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#pragma once
#include <windows.h>
/* This data structure holds one item, and returns you the old item when you replace it
it's sort of a "stack of 1" */
template <class value_t>
class LockFreeItem
{
public:
typedef value_t *ptr_t;
LockFreeItem() { item = 0; }
value_t *GetItem()
{
for(;;) // keep trying until we get this right
{
volatile ptr_t ret;
InterlockedExchangePointer(&ret, item);
if (InterlockedCompareExchangePointer((volatile PVOID *)&item, 0, ret) == ret)
return ret;
}
}
// returns the previous value
value_t *SetItem(value_t *new_item)
{
for(;;) // keep trying until we get this right
{
volatile ptr_t ret;
InterlockedExchangePointer(&ret, item);
if (InterlockedCompareExchangePointer((volatile PVOID *)&item, new_item, ret) == ret)
return ret;
}
}
// if there's already a value, returns what you passed in
value_t *SetItemIfZero(value_t *new_item)
{
if (InterlockedCompareExchangePointer((volatile PVOID *)&item, new_item, 0) == 0)
return 0;
else
return new_item;
}
volatile ptr_t item;
};
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