How many memory an Excel XLL plugin can have?

Question

I'm using C++ to write a .XLL plugin for Microsoft Excel, with the help of XLW library. My operating system is windows 7 64-bit version, with 32 GB RAM; but my Excel is Excel 2010, 32-bits version.

Checking with GlobalMemoryStatusEx, it shows that the code in XLL can only see about 1200 MB virtual memory available (from ullAvailVirtual in struct _MEMORYSTATUSEX), though the physical memory available (ullAvailPhys) is around 23 GB.

As my code requires quite a lot memory (about 100MB per computation thread), after issuing 12 threads it hits the bad allocation error.

Is there a way to increase the memory available?

Is this a limitation of Excel XLL plugin? In a Console Application, GlobalMemoryStatusEx reports around 2034 MB Virtual Memory available.
Is this a limitation of XLW library?
Is this a limitation of 32-bit Excel?

Martin Bonner supports Monica · Accepted Answer · 2016-12-08T11:46:33.013

1

An XLL is actually just a renamed DLL. If you have a 32-bit Excel, then the whole Excel process has a 32-bit virtual address space to live in (and Windows reserves half of that for the OS). So your process (both XLL and Excel itself), is limited to a total of 2G.

Your choices are:

Switch to a 64-bit Excel (which implies that your XLL will need to be 64-bit)
Let the XLL remain 32-bit, and make it launch a separate (possibly 64-bit) process, and do the processing in that.

The latter option is obviously much more complicated, and copying data between processes will not be that snappy - but it is an option.

edited Dec 08 '16 at 11:46

answered Dec 08 '16 at 11:41

Martin Bonner supports Monica

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Do you mean that, my `A.XLL` is still a 32-bit DLL, but it lanches a separate (possibly 64-bit) process `B.exe`, and have the `32-bit Excel` - `32-bit A.XLL` - `64-bit B.exe` communication? – athos Dec 08 '16 at 11:45
@athos: Yes, exactly that. – Martin Bonner supports Monica Dec 08 '16 at 11:45
If so, how could `A.XLL` talks with `B.exe` efficiently? The speed is my concern. – athos Dec 08 '16 at 11:46
Probably the fastest way is going to be memory mapped files for bulk data transfer. You might want to use some other mechanism for notifications (Windows messages, TCP IP, Windows Events, etc). – Martin Bonner supports Monica Dec 08 '16 at 11:47

How many memory an Excel XLL plugin can have?

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