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ServiceLoader double iterator issues

- by buge

Is this a known issue? I had trouble finding any search results. When iterating over a ServiceLoader while an iteration already is in progress, the first iteration will be aborted. For example, assuming there are at least two implementations of Foo, the following code will fail with an AssertionError: ServiceLoader<Foo> loader = ServiceLoader.load(Foo.class); Iterator<Foo> iter1 = loader.iterator(); iter1.next(); Iterator<Foo> iter2 = loader.iterator(); while (iter2.hasNext()) { iter2.next(); } assert iter1.hasNext(); This only seems to occur, if the second iterator really terminates. The code will succeed in this variation for example: ServiceLoader<Foo> loader = ServiceLoader.load(Foo.class); Iterator<Foo> iter1 = loader.iterator(); iter1.next(); Iterator<Foo> iter2 = loader.iterator(); iter2.next(); assert iter1.hasNext(); Is this a bug or a feature? :p Is there a ticket for this already anywhere?

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MySQLDB query not returning all rows

- by RBK

I am trying to do a simple fetch using MySQLDB in Python. I have 2 tables(Accounts & Products). I have to look up Accounts table, get acc_id from it & query the Products table using it. The Products tables has more than 10 rows. But when I run this code it randomly returns between 0 & 6 rows each time I run it. Here's the code snippet: # Set up connection con = mdb.connect('db.xxxxx.com', 'user', 'password', 'mydb') # Create cursor cur = con.cursor() # Execute query cur.execute("SELECT acc_id FROM Accounts WHERE ext_acc = '%s'" % account_num ) # account_num is alpha-numberic and is got from preceding part of the program # A tuple is returned, so get the 0th item from it acc_id = cur.fetchone()[0] print "account_id = ", acc_id # Close the cursor - I was not sure if I can reuse it cur.close() # Reopen the cursor cur = con.cursor() # Second query cur.execute("SELECT * FROM Products WHERE account_id = %d" % acc_id) keys = cur.fetchall() print cur.rowcount # This prints incorrect row count for key in keys: # Does not print all rows. Tried to directly print keys instead of iterating - same result :( print key # Closing the cursor & connection cur.close() con.close() The weird part is, I tried to step through the code using a debugger(PyDev on Eclipse) and it correctly gets all rows(both the value stored in the variable 'keys' as well as console output are correct). I am sure my DB has correct data since I ran the same SQL on MySQL console & got the correct result. Just to be sure I was not improperly closing the connection, I tried using with con instead of manually closing the connection and it's the same result. I did RTFM but I couldn't find much in it to help me with this issue. Where am I going wrong? Thank you. EDIT: I noticed another weird thing now. In the line cur.execute("SELECT * FROM Products WHERE account_id = %d" % acc_id), I hard-coded the acc_id value, i.e made it cur.execute("SELECT * FROM Products WHERE account_id = %d" % 322) and it returns all rows

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Thread-Safe lazy instantiating using MEF

- by Xaqron

// Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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Permuting output of a tree of closures

- by yan

This a conceptual question on how one would implement the following in Lisp (assuming Common Lisp in my case, but any dialect would work). Assume you have a function that creates closures that sequentially iterate over an arbitrary collection (or otherwise return different values) of data and returns nil when exhausted, i.e. (defun make-counter (up-to) (let ((cnt 0)) (lambda () (if (< cnt up-to) (incf cnt) nil)))) CL-USER> (defvar gen (make-counter 3)) GEN CL-USER> (funcall gen) 1 CL-USER> (funcall gen) 2 CL-USER> (funcall gen) 3 CL-USER> (funcall gen) NIL CL-USER> (funcall gen) NIL Now, assume you are trying to permute a combinations of one or more of these closures. How would you implement a function that returns a new closure that subsequently creates a permutation of all closures contained within it? i.e.: (defun permute-closures (counters) ......) such that the following holds true: CL-USER> (defvar collection (permute-closures (list (make-counter 3) (make-counter 3)))) CL-USER> (funcall collection) (1 1) CL-USER> (funcall collection) (1 2) CL-USER> (funcall collection) (1 3) CL-USER> (funcall collection) (2 1) ... and so on. The way I had it designed originally was to add a 'pause' parameter to the initial counting lambda such that when iterating you can still call it and receive the old cached value if passed ":pause t", in hopes of making the permutation slightly cleaner. Also, while the example above is a simple list of two identical closures, the list can be an arbitrarily-complicated tree (which can be permuted in depth-first order, and the resulting permutation set would have the shape of the tree.). I had this implemented, but my solution wasn't very clean and am trying to poll how others would approach the problem. Thanks in advance.

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Optimising ruby regexp -- lots of match groups

- by Farcaller

I'm working on a ruby baser lexer. To improve performance, I joined up all tokens' regexps into one big regexp with match group names. The resulting regexp looks like: /\A(?<__anonymous_-1038694222803470993>(?-mix:\n+))|\A(?<__anonymous_-1394418499721420065>(?-mix:\/\/[\A\n]*))|\A(?<__anonymous_3077187815313752157>(?-mix:include\s+"[\A"]+"))|\A(?<LET>(?-mix:let\s))|\A(?<IN>(?-mix:in\s))|\A(?<CLASS>(?-mix:class\s))|\A(?<DEF>(?-mix:def\s))|\A(?<DEFM>(?-mix:defm\s))|\A(?<MULTICLASS>(?-mix:multiclass\s))|\A(?<FUNCNAME>(?-mix:![a-zA-Z_][a-zA-Z0-9_]*))|\A(?<ID>(?-mix:[a-zA-Z_][a-zA-Z0-9_]*))|\A(?<STRING>(?-mix:"[\A"]*"))|\A(?<NUMBER>(?-mix:[0-9]+))/ I'm matching it to my string producing a MatchData where exactly one token is parsed: bigregex =~ "\n ... garbage" puts $~.inspect Which outputs #<MatchData "\n" __anonymous_-1038694222803470993:"\n" __anonymous_-1394418499721420065:nil __anonymous_3077187815313752157:nil LET:nil IN:nil CLASS:nil DEF:nil DEFM:nil MULTICLASS:nil FUNCNAME:nil ID:nil STRING:nil NUMBER:nil> So, the regex actually matched the "\n" part. Now, I need to figure the match group where it belongs (it's clearly visible from #inspect output that it's _anonymous-1038694222803470993, but I need to get it programmatically). I could not find any option other than iterating over #names: m.names.each do |n| if m[n] type = n.to_sym resolved_type = (n.start_with?('__anonymous_') ? nil : type) val = m[n] break end end which verifies that the match group did have a match. The problem here is that it's slow (I spend about 10% of time in the loop; also 8% grabbing the @input[@pos..-1] to make sure that \A works as expected to match start of string (I do not discard input, just shift the @pos in it). You can check the full code at GH repo. Any ideas on how to make it at least a bit faster? Is there any option to figure the "successful" match group easier?

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[C++] Parent-Child scheme

- by rubenvb

I'm writing a class that holds a pointer to a parent object of the same type (think Qt's QObject system). Each object has one parent, and the parent should not be destroyed when a child is destroyed (obviously). class MyClass { public: MyClass(const MyClass* ptr_parent): parent(parent){}; ~MyClass(){ delete[] a_children; }; private: const MyClass* ptr_parent; // go to MyClass above MyClass* a_children; // go to MyClass below size_t sz_numChildren; // for iterating over a_children } (Excuse my inline coding, it's only for brevity) Will destroying the "Master MyClass" take care of all children? No child should be able to kill it's parent, because I would then have pointers in my main program to destroyed objects, correct? Why might you ask? I need a way to "iterate" through all subdirectories and find all files on a platform independent level. The creation of this tree will be handled by native API's, the rest won't. Is this a good idea to start with? Thanks!

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Toggle classes with radio button in jQuery

- by dardub

I have a set of radio buttons where when I click a radio button, I want the label to change color or whatever. But when I click another radio button, the color goes away. Therefore I have something like this: jQuery('label').mouseup(function(){ jQuery(this).prev().attr('checked', 'checked'); jQuery('input').next().removeClass('selected'); jQuery('input:checked').next().addClass('selected'); }); if you need to see some html: <input type="radio" id="radio1" name="myRadio" value="option-1" /> <label for="radio1">Swing Gate</label> <input type="radio" id="radio2" name="myRadio" value="option-2" /> <label for="radio2">Swing Gate</label> This first removes 'selected' class from all the labels and then re-applies to only the checked labels. It works and is simple, but I was thinking this might not be the most efficient way of doing this. I imagine that javascript is iterating through each input element and using more resources than necessary. I'm curious if anyone knows of a common way of doing this more efficiently. I seem to be doing this type of thing quite often in my jQuery code. I've just been using jQuery for the past 3 months or so btw.

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LinQ optimization

- by Budda

Here is a peace of code: void MyFunc(List<MyObj> objects) { MyFunc1(objects); foreach( MyObj obj in objects.Where(obj1=>obj1.Good)) { // Do Action With Good Object } } void MyFunc1(List<MyObj> objects) { int iGoodCount = objects.Where(obj1=>obj1.Good).Count(); BeHappy(iGoodCount); // do other stuff with 'objects' collection } Here we see that collection is analyzed twice and each time the value of 'Good' property is checked for each member: 1st time when calculating count of good objects, 2nd - when iterating through all good objects. It is desirable to have that optimized, and here is a straightforward solution: before call to MyFunc1 makecreate an additional temporary collection of good objects only (goodObjects, it can be IEnumerable); get count of these objects and pass it as an additional parameter to MyFunc1; in the 'MyFunc' method iterate not through 'objects.Where(...)' but through the 'goodObjects' collection. Not too bad approach (as far as I see), but additional parameter is required to be passed. Question: is there any LinQ out-of-the-box functionality that allows any caching during 1st Where().Count(), remembering a processed collection and use it in the next iteration? Any thoughts are welcome. Thanks.

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How do I implement IEnumerable?

- by Stacey

I have a class that contains a static number of objects. This class needs to be frequently 'compared' to other classes that will be simple List objects. public partial class Sheet { public Item X{ get; set; } public Item Y{ get; set; } public Item Z{ get; set; } } the items are obviously not going to be "X" "Y" "Z", those are just generic names for example. The problem is that due to the nature of what needs to be done, a List won't work; even though everything in here is going to be of type Item. It is like a checklist of very specific things that has to be tested against in both code and runtime. This works all fine and well; it isn't my issue. My issue is iterating it. For instance I want to do the following... List<Item> UncheckedItems = // Repository Logic Here. UncheckedItems contains all available items; and the CheckedItems is the Sheet class instance. CheckedItems will contain items that were moved from Unchecked to Checked; however due to the nature of the storage system, items moved to Checked CANNOT be REMOVED from Unchecked. I simply want to iterate through "Checked" and remove anything from the list in Unchecked that is already in "Checked". So naturally, that would go like this with a normal list. foreach(Item item in Unchecked) { if( Checked.Contains(item) ) Unchecked.Remove( item ); } But since "Sheet" is not a 'List', I cannot do that. So I wanted to implement IEnumerable so that I could. Any suggestions? I've never implemented IEnumerable directly before and I'm pretty confused as to where to begin.

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What is the best way to properly test object equality against an array of objects?

- by radesix

My objective is to abort the NSXMLParser when I parse an item that already exists in cache. The basic flow of the program works like this: 1) Program starts and downloads an XML feed. Each item in the feed is represented by a custom object (FeedItem). Each FeedItem gets added to an array. 2) When the parsing is complete the contents of the array (all FeedItem objects) are archived to the disk. The next time the program is executed or the feed is refreshed by the user I begin parsing again; however, since a cache (array) now exists as each item is parsed I want to see if the object exists in the cache. If it does then I know I have downloaded all the new items and no longer need to continue parsing. What I am learning, I think, is that I can't use indexOfObject or indexOfObjectIDenticalTo: because these really seem to be checking to see that the objects are using the same memory address (thus identical). What I want to do is see if the contents of the object are equal (or at least some of the contents). I've done some research and found that I can override the IsEqual method; however, I really don't want to iterate/enumerate through the entire cache contents table for every newly parsed XML FeedItem. Is iterating through the collection and testing each one for equality the only way to do this or is there a better technique I am not aware of? Currently I am using the following code though I know it needs to change: NSUInteger index = [self.feedListCache.feedList indexOfObject:self.currentFeedItem]; if (index == NSNotFound) { }

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Vectors or Java arrays for Tetris?

- by StackedCrooked

I'm trying to create a Tetris-like game with Clojure and I'm having some trouble deciding the data structure for the playing field. I want to define the playing field as a mutable grid. The individual blocks are also grids, but don't need to be mutable. My first attempt was to define a grid as a vector of vectors. For example an S-block looks like this: :s-block { :grids [ [ [ 0 1 1 ] [ 1 1 0 ] ] [ [ 1 0 ] [ 1 1 ] [ 0 1 ] ] ] } But that turns out to be rather tricky for simple things like iterating and painting (see the code below). For making the grid mutable my initial idea was to make each row a reference. But then I couldn't really figure out how to change the value of a specific cell in a row. One option would have been to create each individual cell a ref instead of each row. But that feels like an unclean approach. I'm considering using Java arrays now. Clojure's aget and aset functions will probably turn out to be much simpler. However before digging myself in a deeper mess I want to ask ideas/insights. How would you recommend implementing a mutable 2d grid? Feel free to share alternative approaches as well. Source code current state: Tetris.clj (rev452)

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Best Approach for Checking and Inserting Records

- by nevets1219

In one of our existing C programs which purpose is: Open connection to DB for record in all_record: if record contain certain data: if record is NOT in table A: // see #1 insert record information into table A and B // see #2 Close connection to DB select field from table where field=XXX 2 inserts This is typically done every X months to sync everything up or so I'm told. I've also been told that this process takes roughly a couple of days. There is (currently) at most 2.5million records (though not necessarily all 2.5m will be inserted). One of the table contains 10 fields and the other 5 fields. There isn't much to be done about iterating through the records since that part can't be changed at the moment. What I would like to do is speed up the part where I query MySQL. I'm not sure if I have left out any important details -- please let me know! I'm also no SQL expert so feel free to point out the obvious. I thought about: Putting all the inserts into a transaction (at the moment I'm not sure how important it is for the transaction to be all-or-none or if this affects performance) Using Insert X Where Not Exists Y LOAD DATA INFILE (but that would require I create a (possibly) large temp file) I read that (hopefully someone can confirm) I should drop indexes so they aren't re-calculated. mysql Ver 14.7 Distrib 4.1.22, for sun-solaris2.10 (sparc) using readline 4.3

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JavaScript: Is there a better way to retain your array but efficiently concat or replace items?

- by Michael Mikowski

I am looking for the best way to replace or add to elements of an array without deleting the original reference. Here is the set up: var a = [], b = [], c, i, obj; for ( i = 0; i < 100000; i++ ) { a[ i ] = i; b[ i ] = 10000 - i; } obj.data_list = a; Now we want to concatenate b INTO a without changing the reference to a, since it is used in obj.data_list. Here is one method: for ( i = 0; i < b.length; i++ ) { a.push( b[ i ] ); } This seems to be a somewhat terser and 8x (on V8) faster method: a.splice.apply( a, [ a.length, 0 ].concat( b ) ); I have found this useful when iterating over an "in-place" array and don't want to touch the elements as I go (a good practice). I start a new array (let's call it keep_list) with the initial arguments and then add the elements I wish to retain. Finally I use this apply method to quickly replace the truncated array: var keep_list = [ 0, 0 ]; for ( i = 0; i < a.length; i++ ){ if ( some_condition ){ keep_list.push( a[ i ] ); } // truncate array a.length = 0; // And replace contents a.splice.apply( a, keep_list ); There are a few problems with this solution: there is a max call stack size limit of around 50k on V8 I have not tested on other JS engines yet. This solution is a bit cryptic Has anyone found a better way?

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Strange Puzzle - Invalid memory access of location

- by Rob Graeber

The error message I'm getting consistently is: Invalid memory access of location 0x8 rip=0x10cf4ab28 What I'm doing is making a basic stock backtesting system, that is iterating huge arrays of stocks/historical data across various algorithms, using java + eclipse on the latest Mac Os X. I tracked down the code that seems to be causing it. A method that is used to get the massive arrays of data and is called thousands of times. Nothing is retained so I don't think there is a memory leak. However there seems to be a set limit of around 7000 times I can iterate over it before I get the memory error. The weird thing is that it works perfectly in debug mode. Does anyone know what debug mode does differently in Eclipse? Giving the jvm more memory doesn't help, and it appears to work fine using -xint. And again it works perfectly in debug mode. public static List<Stock> getStockArray(ExchangeType e){ List<Stock> stockArray = new ArrayList<Stock>(); if(e == ExchangeType.ALL){ stockArray.addAll(getStockArray(ExchangeType.NYSE)); stockArray.addAll(getStockArray(ExchangeType.NASDAQ)); }else if(e == ExchangeType.ETF){ stockArray.addAll(etfStockArray); }else if(e == ExchangeType.NYSE){ stockArray.addAll(nyseStockArray); }else if(e == ExchangeType.NASDAQ){ stockArray.addAll(nasdaqStockArray); } return stockArray; } A simple loop like this, iterated over 1000s of times, will cause the memory error. But not in debug mode. for (Stock stock : StockDatabase.getStockArray(ExchangeType.ETF)) { System.out.println(stock.symbol); }

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JQuery 1.3.1 doesn't find dynamically generated rows

- by Bamelis Steve

I have just installed in the ASP.NET MVC RC2 and with that also using the JQuery 1.3.1 library. Before I was using the 1.2.6 library. Our application works fine under that library. But now I have strange problem. We have a grid view that we build up with the result of an AJAX call. With the result returned we add new rows to a table through cloning a hidden row. The generated HTML from the JQuery is placing extra parameters to the tags. These are in the form of JQuery12345678="null". They all have the same name. In the head of the table there is a checkbox that selects/unselects all the rows of the table. This by iterating through the rows of the table. $("#selectAllCheckbox").click(function() { var checked = this.checked; $("#dgNewTasks tbody tr").find(':input[type="checkbox"]').each(function() { this.checked = checked; }); }); Now by using the new library the check box are no longer set. I have used IE Developer Tools to check the HTML. If I remove the JQuery12345678="null" parameter from my rows. It works fine. Could someone tell me what I have to do?

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seriouosly elusive for loop (racking my brains!)

- by user1693359

I've got a loop issue in Python 2.72 that's really frustrating me. Basically the loop is not iterating fast the first index (j), and I've tried all sorts of ways to fix it with no luck. def learn(dataSet): for i in dataSet.getNext(): recall = raw_input("Enter all members of %s you are able to recall >>> (separated by commas) " % (i.getName())) missed = i.getMembers() missedString = [] for a in missed: missedString.append(a.getName()) Here is the loop I can't get to iterate. The first for loop only goes through the first iteration of 'j' in the split string list, then removes it from 'missedString'. I would like for all members of the split-string 'recall' to be removed from 'missedString'. for j in string.split(recall, ','): if j in missedString: missedString.remove(j) continue for b in missed: if b.getName() not in missedString: missed.remove(b) print 'You missed %d. ' % (len(missed)) if (len(missed)) > 0: print 'Maybe a hint or two will help...' for miss in missed: remind(miss.getSecs(), i.getName(), missed) I really have no clue, help would be appreciated!

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Determining difference in timestamps for two values in the same MySQL table

- by JayRizzo03

I am relatively new to programming in PHP, so I apologize if this is a rather simple question. I have a MySQL database table called MachineReports that contains the following values: ReportNum(primary key, auto increment), MachineID and Timestamp Here is some example data: |ReportNum | MachineID | Timestamp | |1 | AD3203 | 2012-11-18 06:32:28| |2 | AD3203 | 2012-11-19 04:00:15| |3 | BC4300 | 2012-11-19 04:00:15| What I am attempting to do is find the difference in timestamps in seconds for each machine ID by iterating over each row set. I am getting stuck on the best way to do this, however. Here is the code I've written so far: <?php include '../dbconnect/dbconnect.php'; $machineID=[]; //Get a list of all MachineIDs in the database foreach($dbh->query('SELECT DISTINCT(MachineID) FROM MachineReports') as $row) { array_push($machineID, $row[0]); } for($i=0;$i<count($machineID);$i++){ foreach($dbh->query("SELECT MachineID FROM MachineReports WHERE MachineID='$machineID[$i]' ORDER BY MachineID") as $row) { //code to associate each machineID with two time stamps goes here } } ? This code just lists out the contents of the table row by row. My ultimate goal is to find the difference in timestamps for a certain MachineID. One of the things I've considered is using a multidimensional array in php - using the $machineID as the key and then storing the timestamp inside the array the key points to. However, I'm uncertain how to do that since my query parses row by row. I have quite a few questions. 1) Is this the most efficient way to be doing this? I suspect my database table design may not be the best. 2)What would be the best way to determine the difference in timestamps for a certain machineID? Even just a pointer to a topic that would prompt me to think about this in a different way would be helpful - I'm not afraid to do research. Thanks!

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Why is this removing all elements from my LinkedList?

- by Brian

Why is my remove method removing every element from my Doubly Linked List? If I take out that if/else statements then I can successfully remove middle elements, but elements at the head or tail of the list still remain. However, I added the if/else statements to take care of elements at the head and tail, unfortunately this method now removes every element in my list. What am I do wrong? public void remove(int n) { LinkEntry<E> remove_this = new LinkEntry<E>(); //if nothing comes before remove_this, set the head to equal the element after remove_this if (remove_this.previous == null) head = remove_this.next; //otherwise set the element before remove_this equal to the element after remove_this else remove_this.previous.next = remove_this.next; //if nothing comes after remove_this, set the tail equal to the element before remove_this if (remove_this.next == null) tail = remove_this.previous; //otherwise set the next element's previous pointer to the element before remove_this else remove_this.next.previous = remove_this.previous; //if remove_this is located in the middle of the list, enter this loop until it is //found, then remove it, closing the gap afterwards. int i = 0; for (remove_this = head; remove_this != null; remove_this = remove_this.next) { //if i == n, stop and delete 'remove_this' from the list if (i == n) { //set the previous element's next to the element that comes after remove_this remove_this.previous.next = remove_this.next; //set the element after remove_this' previous pointer to the element before remove_this remove_this.next.previous = remove_this.previous; break; } //if i != n, keep iterating through the list i++; } }

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SSAS: Utility to export SQL code from your cube's Data Source View (DSV)

- by DrJohn

When you are working on a cube, particularly in a multi-person team, it is sometimes necessary to review what changes that have been done to the SQL queries in the cube's data source view (DSV). This can be a problem as the SQL editor in the DSV is not the best interface to review code. Now of course you can cut and paste the SQL into SSMS, but you have to do each query one-by-one. What is worse your DBA is unlikely to have BIDS installed, so you will have to manually export all the SQL yourself and send him the files. To make it easy to get hold of the SQL in a Data Source View, I developed a C# utility which connects to an OLAP database and uses Analysis Services Management Objects (AMO) to obtain and export all the SQL to a series of files. The added benefit of this approach is that these SQL files can be placed under source code control which means the DBA can easily compare one version with another. The Trick When I came to implement this utility, I quickly found that the AMO API does not give direct access to anything useful about the tables in the data source view. Iterating through the DSVs and tables is easy, but getting to the SQL proved to be much harder. My Google searches returned little of value, so I took a look at the idea of using the XmlDom to open the DSV’s XML and obtaining the SQL from that. This is when the breakthrough happened. Inspecting the DSV’s XML I saw the things I was interested in were called TableType DbTableName FriendlyName QueryDefinition Searching Google for FriendlyName returned this page: Programming AMO Fundamental Objects which hinted at the fact that I could use something called ExtendedProperties to obtain these XML attributes. This simplified my code tremendously to make the implementation almost trivial. So here is my code with appropriate comments. The full solution can be downloaded from here: ExportCubeDsvSQL.zip using System;using System.Data;using System.IO;using Microsoft.AnalysisServices; ... class code removed for clarity// connect to the OLAP server Server olapServer = new Server();olapServer.Connect(config.olapServerName);if (olapServer != null){ // connected to server ok, so obtain reference to the OLAP databaseDatabase olapDatabase = olapServer.Databases.FindByName(config.olapDatabaseName);if (olapDatabase != null){ Console.WriteLine(string.Format("Succesfully connected to '{0}' on '{1}'", config.olapDatabaseName, config.olapServerName));// export SQL from each data source view (usually only one, but can be many!)foreach (DataSourceView dsv in olapDatabase.DataSourceViews){ Console.WriteLine(string.Format("Exporting SQL from DSV '{0}'", dsv.Name));// for each table in the DSV, export the SQL in a fileforeach (DataTable dt in dsv.Schema.Tables){ Console.WriteLine(string.Format("Exporting SQL from table '{0}'", dt.TableName)); // get name of the table in the DSV// use the FriendlyName as the user inputs this and therefore has control of itstring queryName = dt.ExtendedProperties["FriendlyName"].ToString().Replace(" ", "_");string sqlFilePath = Path.Combine(targetDir.FullName, queryName + ".sql"); // delete the sql file if it exists... file deletion code removed for clarity// write out the SQL to a fileif (dt.ExtendedProperties["TableType"].ToString() == "View"){ File.WriteAllText(sqlFilePath, dt.ExtendedProperties["QueryDefinition"].ToString());}if (dt.ExtendedProperties["TableType"].ToString() == "Table"){ File.WriteAllText(sqlFilePath, dt.ExtendedProperties["DbTableName"].ToString()); } } } Console.WriteLine(string.Format("Successfully written out SQL scripts to '{0}'", targetDir.FullName)); } } Of course, if you are following industry best practice, you should be basing your cube on a series of views. This will mean that this utility will be of limited practical value unless of course you are inheriting a project and want to check if someone did the implementation correctly.

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Strategies for invoking subclass methods on generic objects

- by Brad Patton

I've run into this issue in a number of places and have solved it a bunch of different ways but looking for other solutions or opinions on how to address. The scenario is when you have a collection of objects all based off of the same superclass but you want to perform certain actions based only on instances of some of the subclasses. One contrived example of this might be an HTML document made up of elements. You could have a superclass named HTMLELement and subclasses of Headings, Paragraphs, Images, Comments, etc. To invoke a common action across all of the objects you declare a virtual method in the superclass and specific implementations in all of the subclasses. So to render the document you could loop all of the different objects in the document and call a common Render() method on each instance. It's the case where again using the same generic objects in the collection I want to perform different actions for instances of specific subclass (or set of subclasses). For example (an remember this is just an example) when iterating over the collection, elements with external links need to be downloaded (e.g. JS, CSS, images) and some might require additional parsing (JS, CSS). What's the best way to handle those special cases. Some of the strategies I've used or seen used include: Virtual methods in the base class. So in the base class you have a virtual LoadExternalContent() method that does nothing and then override it in the specific subclasses that need to implement it. The benefit being that in the calling code there is no object testing you send the same message to each object and let most of them ignore it. Two downsides that I can think of. First it can make the base class very cluttered with methods that have nothing to do with most of the hierarchy. Second it assumes all of the work can be done in the called method and doesn't handle the case where there might be additional context specific actions in the calling code (i.e. you want to do something in the UI and not the model). Have methods on the class to uniquely identify the objects. This could include methods like ClassName() which return a string with the class name or other return values like enums or booleans (IsImage()). The benefit is that the calling code can use if or switch statements to filter objects to perform class specific actions. The downside is that for every new class you need to implement these methods and can look cluttered. Also performance could be less than some of the other options. Use language features to identify objects. This includes reflection and language operators to identify the objects. For example in C# there is the is operator that returns true if the instance matches the specified class. The benefit is no additional code to implement in your object hierarchy. The only downside seems to be the lack of using something like a switch statement and the fact that your calling code is a little more cluttered. Are there other strategies I am missing? Thoughts on best approaches?

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LINQ and ArcObjects

- by Marko Apfel

Motivation LINQ (language integrated query) is a component of the Microsoft. NET Framework since version 3.5. It allows a SQL-like query to various data sources such as SQL, XML etc. Like SQL also LINQ to SQL provides a declarative notation of problem solving – i.e. you don’t need describe in detail how a task could be solved, you describe what to be solved at all. This frees the developer from error-prone iterator constructs. Ideally, of course, would be to access features with this way. Then this construct is conceivable: var largeFeatures = from feature in features where (feature.GetValue("SHAPE_Area").ToDouble() > 3000) select feature; or its equivalent as a lambda expression: var largeFeatures = features.Where(feature => (feature.GetValue("SHAPE_Area").ToDouble() > 3000)); This requires an appropriate provider, which manages the corresponding iterator logic. This is easier than you might think at first sight - you have to deliver only the desired entities as IEnumerable<IFeature>. LINQ automatically establishes a state machine in the background, whose execution is delayed (deferred execution) - when you are really request entities (foreach, Count (), ToList (), ..) an instantiation processing takes place, although it was already created at a completely different place. Especially in multiple iteration through entities in the first debuggings you are rubbing your eyes when the execution pointer jumps magically back in the iterator logic. Realization A very concise logic for constructing IEnumerable<IFeature> can be achieved by running through a IFeatureCursor. You return each feature via yield. For an easier usage I have put the logic in an extension method Getfeatures() for IFeatureClass: public static IEnumerable<IFeature> GetFeatures(this IFeatureClass featureClass, IQueryFilter queryFilter, RecyclingPolicy policy) { IFeatureCursor featureCursor = featureClass.Search(queryFilter, RecyclingPolicy.Recycle == policy); IFeature feature; while (null != (feature = featureCursor.NextFeature())) { yield return feature; } //this is skipped in unit tests with cursor-mock if (Marshal.IsComObject(featureCursor)) { Marshal.ReleaseComObject(featureCursor); } } So you can now easily generate the IEnumerable<IFeature>: IEnumerable<IFeature> features = _featureClass.GetFeatures(RecyclingPolicy.DoNotRecycle); You have to be careful with the recycling cursor. After a delayed execution in the same context it is not a good idea to re-iterated on the features. In this case only the content of the last (recycled) features is provided and all the features are the same in the second set. Therefore, this expression would be critical: largeFeatures.ToList(). ForEach(feature => Debug.WriteLine(feature.OID)); because ToList() iterates once through the list and so the the cursor was once moved through the features. So the extension method ForEach() always delivers the same feature. In such situations, you must not use a recycling cursor. Repeated executions of ForEach() is not a problem, because for every time the state machine is re-instantiated and thus the cursor runs again - that's the magic already mentioned above. Perspective Now you can also go one step further and realize your own implementation for the interface IEnumerable<IFeature>. This requires that only the method and property to access the enumerator have to be programmed. In the enumerator himself in the Reset() method you organize the re-executing of the search. This could be archived with an appropriate delegate in the constructor: new FeatureEnumerator<IFeatureclass>(_featureClass, featureClass => featureClass.Search(_filter, isRecyclingCursor)); which is called in Reset(): public void Reset() { _featureCursor = _resetCursor(_t); } In this manner, enumerators for completely different scenarios could be implemented, which are used on the client side completely identical like described above. Thus cursors, selection sets, etc. merge into a single matter and the reusability of code is increasing immensely. On top of that in automated unit tests an IEnumerable could be mocked very easily - a major step towards better software quality. Conclusion Nevertheless, caution should be exercised with these constructs in performance-relevant queries. Because of managing a state machine in the background, a lot of overhead is created. The processing costs additional time - about 20 to 100 percent. In addition, working without a recycling cursor is fast a performance gap. However declarative LINQ code is much more elegant, flawless and easy to maintain than manually iterating, compare and establish a list of results. The code size is reduced according to experience an average of 75 to 90 percent! So I like to wait a few milliseconds longer. As so often it has to be balanced between maintainability and performance - which for me is gaining in priority maintainability. In times of multi-core processors, the processing time of most business processes is anyway not dominated by code execution but by waiting for user input. Demo source code The source code for this prototype with several unit tests, you can download here: https://github.com/esride-apf/Linq2ArcObjects. .

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Good jquery pagination plugin to use with json Data...

- by bala3569

I am looking for a good jquery pagination plugin to use in my aspx page.... I have the following parameters currentpage,pagesize,TotalRecords,NumberofPages... I would like my plugin to same as stackoverflow paging .... EDIT: It should paginate through json data.... similar to this I use my json data and iterating with jquery var jsonObj = jQuery.parseJSON(HfJsonValue); for (var i = jsonObj.Table.length - 1; i >= 0; i--) { var employee = jsonObj.Table[i]; $('<div class="resultsdiv"> ' + employee.Emp_Name + 'Category : ' + employee.Desig_Name + ' Salary Basis : ' + employee.SalaryBasis + 'Salary : ' + employee.FixedSalary + 'Address : ' + employee.Address + '</div>').insertAfter('#ResultsDiv'); } There are 25 divs in my page as a result i want to show first five divs in page 1 and so on... Any suggestion... My HfJsonValue contains the following json data {"Table" : [{"Emp_Id" : "3","Identity_No" : "","Emp_Name" : "Jerome","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Supervisior","Desig_Description" : "Supervisior of the Construction","SalaryBasis" : "Monthly","FixedSalary" : "25000.00"},{"Emp_Id" : "4","Identity_No" : "","Emp_Name" : "Mohan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Acc ","Desig_Description" : "Accountant","SalaryBasis" : "Monthly","FixedSalary" : "200.00"},{"Emp_Id" : "5","Identity_No" : "","Emp_Name" : "Murugan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "150.00"},{"Emp_Id" : "6","Identity_No" : "","Emp_Name" : "Ram","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "120.00"},{"Emp_Id" : "7","Identity_No" : "","Emp_Name" : "Raja","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "135.00"},{"Emp_Id" : "8","Identity_No" : "","Emp_Name" : "Raja kumar","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "9","Identity_No" : "","Emp_Name" : "Lakshmi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "100.00"},{"Emp_Id" : "10","Identity_No" : "","Emp_Name" : "Palani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "200.00"},{"Emp_Id" : "11","Identity_No" : "","Emp_Name" : "Annamalai","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "12","Identity_No" : "","Emp_Name" : "David","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "13","Identity_No" : "","Emp_Name" : "Chandru","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "14","Identity_No" : "","Emp_Name" : "Mani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Helper","Desig_Description" : "Steel Helper","SalaryBasis" : "Weekly","FixedSalary" : "175.00"},{"Emp_Id" : "15","Identity_No" : "","Emp_Name" : "Karthik","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "195.00"},{"Emp_Id" : "16","Identity_No" : "","Emp_Name" : "Bala","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "17","Identity_No" : "","Emp_Name" : "Tamil arasi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Helper","Desig_Description" : "Wood Helper","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "18","Identity_No" : "","Emp_Name" : "Perumal","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Cook","Desig_Description" : "Cook","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "19","Identity_No" : "","Emp_Name" : "Andiappan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Watchman","Desig_Description" : "Watchman","SalaryBasis" : "Weekly","FixedSalary" : "150.00"}]}

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Page expired issue with back button and wicket SortableDataProvider and DataTable

- by David

Hi, I've got an issue with SortableDataProvider and DataTable in wicket. I've defined my DataTable as such: IColumn<Column>[] columns = new IColumn[9]; //column values are mapped to the private attributes listed in ColumnImpl.java columns[0] = new PropertyColumn(new Model("#"), "columnPosition", "columnPosition"); columns[1] = new PropertyColumn(new Model("Description"), "description"); columns[2] = new PropertyColumn(new Model("Type"), "dataType", "dataType"); Adding it to the table: DataTable<Column> dataTable = new DataTable<Column>("columnsTable", columns, provider, maxRowsPerPage) { @Override protected Item<Column> newRowItem(String id, int index, IModel<Column> model) { return new OddEvenItem<Column>(id, index, model); } }; My data provider: public class ColumnSortableDataProvider extends SortableDataProvider<Column> { private static final long serialVersionUID = 1L; private List list = null; public ColumnSortableDataProvider(Table table, String sortProperty) { this.list = Arrays.asList(table.getColumns().toArray(new Column[0])); setSort(sortProperty, true); } public ColumnSortableDataProvider(List list, String sortProperty) { this.list = list; setSort(sortProperty, true); } @Override public Iterator iterator(int first, int count) { /* first - first row of data count - minimum number of elements to retrieve So this method returns an iterator capable of iterating over {first, first+count} items */ Iterator iterator = null; try { if(getSort() != null) { Collections.sort(list, new Comparator() { private static final long serialVersionUID = 1L; @Override public int compare(Column c1, Column c2) { int result=1; PropertyModel<Comparable> model1= new PropertyModel<Comparable>(c1, getSort().getProperty()); PropertyModel<Comparable> model2= new PropertyModel<Comparable>(c2, getSort().getProperty()); if(model1.getObject() == null && model2.getObject() == null) result = 0; else if(model1.getObject() == null) result = 1; else if(model2.getObject() == null) result = -1; else result = ((Comparable)model1.getObject()).compareTo(model2.getObject()); result = getSort().isAscending() ? result : -result; return result; } }); } if (list.size() (first+count)) iterator = list.subList(first, first+count).iterator(); else iterator = list.iterator(); } catch (Exception e) { e.printStackTrace(); } return iterator; } The problem is the following: - I click a column header to sort by that column. - I navigate to a different page - I click Back (or Forward if I do the opposite scenario) - Page has expired. It'd be nice to generate the page using PageParameters but I somehow need to intercept the sort event to do so. Any pointers would be greatly appreciated. Thanks a ton!! David

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Why does one loop take longer to detect a shared memory update than another loop?

- by Joseph Garvin

I've written a 'server' program that writes to shared memory, and a client program that reads from the memory. The server has different 'channels' that it can be writing to, which are just different linked lists that it's appending items too. The client is interested in some of the linked lists, and wants to read every node that's added to those lists as it comes in, with the minimum latency possible. I have 2 approaches for the client: For each linked list, the client keeps a 'bookmark' pointer to keep its place within the linked list. It round robins the linked lists, iterating through all of them over and over (it loops forever), moving each bookmark one node forward each time if it can. Whether it can is determined by the value of a 'next' member of the node. If it's non-null, then jumping to the next node is safe (the server switches it from null to non-null atomically). This approach works OK, but if there are a lot of lists to iterate over, and only a few of them are receiving updates, the latency gets bad. The server gives each list a unique ID. Each time the server appends an item to a list, it also appends the ID number of the list to a master 'update list'. The client only keeps one bookmark, a bookmark into the update list. It endlessly checks if the bookmark's next pointer is non-null ( while(node->next_ == NULL) {} ), if so moves ahead, reads the ID given, and then processes the new node on the linked list that has that ID. This, in theory, should handle large numbers of lists much better, because the client doesn't have to iterate over all of them each time. When I benchmarked the latency of both approaches (using gettimeofday), to my surprise #2 was terrible. The first approach, for a small number of linked lists, would often be under 20us of latency. The second approach would have small spats of low latencies but often be between 4,000-7,000us! Through inserting gettimeofday's here and there, I've determined that all of the added latency in approach #2 is spent in the loop repeatedly checking if the next pointer is non-null. This is puzzling to me; it's as if the change in one process is taking longer to 'publish' to the second process with the second approach. I assume there's some sort of cache interaction going on I don't understand. What's going on?

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conversion of DNA to Protein - c structure issue

- by sam

I am working on conversion of DNA sequence to Protein sequence. I had completed all program only one error I found there is of structure. dna_codon is a structure and I am iterating over it.In first iteration it shows proper values of structure but from next iteration, it dont show the proper value stored in structure. Its a small error so do not think that I havnt done anything and downvote. I am stucked here because I am new in c for structures. CODE : #include <stdio.h> #include<string.h> void main() { int i, len; char short_codons[20]; char short_slc[1000]; char sequence[1000]; struct codons { char amino_acid[20], slc[20], dna_codon[40]; }; struct codons c1 [20]= { {"Isoleucine", "I", "ATT, ATC, ATA"}, {"Leucine", "L", "CTT, CTC, CTA, CTG, TTA, TTG"}, {"Valine", "V", "GTT, GTC, GTA, GTG"}, {"Phenylalanine", "F", "TTT, TTC"}, {"Methionine", "M", "ATG"}, {"Cysteine", "C", "TGT, TGC"}, {"Alanine", "A", "GCT, GCC, GCA, GCG"}, {"Proline", "P", "CCT, CCC, CCA,CCG "}, {"Threonine", "T", "ACT, ACC, ACA, ACG"}, {"Serine", "S", "TCT, TCC, TCA, TCG, AGT, AGC"}, {"Tyrosine", "Y", "TAT, TAC"}, {"Tryptophan", "W", "TGG"}, {"Glutamine", "Q", "CAA, CAG"}, {"Aspargine","N" "AAT, AAC"}, {"Histidine", "H", "CAT, CAC"}, {"Glutamic acid", "E", "GAA, GAG"}, {"Aspartic acid", "D", "GAT, GAC"}, {"Lysine", "K", "AAA, AAG"}, {"Arginine", "R", "CGT, CGC, CGA, CGG, AGA, AGG"}, {"Stop codons", "Stop", "AA, TAG, TGA"} }; int count = 0; printf("Enter the sequence: "); gets(sequence); char *input_string = sequence; char *tmp_str = input_string; int k; char *pch; while (*input_string != '\0') { char string_3l[4] = {'\0'}; strncpy(string_3l, input_string, 3); printf("\n-----------%s & %s----------", string_3l, tmp_str ); for(k=0;k<20;k++) { //printf("@REAL - %s", c1[0].dna_codon); printf("@ %s", c1[k].dna_codon); int x; x = c1[k].dna_codon; pch = strtok(x, ","); while (pch != NULL) { printf("\n%d : %s with %s", k, string_3l, pch); count=strcmp(string_3l, pch); if(count==0) { strcat(short_slc, c1[k].slc); printf("\n==>%s", short_slc); } pch = strtok (NULL, " ,.-"); } } input_string = input_string+3; } printf("\nProtien sequence is : %s\n", short_slc); } INPUT : TAGTAG OUTPUT : If you see output of printf("\n-----------%s & %s----------", string_3l, tmp_str ); in both iterations, we found that values defined in structure are reduced. I want to know why structure reduces it or its my mistake? because I am stucked here

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