lazarus at mfriebe.de
Fri Dec 14 11:16:36 CET 2018
On 14/12/2018 10:30, Michael Van Canneyt wrote:
>> (or as Martin says, it should be documented as such?)
> This is a valid point and I intend to elaborate the TThread documentation
> somewhat, with this in mind.
I did have an error in my initial example:
> t := TThread.create(false); // create not suspended
> // do something
> if foo then begin // decide we do not need the result
> t.FreeOnTerminate:= true;
Obviously "t.terminate" is not save after "t.FreeOnTerminate:= true; "
because by that time t may be dangling. The only thing save to do with
"t" after at that point is "t:=nil".
But that aside, I think there are 2 thinks that can be made part of the
documentation (they may be obvious, but "obvious" here is a relative
term, depending on the readers experience)
A thread that has its FreeOnTerminate property set to "True" must not be
accessed in any for by any other thread.
An exception to this rule, is access to the thread from inside a
synchronize event, that comes from the very thread itself. This is
because the while the synchronize event is executed the thread is on
hold and can not be destroyed.
This is also true for any thread that at any time had its
FreeOnTerminate property set to "True", and then reverted it back to
false (from within the thread itself, as this the thread itself is the
only place that is still allowed access).
Again the exception is that the property can be reverted inside a
synchronize event, in which case the thread can be accessed again after
The FreeOnTerminate property is evaluated once the thread's Execute
method is exited. This is *before* "procedure DoTerminate; virtual;" and
the "OnTerminate: TNotifyEvent" are executed. [[According to
google/stackoverflow, this is the same in Delphi]]
Document relation to property "Finished" / see below
For (2) I have a question/request
The current FPC implementation (3.0.4) is
FreeThread := Thread.FFreeOnTerminate; // property is evaluated /
can no longer be changed
Result := Thread.FReturnValue;
Thread.FFinished := True; // Marked as finished
if FreeThread then
Could "Thread.FFinished := True;" be moved to the top? (potentially
together with "Result := Thread.FReturnValue;" so the order of those 2
The reason is, that then (on a suspended thread) it would be save to
change "FreeOnTerminate" if "Finished = False".
This should be ok, the doc
explicitly states that when it is true "the thread is still cleaning up
(calling OnTerminate, etc)."
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