Advanced Commands - set_lock/free

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Forms Processor Advanced Commands

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set_lock/free_lock Sets or removes an exclusive file access lock. (Used only in rare cases when you write a custom multi-step file update script. Normally, you would not use this parameter, as the form processor handles coordination of multiple simultaneous forms submissions for you automatically when simply inserting data into (or appending data to) an existing file).

&set_lock("filename");
&free_lock("filename");

filename - the name of the file which you want to obtain or release exclusive read and write access to.
Upon successfully locking the file, set_lock returns 0. If set_lock is unabled to obtain a lock after 30 seconds, it will return -1.

Example:

# get exclusive access

if (&set_lock("form/count.dat") != 0)

format screen
This service is very busy - please try again!
.

else

&slurp("counter","form/count.dat");
$counter=$counter+1;

format screen
This form has been submitted $counter times.
.

# now save the new value of the counter

format file form/count.dat overwrite
$counter
.

# release the lock

&free_lock("form/count.dat");

endif

See also: Detailed explanation for the example above [an error occurred while processing this directive]