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for 500pts <> File Locking and Unlocking. How its work?

udanabanana
udanabanana asked
on
Medium Priority
165 Views
Last Modified: 2010-04-30
Hello Experts,
I have a structured file with only 2 records
File name : Gate.dts
Record Length: 3bytes
Structure :
Type Gate
    FileNo As Byte           '1
    atUse As Boolean       '2
End Type


this file open by process 1 (P#2)

Close #400: Open strCachePath & "Gate.dts" For Random Shared As #400 Len = 3

read some data
Get #400, 1, Gate

write some data
    Lock #400, 2
    Gate.atUse = True
    Put #400, 2, Gate
    Unlock #400, 2

This two records are regulary update by a second Process (P#2) say every 30 seconds
Similary P#1 need to  read and write data to Gate.dts
P#1 reading these records every 30 seconds or so

I'd like to give priority to P#2 if I can

now
1) when I reding data do I need to Lock and Unlock?
2) what will hapen if P#2 is writing to Gate.dts record 1 and P#1 want to read it same time? will it crash?

________________________________________
Aditional Information

in this scenario P#1 and P#2 are in different computers connected though network. P#1 act like a server.
some occations there could be more than one clients and can have multiple of P#2 process and Gate.dts.
Gate.dts located in client machines only

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Retired
CERTIFIED EXPERT
Top Expert 2012
Commented:
1) No. Locking is only relevant to writing.
2) No. You can read a locked record.
If you try to write to a locked record, you will can an error, not a crash.
The error is 70, Permission denied.

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