Python Cffi Memory Management Issues

I am programming on Ubuntu, with Python 2.7.3. I am using CFFI to populate a Python list with values coming from some C code. That list is quite big : around 71 000 characters long

Solution 1:

I found how to fix my issues:

I used ffi.gc(cdata, destructor) to create the structure. My Python code now looks like:

data_list = []
for i in range( 0, x ):  
    # Create a pointer to the data structure and tell the garbage collector how to destroy it
    gc_c_pDataStructure = ffi.gc( c.CreateDataStructure(), c.FreeDataStructure )
    c.SomeCFunction( gc_c_pDataStructure )  # Populate the data structure
    datas_list.append( c.GetSomeInfo( gc_c_pDataStructure ) ) # Store some data  

Here are some links related to ffi.gc():

• Python CFFI documentation
• David's thread

And here is the C function to create the data structure (according to the structure example from the question):

PSTRUCT1 CreateDataStructure()
 {
     PSTRUCT1 pStruct1 = ( PSTRUCT1 ) malloc( sizeof( STRUCT1 ) );
     _SetDummyValues( pStruct1 );

     return pStruct1;
 }

As you can see, I had to create the function void _SetDummyValues( PSTRUCT1 pStruct1 ). That function sets the given structure pointers to NULL.

Solution 2:

This may have also been related to this bug which Coverity found in some of our CFFI-generated code:

  x0 = (void *)alloca((size_t)datasize);
  ...
  { 
      free(x0); 
  }

As you can see, it's calling free on stack-allocated memory.