InterlockedExchangeAdd

The InterlockExchangeAdd function performs an atomic addition of an increment value to an addend variable. The function prevents more than one thread from using the same variable simultaneously.

LONG InterlockedExchangeAdd (
  LPLONG Addend,  // addend
  LONG Increment  // increment value
);

Parameters

Addend

[in/out] Pointer to the number that will have the Increment number added to it.

Increment

[in] Specifies the number to be added to the variable pointed to by the Addend parameter.

Return Values

The return value is the initial value of the variable pointed to by the Addend parameter.

Remarks

The functions InterlockedExchangeAdd, InterlockedCompareExchange, InterlockedDecrement, InterlockedExchange, and InterlockedIncrement provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. The threads of different processes can use this mechanism if the variable is in shared memory.

The InterlockedExchangeAdd function performs an atomic addition of the Increment value to the value pointed to by Addend. The result is stored in the address specified by Addend. The initial value of the variable pointed to by Addend is returned as the function value.

The variables for InterlockedExchangeAdd must be aligned on a 32-bit boundary; otherwise, this function will fail on multiprocessor x86 systems and any non-x86 systems.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 98.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Synchronization Overview, Synchronization Functions, Interlocked Variable Access, InterlockedCompareExchange, InterlockedDecrement, InterlockedExchange, InterlockedIncrement