InterlockedCompareExchangeToMode function (usermode_accessors.h)

The InterlockedCompareExchangeToMode function performs an atomic compare-and-exchange operation on a 32-bit value, based on the specified processor mode.

Syntax

LONG InterlockedCompareExchangeToMode(
  LONG volatile   *Destination,
  LONG            ExChange,
  LONG            Comperand,
  KPROCESSOR_MODE Mode
);

Parameters

Destination

[in, out] A pointer to the 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.

Mode

[in] The processor mode that determines how the memory access is performed. Mode can be one of the following values.

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 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 behavior depends on the processor mode specified:

• When Mode is UserMode, the function ensures that the destination address is a valid user-mode address and performs the operation safely for user-mode memory access.
• When Mode is KernelMode, the function operates directly on kernel-mode addresses.

The function raises a structured exception if the operation fails, such as when the destination address is not accessible or is invalid for the specified mode.

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

InterlockedCompareExchangeToUser

InterlockedCompareExchange64ToMode