_InterlockedDecrement Intrinsic Functions

Article
06/05/2017

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The latest version of this topic can be found at _InterlockedDecrement Intrinsic Functions.

Microsoft Specific**

Provides compiler intrinsic support for the Win32 Windows SDK InterlockedDecrement function.

Syntax

long _InterlockedDecrement(  
   long * lpAddend  
);  
long _InterlockedDecrement_acq(  
   long * lpAddend  
);  
long _InterlockedDecrement_rel(  
   long * lpAddend  
);  
long _InterlockedDecrement_nf(  
   long * lpAddend  
);  
short _InterlockedDecrement16(  
   short * lpAddend  
);  
short _InterlockedDecrement16_acq(  
   short * lpAddend  
);  
short _InterlockedDecrement16_rel(  
   short * lpAddend  
);  
short _InterlockedDecrement16_nf(  
   short * lpAddend  
);  
__int64 _InterlockedDecrement64(  
   __int64 * lpAddend  
);  
__int64 _InterlockedDecrement64_acq(  
   __int64 * lpAddend  
);  
__int64 _InterlockedDecrement64_rel(  
   __int64 * lpAddend  
);   
__int64 _InterlockedDecrement64_nf(  
   __int64 * lpAddend  
);

Parameters

[in, out] lpAddend
Pointer to the variable to be decremented.

Return Value

The return value is the resulting decremented value.

Requirements

Intrinsic	Architecture
`_InterlockedDecrement`, `_InterlockedDecrement16`, `_InterlockedDecrement64`	x86, ARM, x64
`_InterlockedDecrement_acq`, `_InterlockedDecrement_rel`, `_InterlockedDecrement_nf`, `_InterlockedDecrement16_acq`, `_InterlockedDecrement16_rel`, `_InterlockedDecrement16_nf`, `_InterlockedDecrement64_acq`, `_InterlockedDecrement64_rel`, `_InterlockedDecrement64_nf`,	ARM

Header file <intrin.h>

Remarks

There are several variations on _InterlockedDecrement that vary based on the data types they involve and whether processor-specific acquire or release semantics is used.

While the _InterlockedDecrement function operates on 32-bit integer values, _InterlockedDecrement16 operates on 16-bit integer values and _InterlockedDecrement64 operates on 64-bit integer values.

On ARM platforms, use the intrinsics with _acq and _rel suffixes if you need acquire and release semantics, such as at the beginning and end of a critical section. The intrinsics with an _nf ("no fence") suffix do not act as a memory barrier.

The variable pointed to by the lpAddend parameter must be aligned on a 32-bit boundary; otherwise, this function fails on multiprocessor x86 systems and any non-x86 systems. For more information, see align.

These routines are only available as intrinsics.

Example

// compiler_intrinsics_interlocked.cpp  
// compile with: /Oi  
#define _CRT_RAND_S  
  
#include <cstdlib>  
#include <cstdio>  
#include <process.h>  
#include <windows.h>  
  
// To declare an interlocked function for use as an intrinsic,  
// include intrin.h and put the function in a #pragma intrinsic   
// statement.  
#include <intrin.h>  
  
#pragma intrinsic (_InterlockedIncrement)  
  
// Data to protect with the interlocked functions.  
volatile LONG data = 1;  
  
void __cdecl SimpleThread(void* pParam);  
  
const int THREAD_COUNT = 6;  
  
int main() {  
   DWORD num;  
   HANDLE threads[THREAD_COUNT];  
   int args[THREAD_COUNT];  
   int i;  
  
   for (i = 0; i < THREAD_COUNT; i++) {  
     args[i] = i + 1;  
     threads[i] = reinterpret_cast<HANDLE>(_beginthread(SimpleThread, 0,   
                           args + i));  
      if (threads[i] == reinterpret_cast<HANDLE>(-1))  
         // error creating threads  
         break;  
   }  
  
   WaitForMultipleObjects(i, threads, true, INFINITE);  
}  
  
// Code for our simple thread  
void __cdecl SimpleThread(void* pParam) {  
   int threadNum = *((int*)pParam);  
   int counter;  
   unsigned int randomValue;  
   unsigned int time;  
   errno_t err = rand_s(&randomValue);  
  
   if (err == 0) {  
      time = (unsigned int) ((double) randomValue / (double) UINT_MAX * 500);  
      while (data < 100) {  
         if (data < 100) {  
            _InterlockedIncrement(&data);  
            printf_s("Thread %d: %d\n", threadNum, data);  
         }  
  
         Sleep(time);   // wait up to half of a second  
      }  
   }  
  
   printf_s("Thread %d complete: %d\n", threadNum, data);  
}

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