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• Memory mapped files and "soft" page faults. Unavoidable?

  - by Robert Oschler

  I have two applications (processes) running under Windows XP that share data via a memory mapped file. Despite all my efforts to eliminate per iteration memory allocations, I still get about 10 soft page faults per data transfer. I've tried every flag there is in CreateFileMapping() and CreateFileView() and it still happens. I'm beginning to wonder if it's just the way memory mapped files work. If anyone there knows the O/S implementation details behind memory mapped files I would appreciate comments on the following theory: If two processes share a memory mapped file and one process writes to it while another reads it, then the O/S marks the pages written to as invalid. When the other process goes to read the memory areas that now belong to invalidated pages, this causes a soft page fault (by design) and the O/S knows to reload the invalidated page. Also, the number of soft page faults is therefore directly proportional to the size of the data write. My experiments seem to bear out the above theory. When I share data I write one contiguous block of data. In other words, the entire shared memory area is overwritten each time. If I make the block bigger the number of soft page faults goes up correspondingly. So, if my theory is true, there is nothing I can do to eliminate the soft page faults short of not using memory mapped files because that is how they work (using soft page faults to maintain page consistency). What is ironic is that I chose to use a memory mapped file instead of a TCP socket connection because I thought it would be more efficient. Note, if the soft page faults are harmless please note that. I've heard that at some point if the number is excessive, the system's performance can be marred. If soft page faults intrinsically are not significantly harmful then if anyone has any guidelines as to what number per second is "excessive" I'd like to hear that. Thanks.

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• Fuzzy Search on Material Descriptions including numerical sizes & general descriptions of material t

  - by Kyle

  We're looking to provide a fuzzy search on an electrical materials database (i.e. conduit, cable, etc.). The problem is that, because of a lack of consistency across all material types, we could not split sizes into separate fields from the text description because some materials are rated by things other than size. I've attempted a combination of a full text search & a SQL CLR implementation of the Levenshtein search algorithm (for assistance in ranking), but my results are a little funky (i.e. they are not sorting correctly due to improper ranking). For example, if the search term is "3/4" ABCD Conduit", I'll might get back several irrelevant results in the following order: 1/2" Conduit 1/4" X 3/4" Cable 1/4" Cable Ties 3/4" DFC Conduit Tees 3/4" ABCD Conduit 3/4" Conduit I believe I've nailed the problem down to the fact that these two search algorithms do not factor in the relevance of punctuation & numeric. That is, in such a search, I'd expect the size to take precedence over any fuzzy match on the rest of the description, but my results don't reflect that. My question is: Can anyone recommend better search algorithms or different approaches that may be better suited for searching a combination of alphanumerics & punctuation characters?

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• Enterprise Eclipse Provisioning - Or - How to share your standard Eclipse setup with other developer

  - by nikhil

  We use Eclipse as the IDE for developing all sorts of Java/J2EE applications in our 150 people odd IT department. One of the common problems we have been seeing is that developers download and install different versions of Eclipse and plugins based on their personal likes and dislikes. We have been trying to bring some consistency to this and have standardized on the version and the plugins that developers should be using. So the problem now is how do we distribute this installation to the team. We have zipped the directories and shared it through a shared drive. But I am looking for a better solution using some kind of provisioning tool for Eclipse using which people can install the IDE or get updates. Has anyone faced this problem? What are your solutions to this? How do you ensure a standard Eclipse environment across developers? I found Yoxos as a potential solution to this. Does anyone have any experience with it? Can p2 be used to do this?

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• How does real-time collaboration with multiple clients work in a system using operation transformati

  - by Saikat Chakrabarti

  I just finished reading High-Latency, Low-Bandwidth Windowing in the Jupiter Collaboration System and I mostly followed everything until part 6: global consistency. This part describes how the system described in the paper can be extended to accomodate for multiple clients connected to the server. However, the explanation is very short and essentially says the system will work if the central server merely forwards client messages to all the other clients. I don't really understand how this works though. What state vector would be sent in the message that is sent to all the other clients? Does the server maintain separate state vectors for each client? Does it maintain a separate copy of the widgets locally for each client? The simple example I can think of is this setup: imagine client A, server, and client B with client A and client B both connected to the server. To start, all three have the state object "ABCD". Then, client A sends the message "insert character F at position 0" at the same time client B sends the message "insert character G at position 0" to the server. It seems like simply relaying client A's message to client B and vice versa doesn't actually handle this case. So what exactly does the server do?

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• Is using SharePoint as a intranet/extranet portal a good idea?

  - by Rob

  I work for a fortune 500 company in IT and we have developed many systems/applications to do a variety of things. We are in need of some commonality of these applications and a better portal/dashboard/landing page for these applications. So, our customers and employees would log into this portal and see all the "things" that they can do which then link to their own application. This could maybe just iframe in each application inside of this portal to keep brand and navigation consistency. We are trying to decide whether to use SharePoint 2007 or 2010 for this or develop a portal/dashboard of sorts in house. We would like this portal to look and feel very branded to our needs and really not even feel like its using SharePoint (if needed). An example is to provide our own Menu control that drives the navigation if needed. Does anyone have any pros/cons for using SharePoint in such a way? Any advice on implementation (e.g. use 2010, much easier to customize design than 2007, etc)?

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• Django stupid mark_safe?

  - by Mark

  I wrote this little function for writing out HTML tags: def html_tag(tag, content=None, close=True, attrs={}): lst = ['<',tag] for key, val in attrs.iteritems(): lst.append(' %s="%s"' % (key, escape_html(val))) if close: if content is None: lst.append(' />') else: lst.extend(['>', content, '</', tag, '>']) else: lst.append('>') return mark_safe(''.join(lst)) Which worked great, but then I read this article on efficient string concatenation (I know it doesn't really matter for this, but I wanted consistency) and decided to update my script: def html_tag(tag, body=None, close=True, attrs={}): s = StringIO() s.write('<%s'%tag) for key, val in attrs.iteritems(): s.write(' %s="%s"' % (key, escape_html(val))) if close: if body is None: s.write(' />') else: s.write('>%s</%s>' % (body, tag)) else: s.write('>') return mark_safe(s.getvalue()) But now my HTML get escaped when I try to render it from my template. Everything else is exactly the same. It works properly if I replace the last line with return mark_safe(unicode(s.getvalue())). I checked the return type of s.getvalue(). It should be a str, just like the first function, so why is this failing?? Also fails with SafeString(s.getvalue()) but succeeds with SafeUnicode(s.getvalue()). I'd also like to point out that I used return mark_safe(s.getvalue()) in a different function with no odd behavior.

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• Why put a DAO layer over a persistence layer (like JDO or Hibernate)

  - by Todd Owen

  Data Access Objects (DAOs) are a common design pattern, and recommended by Sun. But the earliest examples of Java DAOs interacted directly with relational databases -- they were, in essence, doing object-relational mapping (ORM). Nowadays, I see DAOs on top of mature ORM frameworks like JDO and Hibernate, and I wonder if that is really a good idea. I am developing a web service using JDO as the persistence layer, and am considering whether or not to introduce DAOs. I foresee a problem when dealing with a particular class which contains a map of other objects: public class Book { // Book description in various languages, indexed by ISO language codes private Map<String,BookDescription> descriptions; } JDO is clever enough to map this to a foreign key constraint between the "BOOKS" and "BOOKDESCRIPTIONS" tables. It transparently loads the BookDescription objects (using lazy loading, I believe), and persists them when the Book object is persisted. If I was to introduce a "data access layer" and write a class like BookDao, and encapsulate all the JDO code within this, then wouldn't this JDO's transparent loading of the child objects be circumventing the data access layer? For consistency, shouldn't all the BookDescription objects be loaded and persisted via some BookDescriptionDao object (or BookDao.loadDescription method)? Yet refactoring in that way would make manipulating the model needlessly complicated. So my question is, what's wrong with calling JDO (or Hibernate, or whatever ORM you fancy) directly in the business layer? Its syntax is already quite concise, and it is datastore-agnostic. What is the advantage, if any, of encapsulating it in Data Access Objects?

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• Parse and read data frame in C?

  - by user253656

  I am writing a program that reads the data from the serial port on Linux. The data are sent by another device with the following frame format: |start | Command | Data | CRC | End | |0x02 | 0x41 | (0-127 octets) | | 0x03| ---------------------------------------------------- The Data field contains 127 octets as shown and octet 1,2 contains one type of data; octet 3,4 contains another data. I need to get these data I know how to write and read data to and from a serial port in Linux, but it is just to write and read a simple string (like "ABD") My issue is that I do not know how to parse the data frame formatted as above so that I can: get the data in octet 1,2 in the Data field get the data in octet 3,4 in the Data field get the value in CRC field to check the consistency of the data Here the sample snip code that read and write a simple string from and to a serial port in Linux: int writeport(int fd, char *chars) { int len = strlen(chars); chars[len] = 0x0d; // stick a <CR> after the command chars[len+1] = 0x00; // terminate the string properly int n = write(fd, chars, strlen(chars)); if (n < 0) { fputs("write failed!\n", stderr); return 0; } return 1; } int readport(int fd, char *result) { int iIn = read(fd, result, 254); result[iIn-1] = 0x00; if (iIn < 0) { if (errno == EAGAIN) { printf("SERIAL EAGAIN ERROR\n"); return 0; } else { printf("SERIAL read error %d %s\n", errno, strerror(errno)); return 0; } } return 1; } Does anyone please have some ideas? Thanks all.

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• Oracle syntax - should we have to choose between the old and the new?

  - by Martin Milan

  Hi, I work on a code base in the region of about 1'000'000 lines of source, in a team of around eight developers. Our code is basically an application using an Oracle database, but the code has evolved over time (we have plenty of source code from the mid nineties in there!). A dispute has arisen amongst the team over the syntax that we are using for querying the Oracle database. At the moment, the overwhelming majority of our queries use the "old" Oracle Syntax for joins, meaning we have code that looks like this... Example of Inner Join select customers.*, orders.date, orders.value from customers, orders where customers.custid = orders.custid Example of Outer Join select customers.custid, contacts.ContactName, contacts.ContactTelNo from customers, contacts where customers.custid = contacts.custid(+) As new developers have joined the team, we have noticed that some of them seem to prefer using SQL-92 queries, like this: Example of Inner Join select customers.*, orders.date, orders.value from customers inner join orders on (customers.custid = orders.custid) Example of Outer Join select customers.custid, contacts.ContactName, contacts.ContactTelNo from customers left join contacts on (customers.custid = contacts.custid) Group A say that everyone should be using the the "old" syntax - we have lots of code in this format, and we ought to value consistency. We don't have time to go all the way through the code now rewriting database queries, and it wouldn't pay us if we had. They also point out that "this is the way we've always done it, and we're comfortable with it..." Group B however say that they agree that we don't have the time to go back and change existing queries, we really ought to be adopting the "new" syntax on code that we write from here on in. They say that developers only really look at a single query at a time, and that so long as developers know both syntax there is nothing to be gained from rigidly sticking to the old syntax, which might be deprecated at some point in the future. Without declaring with which group my loyalties lie, I am interested in hearing the opinions of impartial observers - so let the games commence! Martin. Ps. I've made this a community wiki so as not to be seen as just blatantly chasing after question points...

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• Choosing a distributed shared memory solution

  - by mindas

  I have a task to build a prototype for a massively scalable distributed shared memory (DSM) app. The prototype would only serve as a proof-of-concept, but I want to spend my time most effectively by picking the components which would be used in the real solution later on. The aim of this solution is to take data input from an external source, churn it and make the result available for a number of frontends. Those "frontends" would just take the data from the cache and serve it without extra processing. The amount of frontend hits on this data can literally be millions per second. The data itself is very volatile; it can (and does) change quite rapidly. However the frontends should see "old" data until the newest has been processed and cached. The processing and writing is done by a single (redundant) node while other nodes only read the data. In other words: no read-through behaviour. I was looking into solutions like memcached however this particular one doesn't fulfil all our requirements which are listed below: The solution must at least have Java client API which is reasonably well maintained as the rest of app is written in Java and we are seasoned Java developers; The solution must be totally elastic: it should be possible to add new nodes without restarting other nodes in the cluster; The solution must be able to handle failover. Yes, I realize this means some overhead, but the overall served data size isn't big (1G max) so this shouldn't be a problem. By "failover" I mean seamless execution without hardcoding/changing server IP address(es) like in memcached clients when a node goes down; Ideally it should be possible to specify the degree of data overlapping (e.g. how many copies of the same data should be stored in the DSM cluster); There is no need to permanently store all the data but there might be a need of post-processing of some of the data (e.g. serialization to the DB). Price. Obviously we prefer free/open source but we're happy to pay a reasonable amount if a solution is worth it. In any way, paid 24hr/day support contract is a must. The whole thing has to be hosted in our data centers so SaaS offerings like Amazon SimpleDB are out of scope. We would only consider this if no other options would be available. Ideally the solution would be strictly consistent (as in CAP); however, eventual consistence can be considered as an option. Thanks in advance for any ideas.

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• Java map with values limited by key's type parameter

  - by Ashley Mercer

  Is there a way in Java to have a map where the type parameter of a value is tied to the type parameter of a key? What I want to write is something like the following: public class Foo { // This declaration won't compile - what should it be? private static Map<Class<T>, T> defaultValues; // These two methods are just fine public static <T> void setDefaultValue(Class<T> clazz, T value) { defaultValues.put(clazz, value); } public static <T> T getDefaultValue(Class<T> clazz) { return defaultValues.get(clazz); } } That is, I can store any default value against a Class object, provided the value's type matches that of the Class object. I don't see why this shouldn't be allowed since I can ensure when setting/getting values that the types are correct. EDIT: Thanks to cletus for his answer. I don't actually need the type parameters on the map itself since I can ensure consistency in the methods which get/set values, even if it means using some slightly ugly casts.

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• heterogeneous comparisons in python3

  - by Matt Anderson

  I'm 99+% still using python 2.x, but I'm trying to think ahead to the day when I switch. So, I know that using comparison operators (less/greater than, or equal to) on heterogeneous types that don't have a natural ordering is no longer supported in python3.x -- instead of some consistent (but arbitrary) result we raise TypeError instead. I see the logic in that, and even mostly think its a good thing. Consistency and refusing to guess is a virtue. But what if you essentially want the python2.x behavior? What's the best way to go about getting it? For fun (more or less) I was recently implementing a Skip List, a data structure that keeps its elements sorted. I wanted to use heterogeneous types as keys in the data structure, and I've got to compare keys to one another as I walk the data structure. The python2.x way of comparing makes this really convenient -- you get an understandable ordering amongst elements that have a natural ordering, and some ordering amongst those that don't. Consistently using a sort/comparison key like (type(obj).__name__, obj) has the disadvantage of not interleaving the objects that do have a natural ordering; you get all your floats clustered together before your ints, and your str-derived class separates from your strs. I came up with the following: import operator def hetero_sort_key(obj): cls = type(obj) return (cls.__name__+'_'+cls.__module__, obj) def make_hetero_comparitor(fn): def comparator(a, b): try: return fn(a, b) except TypeError: return fn(hetero_sort_key(a), hetero_sort_key(b)) return comparator hetero_lt = make_hetero_comparitor(operator.lt) hetero_gt = make_hetero_comparitor(operator.gt) hetero_le = make_hetero_comparitor(operator.le) hetero_ge = make_hetero_comparitor(operator.gt) Is there a better way? I suspect one could construct a corner case that this would screw up -- a situation where you can compare type A to B and type A to C, but where B and C raise TypeError when compared, and you can end up with something illogical like a > b, a < c, and yet b > c (because of how their class names sorted). I don't know how likely it is that you'd run into this in practice.

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• Can I get consistent CSS colors across browsers?

  - by Trevor Burnham

  I'm testing a new site, and I have a div with background-color: #bbf6bb; That seems innocuous enough to me. And yet, on my MacBook Pro, the color looks very different in Firefox 3.6 vs. Safari 4. In Safari, it's the color I'd expect from the hex value: a pale green. In Firefox, there's a definite bluish tint, making the color turquoise. I'm aware of color inconsistencies that result from different treatment of images across browsers, but in pure CSS? Really? I'm guessing that Firefox trying to correct for my display in hopes of delivering better consistency with print, but I'd much rather have my site look the same hue to my users regardless of their choice of browser. Any ideas? Can someone confirm that Firefox is the culprit here? [Update: This seems to have been a fluke. Specifically, it's a narrow issue with Firefox—see my answer below. I'm puzzled, but relieved.]

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• Hide a base class method from derived class, but still visible outside of assembly

  - by clintp

  This is a question about tidyness. The project is already working, I'm satisfied with the design but I have a couple of loose ends that I'd like to tie up. My project has a plugin architecture. The main body of the program dispatches work to the plugins that each reside in their own AppDomain. The plugins are described with an interface, which is used by the main program (to get the signature for invoking DispatchTaskToPlugin) and by the plugins themselves as an API contract: namespace AppServer.Plugin.Common { public interface IAppServerPlugin { void Register(); void DispatchTaskToPlugin(Task t); // Other methods omitted } } In the main body of the program Register() is called so that the plugin can register its callback methods with the base class, and then later DispatchTaskToPlugin() is called to get the plugin running. The plugins themselves are in two parts. There's a base class that implements the framework for the plugin (setup, housekeeping, teardown, etc..). This is where DispatchTaskToPlugin is actually defined: namespace AppServer.Plugin { abstract public class BasePlugin : MarshalByRefObject, AppServer.Plugin.Common.IAppServerPlugin { public void DispatchTaskToPlugin(Task t) { // ... // Eventual call to actual plugin code // } // Other methods omitted } } The actual plugins themselves only need to implement a Register() method (to give the base class the delegates to call eventually) and then their business logic. namespace AppServer.Plugin { public class Plugin : BasePlugin { override public void Register() { // Calls a method in the base class to register itself. } // Various callback methods, business logic, etc... } } Now in the base class (BasePlugin) I've implemented all kinds of convenience methods, collected data, etc.. for the plugins to use. Everything's kosher except for that lingering method DispatchTaskToPlugin(). It's not supposed to be callable from the Plugin class implementations -- they have no use for it. It's only needed by the dispatcher in the main body of the program. How can I prevent the derived classes (Plugin) from seeing the method in the base class (BasePlugin/DispatchTaskToPlugin) but still have it visible from outside of the assembly? I can split hairs and have DispatchTaskToPlugin() throw an exception if it's called from the derived classes, but that's closing the barn door a little late. I'd like to keep it out of Intellisense or possibly have the compiler take care of this for me. Suggestions?

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• Programming style question on how to code functions

  - by shawnjan

  Hey all! So, I was just coding a bit today, and I realized that I don't have much consistency when it comes to a coding style when programming functions. One of my main concerns is whether or not its proper to code it so that you check that the input of the user is valid OUTSIDE of the function, or just throw the values passed by the user into the function and check if the values are valid in there. Let me sketch an example: I have a function that lists hosts based on an environment, and I want to be able to split the environment into chunks of hosts. So an example of the usage is this: listhosts -e testenv -s 2 1 This will get all the hosts from the "testenv", split it up into two parts, and it is displaying part one. In my code, I have a function that you pass it in a list, and it returns a list of lists based on you parameters for splitting. BUT, before I pass it a list, I first verify the parameters in my MAIN during the getops process, so in the main I check to make sure there are no negatives passed by the user, I make sure the user didnt request to split into say, 4 parts, but asking to display part 5 (which would not be valid), etc. tl;dr: Would you check the validity of a users input the flow of you're MAIN class, or would you do a check in your function itself, and either return a valid response in the case of valid input, or return NULL in the case of invalid input? Obviously both methods work, I'm just interested to hear from experts as to which approach is better :) Thanks for any comments and suggestions you guys have!

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• Are there solutions for streamlining the update of legacy code in multiple places?

  - by ccomet

  I'm working in some old code which was originally designed for handling two different kinds of files. I was recently tasked with adding a new kind of file to this code. Most of my problems were solved by filling out an extensive XML file with a new entry that handled everything from what lists were named to how the file is written in plural lower case. But this ended up being insufficient, as there were maybe 50 different places in 24 different code files where I had to update hardcoded switch-statements that only branched for the original two file types. Unfortunately there is no consistency in this; there are methods which operate half from the XML file, and half off of hardcode. Some of the files which look like they would operate off of the XML file don't, and some that I would expect that I'd need to update the hardcode don't need it. So the only way to find the majority of these is to run through testing the whole system when only part of it is operational, finding that one step to fix (when I'm lucky that error logging actually tells me what is going on), and then running the whole thing again. This wastes time testing the parts of the code which are already confirmed to work, time better spent testing the new parts I have to add on top of it all. It's a hassle and a half, and to my luck I can expect that I will have to add yet another new kind of file in the near future. Are there any solutions out there which can aid in this kind of endeavour? Something which I can input some parameters of current features, document what points in a whole code project actually need to be updated, and run something nice the next time I need to add a new feature to the code. It needn't even be fully automated, something that'll help me navigate straight to the specific points in everything and maybe even record what kind of parameters need to be loaded. Doubt it matters specifically, but the code is comprised of ASP.NET pages, some ASP.NET controls, hundreds of C# code files, and a handful of additional XML files. It's all currently in a couple big Visual Studio 2008 projects.

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• RegisterStartupScript doesn't appear to be working on page postback within update panel

  - by Jen

  OK - so am working on a system that uses a custom datepicker control (I know there are other ones out there.. but for consistency would like to understand why my current issue is happening and fix it). So its a custom user control with a textbox and on Page_PreRender does this: protected void Page_PreRender(object sender, EventArgs e) { string clientScript = @" $(function(){ $('#" + this.Date1.ClientID + @"').datepicker({dateFormat: 'dd/mm/yy', constrainInput: true}); });"; Page.ClientScript.RegisterStartupScript(this.GetType(), this.ClientID, clientScript, true); //Type t = this.GetType(); //if (!Page.ClientScript.IsStartupScriptRegistered(t, this.ClientID)) //{ // Page.ClientScript.RegisterStartupScript(t, this.ClientID, clientScript, true); //} } Ignore commented out stuff - that was me trying something different - didn't help. My issue is that this all works fine when I load the page. But if I select something from a dropdownlist causing a page postback - when I click into my date fields they stop working. As in I should be able to click into the textbox and a nice calendar control appears. But after postback there is no nice calendar control appearing! It's currently all wrapped (in the hosting page) inside an update panel. So I comment out the update panel stuff and the dates are working after page postback. So it appears to be something related to that update panel. Any suggestions please? Thanks!!

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• Utility of List<T>.Sort() versus List<T>.OrderBy() for a member of a custom container class

  - by ccomet

  I've found myself running back through some old 3.5 framework legacy code, and found some points where there are a whole bunch of lists and dictionaries that must be updated in a synchronized fashion. I've determined that I can make this process infinitely easier to both utilize and understand by converging these into custom container classes of new custom classes. There are some points, however, where I came to concerns with organizing the contents of these new container classes by a specific inner property. For example, sorting by the ID number property of one class. As the container classes are primarily based around a generic List object, my first instinct was to write the inner classes with IComparable, and write the CompareTo method that compares the properties. This way, I can just call items.Sort() when I want to invoke the sorting. However, I've been thinking instead about using items = items.OrderBy(Func) instead. This way it is more flexible if I need to sort by any other property. Readability is better as well, since the property used for sorting will be listed in-line with the sort call rather than having to look up the IComparable code. The overall implementation feels cleaner as a result. I don't care for premature or micro optimization, but I like consistency. I find it best to stick with one kind of implementation for as many cases as it is appropriate, and use different implementations where it is necessary. Is it worth it to convert my code to use the LINQ OrderBy instead of using List.Sort? Is it a better practice to stick with the IComparable implementation for these custom containers? Are there any significant mechanical advantages offered by either path that I should be weighing the decision on? Or is their end-functionality equivalent to the point that it just becomes coder's preference?

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• Infinite loop when adding a row to a list in a class in python3

  - by Margaret

  I have a script which contains two classes. (I'm obviously deleting a lot of stuff that I don't believe is relevant to the error I'm dealing with.) The eventual task is to create a decision tree, as I mentioned in this question. Unfortunately, I'm getting an infinite loop, and I'm having difficulty identifying why. I've identified the line of code that's going haywire, but I would have thought the iterator and the list I'm adding to would be different objects. Is there some side effect of list's .append functionality that I'm not aware of? Or am I making some other blindingly obvious mistake? class Dataset: individuals = [] #Becomes a list of dictionaries, in which each dictionary is a row from the CSV with the headers as keys def field_set(self): #Returns a list of the fields in individuals[] that can be used to split the data (i.e. have more than one value amongst the individuals def classified(self, predicted_value): #Returns True if all the individuals have the same value for predicted_value def fields_exhausted(self, predicted_value): #Returns True if all the individuals are identical except for predicted_value def lowest_entropy_value(self, predicted_value): #Returns the field that will reduce <a href="http://en.wikipedia.org/wiki/Entropy_%28information_theory%29">entropy</a> the most def __init__(self, individuals=[]): and class Node: ds = Dataset() #The data that is associated with this Node links = [] #List of Nodes, the offspring Nodes of this node level = 0 #Tree depth of this Node split_value = '' #Field used to split out this Node from the parent node node_value = '' #Value used to split out this Node from the parent Node def split_dataset(self, split_value): fields = [] #List of options for split_value amongst the individuals datasets = {} #Dictionary of Datasets, each one with a value from fields[] as its key for field in self.ds.field_set()[split_value]: #Populates the keys of fields[] fields.append(field) datasets[field] = Dataset() for i in self.ds.individuals: #Adds individuals to the datasets.dataset that matches their result for split_value datasets[i[split_value]].individuals.append(i) #<---Causes an infinite loop on the second hit for field in fields: #Creates subnodes from each of the datasets.Dataset options self.add_subnode(datasets[field],split_value,field) def add_subnode(self, dataset, split_value='', node_value=''): def __init__(self, level, dataset=Dataset()): My initialisation code is currently: if __name__ == '__main__': filename = (sys.argv[1]) #Takes in a CSV file predicted_value = "# class" #Identifies the field from the CSV file that should be predicted base_dataset = parse_csv(filename) #Turns the CSV file into a list of lists parsed_dataset = individual_list(base_dataset) #Turns the list of lists into a list of dictionaries root = Node(0, Dataset(parsed_dataset)) #Creates a root node, passing it the full dataset root.split_dataset(root.ds.lowest_entropy_value(predicted_value)) #Performs the first split, creating multiple subnodes n = root.links[0] n.split_dataset(n.ds.lowest_entropy_value(predicted_value)) #Attempts to split the first subnode.

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• Windows splash screen using GDI+

  - by Luther

  The eventual aim of this is to have a splash screen in windows that uses transparency but that's not what I'm stuck on at the moment. In order to create a transparent window, I'm first trying to composite the splash screen and text on an off screen buffer using GDI+. At the moment I'm just trying to composite the buffer and display it in response to a 'WM_PAINT' message. This isn't working out at the moment; all I see is a black window. I imagine I've misunderstood something with regards to setting up render targets in GDI+ and then rendering them (I'm trying to render the screen using straight forward GDI blit) Anyway, here's the code so far: //my window initialisation code void MyWindow::create_hwnd(HINSTANCE instance, const SIZE &dim) { DWORD ex_style = WS_EX_LAYERED ; //eventually I'll be making use of this layerd flag m_hwnd = CreateWindowEx( ex_style, szFloatingWindowClass , L"", WS_POPUP , 0, 0, dim.cx, dim.cy, null, null, instance, null); SetWindowLongPtr(m_hwnd ,0, (__int3264)(LONG_PTR)this); m_display_dc = GetDC(NULL); //This was sanity check test code - just loading a standard HBITMAP and displaying it in WM_PAINT. It worked fine //HANDLE handle= LoadImage(NULL , L"c:\\test_image2.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE); m_gdip_offscreen_bm = new Gdiplus::Bitmap(dim.cx, dim.cy); m_gdi_dc = Gdiplus::Graphics::FromImage(m_gdip_offscreen_bm);//new Gdiplus::Graphics(m_splash_dc );//window_dc ;m_splash_dc //this draws the conents of my splash screen - this works if I create a GDI+ context for the window, rather than for an offscreen bitmap. //For all I know, it might actually be working but when I try to display the contents on screen, it shows a black image draw_all(); //this is just to show that drawing something simple on the offscreen bit map seems to have no effect Gdiplus::Pen pen(Gdiplus::Color(255, 0, 0, 255)); m_gdi_dc->DrawLine(&pen, 0,0,100,100); DWORD last_error = GetLastError(); //returns '0' at this stage } And here's the snipit that handles the WM_PAINT message: ---8<----------------------- //Paint message snippit case WM_PAINT: { BITMAP bm; PAINTSTRUCT ps; HDC hdc = BeginPaint(vg->m_hwnd, &ps); //get the HWNDs DC HDC hdcMem = vg->m_gdi_dc->GetHDC(); //get the HDC from our offscreen GDI+ object unsigned int width = vg->m_gdip_offscreen_bm->GetWidth(); //width and height seem fine at this point unsigned int height = vg->m_gdip_offscreen_bm->GetHeight(); BitBlt(hdc, 0, 0, width, height, hdcMem, 0, 0, SRCCOPY); //this blits a black rectangle DWORD last_error = GetLastError(); //this was '0' vg->m_gdi_dc->ReleaseHDC(hdcMem); EndPaint(vg->m_hwnd, &ps); //end paint return 1; } ---8<----------------------- My apologies for the long post. Does anybody know what I'm not quite understanding regarding how you write to an offscreen buffer using GDI+ (or GDI for that matter)and then display this on screen? Thank you for reading.

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• ASP.NET SqlDataSource update and create FK reference

  - by William

  The short version: I have a grid view bound to a data source which has a SelectCommand with a left join in it because the FK can be null. On Update I want to create a record in the FK table if the FK is null and then update the parent table with the new records ID. Is this possible to do with just SqlDataSources? The detailed version: I have two tables: Company and Address. The column Company.AddressId can be null. On my ascx page I am using a SqlDataSource to select a left join of company and address and a GridView to display the results. By having my UpdateCommand and DeleteCommand of the SqlDataSource execute two statements separated by a semi-colon I am able to use the GridView's Edit and Delete functionality to update both table simultaneously. The problem I have is when the Company.AddressId is null. What I need to have happen is have the data source create a record in the Address table and then update the Company table with the new Address.ID then proceed with the update as usual. I would like to do this with just data sources if possible for consistency/simplicity sake. Is it possible to have my data source do this, or perhaps add a second data source to the page to handle some of this? Once I have that working I can probably figure out how to make it work with the InsertCommand as well but if you are on a roll and have an answer for how to make that fly as well feel free to provide it. Thanks.

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• [N]Hibernate: view-like fetching properties of associated class

  - by chiccodoro

  (Felt quite helpless in formulating an appropriate title...) In my C# app I display a list of "A" objects, along with some properties of their associated "B" objects and properties of B's associated "C" objects: A.Name B.Name B.SomeValue C.Name Foo Bar 123 HelloWorld Bar Hello 432 World ... To clarify: A has an FK to B, B has an FK to C. (Such as, e.g. BankAccount - Person - Company). I have tried two approaches to load these properties from the database (using NHibernate): A fast approach and a clean approach. My eventual question is how to do a fast & clean approach. Fast approach: Define a view in the database which joins A, B, C and provides all these fields. In the A class, define properties "BName", "BSomeValue", "CName" Define a hibernate mapping between A and the View, whereas the needed B and C properties are mapped with update="false" insert="false" and do actually stem from B and C tables, but Hibernate is not aware of that since it uses the view. This way, the listing only loads one object per "A" record, which is quite fast. If the code tries to access the actual associated property, "A.B", I issue another HQL query to get B, set the property and update the faked BName and BSomeValue properties as well. Clean approach: There is no view. Class A is mapped to table A, B to B, C to C. When loading the list of A, I do a double left-join-fetch to get B and C as well: from A a left join fetch a.B left join fetch a.B.C B.Name, B.SomeValue and C.Name are accessed through the eagerly loaded associations. The disadvantage of this approach is that it gets slower and takes more memory, since it needs to created and map 3 objects per "A" record: An A, B, and C object each. Fast and clean approach: I feel somehow uncomfortable using a database view that hides a join and treat that in NHibernate as if it was a table. So I would like to do something like: Have no views in the database. Declare properties "BName", "BSomeValue", "CName" in class "A". Define the mapping for A such that NHibernate fetches A and these properties together using a join SQL query as a database view would do. The mapping should still allow for defining lazy many-to-one associations for getting A.B.C My questions: Is this possible? Is it [un]artful? Is there a better way?

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• PHP/MySQL time zone migration

  - by El Yobo

  I have an application that currently stores timestamps in MySQL DATETIME and TIMESTAMP values. However, the application needs to be able to accept data from users in multiple time zones and show the timestamps in the time zone of other users. As such, this is how I plan to amend the application; I would appreciate any suggestions to improve the approach. Database modifications All TIMESTAMPs will be converted to DATETIME values; this is to ensure consistency in approach and to avoid having MySQL try to do clever things and convert time zones (I want to keep the conversion in PHP, as it involves less modification to the application, and will be more portable when I eventually manage to escape from MySQL). All DATETIME values will be adjusted to convert them to UTC time (currently all in Australian EST) Query modifications All usage of NOW() to be replaced with UTC_TIMESTAMP() in queries, triggers, functions, etc. Application modifications The application must store the time zone and preferred date format (e.g. US vs the rest of the world) All timestamps will be converted according to the user settings before being displayed All input timestamps will be converted to UTC according to the user settings before being input Additional notes Converting formats will be done at the application level for several main reasons The approach to converting time zones varies from DB to DB, so handing it there will be non-portable (and I really hope to be migrating away from MySQL some time in the not-to-distant future). MySQL TIMESTAMPs have limited ranges to the permitted dates (~1970 to ~2038) MySQL TIMESTAMPs have other undesirable attributes, including bizarre auto-update behaviour (if not carefully disabled) and sensitivity to the server zone settings (and I suspect I might screw these up when I migrate to Amazon later in the year). Is there anything that I'm missing here, or does anyone have better suggestions for the approach?

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• Speed of QHash lookups using QStrings as keys.

  - by Ryan R.

  I need to draw a dynamic overlay on a QImage. The component parts of the overlay are defined in XML and parsed out to a QHash<QString, QPicture> where the QString is the name (such as "crosshairs") and the QPicture is the resolution independent drawing. I then draw components of the overlay as they are needed at a position determined during runtime. Example: I have 10 pictures in my QHash composing every possible element in a HUD. During a particular frame of video I need to draw 6 of them at different positions on the image. During the next frame something has changed and now I only need to draw 4 of them but 2 of those positions have changed. Now to my question: If I am trying to do this quickly, should I redefine my QHash as QHash<int, QPicture> and enumerate the keys to counteract the overhead caused by string comparisons; or are the comparisons not going to make a very big impact on performance? I can easily make the conversion to integer keys as the XML parser and overlay composer are completely separate classes; but I would like to use a consistent data structure across the application. Should I overcome my desire for consistency and re-usability in order to increase performance? Will it even matter very much if I do?

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• What's the best way to store Logon User information for Web Application?

  - by Morgan Cheng

  I was once in a project of web application developed on ASP.NET. For each logon user, there is an object (let's call it UserSessionObject here) created and stored in RAM. For each HTTP request of given user, matching UserSessoinObject instance is used to visit user state information and connection to database. So, this UserSessionObject is pretty important. This design brings several problems found later: 1) Since this UserSessionObject is cached in ASP.NET memory space, we have to config load balancer to be sticky connection. That is, HTTP request in single session would always be sent to one web server behind. This limit scalability and maintainability. 2) This UserSessionObject is accessed in every HTTP request. To keep the consistency, there is a exclusive lock for the UserSessionObject. Only one HTTP request can be processed at any given time because it must to obtain the lock first. The performance and response time is affected. Now, I'm wondering whether there is better design to handle such logon user case. It seems Sharing-Nothing-Architecture helps. That means long user info is retrieved from database each time. I'm afraid that would hurt performance. Is there any design pattern for long user web app? Thanks.

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