Am Tuesday 12 January 2010 15:17:05 schrieb Vicente Botet Escriba:
thread_specific_ptr operator*: one branch to make sure the vector is large enough(a new thread_specific_ptr might have been created by another thread), one indirection. constant-time average, linear to vector if reallocation is necessary. but that can only happen when a new thread_specific_ptr was created.
I think the branch also could be avoided with some effort and a second indirection(using pages to avoid reallocating and making sure the page exists in each thread on thread_specific_ptr construction) but to me the branch is acceptable.
For me it is unacceptable to use reallocation of the vector on the operator*. More, any non-constant time operator* don't satisfy my requirements for some specific contexts.
I'd prefer reallocation, but reallocation can be avoided using pages at the cost of a second or third indirection. struct page{ user_ptr ptr[0x10000]; }; page *pages[0x10000]; operator*(){ size_t pagenr=this->index & 0xffff0000]; page *p=pages[pagenr]; if(!p) p=pages[pagenr]=new page; return p[this->index & 0xffff]; } if 64K*sizeof(user_ptr) per page is too much that can be reduced by setting a reasonable maximum below 4 billion or by using a third indirection. could you ellaborate on your case that can't accept reallocation? I can't think of a case. as long as there is an allocation (and there is one in the current implementation, too) there's a mutex lock and no guarantee on the time it takes to return anyway.