InterlockedCompareExchangeToUser function (usermode_accessors.h)

The InterlockedCompareExchangeToUser function performs an atomic compare-and-exchange operation on a 32-bit value in user-mode memory.

Syntax

LONG InterlockedCompareExchangeToUser(
  LONG volatile *Destination,
  LONG          ExChange,
  LONG          Comperand
);

Parameters

Destination

[in, out] A pointer to the user-mode memory location containing the destination value. The pointer must be naturally aligned for the data type; that is, the memory location must be 4-byte aligned since Destination points to a 4-byte type.

ExChange

[in] The exchange value.

Comperand

[in] The value to compare to Destination.

Return value

The function returns the initial value of the Destination parameter.

Remarks

The interlocked functions provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. This function is atomic with respect to calls to other interlocked functions. It generates a full memory barrier to ensure that memory operations are completed in order.

This function provides atomic compare-and-exchange access to a 32-bit value in user-mode memory. The function compares the Destination value with the Comperand value. If the Destination value is equal to the Comperand value, the ExChange value is stored in the address specified by Destination. Otherwise, no operation is performed.

The function raises a structured exception if the operation fails, such as when the destination address is not a valid user-mode address or is inaccessible.

This function works on all versions of Windows, not just the latest. You need to consume the latest WDK to get the function declaration from the usermode_accessors.h header. You also need the library (umaccess.lib) from the latest WDK. However, the resulting driver will run fine on older versions of Windows.

Requirements

See also

InterlockedCompareExchangeToMode

InterlockedCompareExchange64ToUser