What exactly is the Dart_Handle type?

[Benjamin Summerton (@def-pri-pub)]

I've been a little interested lately in doing some Dart native development, and everywhere I've seen this `Dart_Handle` type.  When poking through through the source, this is all that I could find on it.  Which is just a typdef to a `_Dart_Handle *`, which I couldn't find anything else on in the SDK repo.

So my question is the title of the topic: "What exactly is the Dart_Handle type?"

[Michael Francis]

Dart_Handle is a reference to a Dart Object. To use the Dart_Handle you will need to use the other methods found in dart_api.h
Starting about line number 1361 you will begin to see functions that translate a Dart_Handle to c types.

On Tue, Oct 4, 2016 at 2:07 PM Benjamin Summerton (@def-pri-pub) <def.p...@gmail.com> wrote:

I've been a little interested lately in doing some Dart native development, and everywhere I've seen this `Dart_Handle` type.  When poking through through the source, this is all that I could find on it.  Which is just a typdef to a `_Dart_Handle *`, which I couldn't find anything else on in the SDK repo.

So my question is the title of the topic: "What exactly is the Dart_Handle type?"

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[William Hesse]

To be more clear about the purpose of Dart_Handle:

Because Dart has a garbage-collected heap of objects, and the garbage collector can move objects around, you can't keep pointers to objects in C++ code that could be interrupted by garbage collections.  So you allocate Dart_Handles, which are a bunch of places THAT THE GC KNOWS ABOUT holding pointers to objects.  That way, when the GC moves an object, it updates the pointer in that place (that Dart_Handle).  So your C++ code, but more importantly the Dart embedding API calls that your code makes, can grab the object pointer out of that handle and do stuff with it (but reloading the pointer from the handle any time a GC could have happened).

The Dart_Handles that the GC knows about can be created in various ways: in Zones, as permanent handles, etc.  You can't just make one using 'new'.  The memory management of the handles has to be done more carefully and explicitly, and they aren't GCd, since their reason for existing is to be a C++ pointer that isn't touched by the GC, that points to a Dart object pointer.

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William Hesse