[PATCH] getStreamedBitcodeModule: take StreamingMemoryObject instead of DataStreamer

[Rafael Espíndola]

> Hi Rafael,
>
> DataStreamer's interface is pretty much just one method that "pulls N bytes"
> from the current position and advances the current position for the next
> pull. So it doesn't have random access.
>
> On the other hand, the StreamableMemoryObject interface adds random access
> and it is the interface that the bitcode reader interacts with. Given that,
> it made more sense for us to have a thread cache at the random-access level
> than at the DataStreamer stream level.
>
> If it helps clarify things, the way we have an out-of-tree implementation
> set up is to have:
>
> (*) One instance of a DataStreamer to pull bytes from. It gets bytes from an
> URL downloader and may block if bytes haven't been downloaded yet (involves
> two threads).
>
> (*) One plain StreamingMemoryObject(Impl) instance talking to the
> DataStreamer, to buffer things from the DataStreamer and provide basic
> random access.
>
> (*) N instances of thread cached memory objects that also implement the
> StreamingMemoryObject interface, wrapping the plain StreamingMemoryObject
> instance to provide some thread local caching and thread safety, while also
> providing random access.
>
> (*) N threads w/ N contexts and N modules materialized by N bitcode readers
> that each get one of the N thread cached StreamingMemoryObjects (the bitcode
> reader is able to use the thread cached memory objects instead of the plain
> non-thread-safe memory objects, because of this refactoring).
>
>
>>
>> In general having an interface with just one implementation is
>> undesirable.
>
>
> Yes, I can see that as not being too desirable, but does the above make
> sense as to why the interface is separated out from the implementation and
> why we don't add the features to the DataStreamer instead?

I guess so, but then the question is why do we need 2 interfaces? If
the module reader uses StreamableMemoryObject, can we make it virtual
(as you propose) but merge DataStreamer into the in-tree
implementation so that we still have only one (now more generic)
interface?

Cheers,
Rafael