[lldb-dev] SBListener not using a shared_ptr internally?

[Paul Peet via lldb-dev]

I am currently using the package from Arch Linux's repository, it's 3.7.1.
So I guess this "patch" will be in llvm/lldb 3.8.1?

2016-03-25 22:42 GMT+01:00 Jim Ingham <jingham at apple.com>:
> What version of the lldb sources are you working with?  I changed the SBListener over to using only the ListenerSP internally
> in r262863.
>
> Jim
>
>> On Mar 25, 2016, at 1:03 PM, Paul Peet via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>>
>> Hey,
>>
>> I am currently working on lldb bindings for javascript (v8) but it
>> seems that the API is giving me some troubles.
>>
>> What I am doing is to basically wrap SB* objects into V8 objects, and
>> since SB objects contain a shared_ptr into an internal class I think I
>> can simply copy construct them.
>>
>> To return a wrapped SB object by some Javascript function, I am simply
>> copy constructing the SB object into the wrapper object which is
>> dynamically allocated and when the Javascript object is garbage
>> collected it will also destroy the SBObject (And also the shared_ptr,
>> So it should be save I guess?).
>>
>> Okay, so far so good but I detected some inconsistency when trying to
>> wrap SBListener. The deal was to make SBListener::WaitForEvent
>> non-blocking, to do that I am creating a new thread which calls
>> WaitForEvents, when it returns and the event is valid, the callbacks
>> given from the Javascript code is called.
>>
>> There is a catch when doing this. I have to track the threads which
>> belong to a specific SBListener. But there is not actually easy way to
>> do this because SB objects are just simply shared_ptr. I noticed the
>> GetSP function which returns the shared_ptr of an SBListener, this
>> would be a way to solve this issue as I could use a map which maps the
>> internal SBListener pointer to a Class object which manages the thread
>> and stuff (SBListenerWorker).
>>
>> // etc. mutex, ...
>> static std::unordered_map<void*, SBListenerWorker*> ListenerWorkers;
>>
>> GetSP is protected so I had to create a new derived class:
>>
>> class SBListener_Internal : public lldb::SBListener {
>> public:
>>  SBListener_Internal() = default;
>>  SBListener_Internal(const lldb::SBListener& listener)
>>      : lldb::SBListener{listener} {
>>  }
>>  ~SBListener_Internal() = default;
>>
>>  void* GetInternalPtr() {
>>    return reinterpret_cast<void*>(GetSP().get());
>>  }
>> };
>>
>> I had some worried about if the SBListener object could be destroyed
>> at some point and the internal pointer would still be in the
>> "ListenerWorkers" map so
>> to avoid that I copied the the SBListener object into the class which
>> manages the thread and stuff (SBListenerWorker), that means that the
>> reference counter should be still > 0 when all other shared_ptrs are
>> destroyed.
>>
>> Now to the actual problem, it turns out that GetInternalPtr() actually
>> returns nullptr and instead uses m_opaque_ptr for calling internal
>> functions.
>> This means that the SBListener object isn't actually using a
>> shared_ptr internally, which brings another question up if it is save
>> to use the SBListener across thread? What happens if the SBListener
>> gets destroyed.
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>