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November 14, 2012
What's the deal with __thread?
IIRC it was used prior to 2.030. In the spec, it is in the keyword list, 
and it's also listed in the "Migrating to shared" article. That's all. 
There are a small number of uses of it in the DMD test suite.

Is it still valid? Is it useful? Or has everyone forgotten that it still 
exists?
November 14, 2012
Re: What's the deal with __thread?
On Nov 14, 2012, at 6:26 AM, Don Clugston <dac@nospam.com> wrote:

> IIRC it was used prior to 2.030. In the spec, it is in the keyword list, and it's also listed in the "Migrating to shared" article. That's all. There are a small number of uses of it in the DMD test suite.
> 
> Is it still valid? Is it useful? Or has everyone forgotten that it still exists?

I think __thread was for explicit TLS before TLS became the default.  I don't see a continued use for it.
November 14, 2012
Re: What's the deal with __thread?
On 11/14/2012 12:06 PM, Sean Kelly wrote:
> On Nov 14, 2012, at 6:26 AM, Don Clugston <dac@nospam.com> wrote:
>
>> IIRC it was used prior to 2.030. In the spec, it is in the keyword list,
>> and it's also listed in the "Migrating to shared" article. That's all.
>> There are a small number of uses of it in the DMD test suite.
>>
>> Is it still valid? Is it useful? Or has everyone forgotten that it still
>> exists?
>
> I think __thread was for explicit TLS before TLS became the default.  I don't
> see a continued use for it.
>

Sean's right.
November 15, 2012
Re: What's the deal with __thread?
On 14/11/12 23:16, Walter Bright wrote:
> On 11/14/2012 12:06 PM, Sean Kelly wrote:
>> On Nov 14, 2012, at 6:26 AM, Don Clugston <dac@nospam.com> wrote:
>>
>>> IIRC it was used prior to 2.030. In the spec, it is in the keyword list,
>>> and it's also listed in the "Migrating to shared" article. That's all.
>>> There are a small number of uses of it in the DMD test suite.
>>>
>>> Is it still valid? Is it useful? Or has everyone forgotten that it still
>>> exists?
>>
>> I think __thread was for explicit TLS before TLS became the default.
>> I don't
>> see a continued use for it.
>>
>
> Sean's right.

Good, that's what I thought. Lets remove it from the spec, and deprecate 
it. There is probably no extant code that uses it, outside of the test 
suite.

However, there is one case in the test suite which is unclear to me:

extern(C) __thread int x;

Is there any other way to do this?
November 15, 2012
Re: What's the deal with __thread?
On 2012-11-15 11:28, Don Clugston wrote:

> However, there is one case in the test suite which is unclear to me:
>
> extern(C) __thread int x;
>
> Is there any other way to do this?

extern (C) int x;

"extern(C)" doesn't make it global.

-- 
/Jacob Carlborg
November 15, 2012
Re: What's the deal with __thread?
On 11/15/2012 2:28 AM, Don Clugston wrote:
> However, there is one case in the test suite which is unclear to me:
>
> extern(C) __thread int x;
>
> Is there any other way to do this?

extern(C) int x;
November 15, 2012
Re: What's the deal with __thread?
On 15/11/12 11:54, Walter Bright wrote:
> On 11/15/2012 2:28 AM, Don Clugston wrote:
>> However, there is one case in the test suite which is unclear to me:
>>
>> extern(C) __thread int x;
>>
>> Is there any other way to do this?
>
> extern(C) int x;
>

What about extern(C) variables which are not thread local?
(which I think would be the normal case).
Then from a C header,

extern(C) int x;

must become:

extern(C) __gshared int x;

in D. It's a very rare case, I guess, but it's one of those situations 
where D code silently has different behaviour from identical C code.
November 15, 2012
Re: What's the deal with __thread?
On 15-11-2012 15:42, Don Clugston wrote:
> On 15/11/12 11:54, Walter Bright wrote:
>> On 11/15/2012 2:28 AM, Don Clugston wrote:
>>> However, there is one case in the test suite which is unclear to me:
>>>
>>> extern(C) __thread int x;
>>>
>>> Is there any other way to do this?
>>
>> extern(C) int x;
>>
>
> What about extern(C) variables which are not thread local?
> (which I think would be the normal case).
> Then from a C header,
>
> extern(C) int x;
>
> must become:
>
> extern(C) __gshared int x;
>
> in D. It's a very rare case, I guess, but it's one of those situations
> where D code silently has different behaviour from identical C code.

I think most people are aware of this 'quirk' from what I've seen in 
binding projects, so it's probably not a big deal.

-- 
Alex Rønne Petersen
alex@lycus.org
http://lycus.org
November 15, 2012
Re: What's the deal with __thread?
On 11/15/2012 6:42 AM, Don Clugston wrote:
> On 15/11/12 11:54, Walter Bright wrote:
>> On 11/15/2012 2:28 AM, Don Clugston wrote:
>>> However, there is one case in the test suite which is unclear to me:
>>>
>>> extern(C) __thread int x;
>>>
>>> Is there any other way to do this?
>>
>> extern(C) int x;
>>
>
> What about extern(C) variables which are not thread local?
> (which I think would be the normal case).
> Then from a C header,
>
> extern(C) int x;
>
> must become:
>
> extern(C) __gshared int x;

That's right. extern(C) doesn't change the storage class.

> in D. It's a very rare case, I guess, but it's one of those situations where D
> code silently has different behaviour from identical C code.
November 15, 2012
Re: What's the deal with __thread?
On 11/15/2012 6:46 AM, Alex Rønne Petersen wrote:
> I think most people are aware of this 'quirk' from what I've seen in binding
> projects, so it's probably not a big deal.


Also, remember that C code can now have thread local globals, too. Both are 
expressible in D, it's just that the default is reversed.
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