InterlockedExchange

The InterlockedExchange function atomically exchanges a pair of 32-bit values. The function prevents more than one thread from using the same variable simultaneously.

LONG InterlockedExchange(
  LPLONG Target,
               // pointer to the 32-bit value to exchange
  LONG Value   // new value for the LONG value pointed to by Target
);
 

Parameters

Target

Pointer to the LONG value to exchange. The function sets this LONG value to Value, and returns its prior value.

Value

Specifies a new value for the LONG value pointed to by Target.

Return Values

The function returns the prior value of the LONG value pointed to by Target.

Remarks

The functions InterlockedExchange, InterlockedCompareExchange, InterlockedDecrement, InterlockedExchangeAdd, 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 variable pointed to by the Target parameter must be aligned on a 32-bit boundary; otherwise, this function will fail on multiprocessor x86 systems.

QuickInfo

  Windows NT: Requires version 3.5 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winbase.h.
  Import Library: Use kernel32.lib.

See Also

Synchronization Overview, Synchronization Functions, InterlockedCompareExchange, InterlockedDecrement, InterlockedExchangeAdd, InterlockedIncrement