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std.Io.Threaded: fix QueryPerformanceCounter usage

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Co-authored-by: Andrew Kelley <andrew@ziglang.org>
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Zihad 2025-11-23 16:15:20 +06:00 • committed by Andrew Kelley
parent 5816646aa0
commit e8c2efb0fe
1 changed files with 16 additions and 1 deletions
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17
lib/std/Io/Threaded.zig
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@ -2956,7 +2956,22 @@ fn nowWindows(userdata: ?*anyopaque, clock: Io.Clock) Io.Clock.Error!Io.Timestam
},
.awake, .boot => {
// QPC on windows doesn't fail on >= XP/2000 and includes time suspended.
return .{ .nanoseconds = windows.QueryPerformanceCounter() };
const qpc = windows.QueryPerformanceCounter();
// We don't need to cache QPF as it's internally just a memory read to KUSER_SHARED_DATA
// (a read-only page of info updated and mapped by the kernel to all processes):
// https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddk/ns-ntddk-kuser_shared_data
// https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/ntexapi_x/kuser_shared_data/index.htm
const qpf = windows.QueryPerformanceFrequency();
// 10Mhz (1 qpc tick every 100ns) is a common enough QPF value that we can optimize on it.
// https://github.com/microsoft/STL/blob/785143a0c73f030238ef618890fd4d6ae2b3a3a0/stl/inc/chrono#L694-L701
const common_qpf = 10_000_000;
if (qpf == common_qpf) return .{ .nanoseconds = qpc * (std.time.ns_per_s / common_qpf) };
// Convert to ns using fixed point.
const scale = @as(u64, std.time.ns_per_s << 32) / @as(u32, @intCast(qpf));
const result = (@as(u96, qpc) * scale) >> 32;
return .{ .nanoseconds = @intCast(result) };
},
.cpu_process,
.cpu_thread,