ExInterlockedAddUlong

ULONG
ExInterlockedAddUlong(
IN PULONG Addend,
IN ULONG Increment,
PKSPIN_LOCK Lock
);

ExInterlockedAddUlong adds an unsigned long value to a given unsigned integer as an atomic operation.

Parameters

Addend: Points to an unsigned long integer whose value is to be adjusted by the Increment value.
Increment: Is an unsigned long integer to be added.
Lock: Points to a spin lock to be used to synchronize access to the Addend.

Return Value

ExInterlockedAddUlong returns the original (unsummed) value of the Addend.

Comments

Consider using InterlockedExchangeAdd instead of this routine. InterlockedExchangeAdd can be more efficient because it does not use a spin lock and it is inlined by the compiler.

Support routines that do interlocked operations are assumed to be incapable of causing a page fault. That is, neither their code nor any of the data they touch can cause a page fault without bringing down the system. They use spin locks to achieve atomicity in SMP machines. The caller must provide resident storage for the Lock, which must be initialized with KeInitializeSpinLock before the initial call to an ExInterlockedXxx.

The Lock passed to ExInterlockedAddULong is used to assure that the add operation on Addend is atomic with respect to any other operations on the same value which synchronize with this same spin lock.

ExInterlockedAddUlong masks interrupts. Consequently, it can be used for synchronization between an ISR and other driver code, provided that the same Lock is never reused in a call to a routine that runs at IRQL DISPATCH_LEVEL.

Note that calls to InterlockedXxxxxxx are guaranteed to be atomic with respect to other InterlockedXxxxxx calls without caller supplied spin locks.

Callers of ExInterlockedAddUlong run at any IRQL.