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| Related Syntax | Other Library Functions | |||||
| function |
vfs.lock |
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Library: General, File system utilities (OMVFS)
Import: omvfs.xmd |
export external function lock
value file file-ref
from value integer start optional
to value integer end optional
timeout value integer timeout optional
id modifiable integer lock-id optional
Argument definitions
Use vfs.lock to lock an entire file or a specific area of it.
This program locks the region from byte 200 up to and including byte 400. It will wait 2 seconds for the lock to be completed. It will obtain an identifier for the lock. It tests to see if the lock was obtained. Note how the do ... done block is used to scope the catch #external-exception that handles the case in which the lock is not available.
import "omvfs.xmd" prefixed by vfs.
process
local vfs.file exclusive-file
local integer lock-id
set exclusive-file
to vfs.open "test.doc"
do
vfs.lock exclusive-file
from 200 to 400
timeout 2000
id lock-id
log-message "File locked with id: %d(lock-id)%n"
catch #external-exception identity error-code
do when error-code = "VFS217"
log-message "Could not lock file%n"
else
rethrow
done
done
The type of lock generated by this function depends on how the file was opened. If it was opened with write access, an exclusive lock is generated. No one can read from or write to the locked portion. If it was opened with read access, a shared lock is generated. No one can write to the locked portion.
The timeout parameter allows you to specify the amount of time the program will wait for the specified lock to be completed before throwing an exception (external exception VFS217). If timeout is not specified, the function will wait until the lock is completed.
If you are putting more than one lock on a single file, you should obtain an identifier for each lock so that you can identify which lock you want to release when calling vfs.unlock.
The following exceptions may occur:
