Re: Problem opening large files into NSDocument
Re: Problem opening large files into NSDocument
- Subject: Re: Problem opening large files into NSDocument
- From: Jens Alfke <email@hidden>
- Date: Wed, 9 Jun 2010 13:30:57 -0700
On Jun 9, 2010, at 12:56 PM, Pascal Harris wrote:
> I'm trying open a (very) large file (4GB) into an NSDocument. Small files open file. The monster fails with the error: "The document "test.pst" could not be opened. The file is too large." What gives - and how do I overcome it? What is the maximum size that I can open using NSDocument?
NSDocument has at least three different methods you can override to get the file contents. You’re using the simplest one, that hands you the entire contents of the file in an NSData. This doesn’t scale well to huge files. You want to override one of the alternative methods where you get handed the path or URL of the file — then you can read the data yourself however you want.
Just keep in mind that in a 32-bit process you only have about 3GB of available address space (regardless of how much physical RAM the computer has.) And that address space gets fragmented as other memory blocks are allocated and freed, so generally the largest contiguous block that can be allocated is a lot smaller.
If possible you should stream the file contents using an NSFileHandle or lower-level I/O calls like fopen/fread/fclose. If you absolutely have to read an entire huge file into an NSData, you’ll get much better performance if you memory-map it (using the NSMappedRead option.)
—Jens_______________________________________________
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