On Fri, Feb 6, 2009 at 6:44 PM, Matt Neuburg <m...@tidbits.com> wrote: > On Tue, 03 Feb 2009 00:42:07 +1100, Jacob Rhoden <li...@jacobrhoden.com> > said: >>I am wondering what the best way to read a text file, line by line, when >>the file size is much larger than available memory. > > Would there be a way to do this with dataWithContentsOfMappedFile? I've long > wondered about that... m.
Yes and no. +dataWithContentsOfMappedFile: can be used to do this kind of efficient parsing, as memory mapping of files means that the file is, essentially, read piecemeal, lazily by the operating system on demand. The trouble is that on a modern Mac, "much larger than available memory" almost always also means "much larger than a 32-bit address space can hold". A 32-bit process only gets 4GB of address space, and realistically you can only allocate about 2GB of that contiguously (the rest is broken up or occupied by system frameworks and the like), and even that you can only do one at a time. Even though the file is read lazily, the address space has to be allocated up-front, and if you don't have it, you can't do it. Realistically, if your files are going to be more than a few dozen megabytes, memory mapping them is only practical if you strictly control how many get opened at once, or if you only run in 64-bit mode. Mike _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
