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Diffstat (limited to 'pod/perlfunc.pod')
| -rw-r--r-- | pod/perlfunc.pod | 41 |
1 files changed, 30 insertions, 11 deletions
diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod index c39dd29298..62a196595a 100644 --- a/pod/perlfunc.pod +++ b/pod/perlfunc.pod @@ -56,9 +56,7 @@ Remember the following rule: =over 8 -=item - -I<THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!> +=item I<THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!> =back @@ -1029,14 +1027,35 @@ value is taken as the name of the filehandle. =item flock FILEHANDLE,OPERATION -Calls flock(2) on FILEHANDLE. See L<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 lock only 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. +Calls flock(2), or an emulation of it, on FILEHANDLE. Returns TRUE for +success, FALSE on failure. Will produce a fatal error if used on a +machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3). +flock() is Perl's portable file locking interface, although it will lock +only entire files, not records. + +OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with +LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but +you can use the symbolic names if you pull them in with an explicit +request to the Fcntl module. The names can be requested as a group with +the :flock tag (or they can be requested individually, of course). +LOCK_SH requests a shared lock, LOCK_EX requests an exclusive lock, and +LOCK_UN releases a previously requested lock. If LOCK_NB is added to +LOCK_SH or LOCK_EX then flock() will return immediately rather than +blocking waiting for the lock (check the return status to see if you got +it). + +Note that the emulation built with lockf(3) doesn't provide shared +locks, and it requires that FILEHANDLE be open with write intent. These +are the semantics that lockf(3) implements. Most (all?) systems +implement lockf(3) in terms of fcntl(2) locking, though, so the +differing semantics shouldn't bite too many people. + +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. If you like you can force Perl to ignore your system's flock(2) +function, and so provide its own fcntl(2)-based emulation, by passing +the switch C<-Ud_flock> to the F<Configure> program when you configure +perl. Here's a mailbox appender for BSD systems. |