine time.time() or time.monotonic() with time.perf_counter() to get an
+    absolute clock with fine resolution.
     """
 
     # Resync every N seconds, to avoid drifting
     RESYNC_EVERY = 600
 
-    def __init__(self):
+    def __init__(self, base: Callable[[], float]):
+        self.base_timer = base
         self.delta = None
         self.last_resync = float("-inf")
 
@@ -59,7 +63,7 @@ def time(self):
         return delta + cur
 
     def resync(self):
-        _time = timemod.time
+        _time = self.base_timer
         _perf_counter = self.perf_counter
         min_samples = 5
         while True:
@@ -77,19 +81,20 @@ def resync(self):
 
 
 # A high-resolution wall clock timer measuring the seconds since Unix epoch
-if sys.platform.startswith("win"):
-    time = _WindowsTime().time
+if WINDOWS:
+    time = _WindowsTime(timemod.time).time
+    monotonic = _WindowsTime(timemod.monotonic).time
 else:
-    # Under modern Unices, time.time() should be good enough
+    # Under modern Unixes, time.time() and time.monotonic() should be good enough
     time = timemod.time
+    monotonic = timemod.monotonic
 
 process_time = timemod.process_time
 
 # Get a per-thread CPU timer function if possible, otherwise
 # use a per-process CPU timer function.
 try:
-    # thread_time is supported on Python 3.7+ but not all platforms
+    # thread_time is not supported on all platforms
     thread_time = timemod.thread_time
 except (AttributeError, OSError):  # pragma: no cover
-    # process_time is supported on Python 3.3+ everywhere
     thread_time = process_time
diff --git a/distributed/tests/test_metrics.py b/distributed/tests/test_metrics.py
index 58c3326689..b87ad962bf 100644
--- a/distributed/tests/test_metrics.py
+++ b/distributed/tests/test_metrics.py
@@ -1,17 +1,20 @@
 import time
 
+import pytest
+
 from distributed import metrics
 
 
-def test_wall_clock():
+@pytest.mark.parametrize("name", ["time", "monotonic"])
+def test_wall_clock(name):
     for i in range(3):
         time.sleep(0.01)
-        t = time.time()
-        samples = [metrics.time() for j in range(50)]
+        t = getattr(time, name)()
+        samples = [getattr(metrics, name)() for _ in range(100)]
         # Resolution
-        deltas = [samples[j + 1] - samples[j] for j in range(len(samples) - 1)]
+        deltas = [sj - si for si, sj in zip(samples[:-1], samples[1:])]
         assert min(deltas) >= 0.0, deltas
-        assert max(deltas) <= 1.0, deltas
-        assert any(lambda d: 0.0 < d < 0.0001 for d in deltas), deltas
-        # Close to time.time()
+        assert max(deltas) <= 0.001, deltas
+        assert any(0.0 < d < 0.0001 for d in deltas), deltas
+        # Close to time.time() / time.monotonic()
         assert t - 0.5 < samples[0] < t + 0.5
diff --git a/distributed/tests/test_variable.py b/distributed/tests/test_variable.py
index 37a7180781..9d4eb63cc1 100644
--- a/distributed/tests/test_variable.py
+++ b/distributed/tests/test_variable.py
@@ -2,13 +2,13 @@
 import logging
 import random
 from datetime import timedelta
-from time import monotonic, sleep
+from time import sleep
 
 import pytest
 
 from distributed import Client, Nanny, TimeoutError, Variable, wait, worker_client
 from distributed.compatibility import WINDOWS
-from distributed.metrics import time
+from distributed.metrics import monotonic, time
 from distributed.utils_test import captured_logger, div, gen_cluster, inc, popen