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When the Erlang VM beam runs some code written in C,the other processes written in Erlang was not scheduled. For example:

static ERL_NIF_TERM
        nifsleep(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
        {
            sleep(10);
            return enif_make_atom(env, "ok");
        }

when you call this C function in Erlang,the other processes was not schedulling normally. I want to know why? Is this a feature or is limited by the implementation(that is,this is a bug)?

The address of the code above is in:https://github.com/davisp/sleepy

Hynek -Pichi- Vychodil
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user1535183
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1 Answers1

6

beam processes are not mapped to OS threads directly. There is normally 1 scheduler per core. Your call to

sleep(10);

is blocking the scheduler that executed it (as expected, otherwise it would have to intercept that call somehow to make it non-blocking), and so the scheduler can't execute any other erlang process until the call returns. Long running nif are strongly discouraged. A quick google is enough to find many references, see for example http://www.erlang.org/doc/man/erl_nif.html#lengthy_work

http://osdir.com/ml/erlang-questions-programming/2013-02/msg00275.html

http://ninenines.eu/articles/erlang-scalability

for comprehensive info about how the scheduler work, see http://jlouisramblings.blogspot.com.ar/2013/01/how-erlang-does-scheduling.html

ppolv
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