Crash on ServerSocket.CanRead()
lazarus / 38-Networking and Web Programming

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Ocye · 2014-01-18 21:21

I'm using Synapse for Client/Server communication via TCP/IP. All
works well but one user reports problems on Bodhi Linux (with
Enlightment desktop). He or she cannot connect to a local server but
is able to connect to a foreign server. With some debug messages we
tracked down the issue to CanRead() when data is available, that means
when a client tries to connect.

Code: [Select]   
procedure TCustomTCPServer.Execute;
begin
  FServerSocket.Bind('0.0.0.0', FPort);
  //FServerSocket.SetLinger(true, 10);
  if FServerSocket.LastError=0 then
  begin
    FServerSocket.Listen;
    FRecvMsg.Clear;
    while not Terminated do
    begin
write('A');
      if FServerSocket.CanRead(100) then
      begin
write(0);
        aSocket:=FServerSocket.Accept;
write(1);
        aSender:=TClient.Create(aSocket, FClients);
        aSender.GroupID:=NextGroupId;
        aSender.OnLog:=@Log;
        FClients.Add(aSender);
      end;
write('B');
...

Output should be ABA01B but is ABA-crash, that is when CanRead() has
data. The error message says "Fatal IO error 11 (Ressource
temporairement non disponible) on X server :0.0."

I run Bodhi myself within a VB and had no problems to connect. Of
course it works well with all other OS. And the user reports no
problems connecting to another, non-local server.

Does anyone have an idea about the reason and how to solve this issue?

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Ocye · 2014-01-19 18:56

After binding to localhost instead of 0.0.0.0 the error message points
to other problems:

[xcb] Unknown sequence number while processing reply
[xcb] Most likely this is a multi-threaded client and XInitThreads has
not been called
[xcb] Aborting, sorry about that.

I have no idea how to solve it.

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User137 · 2014-01-20 03:12

Have you added "cthreads" in the uses list where synapse threads are
used? It is required for linux. Also you might not need to call
CanRead() in the listener thread.

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Ocye · 2014-01-20 06:33

Good idea. But of course, cthreads is included. The same code is run
on the dedicated server too (to that server the user can connect as
client). I use a TLIst for all connected clients (aka blocksockets
with some additional information) and distribute messages. The
distribution depends on the kind of server, either local with only a
few options or non-local with all features, for instance higscore
calculation. Actually its a game server that can be run as local
server/client connection.
The user reports problems when a client connects to the server.