[pyusb-users] Change suggestion

[Hermann Hamann]

 

I want to suggest a small change to pyusb to improve speed.

Currently you can only provide an array.array buffer to put the USB data into.
I use the multiprocessing feature and the final destination of the USB data is a mmap.mmap
Object. I would like to specify this as a receive buffer to save a pickle and
unpickle operation.

It is not so difficult to use the pyapi.PyObject_GetBuffer function to retrieve address and length
of any buffer protocol compliant object.

So this array restriction should be lifted, I assume there are more users who would
appreciate this change. I would not like to distribute my software with a modified pyusb.

Sincerely
Hermann Hamann

Here follows the modifications I made:

-----------------------------------------

# in backend1.py, similar for other backends

from ctypes import *
from struct import unpack

getBuffer = pythonapi.PyObject_GetBuffer

getBuffer.argtypes = [py_object, c_void_p, c_int]

view = create_string_buffer(11*sizeof(int))

def getBufferInfo(someObject):

    pointer_to_sO = py_object(someObject)

    result = getBuffer(pointer_to_sO,view,1) # flag writeable

    ### this call can raise an Exception. However this would be a consequence
    ### of an invalid caller, so no recovery is possible and simply let it
    ### crash, the message is helpful.
   
    if result != 0 : return None,None
   
    bufadr,objadr,buflen,itemsize,readonly,ndim,bformat,shape,strides,\
      suboffsets,internal =  unpack("11I",view)
  
    result = pythonapi.PyBuffer_Release(string_buffer)

    return (bufadr,buflen)
   
# and some lines later

    def __read(self, fn, dev_handle, ep, intf, buff, timeout):
        ### !!!! changed address, length = buff.buffer_info()
        address,length = getBufferInfo(buff)
        ##length *= buff.itemsize changed
       
----------------------------------
# in core.py

        if isinstance(size_or_buffer,int):
          

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