How to make a resource lock

Keywords:  Error 33 Locking Violation  lockfile resource lock

---

Question:

I'm getting the Windows error 33 Locking Violation on different machines at different times.

I have an ini file on the network that I want multiple users to be able to read/write to. What do I need to do to prevent share violations and/or corruption of data when multiple users try to use that file at the same time. I am using iniwritepvt and inireadpvt functions and am not sure how they handle file open/closes. Thanks!

Answer:

If your script updates files on a server, and a number of people might be running the script at any given time, then you will need to lock those files, so that only one person can use them at a time. The lock prevents everyone from stomping all over the files. First figure out what files are being updated, and then use the following script to figure out if the file is open.

It's also a good idea to mark your WinBatch EXEs and DLLs as Read-only, so that they don't get totalled.

For multiple users on the network accessing the same ini file with ini operations requires a lot of care.

1. A Resource lock has to be set up for the ini file.

2. And you must flush the current machines buffers since by default windows is allowed to cache ini files.

Here are two very similar examples:

Example #1:

---

        Netdir="N:\stuff\"
        inifile=strcat(netdir,"yourini.ini")
        lockfile=strcat(netdir,"lock.txt")

        lock=0
        while lock ==0
          Errormode(@off)
           lock=FileOpen(lockfile,"WRITE")
           Errormode(@cancel)
           if lock!=0 then break
           TimeDelay(0.5)
        endwhile

        iniWritePvt("section","key",123,inifile)
        iniwritepvt("","","",inifile)
        FileClose(lock)

---

Example #2:

 ;Lock Code example.


 ;Define lock
 lockfile="X:\someplac\lockfile.lck"


 ;Lock ini file
 ErrorMode(@off)
 for x=1 to 10
   fh=FileOpen(lockfile,"WRITE")
   if fh==0
       TimeDelay(2)
   else
       break
   endif
 next
 ErrorMode(@CANCEL)  ;Don't even consider removing this line
 if fh==0 
     Message("Ooopsie","Could not obtain application lock")
     exit
 endif
 ; lock is secured

 ;Do your stuff here
 z=IniReadPvt(...
 z=z+1
 IniWritePvt(...
 IniWritePvt("","","",inifilename);force ini data to disk.


 ;Release Lock
 FileClose(fh)

Question (continued):

In the sample code above for locking a file so other users on the network wouldn't make changes while you make your own changes, in the statement:

    FileOpen( filename, "WRITE" ) 

does this create a new file, and if the file exists, overwrite it? I tried to open the file with APPEND. This wouldn't zero the file, but now I was not able to do the IniReadPvt() because the file was locked???

The IniReadPvt and IniWritePvt functions work fine if I don't open/lock the file, but they don't work if the file is opened first.

Here's my code:

;Lock ini file
ErrorMode(@off)
fh=FileOpen(lockfile,"WRITE")
ErrorMode(@CANCEL) 
if fh==0 
Message("Ooopsie","Could not lock")
exit
endif
; lock is secured

;Do your stuff here
z=IniReadPvt(...
z=z+1
IniWritePvt(...

;Release Lock
FileClose(fh) 

Answer:

You don't lock the INI file, you lock a different file that you logically associate with the INI file. Pick a name like INIFILE.LCK.

And before you clear the lock (with the release lock of FileClose(fh)) do a:

IniWritePvt("","","",youinifile)
TimeDelay(3)

So here's the general concept:

If WinBatch is the ONLY program that references the file...

1. Lock a DIFFERENT file in the same directory.

2. Do your ini operations.

3. If you do write the file, do a:

   IniWritePvt("","","",inifilename)
   

   to force a dump of the local machine cache of the ini file to disk.

4. Unlock the lock file.

---

Article ID:   W13169

Filename:   Make a resource LOCK.txt