tree cbc1885cfd7f66a58d4d0abd3dcebfc973d7cc29
parent 9a18cc1a127ef2d675532926f714fc62ba0bd881
author Abseil Team <absl-team@google.com> 1726599525 -0700
committer Copybara-Service <copybara-worker@google.com> 1726599578 -0700

Attempt to fix flaky Abseil waiter/sleep tests

The existing implementation uses wall-clock time. However, wall clock can drastically differ from the internal system clock, because the system can be suspended and then resumed.

We want to account for at least some kinds of suspensions that might occur during automated testing, such as VM suspension or hypervisor preemption ("steal time"). These are tricky cases, because the physical (host) CPU is still running -- just the logical (guest) virtual CPU isn't. Therefore, we need to ensure that our time measurements exclude elapsed host-only time.

Unfortunately the correctness of a method depends on the nature & configuration of each VM and the guest. For example, it can depend whether RDTSC is virtualized, or on whether the host and guest support accounting for steal time. Windows, for example, appears to only support steal time measurements if the hypervisor is Hyper-V.

Since this is all for the sake of testing, we use a simpler trick that we hope will work around the problem on our systems: we subtract the so-called "interrupt time bias" from the system uptime in Windows. The interrupt time bias includes sleep/hibernation time, and seems to advance during for VM suspensions as well, so it may take care of the problem.

PiperOrigin-RevId: 675654840
Change-Id: I66150b18912175fa72609d3f137e3ea4fee8fc43