[Lazarus] A few questions on threads

[Frank Church]

On 4 October 2011 10:43, <michael.vancanneyt at wisa.be> wrote:

>
>
> On Tue, 4 Oct 2011, Frank Church wrote:
>
>  What is the purpose of the while not Terminated in a threads execute loop?
>> If a thread is doing its own thing and knows when or not it has finished
>> what is the purpose of the while not Terminated
>>
>> Is Terminated designed to be called by other procedures besides the thread
>> itself? Can a thread be Terminated externally?
>>
>
> Yes.
>
>
>  This also seems to imply that if the code within the while not Terminated
>> loop is a long running sequence a Termniate command will not be processed
>> until control returns to the beginning of the loop
>>
>
> The Execute method is supposed to check Terminated at regular intervals.
>
>
>
>> Can a thread respond to a new Execute command while it already Executing?
>> Do
>> threads have ways of being interrogated about their state while Executing?
>>
>
> No. It is an error to call execute twice.
>
> The only interrogation you can do is check for 'Terminated'.
>
>
Isn't it possible to have add new fields to your thread that can be
interrogated?
e.g. another routine wants to call the thread's Execute method. Whenever the
thread is executing it sets a field named FProcessing:= true, so the routing
which wants to call the thread's execute method can read FProcessing and not
call the execute until FProcessing is false.
Is this possible?



>  Suspend and Resume have been deprecated, and I want to know how a thread
>> can
>> be suspended.
>>
>
> There is - to my knowledge - no safe way of doing so.
>
>
>  If a thread is not set to FreeOnTerminate, can a thread suspend itself by
>> using Terminate or some other custom function, doing some clean ups and
>> waiting so it can be restarted by the Start procedure, by adding some
>> custom
>> fields to make it itself aware that it is an a paused state, so that when
>> an
>> Execute is sent it look up those fields, set Terminated to false and
>> continue as though nothing has happened?
>>
>
> Terminate should only be used to actually terminate the thread.
> You can implement some custom commands to put them in a 'suspended' state,
> if you want. (using mutexes, semaphores and whatnot)
>
>
ie this means that a routine that wants to the thread to stop can call
Terminate, but it is up to the Thread itself to respond, it can't be forced?


> You should assume only that if Execute() exits, the thread will be
> cleaned up.
>
> Michael.
>
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>



-- 
Frank Church

=======================
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