[erlang-questions] Driver Threading & Message Sending

Rickard Green <>
Tue Sep 18 11:32:01 CEST 2007



Rickard Green wrote:
> You can only use driver_output() from "emulator threads".

Correction: The async thread pool are "emulator threads", but you cannot 
call driver_output() from them. You can only call driver_output() from 
the scheduler threads of the emulator.

BR,
Rickard Green, Erlang/OTP, Ericsson AB.

> When the 
> runtime system with smp support is used, you can use driver_send_term() 
> from any thread.
> 
> See http://www.erlang.org/doc/man/erl_driver.html for more info.
> 
> BR,
> Rickard Green, Erlang/OTP, Ericsson AB.
> 
> Benjamin Tolputt wrote:
>> More questions though this time (while related to Stand Along Erlang, it 
>> also applies to general Erlang driver stuff I am developing).
>>
>> The benefit of Erlang which are pushing me to evangelize it to the game 
>> development crew is the high concurrency and CPU utilization on 
>> multi-core machines (i.e. it's SMP capabilities). To this end, they 
>> asked if it would be possible for them to run their physics & AI modules 
>> in a separate started up in a Erlang driver. This seems quite possible, 
>> but I wanted to know a couple of things about how threading & drivers 
>> are allowed to operate.
>>
>> Let's say that a driver is created for the AI engine utilizing whatever 
>> techniques they desire for this. Let's also assume that they are running 
>> this in a permanent loop (the classic "while (true)" thing) with input 
>> coming in from Erlang through the driver interface and sending messages 
>> back out the same way.
>>
>> Is it safe for the driver code to call the "driver_output" function from 
>> a thread other than one in which the emulator "calls into" the driver 
>> (i.e. is it possible to call driver_output from a thread not started by 
>> the emulator)? If not, what is the common method used to get output 
>> generated by the driver independent of queries (i.e. a call to the 
>> drv_output driver callback) from Erlang? Polling for output from the 
>> driver seems a bit strange given the message-centric method of 
>> everything else, but I haven't been this low-level with Erlang before...
>>
>> Regards,
>> B.J.Tolputt
>>
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>> 
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>>
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