Hi, Anthony

I appreciate you spend your time answering my questions. I have no problem with FreeSwitch. Since you ask, I am digging into this code because I am trying to understand how FreeSwitch works inside the core, probably will take me a great deal of time but I am trying.

I wrote a custom EndPoint  in FreeSwitch before to run a modem created by the hardware engineer team. Basically it is similar to Zaptel compatible card. The Modem Endpoint runs in FreeSwitch to provide PSTN Connectivity that uses our specific modem.

While working with FreeSwitch, I have this idea to implement something similar to FreeSwitch in 100% .NET managed code. Of course I am not expecting it to be as mature as FreeSwitch but something basic first. A core that allows me to write pluggable modules, basic dial plan and the the first supported endpoint would be XMMP since I had some experience working with this XMMP .Net library before.

The ultimate aim is code readability, simplicity and maintainability. I have some other aims too but basically this is it, mostly. I am working on this as a personal hobby project only J.

Cheers

Alex To

From: freeswitch-dev-bounces@lists.freeswitch.org [mailto:freeswitch-dev-bounces@lists.freeswitch.org] On Behalf Of Anthony Minessale
Sent: Thursday, January 07, 2010 12:16 AM
To: freeswitch-dev@lists.freeswitch.org
Subject: Re: [Freeswitch-dev] Need some explainations about method switch_core_session_run(switch_core_session_t *session) in switch_core_state_machine.c

On Wed, Jan 6, 2010 at 9:20 AM, Alex To <tonhudung@gmail.com> wrote:

Hi,

First of all, pardon my English. English isn’t my native language J.

I am reading the method switch_core_session_run(switch_core_session_t *session) and I would be really appreciated if someone could shed some light on how the method works. Below is the logic according to my understanding:

1. LINE 303:              while ((state = switch_channel_get_state(session->channel)) != CS_DESTROY)

ð if state is CS_DESTROY return and do nothing ?

state typically starts at CS_NEW the loop runs until state destroy is reached

2. Inside if (state != switch_channel_get_running_state(session->channel) || state >= CS_HANGUP)

{

…

}                                             

a. LINE 308:              state != switch_channel_get_running_state(session->channel) || state >= CS_HANGUP

ð to check if channel->state and channel->running_state not equal. This is to avoid running the STATE_MACRO multiple times. However I don’t understand why do we need (state >= CS_HANGUP) ?.

Once we are >= HANGUP we dont want to do that test anymore.

b. Inside STATE_MACRO code block

i. LINE 229:              midstate = state

ð  to save the current state.

ii. LINE 231:              if (!driver_state_handler->on_##__STATE || (driver_state_handler->on_##__STATE(session) == SWITCH_STATUS_SUCCESS)

ð to check either endpoint_interface->state_handler is NULL or return SWITCH_STATUS_SUCCESS so it will continue to execute handlers in session->channel, runtime.state_handlers and core standard state handlers. It means if the condition is not true, channel->state_handlers, runtime.state_handlers and core standard state handlers will NOT be executed at all ?

iii. LINE 246:              if (!proceed) global_proceed = 0;

ð If something wrong in the previous while loop, do not run core standard state handlers ?

yes the endpoints have the power to veto state handlers from being called

iv. LINE 247:              proceed = 1;                                                                                                                                                                                      

LINE 248:              while (do_extra_handlers && proceed && (application_state_handler = switch_core_get_state_handler(index++)) != 0) { …}

ð Since we set proceed = 1, do we still need (&& proceed) inside the condition in while loop ?

yes because proceed can become 0 within that loop

v. LINE 260:              if (!proceed || midstate != switch_channel_get_state(session->channel)) global_proceed = 0;

ð If not proceed or the channel state has changed by some of the state handlers executed earlier, do not execute core standard state handler ?

Again, veto power.

vi. LINE 266:              while (silly)

ð silly is never changed, does it mean we could go into an endless while loop ?

Its to stop the compiler from getting mad, that's why it's called silly its specific to using a while loop inside a macro

Sorry for the long email and some questions are probably dumb but I am trying to understand about FreeSwitch, especially the core and the core state machine. If it is documented somewhere about the workflow happening inside FreeSwitch, please enlighten me as what I am doing now is to read the code line by line and figure out which may not be the most efficient .

Why are you digging into this code? do you have some problem you are attempting to solve?
The most important thing is that code like this that has taken so long to perfect, even if there could be improvements, is hard to even look at without causing regressions.  So I'm curious what you were looking for.

Thank you for reading this

Regards

Alex To

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