Boost logo

Boost :

Subject: Re: [boost] [gil io_new review] Reading images from in-memorysources
From: Domagoj Saric (dsaritz_at_[hidden])
Date: 2010-12-07 12:12:43

"Kenny Riddile" <kfriddile_at_[hidden]> wrote in message
> Yes, implementations of a spec are free to implement their requirements
> however they like (assuming no other requirements are violated). That
> being said, I just looked at the implementation of array_source and it
> appears that none of the data in the array is being copied.

Yes, AFAICT also, the array_source implementation does not copy the input
data (in fact, even if the documentation does not state it explicitly, it
would IMO be common sense to assume if it did actually copy the data
this would constitute a performance bug by any standard)...

However, redundant copying is only part of the issue here (in some use cases
possibly even a less important one) as boost::iostreams::array_source still
uses the std::iostreams infrastructure which means that includes all of its
redundant horrors (locales, mutexes, virtual functions, RTTI, dynamic memory
allocation, exceptions, transformations......)...
Simply looking at/stepping through the release-mode generated assembly for
merely the boost::iostreams::stream<array_source> constructor will make most
heads dizzy...

A proper (and zero overhead at that) way to model an in memory image would
be a plain boost::iterator_range<> ... Not only because it is free of all
the iostream monstrosities but because with backends like LibJPEG and
LibTIFF reading an image from a boost::iterator_range<> can be accomplished
without the LibXXX backend making a single seek/read callback (back to the
GIL.IO 'device' that is in this case a boost::iterator_range<> or a
transparent wrapper around it) because it already has all the data readily
Additionally with the boost::iterator_range<> approach it is easy to add
memory mapped file support for reading images (where the input image/file is
again represented with a plain boost::iterator_range<> with all the benefits
outlined above)...

"What Huxley teaches is that in the age of advanced technology, spiritual
devastation is more likely to come from an enemy with a smiling face than
from one whose countenance exudes suspicion and hate."
Neil Postman

Boost list run by bdawes at, gregod at, cpdaniel at, john at