flock
flock - lock an entire file with an advisory lock
flock FILEHANDLE,OPERATION
Calls flock(2) on FILEHANDLE. See flock(2) for definition of
OPERATION. Returns TRUE for success, FALSE on failure. Will produce a
fatal error if used on a machine that doesn't implement either flock(2) or
fcntl(2). The fcntl(2) system call will be automatically used if flock(2)
is missing from your system. This makes
flock()
the portable file locking
strategy, although it will only lock entire files, not records. Note also
that some versions of
flock()
cannot lock things over the network; you
would need to use the more system-specific
fcntl()
for that.
Here's a mailbox appender for BSD systems.
<![CDATA[
$LOCK_SH = 1;
$LOCK_EX = 2;
$LOCK_NB = 4;
$LOCK_UN = 8;
sub lock {
flock(MBOX,$LOCK_EX);
# and, in case someone appended
# while we were waiting...
seek(MBOX, 0, 2);
}
sub unlock {
flock(MBOX,$LOCK_UN);
}
]]>
open(MBOX, ``>>/usr/spool/mail/$ENV{'USER'}'')
or die ``Can't open mailbox: $!'';
lock();
print MBOX $msg,"\n\n";
unlock();
See also DB_File for other
flock()
examples.