#1007 / boot_time() / win: consider 1 sec fluctuation between calls acceptable and return always the same value

3 files changed, 27 insertions, 1 deletions

diff --git a/HISTORY.rst b/HISTORY.rst
index c1ad8d84..bf7f6367 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -20,6 +20,9 @@
 
 **Bug fixes**
 
+- 1007_: [Windows] boot_time() can have a 1 sec fluctuation between calls; the
+  value of the first call is now cached so that boot_time() always returns the
+  same value if fluctuation is <= 1 second.
 - 1014_: [Linux] Process class can mask legitimate ENOENT exceptions as
   NoSuchProcess.
 - 1016_: disk_io_counters() raises RuntimeError on a system with no disks.
diff --git a/psutil/_pswindows.py b/psutil/_pswindows.py
index 4b27557c..bd6b091f 100644
--- a/psutil/_pswindows.py
+++ b/psutil/_pswindows.py
@@ -401,9 +401,21 @@ def sensors_battery():
 # =====================================================================
 
 
+_last_btime = 0
+
+
 def boot_time():
     """The system boot time expressed in seconds since the epoch."""
-    return cext.boot_time()
+    # This dirty hack is to adjust the precision of the returned
+    # value which may have a 1 second fluctuation, see:
+    # https://github.com/giampaolo/psutil/issues/1007
+    global _last_btime
+    ret = cext.boot_time()
+    if abs(ret - _last_btime) <= 1:
+        return _last_btime
+    else:
+        _last_btime = ret
+        return ret
 
 
 def users():
diff --git a/psutil/tests/test_windows.py b/psutil/tests/test_windows.py
index ac787283..a4f32315 100755
--- a/psutil/tests/test_windows.py
+++ b/psutil/tests/test_windows.py
@@ -7,6 +7,7 @@
 
 """Windows specific tests."""
 
+import datetime
 import errno
 import glob
 import os
@@ -179,6 +180,16 @@ class TestSystemAPIs(unittest.TestCase):
         self.assertTrue(ps_names & wmi_names,
                         "no common entries in %s, %s" % (ps_names, wmi_names))
 
+    def test_boot_time(self):
+        wmi_os = wmi.WMI().Win32_OperatingSystem()
+        wmi_btime_str = wmi_os[0].LastBootUpTime.split('.')[0]
+        wmi_btime_dt = datetime.datetime.strptime(
+            wmi_btime_str, "%Y%m%d%H%M%S")
+        psutil_dt = datetime.datetime.fromtimestamp(psutil.boot_time())
+        diff = abs((wmi_btime_dt - psutil_dt).total_seconds())
+        # Wmic time is 2 secs lower for some reason; that's OK.
+        self.assertLessEqual(diff, 2)
+
 
 # ===================================================================
 # sensors_battery()