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+--- Thread: Indy10 TCP Client Readln hangs (/thread-515.html)
Indy10 TCP Client Readln hangs - Attix22 - 07-20-2018
Hi all
I'm using Indy10 TCP Client to communicate with a communication partner.
To enable reading and writing at the same time I'm using IOHandler.ReadLn(Self.FETX, Self.FEncoding); inside the Execute of a TThread to read data.
And sending is done outside this Thread by the owner of the thread.
Problem is I sometimes (like every 5 - 10 Minutes) experience a hang on the IOHandler.ReadLn call which can last till I send data over the same TCPClient Instance.
Now I'm asking myself if there is a fundamental flaw in using a TCPClient like this?
Code:
procedure TReadingThread.Execute;
begin
while not (Terminated) do
begin
try
//Logged time here as start
Self.FData := Self.FClient.IOHandler.ReadLn(Self.FETX,1000ms, -1, Self.FEncoding);
//Logged time here as end
//In case of "hang" this can take an infinite amount of time
if (Self.FData <> '') and Assigned(Self.FOnData) then
begin
Synchronize(DataReceived);
end;
except
on EIdException do
begin
;
end;
end;
Sleep(10);
end;
end;Code:
//Outside of TReadingThread, but same TCPClient Instance
Self.FTCPClient.IOHandler.WriteBufferOpen;
Self.FTCPClient.IOHandler.Write(Self.STX + Self.FSendDataBuffer + Self.ETX);
Self.FTCPClient.IOHandler.WriteBufferFlush;
Self.FTCPClient.IOHandler.WriteBufferClose;RE: Indy10 TCP Client Readln hangs - rlebeau - 07-20-2018
(07-20-2018, 07:15 AM)Attix22 Wrote: Problem is I sometimes (like every 5 - 10 Minutes) experience a hang on the IOHandler.ReadLn call which can last till I send data over the same TCPClient Instance.
Sending and receiving are completely independent operations. ReadLn() will freeze until it receives what it is expecting (or until it times out). Sending data to the server will not fix that, unless that data triggers the server to send what ReadLn() is expecting.
(07-20-2018, 07:15 AM)Attix22 Wrote: Now I'm asking myself if there is a fundamental flaw in using a TCPClient like this?
In of itself, no. But what does the rest of your TIdTCPClient code look like? For instance, are you ever calling Connected() on the client? That performs a read operation, so it could corrupt communications by receiving bytes that ReadLn() is waiting for, putting them in the InputBuffer in the wrong order. Just a thought.
RE: Indy10 TCP Client Readln hangs - Attix22 - 07-23-2018
Thanks for your answer.
Indeed I was calling .Connected on the client in quite a regular basis.
Background for this was to detect if the communication partner has gone offline without safely closing the connection first.
I disabled this and the described behavior disappeared, however now I need to check how to safely detected if the communication partner is offline.
Maybe in the except of my reading thread?
RE: Indy10 TCP Client Readln hangs - kudzu - 07-23-2018
Yes, the try..except is where you should catch premature disconnections.
RE: Indy10 TCP Client Readln hangs - Attix22 - 07-24-2018
Thanks all, with handling unexpected connection issues in the except block the problem appears to be solved.