[erlang-questions] How long a NIF can block the Erlang BEAM?

Matthias Lang <>
Tue Nov 23 11:30:40 CET 2010

Kenji> >I wonder how long a NIF can block the Erlang BEAM.  To put it another
Kenji> >way, I want to know the maximum time allowed a NIF can run in the
Kenji> >BEAM.
Kenji> >One millisecond? Or 100 microseconds? Or even shorter?

Alceste> AFAIK, there are no hard limits: a NIF could block its Erlang
Alceste> VM thread as long as needed --- but long-running NIFs will
Alceste> disrupt the scheduling of other Erlang processes, and reduce
Alceste> the responsiveness of unrelated applications running in the
Alceste> same VM.

Exactly. The limit is whatever the tolerable latency in your
application is. If it's fine for your application to freeze for 500ms,
then a NIF which takes 500ms to run is ok.

The rest of Erlang is made so that an application can react to things
within a few milliseconds, so 100 microseconds is unlikely to give
anyone a nasty surprise. 100 milliseconds will.


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