[erlang-questions] Newbie - eldap and threads

Humaira <>
Fri Feb 19 09:17:16 CET 2010


Hi Chandru,

Thanks for the very useful information. I noticed that I have a
different version of eldap than you are referring to. Where would one
find the gen_fsm version? Is there a commonly used repository or is it
the version from ejabberd?

I looked through the version on GitHub and it is not the gen_fsm
version. 

Thanks,
Humaira



On Thu, 2010-02-18 at 17:10 +0000, Chandru wrote:
> Hi,
> 
> On 18 February 2010 08:21, Humaira Surve <> wrote:
> >
> > Hi,
> >
> > I've recently began playing around with erlang and come from a java
> > background.
> >
> > I was quite impressed by the eldap library and its general simplicity to
> > use. I have a question though.
> > If one opens a single connection and binds, but has multiple clients sending
> > requests through this one connection,
> > is there a possiblity of thread-related issues.
> 
> Not really. All requests are multiplexed on to the same connection.
> 
> >
> > What guarantees that a client gets the correct response or that a response
> > is not over-written by more than one simultaneous request?
> > I have looked through the eldap code and noticed that a single connection
> > uses a TCP file descriptor.
> 
> See the source in eldap_fsm:send_command/3. I've added comments.
> 
> send_command(Command, From, S) ->
>     %% Assign a unique id for this request which is the messageID in
> the LDAP request
>     Id = bump_id(S),
> 
>    %% Build the request
>     {Name, Request} = gen_req(Command),
>     Message = #'LDAPMessage'{messageID  = Id,
>                  protocolOp = {Name, Request}},
>     log2("~p~n",[{Name, Request}], S),
> 
>     %% Do ASN.1 encoding
>     {ok, Bytes} = asn1rt:encode('ELDAPv3', 'LDAPMessage', Message),
> 
>     %% Send the request on the socket
>     ok = gen_tcp:send(S#eldap.fd, Bytes),
> 
>     %% Start a timer
>     Timer = erlang:start_timer(?CMD_TIMEOUT, self(), {cmd_timeout, Id}),
> 
>      %% Store the mapping from unique id to 'From' which is a
> reference to the calling process
>     New_dict = dict:store(Id, [{Timer, From, Name}], S#eldap.dict),
> 
>     {ok, S#eldap{id = Id,
>          dict = New_dict}}.
> 
> When a response is received, the LDAP server will include the
> messageID in the response. The eldap_fsm process looks up its state
> and retrieves the reference to the calling process (assuming the
> request has not timed out), and sends the response out.  This is
> handled in eldap_fsm:recvd_packet/2
> 
> cheers
> Chandru




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