Memory leak during com port search

[johnnyd]

Hi good people of LB land,

This code is used to look for a serial device being connected (it's a USB device) and loops round until it detects a string that it spits out.

The code sits in the loop waiting for the device to be connected.

When I run it, it will increase memory usage (4k per increase) and after a short while will crash out with stack overflow.

If I step through it in debug, there is no memory increase. Not sure if it still crashes as I'm not patient enough o keep clicking!

find$=chr$(255)+chr$(255)

[comloop]
   for a=1 to 16
       scan
       oncomerror[comerr]
       open "com"+str$(a)+":,9600,N,8,1,cs0,ds0,rs" for input as #coms
       comopen=1
       calldll #kernel32,"Sleep",200 as ulong,r as void
       a$=input$(#coms,lof(#coms))
       if a$="" then[nextcom]
       pa=instr(a$,find$)
       pb=instr(a$,find$,pa+1)
       if (pb-pa=11) or (pb-pa=22) then
           com$=str$(a)
           exit for
       end if

[comerr]
       oncomerror

[nextcom]
       if comopen=1 then
           close #coms
           comopen=0
       end if
       calldll #kernel32,"Sleep",100 as ulong,r as void
   next a
   if com$<>"" then[csok]
   goto[comloop]

[csok]
   wait



John.

[Rod]

I don't like the scan statement in there and I am not sure if oncomerror "" is getting called every time through the loop. You might be building up a stack of oncomerror events.

Untested code but it does away with the scan and should consistently reset the oncomerror event.


[comloop]
find$=chr$(255)+chr$(255)
a=1
com$=""

while com$=""
   oncomerror[comerr]
   open "com"+str$(a)+":,9600,N,8,1,cs0,ds0,rs" for input as #coms

   comopen=1
   calldll #kernel32,"Sleep",200 as ulong,r as void
   a$=input$(#coms,lof(#coms))
   pa=instr(a$,find$)
   pb=instr(a$,find$,pa+1)
   if (pb-pa=11) or (pb-pa=22) then
       com$=str$(a)
   else
       com$=""
   end if

   [comerr]
   oncomerror

   if comopen=1 then close #coms
   calldll #kernel32,"Sleep",100 as ulong,r as void
   a=a+1 mod 16
wend


wait


[johnnyd]

Hi Rod,

Thanks for the reply, but it still crashes out with stack overflow. Slightly modded your code:
[comloop]
   find$=chr$(255)+chr$(255)
   a=1
   com$=""

while com$=""
   oncomerror[comerr]
   open "com"+str$(a)+":,9600,N,8,1,cs0,ds0,rs" for input as #coms
   comopen=1
   calldll #kernel32,"Sleep",200 as ulong,r as void
   a$=input$(#coms,lof(#coms))
   pa=instr(a$,find$)
   pb=instr(a$,find$,pa+1)
   if (pb-pa=11) or (pb-pa=22) then
       com$=str$(a)
   else
       com$=""
   end if

[comerr]
   oncomerror
   if comopen=1 then
       close #coms
       comopen=0
   end if
   calldll #kernel32,"Sleep",100 as ulong,r as void
   a=(a and 15)+1
wend


wait


If you run it in debug and have task manager open, you will see the memory increment.

If you single step through it, the increment doesn't seem to happen, but I got bored clicking.

I've altered the way I determine the string to look for but it doesn't affect the way the port is determined.

The scan was there because I have a window open with some dialogue and a cancel button, so the button needs to be detected.

John.

[Rod]

Perhaps slow down the looping so that it builds less of a stack?

The scan has the danger that it will deflect your code away to some other point mid process. Choose where you place the scan carefully. Best at the end of the process so that you know the com port is closed. If you have a mouse move event the scan could be jumping out of your com loop hundreds of times a second.

[johnnyd]

Hi Rod,

It still doesn't want to play.

I reinstated the for-next loop so I could place the scan outside so it won't check while in the loop.

It now closes the port after a successful open & read of the port, so doesn't need to check at the end.

I tried increasing the sleep at the end to a second, but memory usage still suffers, albeit more slowly.

I even took the oncomerror out but the memory still crept up.

It looks like LB isn't performing housekeeping with this? Time to point this at Carl.

   find$=chr$(255)+chr$(255)
   com$=""

[comloop]
   scan
   for a=1 to 16
       oncomerror[comerr]
       open "com"+str$(a)+":,9600,N,8,1,cs0,ds0,rs" for input as #coms'
        calldll #kernel32,"Sleep",200 as ulong,r as void
       a$=input$(#coms,lof(#coms))
       close #coms
       if a$="" then[comerr]
       pa=instr(a$,find$)
       if mid$(a$,pa,2)=find$ and mid$(a$,pa+11,2)=find$ then
           com$=str$(a)
           exit for
       end if

[comerr]
       oncomerror
       calldll #kernel32,"Sleep",100 as ulong,r as void
   next a
   if com$<>"" then[csok]
   goto[comloop]

[csok]
   wait




John

[Rod]

There is API code posted that opens the serial port. I think there is a demo on the LBPE. Perhaps that closes down the resource mor efficiently. Away from home and out of time right now. You would only use the API code to establish which port then revert back to native code.

[johnnyd]

Hi Rod,

OK, I'll search it out. Meanwhile, I've posted it under bugs.

John.

[Rod]

The LBPE API code does not seem to have the stack overflow error.

find$=chr$(255)+chr$(255)
com$=""
while com$=""
   for a= 1 to 16
       if CheckCom(a) then
           open "com"+str$(a)+":,9600,N,8,1,cs0,ds0,rs" for input as #coms
           calldll #kernel32,"Sleep",400 as ulong,r as void
           a$=input$(#coms,lof(#coms))
           close #coms
           scan
           pa=instr(a$,find$)
           if mid$(a$,pa,2)=find$ and mid$(a$,pa+11,2)=find$ then com$=str$(a) : exit for
       end if
   next
wend
wait





Function CheckCom(cp)                       'Checks for COM port available. Thanks LB group members!
   lpFileName$ = "COM"; cp                 'Returns true if port can be opened
   dwCreationDistribution = _OPEN_EXISTING
   hTemplateFile = _NULL
   CallDll #kernel32, "CreateFileA", _     'This won't halt the program if the port doesn't exist.
       lpFileName$ as ptr, _
       dwDesiredAccess as ulong, _
       dwShareMode as ulong, _
       lpSecurityAttributes as ulong, _
       dwCreationDistribution as ulong, _
       dwFlagsAndAttributes as ulong, _
       hTemplateFile as ulong, _
       hFileHandle as ulong

   CallDll #kernel32,"CloseHandle",_       'Close the port, so we don't get an error later
       hFileHandle as ulong,_
       ret as long
   If hFileHandle = _INVALID_HANDLE_VALUE Then
       CheckCom = 0
   Else
       CheckCom = 1
   End If
End Function




[johnnyd]

Hi Rod,

You star! This has sorted it.

Thanks for helping.

John.

[Brandon Parker]

Hey John,
     I replied to other, duplicate thread as well since I was unaware that Rod had answered the question here.

Stack overflow issue

{:0)

Brandon Parker