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853天前#----------------------------- |
# download the following standalone program |
#!/usr/bin/perl |
# dblockdemo - demo locking dbm databases |
use DB_File; |
use strict; |
sub LOCK_SH { 1 } # In case you don't have |
sub LOCK_EX { 2 } # the standard Fcntl module. You |
sub LOCK_NB { 4 } # should, but who can tell |
sub LOCK_UN { 8 } # how those chips fall? |
my($oldval, $fd, $db, %db, $value, $key); |
$key = shift || 'default'; |
$value = shift || 'magic'; |
$value .= " $$"; |
$db = tie(%db, 'DB_File', '/tmp/foo.db', O_CREAT|O_RDWR, 0666) |
or die "dbcreat /tmp/foo.db $!"; |
$fd = $db->fd; # need this for locking |
print "$$: db fd is $fd\n"; |
open(DB_FH, "+<&=$fd") |
or die "dup $!"; |
unless (flock (DB_FH, LOCK_SH | LOCK_NB)) { |
print "$$: CONTENTION; can't read during write update! |
Waiting for read lock ( $! ) ...."; |
unless (flock (DB_FH, LOCK_SH)) { die "flock: |
$!" } |
} |
print "$$: |
Read lock granted\n"; |
$oldval = $db{$key}; |
print "$$: |
Old value was $oldval\n"; |
flock(DB_FH, LOCK_UN); |
unless (flock (DB_FH, LOCK_EX | LOCK_NB)) { |
print "$$: |
CONTENTION; |
must have exclusive lock! |
Waiting for write lock ( $! ) ...."; |
unless (flock (DB_FH, LOCK_EX)) { die "flock: |
$!" } |
} |
print "$$: |
Write lock granted\n"; |
$db{$key} = $value; |
$db->sync; # to flush |
sleep 10; |
flock(DB_FH, LOCK_UN); |
undef $db; |
untie %db; |
close(DB_FH); |
print "$$: |
Updated db to $key=$value\n"; |
#----------------------------- |
