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A first general restructuration of the doc according to the pattern [tour|tutorial|reference]. In the reference part, objects are documented per topic. In each topic, [definition|c++|python|hdf5] (not yet implemented)
64 lines
2.2 KiB
ReStructuredText
64 lines
2.2 KiB
ReStructuredText
.. highlight:: c
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.. _arr_view_memory:
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View memory management
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------------------------
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View classes contains a reference counting system to the memory block they view
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(like a std::shared_ptr, but more sophisticated to properly interface to Python numpy).
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This guarantees that memory will not be dellocated before the destruction of the view.
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The memory block will be dellocated when its array and all array_view
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pointing to it or to a portion of it will be destroyed, and only at that moment.
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Example::
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array<int,2> *p = new array<int,2> (2,3); // create an array p
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array_view<int,2> B = *p; // making a view
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delete p; // p is gone...
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B(0,0) = 314; cout<<B<<endl; // B (and the data) is still alive
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.. warning::
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TRIQS arrays, and in particular views are NOT thread-safe, contrary to std::shared_ptr.
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This is a deliberate choice for optimisation.
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Weak views [Advanced]
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^^^^^^^^^^^^^^^^^^^^^^^^
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Unfortunately this cannot be the end of the story, at least on current C++11 compilers.
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It turns out that, in very performance sensitive loops, increasing this tiny
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reference counter can break a lot of optimisations in almost all compilers, including the most
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recent ones (gcc 4.8, clang 3.3).
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It was therefore decided to introduce `weak views`.
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* Weak views are completely similar to "normal" views, except that they do `not` increase the memory
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reference counter.
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* Normal views are be implicitely constructed from weak view (the reverse is also true),
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As soon as you store the weak view into a normal view (e.g. array_view<T,N>)
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the reference counting is again incremented, and the memory guarantee holds.
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* Explicit construction of weak views is intentionally not documented here.
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It is designed to be (almost) an implementation detail.
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* The () operator returns a weak view `on a fully compliant C++11 compiler` (in particular, `rvalue reference for *this` must be implemented)
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allowing therefore for better performance on such compiler, in some loops.
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Older supported compiler will therefore generate code with lower performances.
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* It is however necessary for the advanced user to know about this implementation detail,
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because in some convolved cases, the memory guarantee may not hold.
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Example ::
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TO BE WRITTEN
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