[erlang-questions] The "ei" API and passing *shared* binaries / parts

[Vance Shipley]

You want to use a linked in driver:
http://erlang.org/doc/tutorial/c_portdriver.html

On Thu, Jun 22, 2017 at 12:18 PM, Rick van Rein <rick@REDACTED> wrote:
> Hello,
>
> I have looked at the ei module, both documentation and code.  It looks
> quite efficient, but I am missing something, and I wonder if it is
> somewhere else.
>
> I started a discussion in the Apache Qpid user forum about integration
> their AMQP 1.0 API with Erlang; there does not seem to be a way of
> getting to AMQP 1.0 from Erlang, and given that both are designed for
> rock-solid software construction that would be a useful marriage.  And
> the Go port has a variant API named "electron" that is aimed at
> "synchronous" communication under the assumption of many small processes.
>
> Having to pass a (very) large message into Erlang, and possibly out at
> the other end, requires cloning the entire binary over ei, AFAIK.
> Although Erlang is rumoured to internally use malloc() for binaries,
> with refcounting and parts pointing there (no doubt charging the
> refcount) this functionality (shared memory allocation, sharing parts,
> unsharing) does not seem to be available externally.  Nor did I find a
> way of exchanging shared memory and parts over ei.  Did I miss it?  It
> would improve efficiency in applications where Erlang is on the sending
> or receiving end of AMQP, as well as an intermediate in the pathway.
>
> There is one more use of such an ei facility -- and that is where an
> existing parser in C is asked to decipher a block of text (like SIP,
> XML, ...) or binary (AMQP, DNS, OpenPGP, ...) and return parts thereof
> as components to work on.  It's a pitty to have to copy in both
> directions, rather than using an existing malloc() and simply pointing
> into it.
>
> Are such facilities available but have I missed them?
>
> Cheers,
>  -Rick
>
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-- 
     -Vance