Losing content of TThreadList - multithreading

Question

I got the problem, that my content of my TThreadList seems to get lost in my Thread.
I create following variable in my "PConnect" Class:
var mCustomfunctionCallbackThread: CustomfunctionCallbackThread;
And a global variable like following:
var mCustomfunctionCallbackThreadList: TThreadList;
Now I'm filling this variable in my "PConnect" Class like following:
function PConnect.callCustomfunction(plugin, method: PAnsiChar; param :CustomParam; callback: ICustomfunctionCallback; callId: PAnsiChar): integer;
var paramName: PAnsiChar;
var id: PAnsiChar;
var error: integer;
var callbackList: TList;
var customfunctionCallback : ^CustomfunctionCallbackObject;
begin
callbackList:= mCustomfunctionCallbackThreadList.LockList;
new (customfunctionCallback);
customfunctionCallback.callId:= id;
customfunctionCallback.callbackMethod:= callback;
callbackList.Add(customfunctionCallback);
mCustomfunctionCallbackThreadList.UnlockList;
exit(0);
end;
Following function will be called, after I a Callback received. This Function should append the other missing data to the TThreadList entry and start a Thread after that:
procedure PConnect.customfunctionCallbackReceived(param :CustomParam; callId: PAnsiChar; error: integer);
var customfunctionCallbackList: TList;
var it: TListEnumerator;
var callbackObject: ^CustomfunctionCallbackObject;
begin
customfunctionCallbackList:= mCustomfunctionCallbackThreadList.LockList;
it:= customfunctionCallbackList.GetEnumerator;
while(it.MoveNext) do
begin
callbackObject:= it.GetCurrent;
if strcomp(callbackObject.callId,callId) = 0 then
begin
callbackObject.param:= param;
callbackObject.error:= error;
break;
end;
end;
mCustomfunctionCallbackThreadList.UnlockList;
mCustomfunctionCallbackThread.Start();
end;
The Execute method of the Thread should get the content of the TThreadList and call a function with that parameters.
procedure CustomfunctionCallbackThread.Execute;
var callback: ICustomfunctionCallback;
var customfunctionCallbackList: TList;
var it: TListEnumerator;
var callbackObject: ^CustomfunctionCallbackObject;
var param: CustomParam;
var callId: PAnsiChar;
var error: Integer;
begin
customfunctionCallbackList:= mCustomfunctionCallbackThreadList.LockList;
it:= customfunctionCallbackList.GetEnumerator;
while(it.MoveNext) do
begin
callbackObject:= it.GetCurrent;
if callbackObject.error <> NULL then
begin
callback:= callbackObject.callbackMethod;
param:= callbackObject.param;
error:= callbackObject.error;
callId:= callbackObject.callId;
callback.callCustomfunctionCallback(param, callId, error);
customfunctionCallbackList.Remove(callbackObject);
break;
end;
end;
mCustomfunctionCallbackThreadList.UnlockList;
end;
And heres the Problem, the following variables just got rubbish or Null pointer:
param:= callbackObject.param;
error:= callbackObject.error;
callId:= callbackObject.callId;
I hope it was enough described :)
I would be happy about some help :)

Answer 1

When you do
customfunctionCallback.callId:= id
the variable id has not been initialised. Which means that when you later check
strcomp(callbackObject.callId,callId) = 0
its behaviour is ill-defined, because callbackObject.callId was never initialised. What happens then is that the ill-defined behaviour that you see is that the expression never evaluates to True and so you never assign to the param or error fields. Which is consistent with your observations.
I suspect that you should make callId be a string variable and copy into it the value of the parameter callId that was passed to PConnect.callCustomfunction. But since I don't know all the details of what you are doing, I can't be 100% sure of that.
Some other comments:
Do you really mean to name your class PConnect? Normally we prefix classes with T.
The code would read a lot easier if you used for in loops instead of while loops.
The loop that contains a call to Remove on the list is inefficient. You've already found the item, and calling Remove just searches the list once again. The way to do that loop is with a class for loop using an index. And when you find the item to be deleted, call Delete passing the item's index.
When you remove an item you fail to call Dispose which means that you leak memory.