2010/1/29 Martin Langhoff <[email protected]>:
Hallo, Martin.
> The flock binary in modern linuxes (from util-linux-ng) supports
> flocking a filehandle that is handled by the shell. Combining this
> with per-code-block filehandles / io redirection, it is an incredibly
> useful construct to protect a code block with a lock.
>
> The resulting code looks like this (from man flock on Fedora 11):
>
> (
> flock -s 200
> # ... commands executed under lock ...
> ) 200>/var/lock/mylockfile
>
> I am now discovering that this works in bash, but not in dash.
What about implementation of the race-condition protection or locking
using this scheme:
* `umask 777` -- lock situation using file to be created
* `{ echo “creating file using ‘>’ in a working block” ; do_the_task ;
} > lock_file`
* paralel / concurrent task: `echo “checking file for access using
‘>’” > lock_file && go || echo 'error: access denied' >&2`
* `{ mv lock_file || rm lock_file || …. ; } && chmod 666 lock_file` --
releasing the lock (order matters)
--
sed 'sed && sh + olecom = love' << ''
-o--=O`C
#oo'L O
<___=E M
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