Network collisions ...

[drgarytraub]

When two users attempt to access the same record at the same time, the second user gets an error message. How do I trap that error and avoid program crashes?

Again, thanks for any input ...

Gary Traub

[drgarytraub]

RE: Network collisions ...

Is there a particular error code number that deals with this - I looked in the manual and could not find anything to address this. Any suggestions?

Gary

[Tom Cone Jr]

RE: Network collisions ...

What error message is returned?

I haven't seen this kind of error in practice. In other contexts I've encountered something similar when users try to print reports from one workstation, while others are still editing data in the print range. When 'opening' a table for a report I usually include error traps to warn the user when exclusive access is required.

-- tom

[Tom Cone Jr]

RE: Network collisions ...

If you want to try to trap these events, you probably want to insert the trap before moving the record pointer to the record in question. i.e. before the next fetch... if the fetch fails go to the error handler.

-- tom

[Selwyn Rabins]

RE: Network collisions ...

You should not be getting a crash. Two users trying to access the same record on the network should not be an uncommon situation. It is allowed.

What is not allowed is two users trying to edit the same record. When the first user puts the record into change mode, the second user should see a message box "Unable to lock record" when he tries to go into change mode. But this does NOT cause a crash.

If you are getting a crash, then something else is going on that I would like more details about.

[csda1]

RE: Network collisions ...

Gary,

If you are trying to check if a record is available to be changed, you can use code like the global function below to test and lock the record if available. If avaialable, you must do your changes and then end the change, as in;


tbl=table.current()
IF IsRecordAvail(tbl)
' do changes here
tbl.change_end(.t.)
END IF


The global function is as follows;


function IsRecordAvail as L(TablePointer as P)

' Returns false if current record is not available
' Returns true if current record is available and leaves it in change mode

IsRecordAvail=.t.

on error goto error_handler
TablePointer.change_begin()
on error goto 0

END

error_handler:
'trace.writeln("error text="+error_text_get())
'trace.writeln("error code="+ltrim(str(error_code_get())))
IsRecordAvail=.f.
RESUME NEXT

END

end function


Regards,

Ira J. Perlow
Computer Systems Design & Associates
[email protected]

[drgarytraub]

RE: Network collisions ...

I am not really getting a "crash" - but what happens is that I get an error message and then need to exit the program and re-enter. I'm thinking that I may need to learn more about the use of RW-exclusive, which I hate to admit I have not utilzed at all. All my tables are accessed simply as tbl=table.get(tablename). Is this a big problem??

Gary

[drgarytraub]

RE: Network collisions ...

I am also studying Ira's function and will test it on the network when I get back to the office. Thanks ...

Gary

[martinwcole]

RE: Network collisions ...

Ira

does tablepointer get replaced by the name of the open table in your function? how does it know which table to check?

[martinwcole]

RE: Network collisions ...

never mind - sorry - on looking at the function again it answers my question - sorry