new and VirtualAlloc

Hello everyone,


I heard some points that the memory allocated by new does not belongs to virtual memory, and onlymemory allocated by VirtualAlloc belongs to virtual memory.

1.

I think this statement is not correct. Since all memory touched by current process belongs to virtual memory (either reserved or committed). No matter how (through which API) developer is using.

2.

And new always utilize VirtualAlloc in underlying internal implementation code, so new (in implementation point of view) will consume virtual memory -- the same as what VirtualAlloc does.

Are my points (1) and (2) correct?


thanks in advance,
George

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Originally Posted by George2

I heard some points that the memory allocated by new does not belongs to virtual memory, and onlymemory allocated by VirtualAlloc belongs to virtual memory.

1.

I think this statement is not correct. Since all memory touched by current process belongs to virtual memory (either reserved or committed). No matter how (through which API) developer is using.

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This is false. All memory you allocate is access within your virtual memory, whether it be new, malloc, VirtualAlloc, HeapAlloc, or whatever.

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2.

And new always utilize VirtualAlloc in underlying internal implementation code, so new (in implementation point of view) will consume virtual memory -- the same as what VirtualAlloc does.

Are my points (1) and (2) correct?

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No, that's false. This I would believe is implementation defined, but I can tell you that Microsoft's implementation uses HeapAlloc and not VirtualAlloc.

Thanks Elysia,

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Originally Posted by Elysia

No, that's false. This I would believe is implementation defined, but I can tell you that Microsoft's implementation uses HeapAlloc and not VirtualAlloc.

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1. I think you mean new is using HeapAlloc, right?

2. HeapAlloc is using VirtualAlloc? Or as a standalone implementation?


regards,
George

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Originally Posted by George2

1. I think you mean new is using HeapAlloc, right?

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As I mentioned, every vendor is free to implement the CRT and STL as they want as long as the result is the same. Thus some may use VirtualAlloc, some may use HeapAlloc. It's up to the vendor.
Microsoft is using HeapAlloc.

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2. HeapAlloc is using VirtualAlloc? Or as a standalone implementation?

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They are stand along implementation because they do not do the same thing and do not work the same way.

Thanks Elysia,


It is my mistake that I think HeapAlloc is always based on VirtualAlloc. Now from your description, I understand they have no dependent relationship.

Could you provide some more information about what do you mean "do not do the same thing and do not work the same way"?

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Originally Posted by Elysia

As I mentioned, every vendor is free to implement the CRT and STL as they want as long as the result is the same. Thus some may use VirtualAlloc, some may use HeapAlloc. It's up to the vendor.
Microsoft is using HeapAlloc.


They are stand along implementation because they do not do the same thing and do not work the same way.

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regards,
George

Maybe you should study what a heap is. In Windows, you create several heaps, some private, as well. HeapAlloc creates a heap.
VirtualAlloc on the other hand, simply reserves or commits pages within your virtual memory space.

Thanks Elysia,


I used them before. I remembered some time before, I saw a architecture figure which describes all memory on Windows are based on virtual memory. So, I thought HeapAlloc is just an exported interface to provide application with heap perspective operation, and internally still based on VirtualAlloc (dealing with raw pages). :-)

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Originally Posted by Elysia

Maybe you should study what a heap is. In Windows, you create several heaps, some private, as well. HeapAlloc creates a heap.
VirtualAlloc on the other hand, simply reserves or commits pages within your virtual memory space.

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regards,
George

Even if they are, the API has two different purposes, so they should not be treated the same. Even if they wrap each other in the internal implementation, it doesn't matter to us.

Thanks Elysia,

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Originally Posted by Elysia

Even if they are, the API has two different purposes, so they should not be treated the same. Even if they wrap each other in the internal implementation, it doesn't matter to us.

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Back to my original question, I think my question is answered with your patience help. :-)

I want to confirm with you that the answer is, the space allocatedby either new (memory on heap) or VirtualAlloc (memory on virtual memory page directly) is counted as part of virtual memory, right?


regards,
George

Yes, both are virtual memory.

Thanks Elysia,


I appreciate your patience again on this thread. :-)

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Originally Posted by Elysia

Yes, both are virtual memory.

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regards,
George

In the end, everything comes down to the memory API of VirtualAlloc. This includes CreateHeap/HeapAlloc.

The reason is that the Win32 subsystem (ntdll.dll) provides no other way of getting memory from the OS.

Thanks for your final conclusion, CornedBee!

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Originally Posted by CornedBee

In the end, everything comes down to the memory API of VirtualAlloc. This includes CreateHeap/HeapAlloc.

The reason is that the Win32 subsystem (ntdll.dll) provides no other way of getting memory from the OS.

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have a good weekend,
George