[fpc-devel] TThread.Queue and TThread.Destroy

Martin fpc at mfriebe.de
Thu Jun 21 01:27:43 CEST 2018

fpc 3.0.4 / Linux 64bit (Fedora)

What should happen if:

- A Thread has queued a call with "TThread.Queue"
- The Thread gets Terminated and Destroyed before the queued method can 
be executed.
   That is the thread checks for "Terminated" and exits Execute before 
the queued method can be executed.

Diving into TThread.Destroy I can see: RemoveQueuedEvents(Self);
So I would assume that all the queued calls are removed, and will not be 

I have code where the object to which the queued methods belong is 
destroyed, after TThread.Destroy. It works in about 80% of the cases 
(not enough).
I have put lots of debugln (write to console) in my code.
And according to them one of the queued methods gets called, after the 

It definetely gets called from the queue, I caught it in gdb:
my method
#0  0x000000000139b34a in HANDLEPIPEINPUT (this=0x7fffc9f0c4c0, ADATA=0, 
AREASONS=1) at debugprocess.pas:241
#1  0x000000000139b1ab in THREADDATAAVAIL (this=0x7fffc9f0c4c0) at 
comming from the queue
#2  0x000000000054af14 in EXECUTETHREADQUEUEENTRY 
(AENTRY=0x7fffc9f0c4c0) at ../objpas/classes/classes.inc:272
#3  0x0000000002486c10 in  ()
#4  0x000000000054b333 in CHECKSYNCHRONIZE (TIMEOUT=0) at 
#5  0x000000000050c67b in THREADSYNC_IOCALLBACK (SOURCE=0x255abf0, 
CONDITION=1, DATA=0x7ffff7f84470)
     at gtk2/gtk2widgetset.inc:1843
#6  0x00007ffff65db7cd in g_main_context_dispatch () at 
#7  0x00007ffff65dbb98 in g_main_context_iterate.isra () at 
#8  0x00007ffff65dbc30 in g_main_context_iteration () at 
#9  0x000000000050d920 in APPWAITMESSAGE (this=0x7ffff7f84470) at 
#10 0x000000000048de9f in IDLE (this=0x7ffff7f83d10, WAIT=true) at 

Logging shows, that the process was destroyed before, and had left the 
thread's "Execute" method.

Any ideas.

Some more info. The Thread queued 2 events (actually it queued the 2nd 
event, while the main thread was processing the first event).
The 2nd event is executed as soon as the first one finished.

Possibly I found what happens:
in classes.inc

class procedure TThread.RemoveQueuedEvents(aMethod: TThreadMethod);
   RemoveQueuedEvents(Nil, aMethod);

which I believe is called from TThread.Destroy.

But then
class procedure TThread.RemoveQueuedEvents(aThread: TThread; aMethod: 
   entry, tmpentry, lastentry: PThreadQueueEntry;
   { anything to do at all? }
   if not Assigned(aThread) or not Assigned(aMethod) then

this just exits, if aMethod is nil.

So the events are not removed at all?

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