[Python-checkins] bpo-39847: EnterNonRecursiveMutex() uses GetTickCount64() (GH-18780)

[bobince]

https://github.com/python/cpython/commit/64838ce7172c7a92183b39b22504b433a33a884d
commit: 64838ce7172c7a92183b39b22504b433a33a884d
branch: master
author: bobince <and+github at doxdesk.com>
committer: GitHub <noreply at github.com>
date: 2020-03-12T00:39:02+01:00
summary:

bpo-39847: EnterNonRecursiveMutex() uses GetTickCount64() (GH-18780)

The 32-bit (49-day) TickCount relied on in EnterNonRecursiveMutex can overflow
in the gap between the 'target' time and the 'now' time WaitForSingleObjectEx
returns, causing the loop to think it needs to wait another 49 days. This is
most likely to happen when the machine is hibernated during
WaitForSingleObjectEx.

This makes acquiring a lock/event/etc from the _thread or threading module
appear to never timeout.

Replace with GetTickCount64 - this is OK now Python no longer supports XP which
lacks it, and is in use for time.monotonic().

Co-authored-by: And Clover <and.clover at bromium.com>

files:
A Misc/NEWS.d/next/Windows/2020-03-04-17-05-11.bpo-39847.C3N2m3.rst
M Python/thread_nt.h

diff --git a/Misc/NEWS.d/next/Windows/2020-03-04-17-05-11.bpo-39847.C3N2m3.rst b/Misc/NEWS.d/next/Windows/2020-03-04-17-05-11.bpo-39847.C3N2m3.rst
new file mode 100644
index 0000000000000..acfbce53eb399
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2020-03-04-17-05-11.bpo-39847.C3N2m3.rst
@@ -0,0 +1,2 @@
+Avoid hang when computer is hibernated whilst waiting for a mutex (for
+lock-related objects from :mod:`threading`) around 49-day uptime.
diff --git a/Python/thread_nt.h b/Python/thread_nt.h
index a5246dd0504db..23d585cf9fa6c 100644
--- a/Python/thread_nt.h
+++ b/Python/thread_nt.h
@@ -75,16 +75,16 @@ EnterNonRecursiveMutex(PNRMUTEX mutex, DWORD milliseconds)
         }
     } else if (milliseconds != 0) {
         /* wait at least until the target */
-        DWORD now, target = GetTickCount() + milliseconds;
+        ULONGLONG now, target = GetTickCount64() + milliseconds;
         while (mutex->locked) {
             if (PyCOND_TIMEDWAIT(&mutex->cv, &mutex->cs, (long long)milliseconds*1000) < 0) {
                 result = WAIT_FAILED;
                 break;
             }
-            now = GetTickCount();
+            now = GetTickCount64();
             if (target <= now)
                 break;
-            milliseconds = target-now;
+            milliseconds = (DWORD)(target-now);
         }
     }
     if (!mutex->locked) {