[erlang-questions] How long a NIF can block the Erlang BEAM?
Tue Nov 23 11:10:02 CET 2010
On Tue, 23 Nov 2010 17:34:07 +0900, Kenji Rikitake
> I wonder how long a NIF can block the Erlang BEAM. To put it another
> way, I want to know the maximum time allowed a NIF can run in the
> One millisecond? Or 100 microseconds? Or even shorter?
> I am asking this to find out if I can run a fairly large operation of
> initialized a random number table in a NIF.
AFAIK, there are no hard limits: a NIF could block its Erlang
VM thread as long as needed --- but long-running NIFs will
disrupt the scheduling of other Erlang processes, and reduce
the responsiveness of unrelated applications running in the
If you need to perform a long operation, and latency is not
an issue, you could spawn a dedicated NIF thread (using
enif_thread_create()), and let it send its return value to
the calling Erlang process (using enif_send()).
Thus, in your sfmt.erl file, you could do something like this:
This way, init_gen_rand/0 will still block until the PRNG is
ready, but its Erlang process will be scheduled away.
BTW: if you use this strategy, you may also need to perform
the PRNG initialization within the "on_load" function
(otherwise, you may need to protect the PRNG table with
Alceste Scalas <>
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