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4/8/2010

This function performs an atomic comparison of the specified values and exchanges the values based on the outcome of the comparison. The function prevents more than one thread from using the same variable simultaneously.

Syntax 

LONG InterlockedCompareExchange(
  LPLONG 
Destination,
  LONG 
Exchange,
  LONG 
Comperand
);

Parameters

Destination

[in, out] Specifies the address of the destination value. The sign is ignored.

Exchange

[in] Specifies the exchange value. The sign is ignored.

Comperand

[in] Specifies the value to compare to Destination. The sign is ignored.

Return Value

Initial value of the destination.

Remarks

The InterlockedCompareExchange, InterlockedDecrement, InterlockedExchange, InterlockedExchangeAdd, and InterlockedIncrementfunctions 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 InterlockedCompareExchangefunction performs an atomic comparison of the Destinationvalue with the Comperandvalue. If the Destinationvalue is equal to the Comperandvalue, the Exchangevalue is stored in the address specified by Destination. Otherwise, no operation is performed.

The variables for InterlockedCompareExchangemust be aligned on a 32-bit boundary.

Each object type, such as memory maps, semaphores, events, message queues, mutexes, and watchdog timers, has its own separate namespace. Empty strings ("") are handled as named objects. On Windows desktop-based platforms, synchronization objects all share the same namespace.

Requirements

Header windows.h
Library coredll.lib
Windows Embedded CE Windows CE .NET 4.0 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also

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