On Fri, 04 Feb 2011 07:26:22 -0500, bearophile <bearophileh...@lycos.com>
wrote:
I have found an interesting post by Scott Johnson in this Lambda the
Ultimate thread:
http://lambda-the-ultimate.org/node/724#comment-6621
He says:
9th circle: Concurrent mutable state. The obnoxious practice of
mutating shared state from multiple threads of control, leading into a
predictable cycle of race conditions, deadlocks, and other assorted
misbehavior from which there is no return. And if a correct solution
(for synchronization) is found for a given program, chances are any
substantial change to the program will make it incorrect again. But you
won't find it, instead your customer will. Despite that, reams of code
(and TONS of middleware) has been written to try and make this
tractable. And don't get me started on a certain programming language
which starts with "J" that saw fit to make EVERY object have its very
own monitor....<
This is just one quotation, but I have found similar comments four or
five other times around the Web.
So is the design choice of copying this part of the Java design inside D
good? I'd like opinions on this topic.
Recently I have suggested an optional @nomonitor annotation for D
classes (to optionally remove a word from class instances and to reduce
class instantiation overhead a bit). Another option is doing the
opposite, and defining a @withmonitor annotation where you want a class
to have a monitor.
D's monitors are lazily created, so there should be no issue with resource
allocation. If you don't ever lock an object instance, it's not going to
consume any resources. Most of the time the extra word isn't noticed
because the memory size of a class is usually not exactly a power of 2.
D also allows you to replace it's monitor with a custom monitor object
(i.e. core.sync.Mutex) so you can have more control over the mutex, assign
the same mutex to multiple objects, use conditions, etc. It's much more
flexible than Java or C# IMO.
-Steve