Synapse - How to send data?
lazarus / 38-Networking and Web Programming

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Edson · 2014-03-10 02:10

Hi.

I finally, get my code working. I have implemented my version of the
'echo server' example  of Synapse for conecting two PC:

Code: [Select]type
  TProcesoTCP = class(TThread)
  private
    Sock:TTCPBlockSocket;
    procedure ProcConex(Hsock: TSocket);
  public
    Constructor Create;
    Destructor Destroy; override;
    procedure Execute; override;
  end;

implementation

Constructor TProcesoTCP.Create;
begin
  inherited create(false);
  sock:=TTCPBlockSocket.create;
  FreeOnTerminate:=true;
end;

Destructor TProcesoTCP.Destroy;
begin
  Sock.free;
end;

procedure TProcesoTCP.Execute;
var
  ClientSock:TSocket;
begin
  sock.CreateSocket;
  sock.setLinger(true,10000);
  sock.bind('0.0.0.0','80');
  sock.listen;
  while not terminated do begin
    if sock.canread(1000) then begin
        ClientSock:=sock.accept;
        if sock.lastError=0 then ProcConex(ClientSock);
    end;
  end;
end;

procedure TProcesoTCP.ProcConex(Hsock:TSocket);
var s: string;
    sock2: TTCPBlockSocket;
begin
  sock2:=TTCPBlockSocket.create;
  sock2.socket:=Hsock;
  sock2.GetSins;
  while not terminated do begin
    s := sock2.RecvPacket(60000);
    if sock2.lastError<>0 then break;
    sock2.SendString(s);  //response the same
    if sock2.lastError<>0 then break;
  end;
  sock2.Free;
end;

And it works, but I want to know if it's OK to create a new "Sock2"
variable in ProcConex().

Other problem I can see, is that it just response when receiving data.
How Do I can send data asynchronously? Is it possible?

I have tested this:

Code: [Select]procedure TProcesoTCP.SendData(const s: string);
begin
  sock.SendString(s);
end;

But it doesn't seem to work.

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Edson · 2014-03-11 15:50

Any suggestions?

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snorkel · 2014-03-11 18:25

First Synapse is synchronous, so you can't do async  like you can with
ICS or Lnet.
What you want to do is when a connection comes in spawn a thread and
pass the socket from the accept in the threads constructor.
Then in the thread you can simply use the single passed socket to read
and write to and from the connected client.
You can also keep a list of all connected sockets and have each thread
have a protected write queue, when you need to send a message to all
connected clients you can loop through the list of sockets and drop
the message in each threads write queue, then when the thread is not
reading you can pop a message out of the queue and write to the
threads socket. 
That way you can have a single socket per thread and it performs like
a async system would.
you could easily handle a thousand or so users on a run of the mill
server, maybe a bit more.
The disadvantage is you do get more context swaps.

The other thing is to set the stack space of each thread to better
manage memory, by default a thread gets a stack space of 1 or 2 mb,
not what the default is exactly, but depending on what you are doing
you may be able to set it much lower and that means more simultaneous
connections.

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Edson · 2014-03-16 18:02

Thank for the response.

Quote from: snorkel on March 11, 2014, 07:25:48 pmThen in the thread
you can simply use the single passed socket to read and write to and
from the connected client.
I will try to modify my code.

I don't need to manage with multiple connections. I just want to serve
one connection (I used threads, just because of the example used it).

The important thing for me, is to make the server can send a data to
the client in any moment, no needing that the client send anything.

If Synapse is synchronous, does it mean that this is not possible?

Sorry, I don't understand how using a queue could help.