Alime.146
net.unix-wizards
utcsrgv!utzoo!decvax!ucbvax!ihnss!houxi!houxg!lime!martin
Sat Jan 30 17:42:39 1982
Re: file locking problem
#define lock(f) close(open(f,O_CREAT|O_EXCL))
#define unlock(f) unlink(f)
#define locked(f) access(f,0)
i use these (on UNIX 3.0) to control locking for a lineprinter daemon.
sample code:-
while( lock(LOCK) == FAIL )
sleep(4);
close(lineprinter);
unlock(LOCK);
if( !locked(LOCK) )
fprintf(stderr,"printer in use\n");
where FAIL = -1
martin levy HO(201-949)-2787
NOTE:- O_CREAT|O_EXCL will create the file if it does not exist, but O_EXCL
makes the open() fail if the file exists!. so it only works if the
file does not exist. QED.
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