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