How to use synchronized() {} as the basis for a freely (un)lockable mutex, using stackthreads
Sean Kelly
sean at f4.ca
Wed Jan 9 13:06:55 PST 2008
downs wrote:
> Sean Kelly wrote:
>> downs wrote:
>>> Disclaimer: My StackThreads are neither particularly fast (130 cycles
>>> per context switch), nor particularly stable.
>>> This is primarily intended as a Proof of Concept, even though I do use
>>> it in some of my code. :)
>>>
>>> Have you ever wished D had a Mutex class that could be locked or
>>> unlocked at any time?
>> Tango does :-)
>>
>
> Clarification. D/Phobos.
>
>>> D's synchronized() {} statement is nice and all, but does have some
>>> weaknesses, primarily that it can only be used to
>>> synchronize some scope - it is not possible to unlock the underlying
>>> mutex in the middle of a block.
>> The Tango mutexes can also be used with the 'synchronized' statement.
>> However, I'm not sure I like the idea of being inside a 'synchronized'
>> block and having the mutex unlocked. Why not just break the code into
>> two sequential 'synchronized' blocks?
>>
>>
>> Sean
>
> Because the structure of the code looks like this:
>
> foo;
> synchronized {
> bar;
> whee {
> lol;
> *unsynchronized* { lmao; }
> meep;
> }
> baz;
> }
>
> So, to break it into two synchronized statements, my code would have to look like so ...
>
> foo;
> synchronized {
> bar;
> whee {
> lol;
> }
> lmao;
> synchronized {
> meep;
> } // closing bracket of whee
> baz;
> }
>
> See the problem? :)
I can't say I've ever actually seen the need for such an algorithm in
practice (outside of condition variables), but in Tango you could do:
synchronized( mutex )
{
bar;
whee
{
lol;
{
mutex.unlock;
scope(exit) mutex.lock;
meep;
}
baz;
}
}
Can't say I have a solution for Phobos though.
Sean
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