futexWaitUncancelable

fn futexWaitUncancelable(userdata: ?*anyopaque, ptr: *const u32, expected: u32) void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    var cancel_region: CancelRegion = .initBlocked();
    defer cancel_region.deinit();
    const thread = cancel_region.awaitIoUring() catch |err| switch (err) {
        error.Canceled => unreachable, // blocked
    };
    thread.enqueue().* = .{
        .opcode = .FUTEX_WAIT,
        .flags = 0,
        .ioprio = 0,
        .fd = @bitCast(linux.FUTEX2_FLAGS{ .size = .U32, .private = true }),
        .off = expected,
        .addr = @intFromPtr(ptr),
        .len = 0,
        .rw_flags = 0,
        .user_data = @intFromPtr(cancel_region.fiber),
        .buf_index = 0,
        .personality = 0,
        .splice_fd_in = 0,
        .addr3 = std.math.maxInt(u32),
        .resv = 0,
    };
    ev.yield(null, .nothing);
    switch (cancel_region.errno()) {
        .SUCCESS => {}, // notified by `wake()`
        .INTR, .CANCELED => {}, // caller's responsibility to retry
        .AGAIN => {}, // ptr.* != expect
        .INVAL => {}, // possibly timeout overflow
        .FAULT => recoverableOsBugDetected(), // ptr was invalid
        else => recoverableOsBugDetected(),
    }
}