Also, if you provide me with full instructions on how to reproduce the linking error, I'm happy to look if I can figure out what is going on.
On Tue, Mar 27, 2018 at 1:25 PM, Philipp Moritz <pcmor...@gmail.com> wrote: > Hey Saul, > > The Buffer returned by Plasma's Create is not owning the memory, the > memory management happens via reference counting through the explicit > PlasmaClient::Release call. The reason why we now return a buffer instead > of a plain pointer and length is so we can support both CPU (MutableBuffer) > and GPU (CudaBuffer) memory with the same interface. > > If you only use CPU memory, it is safe to dynamically cast the Buffer > returned by Create to a MutableBuffer and get it's underlying pointer via > the mutable_data() function. > > This behavior might change in the future however if we decide to do > reference counting through the Buffer returned by PlasmaClient::Create. > However if we are merging libplasma into arrow soon I think it is save to > depend on the behavior as it is at the moment. > > -- Philipp. > > On Tue, Mar 27, 2018 at 1:04 PM, Saul Shanabrook <s.shanabr...@gmail.com> > wrote: > >> Yeah, I am writing C++ code that provides a C wrapper around this. But, >> how >> do I access either the protected mutable_data_ or the inline mutable_data >> from my this wrapper? >> >> On Tue, Mar 27, 2018 at 10:52 AM Wes McKinney <wesmck...@gmail.com> >> wrote: >> >> > @Kou, we removed that bit, so Buffer::mutable_data is always inline now. >> > >> > @Saul, you will want to create a C wrapper for arrow::Buffer so you >> > can manage memory lifetime from C. Depending on the kind of Buffer you >> > have, it may not be as simple as calling free(...) on its internal >> > data. >> > >> > - Wes >> > >> > On Tue, Mar 27, 2018 at 10:31 AM, Kouhei Sutou <k...@clear-code.com> >> wrote: >> > > Hi, >> > > >> > > It may be wrong but you may need to add -DNDEBUG flag to C >> > > compiler. >> > > >> > > >> > > Thanks, >> > > -- >> > > kou >> > > >> > > In <CANapY_LzahViR9e7e90H=wq3j0tnbZJe1Vm=j7=vvyqawnc...@mail.gm >> ail.com> >> > > "Re: Using Plasma with xnd" on Tue, 27 Mar 2018 13:41:49 +0000, >> > > Saul Shanabrook <s.shanabr...@gmail.com> wrote: >> > > >> > >> Ah, I see I can use garrow_buffer_get_mutable_data from c_glib. >> > >> >> > >> On Tue, Mar 27, 2018 at 9:29 AM Saul Shanabrook < >> s.shanabr...@gmail.com >> > > >> > >> wrote: >> > >> >> > >>> I am in the process of changing over my C wrapper to work with Arrow >> > >>> 0.9.0. One change is that the plasma APIs now use arrow::Buffer >> > instead of >> > >>> of raw pointers, in Create and Get. >> > >>> >> > >>> In my C wrapper for Create, I need to get the mutable data pointer >> from >> > >>> the arrow::Buffer, after it is created. Here is my current >> > implementation: >> > >>> >> > https://github.com/plures/pxnd/blob/84e9403ef3811e0893e12076 >> 455d7cbc49c39358/libplasma/plasma.cc#L56-L75 >> > >>> I do something similar to the Python wrapper around plasma: >> > >>> >> > https://github.com/apache/arrow/blob/f9f8320339692d4134d1ef4 >> 2c32cb7c8d547593e/python/pyarrow/plasma.pyx#L300-L307 >> > >>> >> > >>> >> > >>> However, this fails to link, I think because the mutable_data >> method is >> > >>> defined in the class and so is inline. So it doesn't show up in the >> > >>> libarrow.dylib/libarrow.a archive. Let me know if I am missing >> > something >> > >>> obvious, this is just my hypothesis for why it isn't working. >> > >>> >> > >>> Is there a way for a third party library to get the pointer to the >> data >> > >>> from a arrow::Buffer? >> > >>> >> > >>> On Wed, Mar 7, 2018 at 10:59 AM Wes McKinney <wesmck...@gmail.com> >> > wrote: >> > >>> >> > >>>> Where are you going to make Plasma requests, in Python or in C? >> > >>>> >> > >>>> * If in Python, use the buffer protocol to access the memory in C >> > >>>> https://docs.python.org/3/c-api/buffer.html#bufferobjects >> > >>>> * If in C, then I would suggest adding extern "C" APIs directly in >> > >>>> libplasma.so so you can connect to the Plasma store and make >> requests >> > >>>> directly in C. >> > >>>> >> > >>>> I want to make 100% sure that you need to interact with the Plasma >> > >>>> client in C before I send you down that path. Here's an example of >> a C >> > >>>> API embedded in an otherwise C++ library >> > >>>> >> > https://github.com/wesm/feather/blob/master/cpp/src/feather/feather-c.h >> . >> > >>>> >> > >>>> - Wes >> > >>>> >> > >>>> On Wed, Mar 7, 2018 at 10:53 AM, Saul Shanabrook < >> > s.shanabr...@gmail.com> >> > >>>> wrote: >> > >>>> > Hey Wes, >> > >>>> > >> > >>>> > Since all our logic for writing and reading the data is written >> in >> > C, we >> > >>>> > need to be get access to the memory in C as well. I think it >> makes >> > sense >> > >>>> > then for me to work on creating a C++ wrapper around Plasma that >> > exports >> > >>>> > what is necessary in C. Should that be in Arrow GLib? >> > >>>> > >> > >>>> > Best, >> > >>>> > Saul >> > >>>> > >> > >>>> > On Tue, Mar 6, 2018 at 11:49 PM Wes McKinney < >> wesmck...@gmail.com> >> > >>>> wrote: >> > >>>> > >> > >>>> >> hi Saul -- I think the easiest solution here is the >> > buffer/memoryview >> > >>>> >> protocol. You won't have to touch the Cython or C++ API from >> > pyarrow >> > >>>> >> if you do this. >> > >>>> >> >> > >>>> >> You can interact with a Buffer object like any other Python >> object >> > >>>> >> implementing the buffer protocol. See numpy.frombuffer as an >> > example >> > >>>> >> of a function that interacts with such objects. I would suggest >> > adding >> > >>>> >> a method to xnd method for this. >> > >>>> >> >> > >>>> >> If you need to interact with Plasma from C then things will be >> more >> > >>>> >> complicated -- Robert or Philipp should be able to advise in >> this >> > >>>> >> case. >> > >>>> >> >> > >>>> >> - Wes >> > >>>> >> >> > >>>> >> On Tue, Mar 6, 2018 at 4:55 PM, Saul Shanabrook < >> > >>>> s.shanabr...@gmail.com> >> > >>>> >> wrote: >> > >>>> >> > Hey Wes, >> > >>>> >> > >> > >>>> >> > I don't have much experience doing C + Python + Cython >> > development, >> > >>>> so I >> > >>>> >> am >> > >>>> >> > probably missing something obvious, but reading the Cython >> docs, >> > >>>> >> > < >> > >>>> >> >> > >>>> >> > https://cython.readthedocs.io/en/latest/src/userguide/extern >> al_C_code.html#public-declarations >> > >>>> >> > >> > >>>> >> > it >> > >>>> >> > seems like I can only access types marked as public from C >> code. >> > >>>> When I >> > >>>> >> > compile arrow locally, I do get some C++ headers for the >> plasma >> > code, >> > >>>> >> but I >> > >>>> >> > don't think I can use them from C code either. >> > >>>> >> > >> > >>>> >> > Best, >> > >>>> >> > Saul >> > >>>> >> > >> > >>>> >> > >> > >>>> >> > >> > >>>> >> > On Tue, Mar 6, 2018 at 3:12 PM Wes McKinney < >> wesmck...@gmail.com >> > > >> > >>>> wrote: >> > >>>> >> > >> > >>>> >> >> hi Saul, >> > >>>> >> >> >> > >>>> >> >> Are you able to use the buffer/memoryview protocol? >> Instances of >> > >>>> >> >> pyarrow.Buffer, like PlasmaBuffer, support this >> > >>>> >> >> >> > >>>> >> >> >> > >>>> >> >> > >>>> >> > https://github.com/apache/arrow/blob/master/python/pyarrow/p >> lasma.pyx#L182 >> > >>>> >> >> >> > >>>> >> >> - Wes >> > >>>> >> >> >> > >>>> >> >> On Tue, Mar 6, 2018 at 3:09 PM, Saul Shanabrook < >> > >>>> s.shanabr...@gmail.com >> > >>>> >> > >> > >>>> >> >> wrote: >> > >>>> >> >> > I am trying to use the Plasma store to back xnd objects. >> Xnd ( >> > >>>> >> >> > https://xnd.readthedocs.io/en/latest/xnd/index.html) is a >> > >>>> container >> > >>>> >> >> library >> > >>>> >> >> > in C that has Python bindings. I would like to get a >> pointer >> > to >> > >>>> the >> > >>>> >> >> > allocated memory after creating or get an object in >> Plasma. I >> > see >> > >>>> that >> > >>>> >> >> this >> > >>>> >> >> > is supported in the C++ API ( >> > >>>> >> >> > >> > >>>> >> >> >> > >>>> >> >> > >>>> >> > https://arrow.apache.org/docs/cpp/classplasma_1_1_plasma_cli >> ent.html#ac18ab9cc792c620a97a3dcb165e0ecd7 >> > >>>> >> >> ) >> > >>>> >> >> > but not in the python API (as far as I can tell). Is it >> > possible >> > >>>> to >> > >>>> >> use >> > >>>> >> >> the >> > >>>> >> >> > C++ Plasma API from a C project? If not, would it make >> sense >> > to >> > >>>> expose >> > >>>> >> >> > pointer access on the Python API using capsules >> > >>>> >> >> > https://docs.python.org/3.6/c-api/capsule.html >> > >>>> >> >> > <https://docs.python.org/3.6/c-api/capsule.html#capsules>? >> > >>>> >> >> >> > >>>> >> >> > >>>> >> > >>> >> > >> > >
