[erlang-questions] map over bitstring

[Morten Krogh]

Thanks, Per. That was also the only reason I could see. And it doesn't 
really hurt to allocate too much, so it is a good idea.

Morten.

On 10/22/10 4:27 PM, Per Gustafsson wrote:
> The reason for 300 MB is an optimizarion for building binaries which 
> allocates extra space for possible future additions to the binary.
>
> Per
>
> 2010/10/22 Morten Krogh <mk@REDACTED <mailto:mk@REDACTED>>
>
>     Hi Jesper
>
>
>
>     On 10/22/10 2:26 PM, Jesper Louis Andersen wrote:
>
>         On Fri, Oct 22, 2010 at 1:15 PM, Morten Krogh<mk@REDACTED
>         <mailto:mk@REDACTED>>  wrote:
>
>             Hi Jesper
>
>             Thanks for the link!
>
>             It seems to me that the requirement that binaries must be
>             contiguous in
>             memory is quite strict.
>             If that requirement was abandoned, binaries could be lists
>             of ProcBins, or
>             whatever they are called, instead.
>
>         This is essentially iolists you are proposing. They are
>         already in the
>         language, see
>
>         http://prog21.dadgum.com/70.html
>
>         for a quick discussion of them.
>
>
>     Yes, but my suggestion would let the VM handle lists of binaries
>     instead of the application programmer.
>     My lists only contain binaries. They are not full iolists, which I
>     guess they could be.
>
>
>
>             Simple example from my module zip2
>
>         [...]
>
>             Why is the memory usage 300 MB. It should have been 100MB,
>             and in worst
>             case, with naive copying, 200MB.
>             But 300 MB.
>
>         My guess is that B has some excess space allocated for
>         appending which
>         amount to around 100Mb (you should probably not go with a
>         100Mb binary
>         in the first place, but rather an iolist of smaller binaries). B's
>         extra space will only get shrunk away when the runtime decide to
>         transfer the binary to another process and it is not before it
>         is sent
>         back to the shell as a message.
>
>         My guess might be wrong though.
>
>     It is actually 200 MB extra.
>
>     Transfering the binaries to the shell, removes 100 MB, so you were
>     right. But 200 MB in total is still allocated.
>
>     It is still not clear to me. At B = <<A/binary, 97>>, 200 MB is
>     allocated behind A? Or somewhere else?
>     And after message passing, 200 MB of extra space is shrunk to
>     100MB beyond the 100MB of actual data?
>
>     Morten.
>
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