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< Advanced Erlang/OTP ~ Concurrency question when interfacing with a C program |
| ptmoy |
 Posted: Thu Dec 24, 2009 6:11 pm |
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Joined: 24 Dec 2009
Posts: 10
Location: New Jersey, U.S.A.
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I have some calculation routines written in C that I would like to call from Erlang programs. If I want to call the same C routine from many Erlang processes simultaneously, what's the best way to handle the inter-communication between the two languages and not loose the concurrency advantages offered by Erlang?
One way to do this seems to be using multiple OS C processes, or multi-threading the external OS C process (and communicate through one or more ports). Another possibility may be to create multiple C-nodes and let Erlang manage concurrency and distribution the usual way.
I am fairly new to Erlang, and can use all the help I can get in thinking this through. Please post if you have an opinion on this. Thanks in advance.  |
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| uwiger |
| Posted: Thu Dec 24, 2009 8:16 pm |
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Joined: 03 Jul 2006
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Location: Sweden
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ptmoy wrote: I have some calculation routines written in C that I would like to call from Erlang programs. If I want to call the same C routine from many Erlang processes simultaneously, what's the best way to handle the inter-communication between the two languages and not loose the concurrency advantages offered by Erlang
There are a number of different alternatives. It is not particularly difficult to make all of them work through the same API from the Erlang point of view.
Keep the C code in a separate OS process and talk to them via pipes, TCP loopback etc. This is safe, but the slowest option
Make a linked-in driver. The driver API supports driver-level or port-level locking, which means you can safely run several instances of the C code - note, "safe" from a locking point of view. If your code misbehaves, it may well bring down the Erlang VM, as it runs in the same memory space.
Write a NIF (Native Implemented Function). This is still experimental, but the fastest way to call C code. It doesn't offer any high-level support for concurrency control, so you need to ensure that multiple invocations of your code do not access shared data in an uncontrolled way. |
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| ptmoy |
| Posted: Sat Jan 02, 2010 8:46 pm |
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Joined: 24 Dec 2009
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If I spawned 10 Erlang processes on the same node, and call the same NIF from each of the 10 spawned processes simultaneously, does each of the NIF calls execute on the same Erlang address space as its caller?
I understand all the NIF calls will run on the same OS-process address space as the VM. What I'm really asking is whether Erlang knows how to take advantage of multi-core or multi-processor computers when processing multiple simultaneous calls to the same NIF. |
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