How best to synchronize memory access shared between kernel and user space, in Windows.

Question

I can't find any function to acquire spinlock in Win32 Apis.
Is there a reason?

When I need to use spinlock, what do I do?

I know there is an CriticalSectionAndSpinCount funtion.
But that's not what I want.

Edit:
I want to synchronize a memory which will be shared between kernel space and user space. -The memory will be mapped.
I should lock it when I access the data structure and the locking time will be very short.
The data structure(suppose it is a queue) manages event handles to interaction each other.
What synchronization mechanism should I use?

Answer 1

A spinlock is clearly not appropriate for user-level synchronization. From http://www.microsoft.com/whdc/driver/kernel/locks.mspx:

All types of spin locks raise the IRQL to DISPATCH_LEVEL or higher. Spin locks are the only synchronization mechanism that can be used at IRQL >= DISPATCH_LEVEL. Code that holds a spin lock runs at IRQL >= DISPATCH_LEVEL, which means that the system’s thread switching code (the dispatcher) cannot run and, therefore, the current thread cannot be pre-empted.

Imagine if it were possible to take a spin lock in user mode: Suddenly the thread would not be able to be pre-empted. So on a single-cpu machine, this is now an exclusive and real-time thread. The user-mode code would now be responsible for handling interrupts and other kernel-level tasks. The code could no longer access any paged memory, which means that the user-mode code would need to know what memory is currently paged and act accordingly. Cats and dogs living together, mass hysteria!

Perhaps a better question would be to tell us what you are trying to accomplish, and ask what synchronization method would be most appropriate.

Answer 2

There is a managed user-mode SpinLock as described here. Handle with care, as advised in the docs - it's easy to go badly wrong with these locks.

The only way to access this in native code is via the Win32 API you named already - CriticalSectionAndSpinCount and its siblings.