I have seen that the Execute method must chect for Terminated in its loop and exit if Terminated is set to true.
But I cannot find mention on what happens if the Execute method exits without Terminated having first been set.
Does this cause the thread itself to terminate and free or what happens?

Yes it will terminate and free (if FreeOnTerminate is true).

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Please excuse the shortness of this mail which was sent from my mobile phone. If necessary, I will send more information later.

Cheers,
Tobias Giesen

Tobias Giesen wrote

Yes it will terminate and free (if FreeOnTerminate is true).

Remember that if it frees itself due to falling out of the Execute() procedure, a variable containing the TThread descendant won't be set nil.

On the other hand, if it doesn't free itself and relies on the main thread checking an "executing" flag, there's a race condition between this being reset and its being safe for the main thread to call FreeAndNil().

Hi Mark, you know about my project from the Lazarus list... But for others:
I am trying to make a TCPIP communications class based on the Indy TIdTCPClient class. It will replace a serial communications object in an existing quite big class.
But to do that I need the TCP receive data handling to be event based so Remy Lebeau adviced to use a thread to handle the receiving and fire off an event when data arrives.

So I have (with his help) created a descendant of the TThread class that contains an Execute method that loops a blocking Read function with a timeout plus a few other things. If there are data received these will be supplied to an OnRead event function (via Synchronize) from the thread to the main application.

Now, where should the TIdTCPClient be located? The first suggestion was in the TThread decendant, but when I wanted to also add the Write function (obviously) I was adviced to move it outside the read thread and supply it as a parameter in the constructor instead. And the thread could then be created in the OnConnect event fired in the context of the main thread when a connection is made.

Now my concern is how to disconnect the TCP connection safely from the main thread? The read thread may well be in the blocking call to Read when this happens....
So I figured I could simply move the disconnect functionality over to the read thread where a call to Disconnect would set a flag which is acted on in the Execute loop.

So if the flag is set then the execute function should disconnect the client and then what?

Exit the Execute loop?
As explained to me here this will free the thread... Or move on in Execute to a loop only checking Terminated and exit when Terminated is true?

I guess that the second way would be the best, since then the main thread retains the responsibility to terminate and free the thread after first commanding Disconnect (and gotten feedback from the OnDisconnect event).....

Any other suggestions?
Threading is tricky business...

Bo Berglund wrote

Now, where should the TIdTCPClient be located?

Regarding the working of your Threads, It does not matter where any Instance is "located" (I suppose you mean what is the creator and with that the Owner of the object)

This is just a question of memory management and not of any relevance to the thread execution. the Thread behavior (including thread safeness or variables etc) is a completely independent issue from the memory (class-instance) organization.

-Michael