On 24/04/17 12:26, Emil Velikov wrote:
On 21 April 2017 at 16:45, Jose Fonseca <jfons...@vmware.com> wrote:
I reread http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf and is
not explicit.
But I checked C11 threads.h implementation and thrd_current also uses
DuplicateHandle.
So C11/threads_win32.h is correct. And ISO C11 standard commited screwed up
here. Maybe they'll introduce thread ids at some point (MSVC's
implementation has a non-standard _Thrd_id() function), and we can use it,
but until then, it's better not pretend that thrd_current meets our needs
because it doesn't.
Right, thanks for the clarification Jose!
Personally I won't go as far as "ISO C11 standard commited screwed up
here", since they are not the ones that wrote the threads
implementation in Windows.
>
> Perhaps MS can address that if they see enough value in it, but even
> then there's the older/released versions of Windows to think about.
No my point is that it's *impossible* for Microsoft, us, or anybody to
do a C11 threads where thrd_current is light weight on Windows. Period.
So that shows a lack of foresight from the committee.
Or perhaps the committee decided that a light weight thrd_current was
unimportant. But in that case I think it was a mistake.
Anyway, I'm sure there might have been other tradeoffs and issues that
lead the committe to come to this, or merely lack of time, or they
willingly decided to get feet wet before dived in. All I mean is that
at least for our use case, the current C threads.h design does not fit
our needs, at least on Windows.
That aside - can we reword the comment to something like the following:
/* GetCurrentThread() returns a pseudo-handle, which we need
* to pass to DuplicateHandle. Only the resulting handle can be used
* from other threads.
*
* Note that neither handle can be compared to the one by thread_create.
* Only the thread IDs - as returned by GetThreadId and GetCurrentThreadId
* can be compared directly.
*
* Other potential solutions would be:
* - define thrd_t as a thread Ids, but this would mean we'd need
to OpenThread for many operations
* - use malloc'ed memory for thrd_t. This would imply using TLS
for current thread.
*
* Neither is particularly nice.
*/
Thanks
Emil
Looks good.
Though the existing
"Life would be much easier if C11 threads had different abstractions for
threads and thread IDs, just like C++11 threads does..."
paragraph could stay. I'm still hoping that one day C standard has
distinct types for threads and thread ids is, as the only way for this
to be resolved to everybody's satisfaction.
Jose
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