From 1cd3af43fd74a8481b35d58c351ae056c1cba362 Mon Sep 17 00:00:00 2001
From: Krzysztof Antonowski <krzysztofantonowski@proton.me>
Date: Mon, 2 Feb 2026 22:19:19 +0100
Subject: [PATCH] std.Io.Threaded: implement CPU-based clocks on Windows
 (#31093)

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31093
Co-authored-by: Krzysztof Antonowski <krzysztofantonowski@proton.me>
Co-committed-by: Krzysztof Antonowski <krzysztofantonowski@proton.me>
---
 lib/std/Io/Threaded.zig | 37 ++++++++++++++++++++++++++++++++++---
 lib/std/os/windows.zig  |  8 ++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 298c3c167f6e6c044d41cf1e83e03f3664e54df6..3f4affcc5ca17b83d5cb99b398b735c363cd4919 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -10849,9 +10849,40 @@ fn nowWindows(clock: Io.Clock) Io.Clock.Error!Io.Timestamp {
             const result = (@as(u96, qpc) * scale) >> 32;
             return .{ .nanoseconds = @intCast(result) };
         },
-        .cpu_process,
-        .cpu_thread,
-        => return error.UnsupportedClock,
+        .cpu_process => {
+            const handle = windows.GetCurrentProcess();
+            var times: windows.KERNEL_USER_TIMES = undefined;
+
+            // https://github.com/reactos/reactos/blob/master/ntoskrnl/ps/query.c#L442-L485
+            if (windows.ntdll.NtQueryInformationProcess(
+                handle,
+                windows.PROCESSINFOCLASS.Times,
+                &times,
+                @sizeOf(windows.KERNEL_USER_TIMES),
+                null,
+            ) != .SUCCESS)
+                return error.Unexpected;
+
+            const sum = @as(i96, times.UserTime) + @as(i96, times.KernelTime);
+            return .{ .nanoseconds = sum * 100 };
+        },
+        .cpu_thread => {
+            const handle = windows.GetCurrentThread();
+            var times: windows.KERNEL_USER_TIMES = undefined;
+
+            // https://github.com/reactos/reactos/blob/master/ntoskrnl/ps/query.c#L2971-L3019
+            if (windows.ntdll.NtQueryInformationThread(
+                handle,
+                windows.THREADINFOCLASS.Times,
+                &times,
+                @sizeOf(windows.KERNEL_USER_TIMES),
+                null,
+            ) != .SUCCESS)
+                return error.Unexpected;
+
+            const sum = @as(i96, times.UserTime) + @as(i96, times.KernelTime);
+            return .{ .nanoseconds = sum * 100 };
+        },
     }
 }
 
diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index b9653b3ac9979d9eb5144822fb7ed27f802a55a7..0f57eed766eba130ece4bafc3b76e5684de2239b 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -6191,6 +6191,14 @@ pub const PROCESS_BASIC_INFORMATION = extern struct {
     InheritedFromUniqueProcessId: ULONG_PTR,
 };
 
+// https://github.com/reactos/reactos/blob/master/sdk/include/ndk/pstypes.h#L977-L983
+pub const KERNEL_USER_TIMES = extern struct {
+    CreationTime: LARGE_INTEGER,
+    ExitTime: LARGE_INTEGER,
+    KernelTime: LARGE_INTEGER,
+    UserTime: LARGE_INTEGER,
+};
+
 pub const ReadMemoryError = error{
     Unexpected,
 };
-- 
2.54.0