Threads, shread and TLS
schveiguy at yahoo.com
Fri Jan 7 10:20:45 PST 2011
On Fri, 07 Jan 2011 11:30:17 -0500, Adam Conner-Sax
<adam_conner_sax at yahoo.com> wrote:
> It's not really about correctness as much as trying to understand how
> different storage classes work. I understand that there is only one foo
> I wanted to see which parts are thread-local and which are shared and
> how the
> constructors work.
A class instance can be shared or unshared. Either way, changing the data
on the same instance updates the same instance, there is not a copy of the
whole world in each thread, just a copy of the thread local storage block.
So you are sort of conflating 'per instance' with 'per thread.'
int x -- per instance (shared or not)
static int x -- per thread (in the TLS block)
shared static int x -- per process, not in any instance.
> I'm working (way over my head) on a more complex threading issue and I
> that I didn't quite understand the storage classes and constructors. Now
> I get it
> a bit more.
> By "untagged sharing" do you mean the "a" variable which is shared in
> the sense
> that all threads see the same copy but does not have storage class
> "shared"? Yes,
> that confuses me too. Should it be an error?
Yes, if you have a piece of data that shared and not marked with __gshared
or shared, then we have a problem. The problem is that a lot of code
assumes that situation cannot happen without casts (you can always cast
and override the type system), so you can make assumptions based on that.
For example, a lot of C++/java code is written *just in case* an object is
shared. With D, the hope is that you are *guaranteed* that it is shared
or not, so you can optimize your code that way (i.e. use a lock or not).
As long as the possibility exists that code not marked as shared can be
easily shared without a cast, we cannot make those assumptions.
I think it should be filed as a bug, but I'm not sure if someone's already
> I have never dealt with bugzilla but I will try to figure out how to do
> what you
> ask :)
Go to http://d.puremagic.com/issues/enter_bug.cgi
You will have to create a user before filing a bug, but bugzilla is
relatively straightforward to use.
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