Attempt to read or write protected memory issue

Question

Hi,

I have a geoprocessing task that uses pyodbc to query a database. The tool works fine when run on the local desktop, but when deployed on the server, it fails the second time round i.e. it works the first time, but when it is run again it crashes. Running again then works, but running again crashes etc. The server logs reveal the task ???crashes???, whilst .dmp files reveal an attempt to read or write to protected memory.

I then included in the code explicit delete for variables and even a gc.collect() call, and the latter seems to have the effect of making the crash occur every 3rd run as opposed to every 2nd.

I have applied SP1 (ArcGIS 10.1), however, this has only had a marginal improvement in that instead of an error being thrown up each 2nd/3rd run, it now just hangs until you cancel it, re-run it and the pattern continues.

Any insights into how to work around this would be great.

Nick

NickRose2 · Answer

Thanks for your interest in this problem. I suspect that there is an issue with python memory management. Here is the code with some comments:

import string, os, sys, locale, arcpy, pyodbc, random

try:
    arcgis_con = pyodbc.connect('Driver={SQL Server Native Client 10.0};Server=xyz,xyz;Database=xyz;Trusted_Connection=yes;')
    arcgis_cur = arcgis_con.cursor()
    Area_of_Interest = arcpy.GetParameterAsText(0) #user defined polygon
    outputFC = arcpy.GetParameterAsText(1) #output
    year = arcpy.GetParameterAsText(2) #year 
    inDesc = arcpy.Describe(Area_of_Interest)
    inRows = arcpy.SearchCursor(Area_of_Interest)
    inRow = inRows.next()
    outLine = ""
    while inRow: #creates a string defining coordinates of polygon
        partnum=0
        feat = inRow.getValue(inDesc.ShapeFieldName) ##when run the second time, degugging reveals script fails here trying to reference inDesc.ShapeFieldName
        while partnum < 1:
            part = feat.getPart(partnum)
            part.reset()
            pnt = part.next()
            pnt_count = 0
            while pnt:
                if pnt_count==0:
                    outLine = str(pnt.X) + " " + str(pnt.Y)
                    
                else:
                    outLine = str(pnt.X) + " " + str(pnt.Y) + " , " + outLine
                pnt = part.next()
                pnt_count += 1
                if not pnt:
                    pnt = part.next()
                   
            partnum += 1
        inRow = inRows.next()
        
    randomTab = "dbo." + ''.join(random.choice(string.ascii_uppercase) for x in range(10)) #table with random name to be inserted into DBMS for query
    querystring = "CREATE TABLE " + randomTab +  " (id int IDENTITY (1,1), GeogCol1 geography);" #creates a sql server table with a geography column based on polygon coordinates
    arcgis_cur.execute(querystring)
    querystring = "INSERT INTO " + randomTab + " (GeogCol1) VALUES (geography::STGeomFromText('POLYGON((" + outLine + "))', 4283));"
    arcgis_cur.execute(querystring)
    querystring = ##sql query which is complex##
    arcgis_cur.execute(querystring)
    arcpy.CopyFeatures_management(Area_of_Interest, outputFC)
    total = 0
    while 1:
        row = arcgis_cur.fetchone()
        if not row:
            break
        age_var = row.age
        age_var = age_var.replace("-","_")
        age_var = age_var.replace(" ","")
        age_var = age_var.replace("+","plus")
        var = row.Sex[0] + "_" + age_var
        arcpy.AddField_management(outputFC, var, "DOUBLE",10,3,"","","NULLABLE")
        arcpy.CalculateField_management(outputFC, var, row.population, "PYTHON_9.3")
        total = total + row.population
    arcpy.AddField_management(outputFC, "Total", "DOUBLE",10,1,"","","NULLABLE")
    arcpy.CalculateField_management(outputFC, "Total", total, "PYTHON_9.3")
    querystring = "DROP TABLE " + randomTab + ";"
    arcgis_cur.execute(querystring)
    arcgis_con.commit()
    arcgis_con.close()

except Exception, ErrorDesc:

The script uses a polygon defined by the user, extracts the coordinates, and inserts in SQL Server so as to carry a spatial join with spatially enabled data there. It then creates a table and polygon for the user. The script runs fine multiple times in desktop. I thought I narrowed down the issue to the line 'feat = inRow.getValue(inDesc.ShapeFieldName)', however, hardcoding a value here just makes the script run successfully one extra time, before failing again somewhere else in the program (haven't search where this time) when run again with the same memory access issue.

Good luck and appreciate any help.

Nick

GISDev1 · Answer

Hi,

I have a geoprocessing task that uses pyodbc to query a database. The tool works fine when run on the local desktop, but when deployed on the server, it fails the second time round i.e. it works the first time, but when it is run again it crashes. Running again then works, but running again crashes etc. The server logs reveal the task �??crashes�??, whilst .dmp files reveal an attempt to read or write to protected memory.

I then included in the code explicit delete for variables and even a gc.collect() call, and the latter seems to have the effect of making the crash occur every 3rd run as opposed to every 2nd.

I have applied SP1 (ArcGIS 10.1), however, this has only had a marginal improvement in that instead of an error being thrown up each 2nd/3rd run, it now just hangs until you cancel it, re-run it and the pattern continues.

Any insights into how to work around this would be great.

Nick

It will be much easier to help you without taking shots in the dark if you post the Python code used in the GP task.