Cannot lock a file.

[Hon Seng Phuah]

Hi all,

I have following code:

use 5.004'
use Fcntl ':flock';

sub check_file_stat us
{
$attempt_lock = 0;
$max_attempts = 3;
open(in_file, "$check_in_file _name");
while (!flock(in_file , LOCK_EX) && $attemp_lock < $max_attempts)
{
sleep(5);

}
close(in_file);
}

I cannot get the exlusive lock for the $check_in_file_ name variable
file name. Any idea? How should I correct my mistake?

[Alex939393929]

Re: Cannot lock a file.

hsphuah@usa.com (Hon Seng Phuah) wrote in message news:<3898598f. 0403240014.4614 c926@posting.go ogle.com>...[color=blue]
> Hi all,
>
> I have following code:
>
> use 5.004'
> use Fcntl ':flock';
>
> sub check_file_stat us
> {
> $attempt_lock = 0;
> $max_attempts = 3;
> open(in_file, "$check_in_file _name");
> while (!flock(in_file , LOCK_EX) && $attemp_lock < $max_attempts)
> {
> sleep(5);
>
> }
> close(in_file);
> }
>
> I cannot get the exlusive lock for the $check_in_file_ name variable
> file name. Any idea? How should I correct my mistake?[/color]

tried it with perl 5.6.0, no problemo, note flock does not
work for network files (e.g. files retrieved via nfs mount point).


see perldoc -f flock

use 5.004;
use Fcntl ':flock';

sub check_file_stat us
{
$attempt_lock = 0;
$max_attempts = 3;
my $check_in_file_ name = 'file1.txt';
open(in_file, "<$check_in_fil e_name")||print "$check_in_file _name:$!\n";
while (!flock(in_file , LOCK_EX) && $attemp_lock < $max_attempts)
{
print "lock attempt $!\n";
sleep(5);
$attemp_lock++;

}
close(in_file);
}

check_file_stat us();

[Hon Seng Phuah]

Re: Cannot lock a file.

If I change the open to be write. the flock return 1. Why open read
file cannot use exclusive lock like my case below? Does anyone have
any idea?

-HS Phuah

hsphuah@usa.com (Hon Seng Phuah) wrote in message news:<3898598f. 0403240014.4614 c926@posting.go ogle.com>...[color=blue]
> Hi all,
>
> I have following code:
>
> use 5.004'
> use Fcntl ':flock';
>
> sub check_file_stat us
> {
> $attempt_lock = 0;
> $max_attempts = 3;
> open(in_file, "$check_in_file _name");
> while (!flock(in_file , LOCK_EX) && $attemp_lock < $max_attempts)
> {
> sleep(5);
>
> }
> close(in_file);
> }
>
> I cannot get the exlusive lock for the $check_in_file_ name variable
> file name. Any idea? How should I correct my mistake?[/color]

[nobull@mail.com]

Re: Cannot lock a file.

hsphuah@usa.com (Hon Seng Phuah) wrote in message news:<3898598f. 0403241640.5de1 12cd@posting.go ogle.com>...[color=blue]
> If I change the open to be write. the flock return 1. Why open read
> file cannot use exclusive lock like my case below? Does anyone have
> any idea?[/color]

To prevent denial of service attacks. (It's an OS feature, nothing to
do with Perl).

Some OSs go futher and disallow taking a shared lock if you have the
file open write-only, which, IMNSHO is just plain dumb.
[color=blue][color=green]
> > while (!flock(in_file , LOCK_EX) && $attemp_lock < $max_attempts)
> > {
> > sleep(5);
> > }[/color][/color]

You have not specified LOCK_NB. There's no point having a re-try
loop. If a blocking flock() fails it is usually because the
filehandle (or the file) in question is of a type that doesn't support
the type of locking locking you are asking for. This isn't something
that will change in 5 seconds.

Oh, and BTW you forgot to increment your counter.

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