Some inter thread/component communication questions

[Menno Valkema]

Hi Norman and Emery,

Thank you for helping me out here! I'll start working with the
techniques you've described.

Cheers, Menno

On 14-04-16 13:43, Emery wrote:
> On Thu, Apr 14, 2016 at 11:48:58AM +0200, Menno Valkema wrote:
>> Hi Everyone,
>>
>> I've some questions with regards to Genode synchronization features
>> between threads and components.
>>
>> First a question about packet streams:
>>
>> 1) Can we expect the packet streams to deliver packets in order to the
>> other component as a FIFO? Thus: can we expect the packet submitted
>> first, to be delivered first at the other component? Also when bursts of
>> packets are send through the packet stream?
> 
> There is a FIFO queue of packets from the source to the sink, and a FIFO
> queue of acknowledge packets from the sink back to the source. However,
> the sink could dequeue a number of packets and then acknowledge them out
> of order. A good component will strive to have minimal state, so it should
> be safe to assume that packets will be processed and acknowledged FIFO.
> Even if you get into the cases of network coding or disk head seek
> optimization, that sort of work would probably be done in a second buffer
> at the sink component and you'll still see FIFO behaviour.
> 
>> 2) Say we have 2 threads in the same component, where Thread A needs to
>> sleep until an event occurs in Thread B. How to address this? If A and B
>> were components, signals would be the answer. Would signals also work
>> between threads within the same component or is there some other approach?
> 
> Signals would work between threads in the same component, but using simple
> primatives like locks and semaphores will give you better performance, because
> issueing signal capabilities and exchanging signals requires work outside the
> component.
> 
>> 3) What if those same 2 threads need to exchange data? When data is
>> shared between components, shared memory would be the answer. How to
>> approach this with 2 threads within the same component. Setup a shared
>> data space? Do those 2 threads share the same heap which we can use for
>> this exchange?
> 
> Multiple threads within a component use the same address space, there shouldn't
> be any extra work in shared data between threads. You have the option of using
> independent heaps on different RAM sessions, but the mapping is still in the
> same space.
> 
> 
> Correct me anyone if I am wrong,
> Emery
> 
> 
> 
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