[erlang-questions] : Subtle behaviour of Erlang scheduler

[Erik Stenman]

Rickard Green wrote:
> KatolaZ wrote:
>
>   
>>>> So, just for the purpose of discussion, why don't think at "virtual"
>>>> synchronisation points for high priority procs ? I.e., if a high
>>>> priority task has not been interrupted for X reductions (beeing X a
>>>> relatively large integer), then goto do_schedule1 anyway, letting
>>>> other high priority process to run....
>>>>         
>>> If I understood you right, you want the scheduling to work as it is
>>> implemented right now.
>>>
>>> Regardless of priority, a process is unconditionally scheduled out when
>>> it has consumed (currently) 2000 reductions (since it was last scheduled
>>> in). I.e., a busy loop in a high priority process will not prevent other
>>> high priority processes from running, but it will prevent normal and low
>>> priority processes from running.
>>>
>>>       
>> Unfortunately, it seems to be false, or I'm missing something!  Here
>> is a simple example where all code for high prio processes is loaded
>> (it is indeed a self-contained module!), and proc_high2 is starved by
>> proc_high:
>>
>>     
>
> No, it is not false. The problem is that proc_high2 never gets the 
> chance the set prio high. It is still on prio normal. You have to spawn 
> it with prio high (see spawn_opt) in order for this example to work as 
> expected (and it will; i've tried it).
>   
I guess spawning with prio high also is a bit dangerous unless the 
process you
are spawing from (p1) also has prio high, otherwise the first spawned 
high prio
process (p2) might starve the spawner. (If p1 is suspended before it 
spawns p3.)

Am I right?

/Happi