[erlang-questions] Small and large (>=64B) binaries? How do they differ?

Frank Muller <>
Wed Sep 20 18:39:25 CEST 2017


Thanks again Dmytro for your time.

Let assume I’m inside my NIF and would like to increment the refcount of a
binary (hope this is the right call: enif_keep_resource).

Can i increment refcount for let say 1 million binaries (or even more)?

What are the consequences of doing that?
I assume I'll release them at the end.

/Frank

>From what I remember (some people who recently have worked with binaries
> might know much more)
>
> Binaries in binary heap (large bins) have own structure, i think the
> master storage structure is called Binary. This is confusing even to me
> so have a spoon of salt with this advice :)
>
> https://github.com/erlang/otp/blob/master/erts/emulator/beam/erl_binary.h
> https://github.com/erlang/otp/blob/master/erts/emulator/beam/binary.c
>
> Binaries stored outside processes (proc-bins ProcBin), smaller than 64b
> (proc-bins, structure ErlHeapBin i think) and sub-bins (ErlSubBin) have
> own tag bit combinations on the process heap. So the GC and VM always know
> what they have found. They might share part of C structure pointing to the
> external binary, you can observe it as a macro included in the respective
> structures, think is called ErtsMagicBinary. Macros is_not_binary, binary_size,
> binary_bytes and ERTS_GET_REAL_BIN might become useful.
>
> Also ref-bins all contain 'next' pointer, as a part of long linked list
> which begins somewhere in process header (one such list belongs to every
> process) and during GC this list is traversed to find out which ref-bins
> are about to die and refcount is decremented.
>
> 2017-09-20 6:08 GMT+02:00 Frank Muller <>:
>
>> Hi Dmytro,
>>
>> Thanks for the hint. I found a lot of references to these keywords ...
>> bit lost.
>>
>> How about the rest of the questions?
>>
>> /Frank
>>
>> Tue. Sept. 19 2017 à 22:13, Dmytro Lytovchenko <
>> > wrote :
>>
>>> Look for binary, procbin, refbin (probably), and sub binary. Use this as
>>> keywords
>>>
>>> On 19 Sep 2017 21:50, "Frank Muller" <> wrote:
>>>
>>>> Hi guys
>>>>
>>>> Newbie here…
>>>>
>>>> Can someone point me please to the C data structure representing small
>>>> and large binaries inside the VM?
>>>> Do they’ve the same C representation (or not)?
>>>> How the VM distinguishes between them internally?
>>>>
>>>> Thank you.
>>>> /Frank
>>>>
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>>>> 
>>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>>
>>>>
>
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