Create multiple threads from within your application

re: Create multiple threads from within your application

Claude Fox — Tue, 16 May 2006 23:36:02 GMT

So a regular VFP exe could call the methods of this class from the mtdll? Or am I missing something? Can you give an operational example of this in a VFP GUI type app that needs to do something like print in the background?

re: Create multiple threads from within your application

Rick Strahl — Wed, 17 May 2006 00:29:59 GMT

Calvin,

Is all that really necessary? It seems to me an easier way to do this is to create a couple of generic methods in a DLL or FLL and have it act as a wrapper around the various COM invokation APIs. Sure you can do this in Fox code with code injection, but man is that messy <s>...

I'm thinking you'd want to have two ways to fire this off - one as you're doing using the VFP runtime objects to execute a PRG file via DoCmd/Evaluate - so you can have have something approaching true dynamic execution - and another to fire off a generic COM Server method from the code so you can call a separately compiled VFP (or other) COM Server.

Sort of like I am doing in the .NET sample I posted.

You've given me a couple of good ideas of things to add to my DLL library here <s>...

re: Create multiple threads from within your application

Franklin Garzón — Wed, 17 May 2006 06:15:15 GMT

I believe that the implementation of multiple threads must be by means of functions added like for example: do form <my form> object type 1 multihead =.t. Or begin multimultithread .... instructions ... endmultithread or select ...(select * from tabla) as calculo from othertable) with multitahread=.t..
Also I believe that in VFP it should add the funsión sleep (200) since at present many programmers use the old trick of for i=1 to 2000 endfor.

re: Create multiple threads from within your application

Sanjay — Wed, 17 May 2006 08:38:28 GMT

Calvin,
I am using DLL's as MTS components to process jobs in seperate threads. This is easy for me as i dont know much about 8086/8088 assembly lanuage.

I found your example quite good and has made my understanding a lot clearer on this subject.

re: Create multiple threads from within your application

Gargon — Wed, 17 May 2006 17:40:36 GMT

Is this better than using a timer/callback in vfp to multitask??
&& server objects (compile into COM-Exe)

DEFINE CLASS oTestServer AS Session OLEPUBLIC

loCallback = .NULL. && saves reference to callback object
lAdvised = .F. && is callbackobject set?
HIDDEN loTimer

FUNCTION Init
DECLARE INTEGER Sleep IN WIN32API INTEGER
THIS.loTimer = CREATEOBJECT('dirTimer',THIS)
ENDFUNC

FUNCTION Destroy
THIS.loTimer = NULL
CLEAR DLLS
ENDFUNC

FUNCTION FireEvent AS VOID
LPARAMETERS lcSomeValue
IF THIS.lAdvised
THIS.loCallBack.EventMethod(lcSomeValue)
ENDIF
ENDFUNC

FUNCTION Advise AS VOID
LPARAMETERS loObj
THIS.loCallback = loObj
THIS.lAdvised = .T.
ENDFUNC

FUNCTION UnAdvise AS VOID
THIS.loCallback = .NULL.
THIS.lAdvised = .F.
ENDFUNC

FUNCTION SomeMethodThatFiresEvents AS Boolean
&& prepare something
THIS.FireEvent('Task startet .. ')
Sleep(5000)
THIS.FireEvent('Task finished X percent ..')
Sleep(5000)
&& do more
THIS.FireEvent('Task fineshied XX percent ..')
&& ..
ENDFUNC

FUNCTION DoSomeAsynWork AS Boolean
THIS.loTimer.Interval = 1
RETURN .T.
ENDFUNC

ENDDEFINE

DEFINE CLASS dirTimer AS Timer

Interval = 0
loParent = NULL

FUNCTION Init
LPARAMETERS loObj
THIS.loParent = loObj
ENDFUNC

FUNCTION Destroy
THIS.loParent = NULL
ENDFUNC

FUNCTION Timer
THIS.Interval = 0
&& do some work
Sleep(1000) && sleep to simulate some work ..
THIS.loParent.FireEvent('Timer Fired')
ENDFUNC

ENDDEFINE

&& client testprogram
startprocess.prg:

PUBLIC loFoxServer, loEventhandler

loFoxServer = CREATEOBJECT('testcom1.oTestServer')
loEventHandler = CREATEOBJECT('oTestCallback')

loFoxServer.Advise(loEventHandler)

DEFINE CLASS oTestCallback AS Session OLEPUBLIC

FUNCTION EventMethod
LPARAMETERS lcSomeParam
? lcSomeParam
ENDFUNC

ENDDEFINE

startasyn.prg:

?loFoxServer.DoSomeAsynWork() && returns immediately ..

&& simulate block situation
DECLARE INTEGER Sleep IN WIN32API INTEGER
Sleep(15000) && the event of ther server is fired when this runs

endprocess.prg:

loFoxServer.Unadvise()
loFoxServer = NULL
loEventhandler = NULL

re: Create multiple threads from within your application

claudefox — Wed, 17 May 2006 20:41:43 GMT

Ok, now I think I see. Once the class is set up, there's not really a lot of set up - just feed it the code. Nice...

re: Create multiple threads from within your application

Leandro — Wed, 17 May 2006 20:45:08 GMT

Dim t as New Thread(addressof Method)
t.Start()

Easy and efficient... It is .Net !

re: Create multiple threads from within your application

claudefox — Wed, 17 May 2006 20:56:01 GMT

Well the equivalent here in vfp is:
ox=CREATEOBJECT("ThreadClass")
cStrIid="{00020400-0000-0000-C000-000000000046}" && IID_IDispatch
ox.StartThreads(nThreads,"do "+SYS(5)+CURDIR()+"MyThreadFunc WITH p2","Thread: %threadnum",cStrIid)

Not a bad way to give VFP some MT capability!!

re: Create multiple threads from within your application

Hans-Peter Grözinger — Fri, 19 May 2006 12:23:09 GMT

Hello Calvin !

Threading is a cool thing in VFP :-)

Is it possible to include this native in Sedna?

This can help me at a project for motorsports time measurement and reporting with the following options:
- One thread to catch the time from a COM-Port, sended by a chronometer with a light barrier
- One thread to send the actual time via COM-Port to a big LED display.
- The main thread is used to append/edit the competitors dates, printing a report and so on.

--
With friendly regards
Hans-Peter Grözinger

re: Create multiple threads from within your application

SednaY — Mon, 22 May 2006 05:20:06 GMT

The main thread is actually being blocked in this example by WaitForMultipleObjects. I changed this and also changed some commands to be backwards compatible with earlier VFP versions. This new version can be downloaded at SednaY: http://codegallery.gotdotnet.com/SednaY (project is called MTmyVFP)...

re: Create multiple threads from within your application

SednaY — Tue, 23 May 2006 13:22:25 GMT

Although using MsgWaitForMultipleObjects is an improvement, 2 problems so far:
1.) Although the main thread is pretty responsive, the command window will not execute a command while the other threads are running even though you can type it in. Any ideas?? This probably has something to do with how the vfp command window works. My thought was that maybe Command Windows events are being blocked..
2.) On Win2K server, it doesn't appear to be starting the threads for some reason!? My guess is that possibly the machine code is picky depending on OS??

More Multithread capabilities: interthread synchronization, error checking

Calvin Hsia's WebLog — Wed, 24 May 2006 04:05:54 GMT

In a prior post: Create multiple threads from within your application, there is a sample Thread Class...

re: Create multiple threads from within your application

Boris — Fri, 02 Jun 2006 18:37:57 GMT

Hi Calvin,

In your post you mentioned a multithreaded runtime. Where can I get it?

Thanks,
Boris

re: Create multiple threads from within your application

SednaY — Fri, 02 Jun 2006 18:55:25 GMT

Boris, VFP6SP5 and above has included the
vfp?t.dll which is the MT VFP runtime.
It looks to me that most of what Calvin is posting is VFP9 specific. I redid the first 2 multi-threading examples to be backward compatible with VFP7 - that can be found on http://codegallery.gotdotnet.com/SednaY
I'm hoping to be able to do the same with the WebCrawler...

re: Create multiple threads from within your application

MSP — Thu, 15 Jun 2006 23:29:31 GMT

Am I the only one experiencing problems with this code. It bombs in the WaitForThreads() method on the line, CloseHandle(this.hThreads[i])

this.nThreads is 10, but, the array is dimensioned 1!

re: Create multiple threads from within your application

claudefox — Fri, 16 Jun 2006 00:18:09 GMT

Are you using VFP9? I had to rewrite some functions to be backwards compat before it worked for me on VFP 7. This example worked alot more smoothly for me than the next example (threadmanager class). BTW, I also had better luck with msgwaitformultipleobjects...

re: Create multiple threads from within your application

MSP — Fri, 16 Jun 2006 16:59:37 GMT

Claude, I am using VFP9SP1 when I'm getting this error.

I've seen a link to your modified version on the wiki and will give that a try.

re: Create multiple threads from within your application

Mike — Wed, 01 Nov 2006 16:41:32 GMT

Doesn't seem to work when (as multithreaded) .DLL and .EXE are recompiled in Fox9 SP1. Running the test prog exits quickly and the ThreadLog table is not created.

How to interrupt your code

Calvin Hsia's WebLog — Fri, 16 May 2008 05:43:49 GMT

I received a question: Simply, is there a way of interrupting a vfp sql query once it has started short

re: Create multiple threads from within your application

Abhay — Thu, 19 Jun 2008 12:01:56 GMT

Gargon's example of trying to run Multiple threads using a VFP class compiled into a COM EXE is not working in my case.

What could be wrong?

Abhay

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