childKill

fn childKill(userdata: ?*anyopaque, child: *process.Child) void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));

    var maybe_sync: CancelRegion.Sync.Maybe = .{ .sync = .initBlocked(ev) };
    defer maybe_sync.deinit(ev);
    defer ev.childCleanup(child);

    const pid = child.id.?;
    while (true) switch (linux.errno(linux.kill(pid, .TERM))) {
        .SUCCESS => break,
        .INTR => {},
        .PERM => return,
        .INVAL => |err| return errnoBug(err) catch {},
        .SRCH => |err| return errnoBug(err) catch {},
        else => |err| return unexpectedErrno(err) catch {},
    };
    maybe_sync.leaveSync(ev);

    var info: linux.siginfo_t = undefined;
    while (true) {
        const thread = maybe_sync.cancel_region.awaitIoUring() catch |err| switch (err) {
            error.Canceled => unreachable, // blocked
        };
        thread.enqueue().* = .{
            .opcode = .WAITID,
            .flags = 0,
            .ioprio = 0,
            .fd = pid,
            .off = @intFromPtr(&info),
            .addr = 0,
            .len = @backingInt(linux.P.PID),
            .rw_flags = 0,
            .user_data = @intFromPtr(maybe_sync.cancel_region.fiber),
            .buf_index = 0,
            .personality = 0,
            .splice_fd_in = linux.W.EXITED,
            .addr3 = 0,
            .resv = 0,
        };
        ev.yield(null, .nothing);
        switch (maybe_sync.cancel_region.errno()) {
            .SUCCESS => return,
            .INTR, .CANCELED => {},
            .CHILD => |err| return errnoBug(err) catch {}, // Double-free.
            else => |err| return unexpectedErrno(err) catch {},
        }
    }
}