Atomically exchange pointer with nullptr

Question

How can I do the following operations in single atomic operation? Is that possible?

 LARGE_INTEGER* ptr; // field

 void method()
 {
       LARGE_INTEGER* local = ptr;
       ptr = nullptr;
 }

So I want to store pointer from field into local pointer and immediately set that field to nullptr.

In other words, I want to move pointer from field into local variable in single atomic operation.

`LARGE_INTEGER* local = InterlockedExchangePointer(&ptr, nullptr);` May need a cast on the first argument. — Igor Tandetnik, Aug 06 '17 at 04:41
@IgorTandetnik it says `LARGE_INTEGER**` is incompatible with parameter of type `volatile PVOID *` — M.kazem Akhgary, Aug 06 '17 at 04:44
is this cast ok? (it compiles but not sure about runtime behavior) `LARGE_INTEGER* local = (LARGE_INTEGER*)InterlockedExchangePointer((PVOID*)&_ptr, nullptr);` if so you can post it as answer, I really appreciate that, thank you @IgorTandetnik — M.kazem Akhgary, Aug 06 '17 at 04:48

score 2 · Accepted Answer · answered Aug 06 '17 at 06:03

2

Since C++11 you can use std::atomic for this purpose like this:

#include <atomic>
LARGE_INTEGER value;
std::atomic<LARGE_INTEGER*> ptr{&value};
LARGE_INTEGER* local = ptr.exchange(nullptr);

answered Aug 06 '17 at 06:03

Dev Null

1 Answers1