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• Java Array Index Out of Bounds Exception

  - by user1302023

  I need help debugging the following program: I'm getting a run time error that reads: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at SearchEngine.main(SearchEngine.java:126) import java.util.*; import java.io.*; public class SearchEngine { public static int getNumberOfWords (File f) throws FileNotFoundException { int numWords = 0; Scanner scan = new Scanner(f); while (scan.hasNext()) { numWords++; scan.next(); } scan.close(); return numWords; } public static void readInWords (File input, String [] x) throws FileNotFoundException { Scanner scan = new Scanner(input); int i = 0; while (scan.hasNext() && i<x.length) { x[i] = scan.next(); i++; } scan.close(); } public static int getNumOfDistinctWords (File input, String [] x) throws FileNotFoundException { Scanner scan = new Scanner(input); int count = 0; int i = 1; while (scan.hasNext() && i<x.length) { if (!x[i].equals(x[i-1])) { count++; } i++; } scan.close(); return count; } public static void readInDistinctWords (String [] x, String [] y) { int i = 1; int k = 0; while (i<x.length) { if (!x[i].equals(x[i-1])) { y[k] = x[i]; k++; } i++; } } public static int getNumberOfLines (File input) throws FileNotFoundException { int numLines = 0; Scanner scan = new Scanner(input); while (scan.hasNextLine()) { numLines++; scan.nextLine(); } scan.close(); return numLines; } public static void readInLines (File input, String [] x) throws FileNotFoundException { Scanner scan = new Scanner(input); int i = 0; while (scan.hasNextLine() && i<x.length) { x[i] = scan.nextLine(); i++; } scan.close(); } public static void main(String [] args) { try { //gets file name System.out.println("Enter the name of the text file you wish to search"); Scanner kb = new Scanner(System.in); String fileName = kb.nextLine(); String TXT = ".txt"; if (!fileName.endsWith(TXT)) { fileName = fileName.concat(TXT); } File input = new File(fileName); //First part of creating index System.out.println("Creating vocabArray"); int NUM_WORDS = getNumberOfWords(input); //System.out.println(NUM_WORDS); String [] wordArray = new String[NUM_WORDS]; readInWords(input, wordArray); Arrays.sort(wordArray); int NUM_DISTINCT_WORDS = getNumOfDistinctWords(input, wordArray); String [] vocabArray = new String[NUM_DISTINCT_WORDS]; readInDistinctWords(wordArray, vocabArray); System.out.println("Finished creating vocabArray"); System.out.println("Creating concordanceArray"); int NUM_LINES = getNumberOfLines(input); String [] concordanceArray = new String[NUM_LINES]; readInLines(input, concordanceArray); System.out.println("Finished creating concordanceArray"); System.out.println("Creating invertedIndex"); int [][] invertedIndex = new int[NUM_DISTINCT_WORDS][10]; int [] wordCountArray = new int[NUM_DISTINCT_WORDS]; int lineNum = 0; while (lineNum<concordanceArray.length) { Scanner scan = new Scanner(concordanceArray[lineNum]); while (scan.hasNext()) { int wordPos = Arrays.binarySearch(vocabArray, scan.next()); wordCountArray[wordPos]+=1; for(int i = 0; i < invertedIndex.length; i++) { for(int j = 0; j < invertedIndex[i].length; j++) { if (invertedIndex[i][j] == 0) { invertedIndex[i][j] = lineNum; break; } } } } lineNum++; } System.out.println("Finished creating invertedIndex"); } catch (FileNotFoundException exception) { System.out.println("File Not Found"); } } //main } //class

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• How to give position zero of spinner a prompt value?

  - by Eugene H

  The database is then transferring the data to a spinner which I want to leave position 0 blank so I can add a item to the spinner with no value making it look like a prompt. I have been going at it all day. FAil after Fail MainActivity public class MainActivity extends Activity { Button AddBtn; EditText et; EditText cal; Spinner spn; SQLController SQLcon; ProgressDialog PD; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); AddBtn = (Button) findViewById(R.id.addbtn_id); et = (EditText) findViewById(R.id.et_id); cal = (EditText) findViewById(R.id.et_cal); spn = (Spinner) findViewById(R.id.spinner_id); spn.setOnItemSelectedListener(new OnItemSelectedListenerWrapper( new OnItemSelectedListener() { @Override public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) { SQLcon.open(); Cursor c = SQLcon.readData(); if (c.moveToPosition(pos)) { String name = c.getString(c .getColumnIndex(DBhelper.MEMBER_NAME)); String calories = c.getString(c .getColumnIndex(DBhelper.KEY_CALORIES)); et.setText(name); cal.setText(calories); } SQLcon.close(); // closing database } @Override public void onNothingSelected(AdapterView<?> parent) { // TODO Auto-generated method stub } })); SQLcon = new SQLController(this); // opening database SQLcon.open(); loadtospinner(); AddBtn.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { new MyAsync().execute(); } }); } public void loadtospinner() { ArrayList<String> al = new ArrayList<String>(); Cursor c = SQLcon.readData(); c.moveToFirst(); while (!c.isAfterLast()) { String name = c.getString(c.getColumnIndex(DBhelper.MEMBER_NAME)); String calories = c.getString(c .getColumnIndex(DBhelper.KEY_CALORIES)); al.add(name + ", Calories: " + calories); c.moveToNext(); } ArrayAdapter<String> aa1 = new ArrayAdapter<String>( getApplicationContext(), android.R.layout.simple_spinner_item, al); spn.setAdapter(aa1); // closing database SQLcon.close(); } private class MyAsync extends AsyncTask<Void, Void, Void> { @Override protected void onPreExecute() { super.onPreExecute(); PD = new ProgressDialog(MainActivity.this); PD.setTitle("Please Wait.."); PD.setMessage("Loading..."); PD.setCancelable(false); PD.show(); } @Override protected Void doInBackground(Void... params) { String name = et.getText().toString(); String calories = cal.getText().toString(); // opening database SQLcon.open(); // insert data into table SQLcon.insertData(name, calories); return null; } @Override protected void onPostExecute(Void result) { super.onPostExecute(result); loadtospinner(); PD.dismiss(); } } } DataBase public class SQLController { private DBhelper dbhelper; private Context ourcontext; private SQLiteDatabase database; public SQLController(Context c) { ourcontext = c; } public SQLController open() throws SQLException { dbhelper = new DBhelper(ourcontext); database = dbhelper.getWritableDatabase(); return this; } public void close() { dbhelper.close(); } public void insertData(String name, String calories) { ContentValues cv = new ContentValues(); cv.put(DBhelper.MEMBER_NAME, name); cv.put(DBhelper.KEY_CALORIES, calories); database.insert(DBhelper.TABLE_MEMBER, null, cv); } public Cursor readData() { String[] allColumns = new String[] { DBhelper.MEMBER_ID, DBhelper.MEMBER_NAME, DBhelper.KEY_CALORIES }; Cursor c = database.query(DBhelper.TABLE_MEMBER, allColumns, null, null, null, null, null); if (c != null) { c.moveToFirst(); } return c; } } Helper public class DBhelper extends SQLiteOpenHelper { // TABLE INFORMATTION public static final String TABLE_MEMBER = "member"; public static final String MEMBER_ID = "_id"; public static final String MEMBER_NAME = "name"; public static final String KEY_CALORIES = "calories"; // DATABASE INFORMATION static final String DB_NAME = "MEMBER.DB"; static final int DB_VERSION = 2; // TABLE CREATION STATEMENT private static final String CREATE_TABLE = "create table " + TABLE_MEMBER + "(" + MEMBER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + MEMBER_NAME + " TEXT NOT NULL," + KEY_CALORIES + " INT NOT NULL);"; public DBhelper(Context context) { super(context, DB_NAME, null, DB_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(CREATE_TABLE); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // TODO Auto-generated method stub db.execSQL("DROP TABLE IF EXISTS " + TABLE_MEMBER); onCreate(db); } }

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• Thread Synchronization and Synchronization Primitives

  When considering synchronization in an application, the decision truly depends on what the application and its worker threads are going to do. I would use synchronization if two or more threads could possibly manipulate the same instance of an object at the same time. An example of this in C# can be demonstrated through the use of storing data in a static object. A static object is initialized once per application and the data within the object can be accessed by all threads. I would use the synchronization primitives to prevent any data from being manipulated by multiple threads simultaneously. This would reduce any data corruption from occurring within the object. On the other hand if all the threads used non static objects and were independent of the other tasks there would be no need to use synchronization. Synchronization Primitives in C#: Basic Blocking Locking Signaling Non-Blocking Synchronization Constructs The Basic Blocking methods include Sleep, Join, and Task.Wait.  These methods force threads to wait until other threads have completed. In addition, these methods can also force a thread to wait a set amount of time before continuing to work.   The Locking primitive prevents a thread from entering a critical section of code while another thread is in the same critical section.  If another thread attempts to enter a locked code, it will wait, until the code block is released. The Signaling primitive allows a thread to temporarily pause work until receiving a notification from another thread that it is ok to continue working. The Signaling primitive removes the need for polling.The Non-Blocking Synchronization Constructs protect access to a common field by calling upon processor primitives.

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• Revisiting ANTS Performance Profiler 7.4

  - by James Michael Hare

  Last year, I did a small review on the ANTS Performance Profiler 6.3, now that it’s a year later and a major version number higher, I thought I’d revisit the review and revise my last post. This post will take the same examples as the original post and update them to show what’s new in version 7.4 of the profiler. Background A performance profiler’s main job is to keep track of how much time is typically spent in each unit of code. This helps when we have a program that is not running at the performance we expect, and we want to know where the program is experiencing issues. There are many profilers out there of varying capabilities. Red Gate’s typically seem to be the very easy to “jump in” and get started with very little training required. So let’s dig into the Performance Profiler. I’ve constructed a very crude program with some obvious inefficiencies. It’s a simple program that generates random order numbers (or really could be any unique identifier), adds it to a list, sorts the list, then finds the max and min number in the list. Ignore the fact it’s very contrived and obviously inefficient, we just want to use it as an example to show off the tool: 1: // our test program 2: public static class Program 3: { 4: // the number of iterations to perform 5: private static int _iterations = 1000000; 6: 7: // The main method that controls it all 8: public static void Main() 9: { 10: var list = new List<string>(); 11: 12: for (int i = 0; i < _iterations; i++) 13: { 14: var x = GetNextId(); 15: 16: AddToList(list, x); 17: 18: var highLow = GetHighLow(list); 19: 20: if ((i % 1000) == 0) 21: { 22: Console.WriteLine("{0} - High: {1}, Low: {2}", i, highLow.Item1, highLow.Item2); 23: Console.Out.Flush(); 24: } 25: } 26: } 27: 28: // gets the next order id to process (random for us) 29: public static string GetNextId() 30: { 31: var random = new Random(); 32: var num = random.Next(1000000, 9999999); 33: return num.ToString(); 34: } 35: 36: // add it to our list - very inefficiently! 37: public static void AddToList(List<string> list, string item) 38: { 39: list.Add(item); 40: list.Sort(); 41: } 42: 43: // get high and low of order id range - very inefficiently! 44: public static Tuple<int,int> GetHighLow(List<string> list) 45: { 46: return Tuple.Create(list.Max(s => Convert.ToInt32(s)), list.Min(s => Convert.ToInt32(s))); 47: } 48: } So let’s run it through the profiler and see what happens! Visual Studio Integration First, let’s look at how the ANTS profilers integrate with Visual Studio’s menu system. Once you install the ANTS profilers, you will get an ANTS menu item with several options: Notice that you can either Profile Performance or Launch ANTS Performance Profiler. These sound similar but achieve two slightly different actions: Profile Performance: this immediately launches the profiler with all defaults selected to profile the active project in Visual Studio. Launch ANTS Performance Profiler: this launches the profiler much the same way as starting it from the Start Menu. The profiler will pre-populate the application and path information, but allow you to change the settings before beginning the profile run. So really, the main difference is that Profile Performance immediately begins profiling with the default selections, where Launch ANTS Performance Profiler allows you to change the defaults and attach to an already-running application. Let’s Fire it Up! So when you fire up ANTS either via Start Menu or Launch ANTS Performance Profiler menu in Visual Studio, you are presented with a very simple dialog to get you started: Notice you can choose from many different options for application type. You can profile executables, services, web applications, or just attach to a running process. In fact, in version 7.4 we see two new options added: ASP.NET Web Application (IIS Express) SharePoint web application (IIS) So this gives us an additional way to profile ASP.NET applications and the ability to profile SharePoint applications as well. You can also choose your level of detail in the Profiling Mode drop down. If you choose Line-Level and method-level timings detail, you will get a lot more detail on the method durations, but this will also slow down profiling somewhat. If you really need the profiler to be as unintrusive as possible, you can change it to Sample method-level timings. This is performing very light profiling, where basically the profiler collects timings of a method by examining the call-stack at given intervals. Which method you choose depends a lot on how much detail you need to find the issue and how sensitive your program issues are to timing. So for our example, let’s just go with the line and method timing detail. So, we check that all the options are correct (if you launch from VS2010, the executable and path are filled in already), and fire it up by clicking the [Start Profiling] button. Profiling the Application Once you start profiling the application, you will see a real-time graph of CPU usage that will indicate how much your application is using the CPU(s) on your system. During this time, you can select segments of the graph and bookmark them, giving them mnemonic names. This can be useful if you want to compare performance in one part of the run to another part of the run. Notice that once you select a block, it will give you the call tree breakdown for that selection only, and the relative performance of those calls. Once you feel you have collected enough information, you can click [Stop Profiling] to stop the application run and information collection and begin a more thorough analysis. Analyzing Method Timings So now that we’ve halted the run, we can look around the GUI and see what we can see. By default, the times are shown in terms of percentage of time of the total run of the application, though you can change it in the View menu item to milliseconds, ticks, or seconds as well. This won’t affect the percentages of methods, it only affects what units the times are shown. Notice also that the major hotspot seems to be in a method without source, ANTS Profiler will filter these out by default, but you can right-click on the line and remove the filter to see more detail. This proves especially handy when a bottleneck is due to a method in the BCL. So now that we’ve removed the filter, we see a bit more detail: In addition, ANTS Performance Profiler gives you the ability to decompile the methods without source so that you can dive even deeper, though typically this isn’t necessary for our purposes. When looking at timings, there are generally two types of timings for each method call: Time: This is the time spent ONLY in this method, not including calls this method makes to other methods. Time With Children: This is the total of time spent in both this method AND including calls this method makes to other methods. In other words, the Time tells you how much work is being done exclusively in this method, and the Time With Children tells you how much work is being done inclusively in this method and everything it calls. You can also choose to display the methods in a tree or in a grid. The tree view is the default and it shows the method calls arranged in terms of the tree representing all method calls and the parent method that called them, etc. This is useful for when you find a hot-spot method, you can see who is calling it to determine if the problem is the method itself, or if it is being called too many times. The grid method represents each method only once with its totals and is useful for quickly seeing what method is the trouble spot. In addition, you can choose to display Methods with source which are generally the methods you wrote (as opposed to native or BCL code), or Any Method which shows not only your methods, but also native calls, JIT overhead, synchronization waits, etc. So these are just two ways of viewing the same data, and you’re free to choose the organization that best suits what information you are after. Analyzing Method Source If we look at the timings above, we see that our AddToList() method (and in particular, it’s call to the List<T>.Sort() method in the BCL) is the hot-spot in this analysis. If ANTS sees a method that is consuming the most time, it will flag it as a hot-spot to help call out potential areas of concern. This doesn’t mean the other statistics aren’t meaningful, but that the hot-spot is most likely going to be your biggest bang-for-the-buck to concentrate on. So let’s select the AddToList() method, and see what it shows in the source window below: Notice the source breakout in the bottom pane when you select a method (from either tree or grid view). This shows you the timings in this method per line of code. This gives you a major indicator of where the trouble-spot in this method is. So in this case, we see that performing a Sort() on the List<T> after every Add() is killing our performance! Of course, this was a very contrived, duh moment, but you’d be surprised how many performance issues become duh moments. Note that this one line is taking up 86% of the execution time of this application! If we eliminate this bottleneck, we should see drastic improvement in the performance. So to fix this, if we still wanted to maintain the List<T> we’d have many options, including: delay Sort() until after all Add() methods, using a SortedSet, SortedList, or SortedDictionary depending on which is most appropriate, or forgoing the sorting all together and using a Dictionary. Rinse, Repeat! So let’s just change all instances of List<string> to SortedSet<string> and run this again through the profiler: Now we see the AddToList() method is no longer our hot-spot, but now the Max() and Min() calls are! This is good because we’ve eliminated one hot-spot and now we can try to correct this one as well. As before, we can then optimize this part of the code (possibly by taking advantage of the fact the list is now sorted and returning the first and last elements). We can then rinse and repeat this process until we have eliminated as many bottlenecks as possible. Calls by Web Request Another feature that was added recently is the ability to view .NET methods grouped by the HTTP requests that caused them to run. This can be helpful in determining which pages, web services, etc. are causing hot spots in your web applications. Summary If you like the other ANTS tools, you’ll like the ANTS Performance Profiler as well. It is extremely easy to use with very little product knowledge required to get up and running. There are profilers built into the higher product lines of Visual Studio, of course, which are also powerful and easy to use. But for quickly jumping in and finding hot spots rapidly, Red Gate’s Performance Profiler 7.4 is an excellent choice. Technorati Tags: Influencers,ANTS,Performance Profiler,Profiler

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• STUN-server using AWS

  - by Yrlec

  We are about to hire some consultants to help us set up an AWS-based server environment that will enable us to handle NAT Traversal for our P2P application. One important part of the NAT Traversal infrastructure is the STUN-server (http://en.wikipedia.org/wiki/STUN). They just told us that in order for the STUN-server to work you must have two public static IP-addresses pointing to the same server. To more specific they said this: It appears that you need 2 static IPs for each server for the STUN to work. Please note, these IPs have to be put into the configuration file, therefore, each time you restart the instance you have to make sure you either use the same IPs or you have to update configuration. As you plan to use AWS for your installation, please confirm that you can have 2 static IP for each server. Our question is if this is possible using AWS and if so, how? If not, do you know any other way to set up a STUN-server using AWS?

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• Linux: setting up an elite/high-anonimity Web proxy on a dedicated server

  - by YellowSquirrel

  I'm renting a dedicated server which I'd like to use to "surf the Web": basically I want to always surf the Web from the same static IP (the one of my dedicated server). I can do it by running Xvnc/FreeNX on the dedicated server, but this is kinda slow and clumsy (I tried it). What are the steps needed to install an "elite/high-anonimity" Web proxy on a dedicated (Debian) Linux server knowing that my two requirements are: I'm the only person that needs access to the proxy all I want is that my broadband (dynamic) IP is completely hidden (I want to always surf from my dedicated server's IP). Note that using the static IP people can find my domains and my real name and I'm perfectly fine with that (actually it is what I want). What I don't want is people knowing from which dynamic IP (broadband) I'm connecting. What are the steps needed to do that? (basically I don't care about "anonimity", what I want is to appear to surf from a static IP and I think I need what is called an "elite" Web proxy to do that, but I'm not sure) Technical infos and sample configuration most welcome :)

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• Connect ViewModel and View using Unity

  - by brainbox

  In this post i want to describe the approach of connecting View and ViewModel which I'm using in my last project.The main idea is to do it during resolve inside of unity container. It can be achived using InjectionFactory introduced in Unity 2.0 public static class MVVMUnityExtensions{    public static void RegisterView<TView, TViewModel>(this IUnityContainer container) where TView : FrameworkElement    {        container.RegisterView<TView, TView, TViewModel>();    }    public static void RegisterView<TViewFrom, TViewTo, TViewModel>(this IUnityContainer container)        where TViewTo : FrameworkElement, TViewFrom    {        container.RegisterType<TViewFrom>(new InjectionFactory(            c =>            {                var model = c.Resolve<TViewModel>();                var view = Activator.CreateInstance<TViewTo>();                view.DataContext = model;                return view;            }         ));    }}}And here is the sample how it could be used:var unityContainer = new UnityContainer();unityContainer.RegisterView<IFooView, FooView, FooViewModel>();IFooView view = unityContainer.Resolve<IFooView>(); // view with injected viewmodel in its datacontextPlease tell me your prefered way to connect viewmodel and view.

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• Inside the Concurrent Collections: ConcurrentBag

  - by Simon Cooper

  Unlike the other concurrent collections, ConcurrentBag does not really have a non-concurrent analogy. As stated in the MSDN documentation, ConcurrentBag is optimised for the situation where the same thread is both producing and consuming items from the collection. We'll see how this is the case as we take a closer look. Again, I recommend you have ConcurrentBag open in a decompiler for reference. Thread Statics ConcurrentBag makes heavy use of thread statics - static variables marked with ThreadStaticAttribute. This is a special attribute that instructs the CLR to scope any values assigned to or read from the variable to the executing thread, not globally within the AppDomain. This means that if two different threads assign two different values to the same thread static variable, one value will not overwrite the other, and each thread will see the value they assigned to the variable, separately to any other thread. This is a very useful function that allows for ConcurrentBag's concurrency properties. You can think of a thread static variable: [ThreadStatic] private static int m_Value; as doing the same as: private static Dictionary<Thread, int> m_Values; where the executing thread's identity is used to automatically set and retrieve the corresponding value in the dictionary. In .NET 4, this usage of ThreadStaticAttribute is encapsulated in the ThreadLocal class. Lists of lists ConcurrentBag, at its core, operates as a linked list of linked lists: Each outer list node is an instance of ThreadLocalList, and each inner list node is an instance of Node. Each outer ThreadLocalList is owned by a particular thread, accessible through the thread local m_locals variable: private ThreadLocal<ThreadLocalList<T>> m_locals It is important to note that, although the m_locals variable is thread-local, that only applies to accesses through that variable. The objects referenced by the thread (each instance of the ThreadLocalList object) are normal heap objects that are not specific to any thread. Thinking back to the Dictionary analogy above, if each value stored in the dictionary could be accessed by other means, then any thread could access the value belonging to other threads using that mechanism. Only reads and writes to the variable defined as thread-local are re-routed by the CLR according to the executing thread's identity. So, although m_locals is defined as thread-local, the m_headList, m_nextList and m_tailList variables aren't. This means that any thread can access all the thread local lists in the collection by doing a linear search through the outer linked list defined by these variables. Adding items So, onto the collection operations. First, adding items. This one's pretty simple. If the current thread doesn't already own an instance of ThreadLocalList, then one is created (or, if there are lists owned by threads that have stopped, it takes control of one of those). Then the item is added to the head of that thread's list. That's it. Don't worry, it'll get more complicated when we account for the other operations on the list! Taking & Peeking items This is where it gets tricky. If the current thread's list has items in it, then it peeks or removes the head item (not the tail item) from the local list and returns that. However, if the local list is empty, it has to go and steal another item from another list, belonging to a different thread. It iterates through all the thread local lists in the collection using the m_headList and m_nextList variables until it finds one that has items in it, and it steals one item from that list. Up to this point, the two threads had been operating completely independently. To steal an item from another thread's list, the stealing thread has to do it in such a way as to not step on the owning thread's toes. Recall how adding and removing items both operate on the head of the thread's linked list? That gives us an easy way out - a thread trying to steal items from another thread can pop in round the back of another thread's list using the m_tail variable, and steal an item from the back without the owning thread knowing anything about it. The owning thread can carry on completely independently, unaware that one of its items has been nicked. However, this only works when there are at least 3 items in the list, as that guarantees there will be at least one node between the owning thread performing operations on the list head and the thread stealing items from the tail - there's no chance of the two threads operating on the same node at the same time and causing a race condition. If there's less than three items in the list, then there does need to be some synchronization between the two threads. In this case, the lock on the ThreadLocalList object is used to mediate access to a thread's list when there's the possibility of contention. Thread synchronization In ConcurrentBag, this is done using several mechanisms: Operations performed by the owner thread only take out the lock when there are less than three items in the collection. With three or greater items, there won't be any conflict with a stealing thread operating on the tail of the list. If a lock isn't taken out, the owning thread sets the list's m_currentOp variable to a non-zero value for the duration of the operation. This indicates to all other threads that there is a non-locked operation currently occuring on that list. The stealing thread always takes out the lock, to prevent two threads trying to steal from the same list at the same time. After taking out the lock, the stealing thread spinwaits until m_currentOp has been set to zero before actually performing the steal. This ensures there won't be a conflict with the owning thread when the number of items in the list is on the 2-3 item borderline. If any add or remove operations are started in the meantime, and the list is below 3 items, those operations try to take out the list's lock and are blocked until the stealing thread has finished. This allows a thread to steal an item from another thread's list without corrupting it. What about synchronization in the collection as a whole? Collection synchronization Any thread that operates on the collection's global structure (accessing anything outside the thread local lists) has to take out the collection's global lock - m_globalListsLock. This single lock is sufficient when adding a new thread local list, as the items inside each thread's list are unaffected. However, what about operations (such as Count or ToArray) that need to access every item in the collection? In order to ensure a consistent view, all operations on the collection are stopped while the count or ToArray is performed. This is done by freezing the bag at the start, performing the global operation, and unfreezing at the end: The global lock is taken out, to prevent structural alterations to the collection. m_needSync is set to true. This notifies all the threads that they need to take out their list's lock irregardless of what operation they're doing. All the list locks are taken out in order. This blocks all locking operations on the lists. The freezing thread waits for all current lockless operations to finish by spinwaiting on each m_currentOp field. The global operation can then be performed while the bag is frozen, but no other operations can take place at the same time, as all other threads are blocked on a list's lock. Then, once the global operation has finished, the locks are released, m_needSync is unset, and normal concurrent operation resumes. Concurrent principles That's the essence of how ConcurrentBag operates. Each thread operates independently on its own local list, except when they have to steal items from another list. When stealing, only the stealing thread is forced to take out the lock; the owning thread only has to when there is the possibility of contention. And a global lock controls accesses to the structure of the collection outside the thread lists. Operations affecting the entire collection take out all locks in the collection to freeze the contents at a single point in time. So, what principles can we extract here? Threads operate independently Thread-static variables and ThreadLocal makes this easy. Threads operate entirely concurrently on their own structures; only when they need to grab data from another thread is there any thread contention. Minimised lock-taking Even when two threads need to operate on the same data structures (one thread stealing from another), they do so in such a way such that the probability of actually blocking on a lock is minimised; the owning thread always operates on the head of the list, and the stealing thread always operates on the tail. Management of lockless operations Any operations that don't take out a lock still have a 'hook' to force them to lock when necessary. This allows all operations on the collection to be stopped temporarily while a global snapshot is taken. Hopefully, such operations will be short-lived and infrequent. That's all the concurrent collections covered. I hope you've found it as informative and interesting as I have. Next, I'll be taking a closer look at ThreadLocal, which I came across while analyzing ConcurrentBag. As you'll see, the operation of this class deserves a much closer look.

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• Dual Nic, one keeps dropping

  - by user1215018

  I'm running windows server 2008 r2 on a dell poweredge 2850. I have 2 NICs, one is configured behind a firewall with a dhcp server on the main local LAN and another one has it's own dedicated connection to one of our 13 static IPs. So in a nutshell we have 2 of our static IPs going to this server, one indirectly through a firewall/dhcp server, and the other directly. I am trying to reach IIS on port 80 and port 443. The problem is that the NIC with the direct connection (NIC2) keeps dropping and says either "No internet connection" or "Unauthenticated". However, the NIC behind the firewall (NIC1) has no problems at all. Update: This is the second time this has happened in 3 days and each time the fix has been enabling the dhcp client on the NIC, allowing it to error out to a 169.x.x.x address, then re-enabling the nic with it's static IP assignment.

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• DocumentDB - Another Azure NoSQL Storage Service

  - by Shaun

  Originally posted on: http://geekswithblogs.net/shaunxu/archive/2014/08/25/documentdb---another-azure-nosql-storage-service.aspxMicrosoft just released a bunch of new features for Azure on 22nd and one of them I was interested in most is DocumentDB, a document NoSQL database service on the cloud.   Quick Look at DocumentDB We can try DocumentDB from the new azure preview portal. Just click the NEW button and select the item named DocumentDB to create a new account. Specify the name of the DocumentDB, which will be the endpoint we are going to use to connect later. Select the capacity unit, resource group and subscription. In resource group section we can select which region our DocumentDB will be located. Same as other azure services select the same location with your consumers of the DocumentDB, for example the website, web services, etc.. After several minutes the DocumentDB will be ready. Click the KEYS button we can find the URI and primary key, which will be used when connecting. Now let's open Visual Studio and try to use the DocumentDB we had just created. Create a new console application and install the DocumentDB .NET client library from NuGet with the keyword "DocumentDB". You need to select "Include Prerelase" in NuGet Package Manager window since this library was not yet released. Next we will create a new database and document collection under our DocumentDB account. The code below created an instance of DocumentClient with the URI and primary key we just copied from azure portal, and create a database and collection. And it also prints the document and collection link string which will be used later to insert and query documents. 1: static void Main(string[] args) 2: { 3: var endpoint = new Uri("https://shx.documents.azure.com:443/"); 4: var key = "LU2NoyS2fH0131TGxtBE4DW/CjHQBzAaUx/mbuJ1X77C4FWUG129wWk2oyS2odgkFO2Xdif9/ZddintQicF+lA=="; 5:  6: var client = new DocumentClient(endpoint, key); 7: Run(client).Wait(); 8:  9: Console.WriteLine("done"); 10: Console.ReadKey(); 11: } 12:  13: static async Task Run(DocumentClient client) 14: { 15:  16: var database = new Database() { Id = "testdb" }; 17: database = await client.CreateDatabaseAsync(database); 18: Console.WriteLine("database link = {0}", database.SelfLink); 19:  20: var collection = new DocumentCollection() { Id = "testcol" }; 21: collection = await client.CreateDocumentCollectionAsync(database.SelfLink, collection); 22: Console.WriteLine("collection link = {0}", collection.SelfLink); 23: } Below is the result from the console window. We need to copy the collection link string for future usage. Now if we back to the portal we will find a database was listed with the name we specified in the code. Next we will insert a document into the database and collection we had just created. In the code below we pasted the collection link which copied in previous step, create a dynamic object with several properties defined. As you can see we can add some normal properties contains string, integer, we can also add complex property for example an array, a dictionary and an object reference, unless they can be serialized to JSON. 1: static void Main(string[] args) 2: { 3: var endpoint = new Uri("https://shx.documents.azure.com:443/"); 4: var key = "LU2NoyS2fH0131TGxtBE4DW/CjHQBzAaUx/mbuJ1X77C4FWUG129wWk2oyS2odgkFO2Xdif9/ZddintQicF+lA=="; 5:  6: var client = new DocumentClient(endpoint, key); 7:  8: // collection link pasted from the result in previous demo 9: var collectionLink = "dbs/AAk3AA==/colls/AAk3AP6oFgA=/"; 10:  11: // document we are going to insert to database 12: dynamic doc = new ExpandoObject(); 13: doc.firstName = "Shaun"; 14: doc.lastName = "Xu"; 15: doc.roles = new string[] { "developer", "trainer", "presenter", "father" }; 16:  17: // insert the docuemnt 18: InsertADoc(client, collectionLink, doc).Wait(); 19:  20: Console.WriteLine("done"); 21: Console.ReadKey(); 22: } the insert code will be very simple as below, just provide the collection link and the object we are going to insert. 1: static async Task InsertADoc(DocumentClient client, string collectionLink, dynamic doc) 2: { 3: var document = await client.CreateDocumentAsync(collectionLink, doc); 4: Console.WriteLine(await JsonConvert.SerializeObjectAsync(document, Formatting.Indented)); 5: } Below is the result after the object had been inserted. Finally we will query the document from the database and collection. Similar to the insert code, we just need to specify the collection link so that the .NET SDK will help us to retrieve all documents in it. 1: static void Main(string[] args) 2: { 3: var endpoint = new Uri("https://shx.documents.azure.com:443/"); 4: var key = "LU2NoyS2fH0131TGxtBE4DW/CjHQBzAaUx/mbuJ1X77C4FWUG129wWk2oyS2odgkFO2Xdif9/ZddintQicF+lA=="; 5:  6: var client = new DocumentClient(endpoint, key); 7:  8: var collectionLink = "dbs/AAk3AA==/colls/AAk3AP6oFgA=/"; 9:  10: SelectDocs(client, collectionLink); 11:  12: Console.WriteLine("done"); 13: Console.ReadKey(); 14: } 15:  16: static void SelectDocs(DocumentClient client, string collectionLink) 17: { 18: var docs = client.CreateDocumentQuery(collectionLink + "docs/").ToList(); 19: foreach(var doc in docs) 20: { 21: Console.WriteLine(doc); 22: } 23: } Since there's only one document in my collection below is the result when I executed the code. As you can see all properties, includes the array was retrieve at the same time. DocumentDB also attached some properties we didn't specified such as "_rid", "_ts", "_self" etc., which is controlled by the service.   DocumentDB Benefit DocumentDB is a document NoSQL database service. Different from the traditional database, document database is truly schema-free. In a short nut, you can save anything in the same database and collection if it could be serialized to JSON. We you query the document database, all sub documents will be retrieved at the same time. This means you don't need to join other tables when using a traditional database. Document database is very useful when we build some high performance system with hierarchical data structure. For example, assuming we need to build a blog system, there will be many blog posts and each of them contains the content and comments. The comment can be commented as well. If we were using traditional database, let's say SQL Server, the database schema might be defined as below. When we need to display a post we need to load the post content from the Posts table, as well as the comments from the Comments table. We also need to build the comment tree based on the CommentID field. But if were using DocumentDB, what we need to do is to save the post as a document with a list contains all comments. Under a comment all sub comments will be a list in it. When we display this post we just need to to query the post document, the content and all comments will be loaded in proper structure. 1: { 2: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 3: "title": "xxxxx", 4: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 5: "postedOn": "08/25/2014 13:55", 6: "comments": 7: [ 8: { 9: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 10: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 11: "commentedOn": "08/25/2014 14:00", 12: "commentedBy": "xxx" 13: }, 14: { 15: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 16: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 17: "commentedOn": "08/25/2014 14:10", 18: "commentedBy": "xxx", 19: "comments": 20: [ 21: { 22: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 23: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 24: "commentedOn": "08/25/2014 14:18", 25: "commentedBy": "xxx", 26: "comments": 27: [ 28: { 29: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 30: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 31: "commentedOn": "08/25/2014 18:22", 32: "commentedBy": "xxx", 33: } 34: ] 35: }, 36: { 37: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 38: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 39: "commentedOn": "08/25/2014 15:02", 40: "commentedBy": "xxx", 41: } 42: ] 43: }, 44: { 45: "id": "xxxxx-xxxxx-xxxxx-xxxxx", 46: "content": "xxxxx, xxxxxxxxx. xxxxxx, xx, xxxx.", 47: "commentedOn": "08/25/2014 14:30", 48: "commentedBy": "xxx" 49: } 50: ] 51: }   DocumentDB vs. Table Storage DocumentDB and Table Storage are all NoSQL service in Microsoft Azure. One common question is "when we should use DocumentDB rather than Table Storage". Here are some ideas from me and some MVPs. First of all, they are different kind of NoSQL database. DocumentDB is a document database while table storage is a key-value database. Second, table storage is cheaper. DocumentDB supports scale out from one capacity unit to 5 in preview period and each capacity unit provides 10GB local SSD storage. The price is $0.73/day includes 50% discount. For storage service the highest price is $0.061/GB, which is almost 10% of DocumentDB. Third, table storage provides local-replication, geo-replication, read access geo-replication while DocumentDB doesn't support. Fourth, there is local emulator for table storage but none for DocumentDB. We have to connect to the DocumentDB on cloud when developing locally. But, DocumentDB supports some cool features that table storage doesn't have. It supports store procedure, trigger and user-defined-function. It supports rich indexing while table storage only supports indexing against partition key and row key. It supports transaction, table storage supports as well but restricted with Entity Group Transaction scope. And the last, table storage is GA but DocumentDB is still in preview.   Summary In this post I have a quick demonstration and introduction about the new DocumentDB service in Azure. It's very easy to interact through .NET and it also support REST API, Node.js SDK and Python SDK. Then I explained the concept and benefit of  using document database, then compared with table storage.   Hope this helps, Shaun All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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• Django Dying on Shared Hosting Environment (Too Many MySQL Connections)

  - by Tom

  I've had a Django site up and running on HostGator (client requirement), following these instructions, for a few weeks now. I had seen two error emails about pages dying with (1040: Too many MySQL connections) but had never been able to recreate the problem. As of today, the site is completely unresponsive and all pages, even the static files, are dying with that error. Two questions: What can I do to fix this (other than caching more stuff)? Why would static files be dying like that? I can request them directly without a problem, so how are they getting run through Django? The shared hosting setup doesn't allow for a <Location> block, but there's a flag in the rewrite rule that says only requests for files that don't exist in the filesystem should be processed. All of my static files exist on the system, though they are symbolically linked files if it matters.

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• KVM-Guests can't get past bridge - no internet connection

  - by tmn29a

  I'm running a backported KVM on a Debian Squeeze. ATM the KVM-Guest can't connect to the internet through the bridge I have set up. The guests can reach each other, the host but nothing outside. I can neither ping, nslookup or do anything to a remote address. The guest are configured to have a static IP. When I didn;t have the bridge but a virtual bridge (the KVM-default) the guest could connect fine. After setting up the bridge things broke, so I think the problem lies there. # The loopback network interface auto lo br0 iface lo inet loopback # Bonding Interface auto bond0 iface bond0 inet static address 10.XXX.XXX.84 netmask 255.255.255.192 network 10.XXX.XXX.64 gateway 10.XXX.XXX.65 slaves eth0 eth1 bond_mode active-backup bond_miimon 100 bond_downdelay 200 bond_updelay 200 iface br0 inet static bridge_ports eth0 eth1 address 172.xxx.xxx.65 broadcast 172.xxx.xxx.127 netmask 255.255.255.192 gateway 172.xxx.xxx.65 bridge_stp on bridge_maxwait 0 Thanks in advance for your help !

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• Cannot Access Web Interface on HP 2510G

  - by Stephen

  I am currently setting up a new infrastructure with HP 2510s as edge switches and an HP E5406 as the main switch. I also have a DHCP and DNS server running on the same network. When i first set up one of my 2510 switches, I gave it a static IP through the console and then went to the web interface to continue my configuration. Later, I realized that I assigned it the wrong IP address, so i went through the web interface and changed the IP address to the correct one. Now, I can't access the web interface. I can telnet to the switch on the new IP address, but the web interface will not load. If I switch from static IP to DHCP, it loads the web interface. Any ideas on what could be causing the web server in the 2510 not to load with the new static IP address?

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• Apache mod_jk replacing mod_rewrite rules

  - by organicveggie

  We have a slightly complex Apache 2.2 setup in front of a Tomcat 6.0 instance. The main Tomcat webapp is deployed in: /opt/tomcat/webapps/ROOT But we also have static content that we update semi-regularly. We didn't want to force a new build and deploy of the webapp, so that's stored separately in folders like: /opt/tomcat/webapps/css /opt/tomcat/webapps/foo /opt/tomcat/webapps/bar To handle this from Apache, we use mod_rewrite and rules look something like the following: RewriteCond %{REQUEST_FILENAME} -f RewriteRule ^/css/(.*)$ - [L] RewriteCond ROOT/%{REQUEST_FILENAME} -f RewriteRule ^/css/(.*)$ ROOT/$1 [L] RewriteCond %{REQUEST_FILENAME} -f RewriteRule ^(.*)\.(jpg|png|html|js)$ - [L] RewriteCond ROOT/%{REQUEST_FILENAME} -f RewriteRule ^(.*)\.(jpg|png|html|js)$ - [L] RewriteRule ^/(.*)$ http://localhost:8080/$1 [P,L] ProxyPassReverse / http://localhost:8080/ I now think I might want to start using mod_jk and I have two questions: Is it even worth using mod_jk? I don't need load balancing. Is it even possible to handle the cases I outlined where the static content is referenced as "http://www.example.com/css/foo.css", but we don't know if it's located in the Tomcat webapp or in one of the static folders.

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• String.IsNullOrWhiteSpace

  - by Scott Dorman

  An empty string is different than an unassigned string variable (which is null), and is a string containing no characters between the quotes (""). The .NET Framework provides String.Empty to represent an empty string, and there is no practical difference between ("") and String.Empty. One of the most common string comparisons to perform is to determine if a string variable is equal to an empty string. The fastest and simplest way to determine if a string is empty is to test if the Length property is equal to 0. However, since strings are reference types it is possible for a string variable to be null, which would result in a runtime error when you tried to access the Length property. Since testing to determine if a string is empty is such a common occurrence, the .NET Framework provides the static method String.IsNullOrEmpty method: public static bool IsNullOrEmpty(string value) { if (value != null) { return (value.Length == 0); }   return true; } It is also very common to determine if a string is empty and contains more than just whitespace characters. For example, String.IsNullOrEmpty("   ") would return false, since this string is actually made up of three whitespace characters. In some cases, this may be acceptable, but in many others it is not. TO help simplify testing this scenario, the .NET Framework 4 introduces the String.IsNullOrWhiteSpace method: public static bool IsNullOrWhiteSpace(string value) { if (value != null) { for (int i = 0; i < value.Length; i++) { if (!char.IsWhiteSpace(value[i])) { return false; } } } return true; }   Using either String.IsNullOrEmpty or String.IsNullOrWhiteSpace helps ensure correctness, readability, and consistency, so they should be used in all situations where you need to determine if a string is null, empty, or contains only whitespace characters. Technorati Tags: .NET,C# 4

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• Web Server Scripting Hack to Maintain State and Keep a Domain Cookieless

  - by jasonspalace

  Hello, I am looking for a solution on a LAMP server to keep a site cookieless such as "example.com", where static content is served from "static.example.com", and with rules in place to rewrite requests for "www.example.com" to "example.com". I am really hoping to avoid setting up a cookieless domain for the static content due to an unanswered SEO concern with regards to CNAMEing to a CDN. Is there a way, (or safe hack), that can be implemented where a second domain such as "www.example2.com" is CNAMEd, aliased, or otherwise used with "example.com" to somehow trick a php application into maintaining state with a cookie dropped on "www.example2.com" therefore keeping all of "example.com" cookieless? If such a solution is feasible, what implications would exists with regards to SSL and cross-browser compatibility other than requiring users to accept cookies from 3rd party domains and possibly needing an additional SSL to keep the cookie secure? Thanks in advance to all.

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• PHP Aspect Oriented Design

  - by Devin Dixon

  This is a continuation of this Code Review question. What was taken away from that post, and other aspect oriented design is it is hard to debug. To counter that, I implemented the ability to turn tracing of the design patterns on. Turning trace on works like: //This can be added anywhere in the code Run::setAdapterTrace(true); Run::setFilterTrace(true); Run::setObserverTrace(true); //Execute the functon echo Run::goForARun(8); In the actual log with the trace turned on, it outputs like so: adapter 2012-02-12 21:46:19 {"type":"closure","object":"static","call_class":"\/public_html\/examples\/design\/ClosureDesigns.php","class":"Run","method":"goForARun","call_method":"goForARun","trace":"Run::goForARun","start_line":68,"end_line":70} filter 2012-02-12 22:05:15 {"type":"closure","event":"return","object":"static","class":"run_filter","method":"\/home\/prodigyview\/public_html\/examples\/design\/ClosureDesigns.php","trace":"Run::goForARun","start_line":51,"end_line":58} observer 2012-02-12 22:05:15 {"type":"closure","object":"static","class":"run_observer","method":"\/home\/prodigyview\/public_html\/public\/examples\/design\/ClosureDesigns.php","trace":"Run::goForARun","start_line":61,"end_line":63} When the information is broken down, the data translates to: Called by an adapter or filter or observer The function called was a closure The location of the closure Class:method the adapter was implemented on The Trace of where the method was called from Start Line and End Line The code has been proven to work in production environments and features various examples of to implement, so the proof of concept is there. It is not DI and accomplishes things that DI cannot. I wouldn't call the code boilerplate but I would call it bloated. In summary, the weaknesses are bloated code and a learning curve in exchange for aspect oriented functionality. Beyond the normal fear of something new and different, what are other weakness in this implementation of aspect oriented design, if any? PS: More examples of AOP here: https://github.com/ProdigyView/ProdigyView/tree/master/examples/design

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• Movement and Collision with AABB

  - by Jeremy Giberson

  I'm having a little difficulty figuring out the following scenarios. http://i.stack.imgur.com/8lM6i.png In scenario A, the moving entity has fallen to (and slightly into the floor). The current position represents the projected position that will occur if I apply the acceleration & velocity as usual without worrying about collision. The Next position, represents the corrected projection position after collision check. The resulting end position is the falling entity now rests ON the floor--that is, in a consistent state of collision by sharing it's bottom X axis with the floor's top X axis. My current update loop looks like the following: // figure out forces & accelerations and project an objects next position // check collision occurrence from current position -> projected position // if a collision occurs, adjust projection position Which seems to be working for the scenario of my object falling to the floor. However, the situation becomes sticky when trying to figure out scenario's B & C. In scenario B, I'm attempt to move along the floor on the X axis (player is pressing right direction button) additionally, gravity is pulling the object into the floor. The problem is, when the object attempts to move the collision detection code is going to recognize that the object is already colliding with the floor to begin with, and auto correct any movement back to where it was before. In scenario C, I'm attempting to jump off the floor. Again, because the object is already in a constant collision with the floor, when the collision routine checks to make sure moving from current position to projected position doesn't result in a collision, it will fail because at the beginning of the motion, the object is already colliding. How do you allow movement along the edge of an object? How do you allow movement away from an object you are already colliding with. Extra Info My collision routine is based on AABB sweeping test from an old gamasutra article, http://www.gamasutra.com/view/feature/3383/simple_intersection_tests_for_games.php?page=3 My bounding box implementation is based on top left/bottom right instead of midpoint/extents, so my min/max functions are adjusted. Otherwise, here is my bounding box class with collision routines: public class BoundingBox { public XYZ topLeft; public XYZ bottomRight; public BoundingBox(float x, float y, float z, float w, float h, float d) { topLeft = new XYZ(); bottomRight = new XYZ(); topLeft.x = x; topLeft.y = y; topLeft.z = z; bottomRight.x = x+w; bottomRight.y = y+h; bottomRight.z = z+d; } public BoundingBox(XYZ position, XYZ dimensions, boolean centered) { topLeft = new XYZ(); bottomRight = new XYZ(); topLeft.x = position.x; topLeft.y = position.y; topLeft.z = position.z; bottomRight.x = position.x + (centered ? dimensions.x/2 : dimensions.x); bottomRight.y = position.y + (centered ? dimensions.y/2 : dimensions.y); bottomRight.z = position.z + (centered ? dimensions.z/2 : dimensions.z); } /** * Check if a point lies inside a bounding box * @param box * @param point * @return */ public static boolean isPointInside(BoundingBox box, XYZ point) { if(box.topLeft.x <= point.x && point.x <= box.bottomRight.x && box.topLeft.y <= point.y && point.y <= box.bottomRight.y && box.topLeft.z <= point.z && point.z <= box.bottomRight.z) return true; return false; } /** * Check for overlap between two bounding boxes using separating axis theorem * if two boxes are separated on any axis, they cannot be overlapping * @param a * @param b * @return */ public static boolean isOverlapping(BoundingBox a, BoundingBox b) { XYZ dxyz = new XYZ(b.topLeft.x - a.topLeft.x, b.topLeft.y - a.topLeft.y, b.topLeft.z - a.topLeft.z); // if b - a is positive, a is first on the axis and we should use its extent // if b -a is negative, b is first on the axis and we should use its extent // check for x axis separation if ((dxyz.x >= 0 && a.bottomRight.x-a.topLeft.x < dxyz.x) // negative scale, reverse extent sum, flip equality ||(dxyz.x < 0 && b.topLeft.x-b.bottomRight.x > dxyz.x)) return false; // check for y axis separation if ((dxyz.y >= 0 && a.bottomRight.y-a.topLeft.y < dxyz.y) // negative scale, reverse extent sum, flip equality ||(dxyz.y < 0 && b.topLeft.y-b.bottomRight.y > dxyz.y)) return false; // check for z axis separation if ((dxyz.z >= 0 && a.bottomRight.z-a.topLeft.z < dxyz.z) // negative scale, reverse extent sum, flip equality ||(dxyz.z < 0 && b.topLeft.z-b.bottomRight.z > dxyz.z)) return false; // not separated on any axis, overlapping return true; } public static boolean isContactEdge(int xyzAxis, BoundingBox a, BoundingBox b) { switch(xyzAxis) { case XYZ.XCOORD: if(a.topLeft.x == b.bottomRight.x || a.bottomRight.x == b.topLeft.x) return true; return false; case XYZ.YCOORD: if(a.topLeft.y == b.bottomRight.y || a.bottomRight.y == b.topLeft.y) return true; return false; case XYZ.ZCOORD: if(a.topLeft.z == b.bottomRight.z || a.bottomRight.z == b.topLeft.z) return true; return false; } return false; } /** * Sweep test min extent value * @param box * @param xyzCoord * @return */ public static float min(BoundingBox box, int xyzCoord) { switch(xyzCoord) { case XYZ.XCOORD: return box.topLeft.x; case XYZ.YCOORD: return box.topLeft.y; case XYZ.ZCOORD: return box.topLeft.z; default: return 0f; } } /** * Sweep test max extent value * @param box * @param xyzCoord * @return */ public static float max(BoundingBox box, int xyzCoord) { switch(xyzCoord) { case XYZ.XCOORD: return box.bottomRight.x; case XYZ.YCOORD: return box.bottomRight.y; case XYZ.ZCOORD: return box.bottomRight.z; default: return 0f; } } /** * Test if bounding box A will overlap bounding box B at any point * when box A moves from position 0 to position 1 and box B moves from position 0 to position 1 * Note, sweep test assumes bounding boxes A and B's dimensions do not change * * @param a0 box a starting position * @param a1 box a ending position * @param b0 box b starting position * @param b1 box b ending position * @param aCollisionOut xyz of box a's position when/if a collision occurs * @param bCollisionOut xyz of box b's position when/if a collision occurs * @return */ public static boolean sweepTest(BoundingBox a0, BoundingBox a1, BoundingBox b0, BoundingBox b1, XYZ aCollisionOut, XYZ bCollisionOut) { // solve in reference to A XYZ va = new XYZ(a1.topLeft.x-a0.topLeft.x, a1.topLeft.y-a0.topLeft.y, a1.topLeft.z-a0.topLeft.z); XYZ vb = new XYZ(b1.topLeft.x-b0.topLeft.x, b1.topLeft.y-b0.topLeft.y, b1.topLeft.z-b0.topLeft.z); XYZ v = new XYZ(vb.x-va.x, vb.y-va.y, vb.z-va.z); // check for initial overlap if(BoundingBox.isOverlapping(a0, b0)) { // java pass by ref/value gotcha, have to modify value can't reassign it aCollisionOut.x = a0.topLeft.x; aCollisionOut.y = a0.topLeft.y; aCollisionOut.z = a0.topLeft.z; bCollisionOut.x = b0.topLeft.x; bCollisionOut.y = b0.topLeft.y; bCollisionOut.z = b0.topLeft.z; return true; } // overlap min/maxs XYZ u0 = new XYZ(); XYZ u1 = new XYZ(1,1,1); float t0, t1; // iterate axis and find overlaps times (x=0, y=1, z=2) for(int i = 0; i < 3; i++) { float aMax = max(a0, i); float aMin = min(a0, i); float bMax = max(b0, i); float bMin = min(b0, i); float vi = XYZ.getCoord(v, i); if(aMax < bMax && vi < 0) XYZ.setCoord(u0, i, (aMax-bMin)/vi); else if(bMax < aMin && vi > 0) XYZ.setCoord(u0, i, (aMin-bMax)/vi); if(bMax > aMin && vi < 0) XYZ.setCoord(u1, i, (aMin-bMax)/vi); else if(aMax > bMin && vi > 0) XYZ.setCoord(u1, i, (aMax-bMin)/vi); } // get times of collision t0 = Math.max(u0.x, Math.max(u0.y, u0.z)); t1 = Math.min(u1.x, Math.min(u1.y, u1.z)); // collision only occurs if t0 < t1 if(t0 <= t1 && t0 != 0) // not t0 because we already tested it! { // t0 is the normalized time of the collision // then the position of the bounding boxes would // be their original position + velocity*time aCollisionOut.x = a0.topLeft.x + va.x*t0; aCollisionOut.y = a0.topLeft.y + va.y*t0; aCollisionOut.z = a0.topLeft.z + va.z*t0; bCollisionOut.x = b0.topLeft.x + vb.x*t0; bCollisionOut.y = b0.topLeft.y + vb.y*t0; bCollisionOut.z = b0.topLeft.z + vb.z*t0; return true; } else return false; } }

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• Unit testing statically typed functional code

  - by back2dos

  I wanted to ask you people, in which cases it makes sense to unit test statically typed functional code, as written in haskell, scala, ocaml, nemerle, f# or haXe (the last is what I am really interested in, but I wanted to tap into the knowledge of the bigger communities). I ask this because from my understanding: One aspect of unit tests is to have the specs in runnable form. However when employing a declarative style, that directly maps the formalized specs to language semantics, is it even actually possible to express the specs in runnable form in a separate way, that adds value? The more obvious aspect of unit tests is to track down errors that cannot be revealed through static analysis. Given that type safe functional code is a good tool to code extremely close to what your static analyzer understands. However a simple mistake like using x instead of y (both being coordinates) in your code cannot be covered. However such a mistake could also arise while writing the test code, so I am not sure whether its worth the effort. Unit tests do introduce redundancy, which means that when requirements change, the code implementing them and the tests covering this code must both be changed. This overhead of course is about constant, so one could argue, that it doesn't really matter. In fact, in languages like Ruby it really doesn't compared to the benefits, but given how statically typed functional programming covers a lot of the ground unit tests are intended for, it feels like it's a constant overhead one can simply reduce without penalty. From this I'd deduce that unit tests are somewhat obsolete in this programming style. Of course such a claim can only lead to religious wars, so let me boil this down to a simple question: When you use such a programming style, to which extents do you use unit tests and why (what quality is it you hope to gain for your code)? Or the other way round: do you have criteria by which you can qualify a unit of statically typed functional code as covered by the static analyzer and hence needs no unit test coverage?

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• Taming Hopping Windows

  - by Roman Schindlauer

  At first glance, hopping windows seem fairly innocuous and obvious. They organize events into windows with a simple periodic definition: the windows have some duration d (e.g. a window covers 5 second time intervals), an interval or period p (e.g. a new window starts every 2 seconds) and an alignment a (e.g. one of those windows starts at 12:00 PM on March 15, 2012 UTC). var wins = xs     .HoppingWindow(TimeSpan.FromSeconds(5),                    TimeSpan.FromSeconds(2),                    new DateTime(2012, 3, 15, 12, 0, 0, DateTimeKind.Utc)); Logically, there is a window with start time a + np and end time a + np + d for every integer n. That’s a lot of windows. So why doesn’t the following query (always) blow up? var query = wins.Select(win => win.Count()); A few users have asked why StreamInsight doesn’t produce output for empty windows. Primarily it’s because there is an infinite number of empty windows! (Actually, StreamInsight uses DateTimeOffset.MaxValue to approximate “the end of time” and DateTimeOffset.MinValue to approximate “the beginning of time”, so the number of windows is lower in practice.) That was the good news. Now the bad news. Events also have duration. Consider the following simple input: var xs = this.Application                 .DefineEnumerable(() => new[]                     { EdgeEvent.CreateStart(DateTimeOffset.UtcNow, 0) })                 .ToStreamable(AdvanceTimeSettings.IncreasingStartTime); Because the event has no explicit end edge, it lasts until the end of time. So there are lots of non-empty windows if we apply a hopping window to that single event! For this reason, we need to be careful with hopping window queries in StreamInsight. Or we can switch to a custom implementation of hopping windows that doesn’t suffer from this shortcoming. The alternate window implementation produces output only when the input changes. We start by breaking up the timeline into non-overlapping intervals assigned to each window. In figure 1, six hopping windows (“Windows”) are assigned to six intervals (“Assignments”) in the timeline. Next we take input events (“Events”) and alter their lifetimes (“Altered Events”) so that they cover the intervals of the windows they intersect. In figure 1, you can see that the first event e1 intersects windows w1 and w2 so it is adjusted to cover assignments a1 and a2. Finally, we can use snapshot windows (“Snapshots”) to produce output for the hopping windows. Notice however that instead of having six windows generating output, we have only four. The first and second snapshots correspond to the first and second hopping windows. The remaining snapshots however cover two hopping windows each! While in this example we saved only two events, the savings can be more significant when the ratio of event duration to window duration is higher. Figure 1: Timeline The implementation of this strategy is straightforward. We need to set the start times of events to the start time of the interval assigned to the earliest window including the start time. Similarly, we need to modify the end times of events to the end time of the interval assigned to the latest window including the end time. The following snap-to-boundary function that rounds a timestamp value t down to the nearest value t' <= t such that t' is a + np for some integer n will be useful. For convenience, we will represent both DateTime and TimeSpan values using long ticks: static long SnapToBoundary(long t, long a, long p) {     return t - ((t - a) % p) - (t > a ? 0L : p); } How do we find the earliest window including the start time for an event? It’s the window following the last window that does not include the start time assuming that there are no gaps in the windows (i.e. duration < interval), and limitation of this solution. To find the end time of that antecedent window, we need to know the alignment of window ends: long e = a + (d % p); Using the window end alignment, we are finally ready to describe the start time selector: static long AdjustStartTime(long t, long e, long p) {     return SnapToBoundary(t, e, p) + p; } To find the latest window including the end time for an event, we look for the last window start time (non-inclusive): public static long AdjustEndTime(long t, long a, long d, long p) {     return SnapToBoundary(t - 1, a, p) + p + d; } Bringing it together, we can define the translation from events to ‘altered events’ as in Figure 1: public static IQStreamable<T> SnapToWindowIntervals<T>(IQStreamable<T> source, TimeSpan duration, TimeSpan interval, DateTime alignment) {     if (source == null) throw new ArgumentNullException("source");     // reason about DateTime and TimeSpan in ticks     long d = Math.Min(DateTime.MaxValue.Ticks, duration.Ticks);     long p = Math.Min(DateTime.MaxValue.Ticks, Math.Abs(interval.Ticks));     // set alignment to earliest possible window     var a = alignment.ToUniversalTime().Ticks % p;     // verify constraints of this solution     if (d <= 0L) { throw new ArgumentOutOfRangeException("duration"); }     if (p == 0L || p > d) { throw new ArgumentOutOfRangeException("interval"); }     // find the alignment of window ends     long e = a + (d % p);     return source.AlterEventLifetime(         evt => ToDateTime(AdjustStartTime(evt.StartTime.ToUniversalTime().Ticks, e, p)),         evt => ToDateTime(AdjustEndTime(evt.EndTime.ToUniversalTime().Ticks, a, d, p)) -             ToDateTime(AdjustStartTime(evt.StartTime.ToUniversalTime().Ticks, e, p))); } public static DateTime ToDateTime(long ticks) {     // just snap to min or max value rather than under/overflowing     return ticks < DateTime.MinValue.Ticks         ? new DateTime(DateTime.MinValue.Ticks, DateTimeKind.Utc)         : ticks > DateTime.MaxValue.Ticks         ? new DateTime(DateTime.MaxValue.Ticks, DateTimeKind.Utc)         : new DateTime(ticks, DateTimeKind.Utc); } Finally, we can describe our custom hopping window operator: public static IQWindowedStreamable<T> HoppingWindow2<T>(     IQStreamable<T> source,     TimeSpan duration,     TimeSpan interval,     DateTime alignment) {     if (source == null) { throw new ArgumentNullException("source"); }     return SnapToWindowIntervals(source, duration, interval, alignment).SnapshotWindow(); } By switching from HoppingWindow to HoppingWindow2 in the following example, the query returns quickly rather than gobbling resources and ultimately failing! public void Main() {     var start = new DateTimeOffset(new DateTime(2012, 6, 28), TimeSpan.Zero);     var duration = TimeSpan.FromSeconds(5);     var interval = TimeSpan.FromSeconds(2);     var alignment = new DateTime(2012, 3, 15, 12, 0, 0, DateTimeKind.Utc);     var events = this.Application.DefineEnumerable(() => new[]     {         EdgeEvent.CreateStart(start.AddSeconds(0), "e0"),         EdgeEvent.CreateStart(start.AddSeconds(1), "e1"),         EdgeEvent.CreateEnd(start.AddSeconds(1), start.AddSeconds(2), "e1"),         EdgeEvent.CreateStart(start.AddSeconds(3), "e2"),         EdgeEvent.CreateStart(start.AddSeconds(9), "e3"),         EdgeEvent.CreateEnd(start.AddSeconds(3), start.AddSeconds(10), "e2"),         EdgeEvent.CreateEnd(start.AddSeconds(9), start.AddSeconds(10), "e3"),     }).ToStreamable(AdvanceTimeSettings.IncreasingStartTime);     var adjustedEvents = SnapToWindowIntervals(events, duration, interval, alignment);     var query = from win in HoppingWindow2(events, duration, interval, alignment)                 select win.Count();     DisplayResults(adjustedEvents, "Adjusted Events");     DisplayResults(query, "Query"); } As you can see, instead of producing a massive number of windows for the open start edge e0, a single window is emitted from 12:00:15 AM until the end of time: Adjusted Events StartTime EndTime Payload 6/28/2012 12:00:01 AM 12/31/9999 11:59:59 PM e0 6/28/2012 12:00:03 AM 6/28/2012 12:00:07 AM e1 6/28/2012 12:00:05 AM 6/28/2012 12:00:15 AM e2 6/28/2012 12:00:11 AM 6/28/2012 12:00:15 AM e3 Query StartTime EndTime Payload 6/28/2012 12:00:01 AM 6/28/2012 12:00:03 AM 1 6/28/2012 12:00:03 AM 6/28/2012 12:00:05 AM 2 6/28/2012 12:00:05 AM 6/28/2012 12:00:07 AM 3 6/28/2012 12:00:07 AM 6/28/2012 12:00:11 AM 2 6/28/2012 12:00:11 AM 6/28/2012 12:00:15 AM 3 6/28/2012 12:00:15 AM 12/31/9999 11:59:59 PM 1 Regards, The StreamInsight Team

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• Keeping Aspect Screen Ration While Stays in Center

  - by David Dimalanta

  I sqw and I tried this suggestion on PISTACHIO BRAINSTORMIN* on how to make a good and adaptive screen ration. For every different screen size, let's say I put the perfect circle as a Texture in LibGDX and played it on screen. Here's the blueberry image example and it's perfectly rounded: When I played it on the Google Nexus 7, the circle turn into a slightly oblonng shape, resembling as it was being flatten a bit. Please observe this snapshot below and you can see the blueberry is almost but slightly not perfectly rounded: Now, when I tried the suggested code for aspect ratio, the perfect circle retained but another problem is occured. The problem is that I expecting for a view on center but instead it's been moved to the right offset leaving with a half black screen. This would be look like this: Here is my code using the suggested screen aspect ratio code: Class' Field // Ingredients Needed for Screen Aspect Ratio private static final int VIRTUAL_WIDTH = 720; private static final int VIRTUAL_HEIGHT = 1280; private static final float ASPECT_RATIO = ((float) VIRTUAL_WIDTH)/((float) VIRTUAL_HEIGHT); private Camera Mother_Camera; private Rectangle Viewport; render() // Camera updating... Mother_Camera.update(); Mother_Camera.apply(Gdx.gl10); // Reseting viewport... Gdx.gl.glViewport((int) Viewport.x, (int) Viewport.y, (int) Viewport.width, (int) Viewport.height); // Clear previous frame. Gdx.gl.glClearColor(0, 0, 0, 1); Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); show() Mother_Camera = new OrthographicCamera(VIRTUAL_WIDTH, VIRTUAL_HEIGHT); Was this code useful for screen aspect ratio-proportion fixing or it is statically dependent on actual device's width and height? *see http://blog.acamara.es/2012/02/05/keep-screen-aspect-ratio-with-different-resolutions-using-libgdx/#comment-317

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• What is the evidence that an API has exceeded its orthogonality in the context of types?

  - by hawkeye

  Wikipedia defines software orthogonality as: orthogonality in a programming language means that a relatively small set of primitive constructs can be combined in a relatively small number of ways to build the control and data structures of the language. The term is most-frequently used regarding assembly instruction sets, as orthogonal instruction set. Jason Coffin has defined software orthogonality as Highly cohesive components that are loosely coupled to each other produce an orthogonal system. C.Ross has defined software orthogonality as: the property that means "Changing A does not change B". An example of an orthogonal system would be a radio, where changing the station does not change the volume and vice-versa. Now there is a hypothesis published in the the ACM Queue by Tim Bray - that some have called the Bánffy Bray Type System Criteria - which he summarises as: Static typings attractiveness is a direct function (and dynamic typings an inverse function) of API surface size. Dynamic typings attractiveness is a direct function (and static typings an inverse function) of unit testing workability. Now Stuart Halloway has reformulated Banfy Bray as: the more your APIs exceed orthogonality, the better you will like static typing My question is: What is the evidence that an API has exceeded its orthogonality in the context of types? Clarification Tim Bray introduces the idea of orthogonality and APIs. Where you have one API and it is mainly dealing with Strings (ie a web server serving requests and responses), then a uni-typed language (python, ruby) is 'aligned' to that API - because the the type system of these languages isn't sophisticated, but it doesn't matter since you're dealing with Strings anyway. He then moves on to Android programming, which has a whole bunch of sensor APIs, which are all 'different' to the web server API that he was working on previously. Because you're not just dealing with Strings, but with different types, the API is non-orthogonal. Tim's point is that there is a empirical relationship between your 'liking' of types and the API you're programming against. (ie a subjective point is actually objective depending on your context).

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• Looking for some OO design advice

  - by Andrew Stephens

  I'm developing an app that will be used to open and close valves in an industrial environment, and was thinking of something simple like this:- public static void ValveController { public static void OpenValve(string valveName) { // Implementation to open the valve } public static void CloseValve(string valveName) { // Implementation to close the valve } } (The implementation would write a few bytes of data to the serial port to control the valve - an "address" derived from the valve name, and either a "1" or "0" to open or close the valve). Another dev asked whether we should instead create a separate class for each physical valve, of which there are dozens. I agree it would be nicer to write code like PlasmaValve.Open() rather than ValveController.OpenValve("plasma"), but is this overkill? Also, I was wondering how best to tackle the design with a couple of hypothetical future requirements in mind:- We are asked to support a new type of valve requiring different values to open and close it (not 0 and 1). We are asked to support a valve that can be set to any position from 0-100, rather than simply "open" or "closed". Normally I would use inheritance for this kind of thing, but I've recently started to get my head around "composition over inheritance" and wonder if there is a slicker solution to be had using composition?

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• How to configure cookieless virtual host in Apache2?

  - by xzyfer

  We run over a hundred web applications (growing daily) on a LAMP stack using Apache2 on Ubuntu 10.04. We've would like all requests to static content to be cookieless. We host applications on many different domains, a majority of which as SaSS applications. Many of the domains host instances of the applications on sub domains, ie. myapp.example.com, myapp2.example.com myapp.otherexample.com etc.. At the moment all static content is server relative to the (sub)domain requesting it. As far as I understand the process, I would need to setup a new domain, eg. staticexample.com. In this case is special configuration in the virtual host for this domain required to ensure no cookies are served? Also, would it be possible to instead use static.example.com? In this case what configurations would I need in my virtual host for this subdomain to ensure no cookies are served?

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• Proxmox 31 + KVM routing + IP subnet + csf

  - by KeyJey

  We have proxmox 3.1 server in netzner with routuing network and IP subnet block. We want to implement csf firewall without interfering the traffic of the KVM VMs, what would be the easiest way? We readed that we should add this lines to /etc/csf/csfpost.sh: iptables -A FORWARD -d 144.76.223.155 -j ACCEPT iptables -A FORWARD -d 144.76.223.156 -j ACCEPT iptables -A FORWARD -d 144.76.223.157 -j ACCEPT iptables -A FORWARD -d 144.76.223.158 -j ACCEPT iptables -A FORWARD -d 144.76.223.159 -j ACCEPT iptables -A FORWARD -d 144.99.183.323 -j ACCEPT But when we enable csf the ping breaks, this is the network config (IPs are modified): auto lo iface lo inet loopback # device: eth0 auto eth0 iface eth0 inet static address 144.76.166.100 netmask 255.255.255.255 pointopoint 144.76.183.97 gateway 144.76.183.97 # for single IPs auto vmbr0 iface vmbr0 inet static address 144.76.166.100 netmask 255.255.255.255 bridge_ports none bridge_stp off bridge_fd 0 up ip route add 144.99.183.323/32 dev vmbr0 # for a subnet auto vmbr1 iface vmbr1 inet static address 144.76.166.100 netmask 255.255.255.248 bridge_ports none bridge_stp off bridge_fd 0 Thanks in advanced ! :)

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