Ping qznc: Re: A little of coordination for Rosettacode

[monarch_dodra]

On Saturday, 16 February 2013 at 07:58:56 UTC, qznc wrote:
> On Saturday, 16 February 2013 at 06:58:01 UTC, qznc wrote:
>> On Saturday, 16 February 2013 at 02:23:42 UTC, Jos van Uden 
>> wrote:
>>> On 5-2-2013 20:45, Jos van Uden wrote:
>>> 
>>>> By the way, I think 'Qznc' may want to have a look at 'The 
>>>> dining
>>>> philosophers':
>>>>
>>>> http://rosettacode.org/wiki/Dining_philosophers
>>
>> I should find the time to solve it this weekend.
>
> Wow, my kid let me do some hacking right now and it was simpler 
> than expected.
> Posted a solution already.

Hum...

//----
	Mutex[5] forks = new Mutex();
//----

This will allocate a single Mutex, and place the same reference 
in all five entries of forks.

In a word: There is actually only one fork. The philosophers can 
still dine, because a single thread is allowed to lock the same 
resource twice, making the problem trivial. Basically, they are 
dual wielding the fork ;)

The correct line of code should be:
//----
	Mutex[5] forks;
	foreach(ref fork; forks) fork = new Mutex();
//----

Or some variation thereof of course. The code still works with 
this change.

I'm reporting it instead of correcting it directly, so as to 
better explain how and why.