[PyOpenCL] Segementation fault

[Nick Gaens]

Hello all,

we're trying to get a variation on the Dijkstra algorithm to run in 
pyOpenCL, but we're getting a weird segmentation fault on the line where 
the ALERT comment is located. A print statement before and after this 
line indicates this position.

Following is the code that initializes the arrays and stuff and loads 
the C code of Dijkstra (located in Dijkstra.cl):

Dijkstra_cl.py:
       ...
        ctx = cl.Context([device])
        queue = cl.CommandQueue(ctx, 
properties=cl.command_queue_properties.PROFILING_ENABLE)

        # Contains the resistance map
        table = numpy.zeros(shape=(100,100))
        
        # Contains the remaining arguments for the Dijkstra call
        # [no_data_value, start_x, start_y, end_x, end_y]
        Dijkstra_args = numpy.ndarray((5,), buffer=numpy.array([-9999, 
0, 1, 2, 3]), dtype = numpy.int32)
        
        # The map 'table' will be read from and written to by the 
Dijkstra-method
        mf = cl.mem_flags
        table_buff = cl.Buffer(ctx, mf.READ_WRITE | mf.USE_HOST_PTR, 
hostbuf = table)

        Dijkstra_cl_src = ""
        try:
            Dijkstra_cl_file = open("Dijkstra.cl")
            Dijkstra_cl_src = Dijkstra_cl_file.read()
            Dijkstra_cl_file.close()
        except IOError as error:
            print error
        prg = cl.Program(ctx, Dijkstra_cl_src).build()

        exec_evt = prg.Dijkstra(queue, table.shape, table_buff, 
Dijkstra_args) # ALERT: segfaults here
        exec_evt.wait()
        
        elapsed = 1e-9 * (exec_evt.profile.end - exec_evt.profile.start)
        print "Execution time of test: %g s" % elapsed

        c = numpy.empty_like(table)
        cl.enqueue_read_buffer(queue, table, c).wait()

Dijkstra.cl:
        ...
        __kernel void Dijkstra ( __global float* resistancemap, __global 
const int* args ) {
                // Dijkstra
                // Remark: the parameter "resistancemap" is read from 
and written to, but since we've previously set the READ_WRITE flag, this 
should not be a problem or is it?
        }

Can someone point us out what exactly is going wrong? I've attached both 
source files in case important information is missing.

A second question is: is it possible to somehow debug the C-code that 
you build and run via print-statements or so?
Regarding the second question: what about #include statements in C? The 
compiler just says e.g.: "file <math.h> not found" when trying to 
regularly including it.

Thx in advance,

Nick
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