Draft implementation of Context. #200
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Context holds information specific to an operation, such as a TagMap and Span. Each thread has a currently active Context. Contexts are conceptually immutable: the contents of a Context cannot be modified in-place.
| opencensus::context::WithContext wc(std::move(ctx)); | ||
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| #if 0 |
opencensus/context/context.h
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| class Context { | ||
| public: | ||
| // Creates a default Context. | ||
| Context(); |
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Need this public? Please make it private until we need it.
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| // WithContext is an RAII object, only ever stack-allocate it. While it's in | ||
| // scope, the execution will happen under a copy of the given Context. | ||
| class WithContext { |
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We probably need a version of this that accepts a boolean condition to avoid duplicate code:
if (condition) {
WithContext wc(ctx);
... // code
} else {
... // same code
}
| WithContext& operator=(const WithContext&) = delete; | ||
| WithContext& operator=(WithContext&&) = delete; | ||
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| Context swapped_context_; |
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Based on some experience that I have from dealing with other context implementation it is better if we have a way to check that objects are allocated and deallocated on the same thread. I suggest to put this check under the NDEBUG macro.
Remove guard macro and NC tests that checked for it.
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| // Shared pointer to the underlying Span representation. This is nullptr for | ||
| // Spans which are not recording events. This is an implementation detail, not | ||
| // part of the public API. | ||
| const std::shared_ptr<SpanImpl> span_impl_; | ||
| std::shared_ptr<SpanImpl> span_impl_; |
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We made the shared_ptr non-const (and also the SpanContext above) so that we can use swap() (L170) and operator= (#191) to modify a Span object in-place, so that Context can have a Span member (as opposed to pointer to Span).
Also in (#191) we marked all Span methods const because:
- They don't act on the shared_ptr, they act on the pointee.
- In future we can replace the shared_ptr with something like opencensus-java's approach.
Context holds information specific to an operation, such as a TagMap and
Span. Each thread has a currently active Context. Contexts are conceptually
immutable: the contents of a Context cannot be modified in-place.