The "no gc" crowd

[Michel Fortin]

On 2013-10-11 02:08:02 +0000, Andrei Alexandrescu 
<SeeWebsiteForEmail at erdani.org> said:

> On 10/10/13 7:04 PM, Jonathan M Davis wrote:
>> On Thursday, October 10, 2013 18:21:52 Andrei Alexandrescu wrote:
>>> You can't EVER expect to obtain all of that magic by plastering "shared"
>>> on top of your type.
>> 
>> It works just fine with the idiom that I described where you protect the usage
>> of the object with a lock, cast it to thread-local to do stuff on it, and then
>> release the lock (making sure that no thread-local references remain).
> 
> TDPL describes how synchronized automatically peels off the "shared" 
> off of direct members of the object. Unfortunately that feature is not 
> yet implemented.

That "direct member" limitation makes the feature pretty much 
worthless. It's rare you want to protect a single integer behind a 
mutex, generally you protect data structures like arrays or trees, and 
those always have indirections.

You could loosen it up a bit by allowing pure functions to use the 
member. But you must then make sure those functions won't escape a 
pointer to the protected structure through one of its argument, or the 
return value. That won't work with something like std.range.front on an 
array.

Anyway, that whole concept of synchronized class is a deadlock 
honeypot. It should be scrapped altogether.

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca