Commit fdf1ee973e9f3cb01f6fec9e460950622cdf92e4 | zig

author	Andrew Kelley <andrew@ziglang.org> 2026-01-27 13:24:27-08:00
committer	Andrew Kelley <andrew@ziglang.org> 2026-01-30 22:03:14-08:00
log	fdf1ee973e9f3cb01f6fec9e460950622cdf92e4
tree	118ef95b64df5e44c73db969e69bb8703d1de925
parent	2fb224cb845c18044186c1348ca9a1b2a3152948

std.Io.Threaded: move the NtDelayExecution later in batchWait

also guard against receiving SUCCESS with 0 byte read

ms docs say that pipes can do this if there is a 0 byte write

2 files changed, 29 insertions(+), 16 deletions(-)

lib
- std
  - Io
    Threaded.zig
  - os
    windows
    kernel32.zig

lib/std/Io/Threaded.zig+29-13

 @@ -2705,18 +2705,6 @@ fn batchWaitWindows(t: *Threaded, b: *Io.Batch, timeout: Io.Timeout) Io.Batch.Wa
     var delay_interval: windows.LARGE_INTEGER = timeoutToWindowsInterval(timeout);
     while (true) {
-        const alertable_syscall = try AlertableSyscall.start();
-        const delay_rc = windows.ntdll.NtDelayExecution(windows.TRUE, &delay_interval);
-        alertable_syscall.finish();
-        switch (delay_rc) {
-            .SUCCESS => {
-                // The thread woke due to the timeout. Although spurious
-                // timeouts are OK, when no deadline is passed we must not
-                // return `error.Timeout`.
-                if (timeout != .none) return error.Timeout;
-            },
-            else => {},
-        }
         var any_done = false;
         var any_pending = false;
         for (metadatas, 0..) |*metadata, op_usize| {
 @@ -2738,6 +2726,18 @@ fn batchWaitWindows(t: *Threaded, b: *Io.Batch, timeout: Io.Timeout) Io.Batch.Wa
         }
         if (any_done) return;
         if (!any_pending) return;
+        const alertable_syscall = try AlertableSyscall.start();
+        const delay_rc = windows.ntdll.NtDelayExecution(windows.TRUE, &delay_interval);
+        alertable_syscall.finish();
+        switch (delay_rc) {
+            .SUCCESS => {
+                // The thread woke due to the timeout. Although spurious
+                // timeouts are OK, when no deadline is passed we must not
+                // return `error.Timeout`.
+                if (timeout != .none) return error.Timeout;
+            },
+            else => {},
+        }
     }
 }
 @@ -8707,7 +8707,11 @@ fn fileReadStreamingWindows(file: File, data: []const []u8) File.Reader.Error!us
 fn ntReadFileResult(io_status_block: *windows.IO_STATUS_BLOCK) !usize {
     switch (io_status_block.u.Status) {
-        .SUCCESS, .END_OF_FILE, .PIPE_BROKEN => return io_status_block.Information,
+        .SUCCESS => {
+            assert(io_status_block.Information != 0);
+            return io_status_block.Information;
+        },
+        .END_OF_FILE, .PIPE_BROKEN => return 0,
         .PENDING => unreachable,
         .INVALID_DEVICE_REQUEST => return error.IsDir,
         .LOCK_NOT_GRANTED => return error.LockViolation,
 @@ -8744,6 +8748,17 @@ fn ntReadFile(handle: windows.HANDLE, data: []const []u8, iosb: *windows.IO_STAT
                 syscall.finish();
                 return .pending;
             },
+            .SUCCESS => {
+                // Only END_OF_FILE is the true end.
+                if (iosb.Information == 0) {
+                    try syscall.checkCancel();
+                    continue;
+                } else {
+                    syscall.finish();
+                    iosb.u.Status = .SUCCESS;
+                    return .status;
+                }
+            },
             .CANCELLED => {
                 try syscall.checkCancel();
                 continue;
 @@ -9709,6 +9724,7 @@ fn writeFileStreamingWindows(
     handle: windows.HANDLE,
     bytes: []const u8,
 ) File.Writer.Error!usize {
+    assert(bytes.len != 0);
     var bytes_written: windows.DWORD = undefined;
     const adjusted_len = std.math.lossyCast(u32, bytes.len);
     const syscall: Syscall = try .start();

lib/std/os/windows/kernel32.zig-3

 @@ -188,9 +188,6 @@ pub extern "kernel32" fn PostQueuedCompletionStatus(
     lpOverlapped: ?*OVERLAPPED,
 ) callconv(.winapi) BOOL;
-// TODO:
-// GetOverlappedResultEx with bAlertable=false, which calls: GetStdHandle + WaitForSingleObjectEx.
-// Uses the SwitchBack system to run implementations for older programs; Do we care about this?
 pub extern "kernel32" fn GetOverlappedResult(
     hFile: HANDLE,
     lpOverlapped: *OVERLAPPED,