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std.Io.Threaded: improve various Windows logic

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* cache nul handle for child process execution
* make opening the nul file integrate properly with cancelation
* replace all calls to SleepEx to parking_sleep.sleep instead, making
  them properly cancelable. These sleeps are workarounds for Windows
  kernel bugs. Now you can even cancel while waiting for kernel bug
  workarounds!
This commit is contained in:
Andrew Kelley
2026-01-03 16:57:55 -08:00
parent be977e1934
commit 2b326d27d5
1 changed files with 113 additions and 32 deletions
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lib/std/Io/Threaded.zig
+113 -32
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@@ -64,6 +64,8 @@ stderr_writer_initialized: bool = false,
argv0: Argv0,
environ: Environ,
nul_handle: if (is_windows) ?windows.HANDLE else void = if (is_windows) null else {},
pub const Argv0 = switch (native_os) {
.openbsd, .haiku => struct {
value: ?[*:0]const u8,
@@ -1247,8 +1249,13 @@ pub fn setAsyncLimit(t: *Threaded, new_limit: Io.Limit) void {
pub fn deinit(t: *Threaded) void {
t.join();
if (is_windows and t.wsa.status == .initialized) {
if (ws2_32.WSACleanup() != 0) recoverableOsBugDetected();
if (is_windows) {
if (t.wsa.status == .initialized) {
if (ws2_32.WSACleanup() != 0) recoverableOsBugDetected();
}
if (t.nul_handle) |handle| {
windows.CloseHandle(handle);
}
}
if (posix.Sigaction != void and t.have_signal_handler) {
if (have_sig_io) posix.sigaction(.IO, &t.old_sig_io, null);
@@ -3666,7 +3673,10 @@ pub fn dirOpenFileWtf16(
// kernel bug with retry attempts.
syscall.finish();
if (max_attempts - attempt == 0) return error.SharingViolation;
_ = w.kernel32.SleepEx((@as(u32, 1) << attempt) >> 1, w.TRUE);
try parking_sleep.sleep(.{ .duration = .{
.raw = .fromMilliseconds((@as(u32, 1) << attempt) >> 1),
.clock = .awake,
} });
attempt += 1;
syscall = try .start();
continue;
@@ -3688,7 +3698,10 @@ pub fn dirOpenFileWtf16(
// fixed by sleeping and retrying until the error goes away.
syscall.finish();
if (max_attempts - attempt == 0) return error.SharingViolation;
_ = w.kernel32.SleepEx((@as(u32, 1) << attempt) >> 1, w.TRUE);
try parking_sleep.sleep(.{ .duration = .{
.raw = .fromMilliseconds((@as(u32, 1) << attempt) >> 1),
.clock = .awake,
} });
attempt += 1;
syscall = try .start();
continue;
@@ -13377,34 +13390,7 @@ fn processSpawnWindows(userdata: ?*anyopaque, options: process.SpawnOptions) pro
options.stdout == .ignore or
options.stderr == .ignore;
// TODO: cache the handle to null file!
const nul_handle = if (any_ignore)
// "\Device\Null" or "\??\NUL"
windows.OpenFile(&[_]u16{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'N', 'u', 'l', 'l' }, .{
.access_mask = .{
.STANDARD = .{ .SYNCHRONIZE = true },
.GENERIC = .{ .WRITE = true, .READ = true },
},
.sa = &saAttr,
.creation = .OPEN,
}) catch |err| switch (err) {
error.PathAlreadyExists => return error.Unexpected, // not possible for "NUL"
error.PipeBusy => return error.Unexpected, // not possible for "NUL"
error.NoDevice => return error.Unexpected, // not possible for "NUL"
error.FileNotFound => return error.Unexpected, // not possible for "NUL"
error.AccessDenied => return error.Unexpected, // not possible for "NUL"
error.NameTooLong => return error.Unexpected, // not possible for "NUL"
error.WouldBlock => return error.Unexpected, // not possible for "NUL"
error.NetworkNotFound => return error.Unexpected, // not possible for "NUL"
error.AntivirusInterference => return error.Unexpected, // not possible for "NUL"
error.OperationCanceled => return error.Unexpected, // we're not canceling the operation
else => |e| return e,
}
else
undefined;
defer {
if (any_ignore) posix.close(nul_handle);
}
const nul_handle = if (any_ignore) try getNulHandle(t) else undefined;
var g_hChildStd_IN_Rd: ?windows.HANDLE = null;
var g_hChildStd_IN_Wr: ?windows.HANDLE = null;
@@ -13647,6 +13633,101 @@ fn processSpawnWindows(userdata: ?*anyopaque, options: process.SpawnOptions) pro
};
}
fn getNulHandle(t: *Threaded) !windows.HANDLE {
{
t.mutex.lock();
defer t.mutex.unlock();
if (t.nul_handle) |handle| return handle;
}
const device_path = [_]u16{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'N', 'u', 'l', 'l' };
var nt_name: windows.UNICODE_STRING = .{
.Length = device_path.len * 2,
.MaximumLength = device_path.len * 2,
.Buffer = @constCast(&device_path),
};
const attr: windows.OBJECT_ATTRIBUTES = .{
.Length = @sizeOf(windows.OBJECT_ATTRIBUTES),
.RootDirectory = null,
.Attributes = .{
.INHERIT = true,
},
.ObjectName = &nt_name,
.SecurityDescriptor = null,
.SecurityQualityOfService = null,
};
var io_status_block: windows.IO_STATUS_BLOCK = undefined;
var fresh_handle: windows.HANDLE = undefined;
var syscall: Syscall = try .start();
while (true) switch (windows.ntdll.NtCreateFile(
&fresh_handle,
.{
.STANDARD = .{ .SYNCHRONIZE = true },
.GENERIC = .{ .WRITE = true, .READ = true },
},
&attr,
&io_status_block,
null,
.{ .NORMAL = true },
.VALID_FLAGS,
.OPEN,
.{
.DIRECTORY_FILE = false,
.NON_DIRECTORY_FILE = true,
.IO = .SYNCHRONOUS_NONALERT,
.OPEN_REPARSE_POINT = false,
},
null,
0,
)) {
.SUCCESS => {
syscall.finish();
t.mutex.lock(); // Another thread might have won the race.
defer t.mutex.unlock();
if (t.nul_handle) |prev_handle| {
windows.CloseHandle(fresh_handle);
return prev_handle;
} else {
t.nul_handle = fresh_handle;
return fresh_handle;
}
},
.DELETE_PENDING => {
// This error means that there *was* a file in this location on
// the file system, but it was deleted. However, the OS is not
// finished with the deletion operation, and so this CreateFile
// call has failed. There is not really a sane way to handle
// this other than retrying the creation after the OS finishes
// the deletion.
syscall.finish();
try parking_sleep.sleep(.{ .duration = .{
.raw = .fromMilliseconds(1),
.clock = .awake,
} });
syscall = try .start();
continue;
},
.CANCELLED => {
try syscall.checkCancel();
continue;
},
.INVALID_PARAMETER => |status| return syscall.ntstatusBug(status),
.OBJECT_PATH_SYNTAX_BAD => |status| return syscall.ntstatusBug(status),
.INVALID_HANDLE => |status| return syscall.ntstatusBug(status),
.OBJECT_NAME_INVALID => return syscall.fail(error.BadPathName),
.OBJECT_NAME_NOT_FOUND => return syscall.fail(error.FileNotFound),
.OBJECT_PATH_NOT_FOUND => return syscall.fail(error.FileNotFound),
.NO_MEDIA_IN_DEVICE => return syscall.fail(error.NoDevice),
.SHARING_VIOLATION => return syscall.fail(error.AccessDenied),
.ACCESS_DENIED => return syscall.fail(error.AccessDenied),
.PIPE_NOT_AVAILABLE => return syscall.fail(error.NoDevice),
.FILE_IS_A_DIRECTORY => return syscall.fail(error.IsDir),
.NOT_A_DIRECTORY => return syscall.fail(error.NotDir),
.USER_MAPPED_FILE => return syscall.fail(error.AccessDenied),
else => |status| return syscall.unexpectedNtstatus(status),
};
}
/// Expects `app_buf` to contain exactly the app name, and `dir_buf` to contain exactly the dir path.
/// After return, `app_buf` will always contain exactly the app name and `dir_buf` will always contain exactly the dir path.
/// Note: `app_buf` should not contain any leading path separators.