_AcquireSpinLock
Microsoft Specific
Used to enter a critical section, effectively ensuring that no other thread is able to execute the code path between the call to _AcquireSpinLock and the call to _ReleaseSpinLock.
void _AcquireSpinLock(
unsigned __int64 * Lock
)
Parameters
- [out] Lock
The lock variable: set to 1 when a lock is acquired.
Remarks
Other threads attempting to execute _AcquireSpinLock block until the thread with the lock calls _ReleaseSpinLock.
This routine is only available as an intrinsic.
Requirements
| Intrinsic | Architecture |
|---|---|
_AcquireSpinLock |
IPF |
Header file <intrin.h>
Example
// spinlock.cpp
// compile with: /MT
// processor: IPF
#include <cstdlib>
#include <cstdio>
#include <process.h>
#include <windows.h>
#include <intrin.h>
#pragma intrinsic(_AcquireSpinLock, _ReleaseSpinLock)
// Data to protect.
volatile LONG data = 0;
unsigned __int64 lock = 0;
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 the simple thread
void __cdecl SimpleThread(void* pParam)
{
int thread = *( (int*) pParam);
int k = 1;
_AcquireSpinLock(&lock);
int x1 = data++;
for (int i = 0; i < 10000; i++)
{
// Perform some calculations to create a delay
k += i;
k %= 10000;
}
int x2 = data++;
printf_s("%I64d %d %d %d\n", lock, thread, x1, k);
printf_s("%I64d %d %d %d\n", lock, thread, x2, k);
_ReleaseSpinLock(&lock);
if (x2 - x1 != 1)
printf_s("Error!\n");
}
Sample Output
1 1 0 5001 1 1 1 5001 1 3 2 5001 1 3 3 5001 1 2 4 5001 1 2 5 5001 1 4 6 5001 1 4 7 5001 1 5 8 5001 1 5 9 5001 1 6 10 5001 1 6 11 5001