From ef77cc0de1f4453d89d8841116eaa65a42a9c89f Mon Sep 17 00:00:00 2001 From: Lucas Santos Date: Thu, 25 Dec 2025 22:08:34 -0300 Subject: [PATCH] Fixes doc comment of Futex.wait On Windows, changing the value at the target address is not sufficient, there needs to be a wake call. From [MSDN](https://learn.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-waitonaddress): > If the value at Address differs from the value at CompareAddress, the function returns immediately. If the values are the same, the function does not return until another thread in the same process signals that the value at Address has changed by calling WakeByAddressSingle or WakeByAddressAll or the timeout elapses, whichever comes first. We could note that this behavior is only observed on Windows. However, if we want the function to have consistent behavior across all platforms, we should require users to call wake. On platforms where changing the value is sufficient to wake the waiting thread, an unblocking of the thread without a matching wake would just be considered a spurious wake. --- lib/std/Thread/Futex.zig | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/lib/std/Thread/Futex.zig b/lib/std/Thread/Futex.zig index b61062c361a0af2b1bd7312c843264e022dd68ec..7c44621d7221797a14e6163ce92c6b9e019c8cfd 100644 --- a/lib/std/Thread/Futex.zig +++ b/lib/std/Thread/Futex.zig @@ -20,8 +20,7 @@ const testing = std.testing; const atomic = std.atomic; /// Checks if `ptr` still contains the value `expect` and, if so, blocks the caller until either: -/// - The value at `ptr` is no longer equal to `expect`. -/// - The caller is unblocked by a matching `wake()`. +/// - The value at `ptr` is no longer equal to `expect` and `wake()` is called on the same address. /// - The caller is unblocked spuriously ("at random"). /// /// The checking of `ptr` and `expect`, along with blocking the caller, is done atomically -- 2.54.0