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?
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

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?

Suspend and Resume have been deprecated, and I want to know how a thread can be suspended.

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?

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'.

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.

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)

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

Michael.

Your thread is busy chewing up processor time and plans to do this until eternity. Now the user has different plans and decides to close your application. The problem is that the application can not terminate while your thread is chewing up processor time so your application says: "Hey thread, please terminate".

If all of your *while* statements have a not(Terminated) and your *until* statements include a Terminated then your thread will stop and your application will shut down like the user will be happy. -------------- next part --------------
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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

In Lazarus (and Delphi), "Worker Threads" can't have an "Event Loop" and so "event driven programming" (using "On..." procedures for the user code) is not possible. That is why in a Thread the user needs to create the "Loop" himself. Such a Thread should always run to a stall in some blocking library functions, lest it will take 100 % CPU time.

A thread should terminate itself by exiting the Execute procedure. If not "FreeOnTerminate" is set. after termination the main thread should free the TThread object.

Can a thread respond to a new Execute command while it already Executing?

No.

Do threads have ways of being interrogated about their state while Executing?

There are lots of ways of doing inter-thread communication. Simplest: any (no "ThreadVar") variable can mutually be read and written. A good (portable) way of notifying the Main thread about a state change is "Application.QueueAsyncCall". "TThread.Synchronize" calls a main thread event while stalling the thread for some indefinite amount of time.

Suspend and Resume have been deprecated, and I want to know how a thread can be suspended.

Using Semaphores like "TCriticalSection".

In certain applications (if it is not supposed to stall and wait) the main thread needs to check multiple times whether a TThread instance in fact is "Terminated" and thus can be freed.

-Michael

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?

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?

I am and the only parameter it takes
in addition to the method pointer is a PrtInt. That seems to limit the options passed compared with TThread.Synchronize. Can the PtrInt be cast to a pointer to a richer data structure?

Frank Church wrote

Isn't it possible to have add new fields to your thread that can be interrogated?

Of course you can add any variables and properties to your TMyThread Object. (This is just data-handling and completely independent of the Thread "context" the code is running in.)

e.g. another routine wants to call the thread's Execute method.

This is forbidden. "Execute" runs in the Thread context and is (automatically) called just once per thread Object instance when the thread (instance) is started (automatically when created or by explicitly by "resume").

-Michael

TThread.Synchronize allows for no QueueAsyncCall is less limited.

The parameter of course can be a pointer to a record or an object that might hold any information.

But you need to be aware that, while the pointer itself is "safe" (i.e. it does not change when arriving at the main thread even if the sending thread changes the value of the variable it gave to QueueAsyncCall), this of course is not true for the information the pointer points to. Here you might need to create a copy (by "New()" or ".Create") if the threads goes on writing to the original and you need to see a consistent object in the main thread. (beware of Strings doing reference counting here!)

"Synchronize" stalls the thread while doing the AsyncCall, so this problem does not arise.

-Michael

The thread could start spinning/sleeping on a /safe/ place in its code ? But that'll require another variable to tell it to do that ?

(or: 2 variables of type Set of (tsRun, tsPause, tsTerminate) (and (tsRunning, tsPaused, tsTerminating) ?) ) - one for signalling to the thread and the other to signal its current state to the world...?

L.

Michael.

Can a thread safely suspend itself, subject to an external resume? If not, what is the "official" alternative?

A thread can always suspend itself. It's the suspend by another thread that is dangerous.

Michael.

That is possible.

Michael.

Mark Morgan Lloyd wrote

Can a thread safely suspend itself, subject to an external resume? If not, what is the "official" alternative?

A semaphore.

-Michael

Thanks for that Michael. I've got a thread which runs for a stretch in the background to query a database (to avoid a UI glitch), then suspends itself until it's kicked back into life by the main thread approx 30 seconds later. Appears reliable on all tested platforms.

Put another way, I can see the argument for restricting access to Suspend but I hope nobody has got plans to eliminate it completely.

I think it'll do just fine to put Suspend into strict private section so no outside module can call it...

L.

Al 04/10/2011 15:24, En/na Mark Morgan Lloyd ha escrit:

Wait on a TEvent instead of suspending. Then provide a method that signals the TEvent, to be called by the main thread (and signal it also in the destructor, so execute can wake up and properly terminate).

Bye

Do the Start and Resume methods automatically call the Execute method?

======================= http://devblog.brahmancreations.com

Clases.inc: line 115

tthread.inc: 98

func.inc: 143 < this is WinAPI call

thread.inc: 143

threadh.inc: 31

:)

Lukasz