[Freeswitch-users] Receive order guarantee for bgapi command replies over ESL?

Fri Feb 25 02:27:48 MSK 2011

Clarification:

Yes, the event returned from the background job is expceted to be fully 
asynchronous and can arrive at any time in the future (independent of when 
the bgapi commands were issued).
The issue is the reply from the bgapi command itself, _before_ it spawns the 
background thread.
If you, let's say, issue 10 bgapi commands in sequence, will the reply (OK 
Job-UUID:.... / ERR) for each bgapi command return in the same sequence as 
issued?

Example:

ESL socket outputstream (writer thread):
client --> bgapi status --> fs
client --> bgapi status --> fs
client --> bgapi status --> fs

ESL socket inputstream (reader thread):
client <-- +OK Job-UUID:..... <-- fs
client <-- +OK Job-UUID:..... <-- fs
client <-- +OK Job-UUID:..... <-- fs

The ESL socket outputstream and inputstream are written to and read using a 
writer and a reader thread. If we have no guarantee that the order of the OK 
replies from the bgapi commands are returned in the same order as issued, we 
will be forced to do the following:

client --> bgapi status --> fs
wait for reply
client <-- +OK Job-UUID:..... <-- fs

client --> bgapi status --> fs
wait for reply
client <-- +OK Job-UUID:..... <-- fs

client --> bgapi status --> fs
wait for reply
client <-- +OK Job-UUID:..... <-- fs

Only then could we securly map the command to the correct Job-UUID for the 
reply.
But if the replies arrive in correct order we can put the issued commands in 
an ordered queue that can be processed with certainty by the socket reader 
thread, and assign replies to the correct commands.. Did this really make it 
any clearer?? :-)

Had there been a message sequence ID (or similar construct) there would be 
no need to be order specific as we would always have an exact match between 
command and reply, but I don't think FS / CLI / ESL supports this at the 
moment (or ever will... ;-)).

- Mauritz

-----Original Message----- 
From: Anthony Minessale
Sent: Friday, February 25, 2011 12:10 AM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Receive order guarantee for bgapi command 
replies over ESL?

bgapi commands are asynchronous that means when you send the command
it spawns a thread and runs in the background.
When its complete it will send you the event, its completely dependent
on how long the task takes that you asked it to run.
Its no different that doing 12 wgets to a website in the bg, there is
no telling when they will be done.

2011/2/24 Mauritz Løvgren <mauritz.lovgren at hotmail.com>:
> The use case is as follows;
>
> Multi-threaded Java applicaton that sends bgapi commands to several 
> channels
> in parallel over the same ESL connection.
> (bgapi commands are serialized in order to the socket outputstream, but is
> there any guarantee that we will receive the OK / ERR reply for each bgapi
> in the correct order from the socket inputstream?)
>
> And, what about sending bgapi commands on the same socket while a ‘regular’
> api command is currently executing? I suspect the bgapi reply will delay
> until the ‘regular’ (blocking) api command is finished processing?
>
> - Mauritz
>
> From: Michael Collins
> Sent: Thursday, February 24, 2011 9:44 PM
> To: FreeSWITCH Users Help
> Subject: Re: [Freeswitch-users] Receive order guarantee for bgapi command
> replies over ESL?
>
> Just curious - what is the use case where sending a stack of bgapi's 
> without
> listening for the reply is more desirable than looping through the bgapi
> send/reply sequence for each one? I'm no super programmer but it seems to 
> me
> that blindly relying on another system to always send stuff in the exact
> correct order is dangerous and may cause bugs that are difficult to
> diagnose. Personally I would consider it a programming best practice to 
> wait
> for the response of the bgapi before sending another one.
>
> I invite other socket programmers to give their input...
>
> -MC
>
> P.S - you may wish to disable the legal notice at the and of your emails
> when sending to a public list. (We know that some servers tag outgoing
> messages automatically and if that is your case we understand. Go yell at
> the I.T. guy! :)
>
> 2011/2/24 Mauritz Løvgren <mauritz.lovgren at hotmail.com>
>>
>> Hi,
>>
>> Are replies for bgapi commands sent back to an inbound socket connection
>> in the same order as the commands were sent?
>>
>> Example: sending 10 bgapi messages from client to freeswitch socket with
>> no delay inbetween.
>> Will the response for those command messages be sent back by freeswitch 
>> in
>> the exact same order as their commands were received, or should one wait 
>> for
>> each reply before sending a new bgapi command to be sure one gets a reply
>> for the correct command?
>>
>> If there was an option of providing a UUID (or sequenceId) for the
>> command, it would be easier to match the reply with the request upon
>> receival, but this doesn’t seem to be possible with the current
>> implementation?
>>
>> Regards,
>> Mauritz Lovgren
>> Systems Architect
>> IPLink Inc.
>
>
>
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-- 
Anthony Minessale II

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