> DS> I'd definitely rather perl not do any sort of explicit user-level locking.
> DS> That's not our job, and there be dragons.
> Please explain how this is possible?
Just say no...to locks.
> Does this mean that without user specifying a lock, perl will allow
> a chaotic update pattern to be visible to the user?
I don't know what `chaotic' means.
The user can certainly create race conditions.
> thread A thread B
> push(@foo, $bar); ++$bar;
#!/my/path/to/perl
use Thread;
$bar = 0;
async { ++$bar }
push @foo, $bar;
print $foo[0];
Output: 0 or 1
If the user cares whether the output is 0 or 1, they need to program a
lock. Something like
#!/my/path/to/perl
use Thread;
{
$bar = 0;
lock $bar;
async { lock $bar; ++$bar }
push @foo, $bar;
}
print $foo[0];
Output: 0.
> or
> $foo{$bar} = $baz; delete $foo{$bar++};
#!/my/path/to/perl
use Thread;
%foo = ( 1 => 'a', 2 => 'b' );
$bar = 1;
$baz = 'x';
async { delete $foo{$bar++} }
$foo{$bar} = $baz;
print $foo{$bar};
Exeuction trace
Thread1 Thread2
Case 1
$foo{$bar} = $baz;
print $foo{$bar};
delete $foo{$bar}
$bar++
Output: 'x'
Case 2
$foo{$bar} = $baz;
delete $foo{$bar}
print $foo{$bar};
$bar++
Output ''
Case 3
$foo{$bar} = $baz;
delete $foo{$bar}
$bar++
print $foo{$bar};
Output 'b'
Case 4
delete $foo{$bar}
$foo{$bar} = $baz;
$bar++
print $foo{$bar};
Output 'b'
Case 5
delete $foo{$bar}
$bar++
$foo{$bar} = $baz;
print $foo{$bar};
Output 'x'
Hey! This is fun :)
> Will there be some sort of coherence here?
What does coherence mean?
- SWM
