Precondition:
TdxSpellChecker.UseThreadedLoad = True
Description:
If TdxSpellChecker.LoadDictionaries is called while the spell checker is still busy loading dictionaries from a previous call to LoadDictionaries then an Access Violation occurs.
Cause:
TdxCustomSpellChecker.LoadDictionaries calls
TdxCustomSpellChecker.LoadDictionariesUsingThread calls
TdxCustomSpellCheckerDictionary.LoadUsingThread.
TdxCustomSpellCheckerDictionary.LoadUsingThread:
Delphiprocedure TdxCustomSpellCheckerDictionary.LoadUsingThread;
begin
if not CanLoad then Exit;
FreeAndNil(FLoadThread);
FLoadThread := TdxDictionaryLoadThread.Create(Self);
end;
Because FreeAndNil is used, the FLoadThread variable is nilled before the thread is destroyed.
This becomes a problem because the thread OnTerminate handler calls TdxCustomSpellCheckerDictionary.ThreadDone:
Delphiprocedure TdxCustomSpellCheckerDictionary.ThreadDone(Sender: TObject);
begin
if not LoadThread.IsLoadComplete then
Cleanup
else
SpellChecker.CheckCallEnabledDictionariesLoaded;
end;
which fails because LoadThread=nil.
Solution:
The solution is to replace the FreeAndNil with:
DelphiFLoadThread.Free;
FLoadThread := nil;
Hello Anders,
Thank you for the information. I will forward this thread to our developers for research.
Hello Anders,
We tried to replicate the issue, but failed. Would you please provide us with a test project to demonstrate the problem?
No.
It's a race condition and as such the problem will only surface when the timing is right. The timing depends on the CPU speed, the number of cores, the system load, the disk speed etc.
I have already provided you with an analysis which clearly pinpoints exactly where the problem occurs and exactly why it occurs. You don't need a test case to see that there is a problem.
FWIW, there's another place in the code where you use Free instead of FreeAndNil to avoid this exact problem. Just search for FreeAndNil.
As I see the subject of this thread, you mentioned that the Access Violation exception can be raised in our code in some situations.
We tried to make a scenario by your description to replicate this issue, but failed. As we see, our code works correctly. That is why I'm asking you to provide us with a small test example that demonstrates the problem in our sources, i.e. causes the Access Violation exception.
Can you please get someone who understands race conditions to take a look at this problem again. It's getting a little tiresome that we have to patch your source every time we update.
You don't need to be able to reproduce the problem to understand that there is a problem. You just need to understand the analysis I provided.
Anders,
We will try to find an appropriate solution for you. It may require us some time.
Since we cannot reproduce the issue, assistance in testing our solution will be much appreciated.