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• Webcast On-Demand: Building Java EE Apps That Scale

  - by jeckels

  With some awesome work by one of our architects, Randy Stafford, we recently completed a webcast on scaling Java EE apps efficiently. Did you miss it? No problem. We have a replay available on-demand for you. Just hit the '+' sign drop-down for access.Topics include: Domain object caching Service response caching Session state caching JSR-107 HotCache and more! Further, we had several interesting questions asked by our audience, and we thought we'd share a sampling of those here for you - just in case you had the same queries yourself. Enjoy! What is the largest Coherence deployment out there? We have seen deployments with over 500 JVMs in the Coherence cluster, and deployments with over 1000 JVMs using the Coherence jar file, in one system. On the management side there is an ecosystem of monitoring tools from Oracle and third parties with dashboards graphing values from Coherence's JMX instrumentation. For lifecycle management we have seen a lot of custom scripting over the years, but we've also integrated closely with WebLogic to leverage its management ecosystem for deploying Coherence-based applications and managing process life cycles. That integration introduces a new Java EE archive type, the Grid Archive or GAR, which embeds in an EAR and can be seen by a WAR in WebLogic. That integration also doesn't require any extra WebLogic licensing if Coherence is licensed. How is Coherence different from a NoSQL Database like MongoDB? Coherence can be considered a NoSQL technology. It pre-dates the NoSQL movement, having been first released in 2001 whereas the term "NoSQL" was coined in 2009. Coherence has a key-value data model primarily but can also be used for document data models. Coherence manages data in memory currently, though disk persistence is in a future release currently in beta testing. Where the data is managed yields a few differences from the most well-known NoSQL products: access latency is faster with Coherence, though well-known NoSQL databases can manage more data. Coherence also has features that well-known NoSQL database lack, such as grid computing, eventing, and data source integration. Finally Coherence has had 15 years of maturation and hardening from usage in mission-critical systems across a variety of industries, particularly financial services. Can I use Coherence for local caching? Yes, you get additional features beyond just a java.util.Map: you get expiration capabilities, size-limitation capabilities, eventing capabilites, etc. Are there APIs available for GoldenGate HotCache? It's mostly a black box. You configure it, and it just puts objects into your caches. However you can treat it as a glass box, and use Coherence event interceptors to enhance its behavior - and there are use cases for that. Are Coherence caches updated transactionally? Coherence provides several mechanisms for concurrency control. If a project insists on full-blown JTA / XA distributed transactions, Coherence caches can participate as resources. But nobody does that because it's a performance and scalability anti-pattern. At finer granularity, Coherence guarantees strict ordering of all operations (reads and writes) against a single cache key if the operations are done using Coherence's "EntryProcessor" feature. And Coherence has a unique feature called "partition-level transactions" which guarantees atomic writes of multiple cache entries (even in different caches) without requiring JTA / XA distributed transaction semantics.

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• NServiceBus and NHibernate - Message Handler and Transactions

  - by mattcodes

  From my understanding NServiceBus executes the Handle method of an IMessageHandler within a transaction, if an exception propagates out of this method, then NServiceBus will ensure the message is put back on the message queue (up X amount of times before error queue) etc.. so we have an atomic operation so to speak. Now when if I inside my NServiceBus Message Handle method I do something like this using(var trans = session.BeginTransaction()) { person.Age = 10; session.Update<Person>(person); trans.Commit() } using(var trans2 = session.BeginTransaction()) { person.Age = 20; session.Update<Person>(person); // throw new ApplicationException("Oh no"); trans2.Commit() } What is the effect of this on the transaction scope? Is trans1 now counted as a nested transaction in terms of its relationship with the Nservicebus transaction even though we have done nothing to marry them up? (if not how would one link onto the transaction of NServiceBus? Looking at the second block (trans2), if I uncomment the throw statement, will the NServiceBus transaction then rollback trans1 as well? In basic scenarios, say I dump the above into a console app, then trans1 is independent, commit, flushed and won't rollback. I'm trying to clarify what happens now we sit in someone else's transaction like NServiceBus? The above is just example code, im wouldnt be working directly with session, more like through a uow pattern.

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• UIWebView rotation and memory problem

  - by Fer

  Hi. I have an UIWebView that loads a embedded XHTML like this: body = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; body.scalesPageToFit = YES; body.backgroundColor = [UIColor scrollViewTexturedBackgroundColor]; body.autoresizingMask = UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin; [self.view addSubview:body]; [body loadRequest:[NSURLRequest requestWithURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"article16" ofType:@"xhtml"]isDirectory:NO]]]; This XHTML have a lot of images, and when I rotate the device I got some memory warnings, and sometimes the app crashes. If I remove the autoresizing mask, specifically the UIViewAutoresizingFlexibleWidth (I have tryed with only UIViewAutoresizingFlexibleLeftMargin and UIViewAutoresizingFlexibleRightMargin with no problems), the memory warning stops, and the app does not crash anymore. If I remove all autoresizing mask, and set the new webView frame in didRotate or willRotate, I got the same warnings as using the UIViewAutoresizingFlexibleWidth. There's a app, called Atomic Web that could open the same XHTML and rotate with no memory warnings, and safari can open it as well, but if I create a project with only that UIWebView, the app sometimes crashes. Someone knows what this may be? Can I set the webview frame in other way? Why can't I use the autoresizing mask? Thanks for your attention.

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• newline-ignoring diff / diff across multiple lines / reflow-ignoring diff

  - by Adam

  Does anybody know of a diff-like tool that can show me the changes between two text files, but ignore changes in whitespace including newlines? Here's an example: the quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. the quick brown fox jumped over the lazy bear. All I did was delete one word and reflow it, but "diff -b" detects a change on every line (as it should; I'm not saying this is a bug in diff). But for large LaTeX files this is a major problem; change one word in a long paragraph and the diff you get back is basically useless. By the way, I'm aware that this requires way more computational power than the usual lines-are-atomic diff. I'm only doing this on small human-generated files and am happy to wait a long time if I have to.

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• codingbat wordEnds using regex

  - by polygenelubricants

  I'm trying to solve wordEnds from codingbat.com using regex. This is the simplest as I can make it with my current knowledge of regex: public String wordEnds(String str, String word) { return str.replaceAll( String.format( ".*?(?=%s)(?<=(.|^))%1$s(?=(.|$))|.+", java.util.regex.Pattern.quote(word) ), "$1$2" ); } String.format is used to inject word into the pattern for both readability and convenience (it's injected twice). Pattern.quote isn't necessary to pass their tests, but I think it's required for a proper regex-based solution. The regex has two major parts: If after matching as few characters as possible ".*?", word can still be found "(?=%s)", then lookbehind to capture any character immediately preceding it "(?<=(.|^))", match word "%1$s" and lookforward to capture any character following it "(?=(.|$))". The initial "if" test ensures that the atomic lookbehind captures only if there's a word Using lookahead to capture the following character doesn't consume it, so it can be used as part of further matching Otherwise match what's left "|.+" Groups 1 and 2 would capture empty strings I think this works in all cases, but it's obviously quite complex. I'm just wondering if others can suggest a simpler regex to do this. Note: I'm not looking for a solution using indexOf and a loop. I want a regex-based replaceAll solution. I also need a working solution that I can just copy-paste into codingbat and passes.

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• xml to xsl transformation

  - by amirin

  Hi, I have a requirement to extract the uniquie values from the different nodes of the given xml using xsl transformation. XML FILE:- var IPClaimCausesNice = ""; function changeIPClaimCause(){ if(CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Diagnosis") { IPClaimCausesNice = "diagnosis" } if(CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Illness") { IPClaimCausesNice = "illness" } if(CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Accident") { IPClaimCausesNice = "accident" } return IPClaimCausesNice; } <section id="1903879316" name="Logos"> <fraglink id="605609862" resid="1235000151"> <argvalue name="CommJob"> <var name="CommJob" type="Th_1235001170_CommJob" /> </argvalue> </fraglink> </section> <section id="13483397" name="Address Block"> <fraglink id="563800610" resid="986000123"> <argvalue name="PersonInformation"> <var name="AddresseePersonInformation" type="Th_1235000929_PersonInformation" /> </argvalue> </fraglink> </section> <section id="1093480468" name="Details"> <fraglink id="460316501" resid="1195000163"> <argvalue name="currentDateTime"> <var name="getSystemVariables.getCurrentDate" type="date" /> </argvalue> <argvalue name="CommJob"> <var name="CommJob" type="Th_1235000929_CommJob" /> </argvalue> <argvalue name="ShowDOB" /> <argvalue name="ShowYourRef" /> <argvalue name="YourRefLabel" /> </fraglink> <fraglink id="1026044336" resid="1235000070"> <argvalue name="brandKey"> <var name="CommJob.commJobDetails.brandingKey" type="string" /> </argvalue> <argvalue name="brandSponsor"> <var name="CommJob.client.policy.policyDetails.brandSponsor" type="string" /> </argvalue> </fraglink> </section> <section id="2092948772" name="Important info"> <frag id="1180564368" name="frag" no-match="error" type="text"> <edition id="1178777425" name="Any" withdrawn="False"> <edition-content> <p style="bodyTableHeader" align="left" xml:space="preserve">Important information</p> <p style="body" xml:space="preserve">In accordance with the terms and conditions of your policy, your claim has been classified as a <iif><expression><script language="JavaScript">CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Diagnosis" || CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Ill health"</script><description>the IPClaimCause of the CommJob's client policy insurances Insurance Coverages IPCover Claim equals "Diagnosis" or the IPClaimCause of the CommJob's client policy insurances Insurance Coverages IPCover Claim equals "Ill health"sicknessCommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Accident"the IPClaimCause of the CommJob's client policy insurances Insurance Coverages IPCover Claim equals "Accident"accident. Please assist us Please quote your policy and claim numbers / when returning your forms. Your claim has been received Your Thank you for sending your Initial Claim Form which we received on . We are sorry to hear of your recent . Our assessmentThe attending doctor’s statement indicates you are claiming benefits as a result of , CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Diagnosis"the IPClaimCause of the CommJob's client policy Insurance Coverages first Coverage Claim equals "Diagnosis"which was diagnosedCommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Accident"the IPClaimCause of the CommJob's client policy Insurance Coverages first Coverage Claim equals "Accident"which first occuredCommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause == "Ill health"the IPClaimCause of the CommJob's client policy Insurance Coverages first Coverage Claim equals "Ill health"with symptoms commencing on . We note you ceased all work on and consulted your doctor IsNotMissing(CommJob.placeHolders.date.date5)the date5 of the CommJob's placeHolders date is not missingon this day also regarding your condition. Further information is required We’ve enclosed the following forms. Please complete these and return them to us so that we can continue assessing your claim. Progress claim form Attached questionnaire Authority to the Health Insurance Commission Medical authority <<other/ free format>> <<other/ free format>> Please be advised we’ve CommJob.placeHolders._boolean.boolean1 == truethe CommJob's placeHolders boolean is boolean1also requested the following information: Medical report from Dr Medicare history report from the Health Insurance Commission <<other/ free format>> <<other/ free format>> As your claim forms have been submitted months after you ceased work, our ability to properly assess your claim may have been prejudiced. In order to complete our assessment of your claim, the following information is required within 30 days of this letter: Reason for late lodgement of claim. Reason(s) you ceased work on (eg redundancy or due to medical condition). Name and contact details of all doctors and specialists you have consulted since you ceased work. Copies of any medical, radiology, pathology or other reports in your possession. Details of all treatment you have received since you ceased work. Whether you returned to work (paid or unpaid) in either a full-time or part-time capacity. If so, please provide the dates you worked, hours you worked, duties you performed and any income you received. Financial information for any other related entities (if applicable). If you are unable to supply the above information, please contact us by WriteText(FormatDateTime(DateAdd(getSystemVariables.getCurrentDate,"day",30),"dd MMMM yyyy")). To help in the ongoing assessment of your claim, you are required to be under the regular care and attendance of a medical practitioner. We’ve enclosed a Progress Claim Form which needs to be completed and returned to us by . False False False CC: Different nodes to pick the values:- 1. 2.path form 5. Values to be picked form the xml node and display in HTML is like CommJob.client.policy.Insurance.Coverages.Coverage[0].Claim.IPClaimCause CommJob.commJobDetails.stockType CommJob.commJobDetails.targetClient.targetClientName CommJob.client.policy.policyDetails.policyStatus CommJob.client.policy.policyDetails.productType CommJob.commJobDetails.targetClient.targetClientName ........etc can any one help me to provide the solution. This xsl transformation doesn't pick correctly only the values <xsl:template match="@*"/> Any help on this will great.

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• Child objects in MongoDB

  - by Jeremy B.

  I have been following along with Rob Conery's Linq for MongoDB and have come across a question. In the example he shows how you can easily nest a child object. For my current experiment I have the following structure. class Content { ... Profile Profile { get; set; } } class Profile { ... } This works great when looking at content items. The dilemma I'm facing now is if I want to treat the Profile as an atomic object. As it stands, it appears as if I can not query the Profile object directly but that it comes packaged with Content results. If I want it to be inclusive, but also be able to query on just Profile I feel like my first instinct would be to make Profiles a top level object and then create a foreign key like structure under the Content class to tie the two together. To me it feels like I'm falling back on RDBMS practices and that feels like I'm most likely going against the spirit of Mongo. How would you treat an object you need to act upon independently yet also want as a child object of another object?

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• Factory pattern vs ease-of-use?

  - by Curtis White

  Background, I am extending the ASP.NET Membership with custom classes and extra tables. The ASP.NET MembershipUser has a protected constructor and a public method to read the data from the database. I have extended the database structure with custom tables and associated classes. Instead of using a static method to create a new member, as in the original API: I allow the code to instantiate a simple object and fill the data because there are several entities. Original Pattern #1 Protected constructor > static CreateUser(string mydata, string, mydata, ...) > User.Data = mydata; > User.Update() My Preferred Pattern #2 Public constructor > newUser = new MembershipUser(); > newUser.data = ... > newUser.ComplextObject.Data = ... > newUser.Insert() > newUser.Load(string key) I find pattern #2 to be easier and more natural to use. But method #1 is more atomic and ensured to contain proper data. I'd like to hear any opinions on pros/cons. The problem in my mind is that I prefer a simple CRUD/object but I am, also, trying to utilize the underlying API. These methods do not match completely. For example, the API has methods, like UnlockUser() and a readonly property for the IsLockedOut

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• What is the most platform- and Python-version-independent way to make a fast loop for use in Python?

  - by Statto

  I'm writing a scientific application in Python with a very processor-intensive loop at its core. I would like to optimise this as far as possible, at minimum inconvenience to end users, who will probably use it as an uncompiled collection of Python scripts, and will be using Windows, Mac, and (mainly Ubuntu) Linux. It is currently written in Python with a dash of NumPy, and I've included the code below. Is there a solution which would be reasonably fast which would not require compilation? This would seem to be the easiest way to maintain platform-independence. If using something like Pyrex, which does require compilation, is there an easy way to bundle many modules and have Python choose between them depending on detected OS and Python version? Is there an easy way to build the collection of modules without needing access to every system with every version of Python? Does one method lend itself particularly to multi-processor optimisation? (If you're interested, the loop is to calculate the magnetic field at a given point inside a crystal by adding together the contributions of a large number of nearby magnetic ions, treated as tiny bar magnets. Basically, a massive sum of these.) # calculate_dipole # ------------------------- # calculate_dipole works out the dipole field at a given point within the crystal unit cell # --- # INPUT # mu = position at which to calculate the dipole field # r_i = array of atomic positions # mom_i = corresponding array of magnetic moments # --- # OUTPUT # B = the B-field at this point def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) #4pi / mu0 (at the front of the dipole eqn) A = 1e-7 #initalise dipole field B = zeros(3,float) for i in range(len(relative)): #work out the dipole field and add it to the estimate so far B += A*(3*dot(mom_i[i],r_unit[i])*r_unit[i] - mom_i[i]) / sqrt(dot(relative[i],relative[i]))**3 return B

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• How to make Stack.Pop threadsafe

  - by user260197

  I am using the BlockingQueue code posted in this question, but realized I needed to use a Stack instead of a Queue given how my program runs. I converted it to use a Stack and renamed the class as needed. For performance I removed locking in Push, since my producer code is single threaded. My problem is how can thread working on the (now) thread safe Stack know when it is empty. Even if I add another thread safe wrapper around Count that locks on the underlying collection like Push and Pop do, I still run into the race condition that access Count and then Pop are not atomic. Possible solutions as I see them (which is preferred and am I missing any that would work better?): Consumer threads catch the InvalidOperationException thrown by Pop(). Pop() return a nullptr when _stack-Count == 0, however C++-CLI does not have the default() operator ala C#. Pop() returns a boolean and uses an output parameter to return the popped element. Here is the code I am using right now: generic <typename T> public ref class ThreadSafeStack { public: ThreadSafeStack() { _stack = gcnew Collections::Generic::Stack<T>(); } public: void Push(T element) { _stack->Push(element); } T Pop(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Pop(); } finally { System::Threading::Monitor::Exit(_stack); } } public: property int Count { int get(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Count; } finally { System::Threading::Monitor::Exit(_stack); } } } private: Collections::Generic::Stack<T> ^_stack; };

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• Locking issues with replacing files on a website

  - by Moe Sisko

  I want to replace existing files on an IIS website with updated versions. Say these files are large pdf documents, which can be accessed via hyperlinks. The site is up 24x7, so I'm concerned about locking issues when a file is being updated at exactly the same time that someone is trying to read the file. The files are updated using C# code run on the server. I can think of two options for opening the file for writing. Option 1) Open the file for writing, using FileShare.Read : using (FileStream stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read)) While this file is open, and a user requests the same file for reading in a web browser via a hyperlink, the document opens up as a blank page. Option 2) Open the file for writing using FileShare.None : using (FileStream stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None)) While this file is open, and a user requests the same file for reading in a web browser via a hyperlink, the browser shows an error. In IE 8, you get HTTP 500, "The website cannot display the page", and in Firefox 3.5, you get : "The process cannot access the file because it is being used by another process." The browser behaviour kind of makes sense, and seem reasonable. I guess its highly unlikely that a user will attempt to read a file at exactly the same time you are updating it. It would be nice if somehow, the file update was atomic, like updating a database with SQL wrapped around a transaction. I'm wondering if you guys worry about this sort of thing, and prefer either of the above options, or even have other options of your own for updating files.

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• A simple WCF Service (POX) without complex serialization

  - by jammer59

  I'm a complete WCF novice. I'm trying to build a deploy a very, very simple IIS 7.0 hosted web service. For reasons outside of my control it must be WCF and not ASMX. It's a wrapper service for a pre-existing web application that simply does the following: 1) Receives a POST request with the request body XML-encapsulated form elements. Something like valuevalue. This is untyped XML and the XML is atomic (a form) and not a list of records/objects. 2) Add a couple of tags to the request XML and the invoke another HTTP-based service with a simple POST + bare XML -- this will actually be added by some internal SQL ops but that isn't the issue. 3) Receive the XML response from the 3rd party service and relay it as the response to the original calling client in Step 1. The clients (step 1) will be some sort of web-based scripting but could be anything .aspx, python, php, etc. I can't have SOAP and the usual WCF-based REST examples with their contracts and serialization have me confused. This seems like a very common and very simple problem conceptually. It would be easy to implement in code but IIS-hosted WCF is a requirement. Any pointers?

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• "Work stealing" vs. "Work shrugging"?

  - by John

  Why is it that I can find lots of information on "work stealing" and nothing on "work shrugging" as a dynamic load-balancing strategy? By "work-shrugging" I mean busy processors pushing excessive work towards less loaded neighbours rather than idle processors pulling work from busy neighbours ("work-stealing"). I think the general scalability should be the same for both strategies. However I believe that it is much more efficient for busy processors to wake idle processors if and when there is definitely work for them to do than having idle processors spinning or waking periodically to speculatively poll all neighbours for possible work. Anyway a quick google didn't show up anything under the heading of "Work Shrugging" or similar so any pointers to prior-art and the jargon for this strategy would be welcome. Clarification/Confession In more detail:- By "Work Shrugging" I actually envisage the work submitting processor (which may or may not be the target processor) being responsible for looking around the immediate locality of the preferred target processor (based on data/code locality) to decide if a near neighbour should be given the new work instead because they don't have as much work to do. I am talking about an atomic read of the immediate (typically 2 to 4) neighbours' estimated q length here. I do not think this is any more coupling than implied by the thieves polling & stealing from their neighbours - just much less often - or rather - only when it makes economic sense to do so. (I am assuming "lock-free, almost wait-free" queue structures in both strategies). Thanks.

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• PHP inserting Apostrophes where it shouldn't

  - by Jack W-H

  Hi folks Not too sure what's going on here as this doesn't seem like standard practise to me. But basically I have a basic database thingy going on that lets users submit code snippets. They can provide up to 5 tags for their submission. Now I'm still learning so please forgive me if this is obvious! Here's the PHP script that makes it all work (note there may be some CodeIgniter specific functions in there): function submitform() { $this->load->helper(array('form', 'url')); $this->load->library('form_validation'); $this->load->database(); $this->form_validation->set_error_delimiters('<p style="color:#FF0000;">', '</p>'); $this->form_validation->set_rules('title', 'Title', 'trim|required|min_length[5]|max_length[255]|xss_clean'); $this->form_validation->set_rules('summary', 'Summary', 'trim|required|min_length[5]|max_length[255]|xss_clean'); $this->form_validation->set_rules('bbcode', 'Code', 'required|min_length[5]'); // No XSS clean (or <script> tags etc. are gone) $this->form_validation->set_rules('tags', 'Tags', 'trim|xss_clean|required|max_length[254]'); if ($this->form_validation->run() == FALSE) { // Do some stuff if it fails } else { // User's input values $title = $this->db->escape(set_value('title')); $summary = $this->db->escape(set_value('summary')); $code = $this->db->escape(set_value('bbcode')); $tags = $this->db->escape(set_value('tags')); // Stop things like <script> tags working $codesanitised = htmlspecialchars($code); // Other values to be entered $author = $this->tank_auth->get_user_id(); $bi1 = ""; $bi2 = ""; // This long messy bit basically sees which browsers the code is compatible with. if (isset($_POST['IE6'])) {$bi1 .= "IE6, "; $bi2 .= "1, ";} else {$bi1 .= "IE6, "; $bi2 .= "NULL, ";} if (isset($_POST['IE7'])) {$bi1 .= "IE7, "; $bi2 .= "1, ";} else {$bi1 .= "IE7, "; $bi2 .= "NULL, ";} if (isset($_POST['IE8'])) {$bi1 .= "IE8, "; $bi2 .= "1, ";} else {$bi1 .= "IE8, "; $bi2 .= "NULL, ";} if (isset($_POST['FF2'])) {$bi1 .= "FF2, "; $bi2 .= "1, ";} else {$bi1 .= "FF2, "; $bi2 .= "NULL, ";} if (isset($_POST['FF3'])) {$bi1 .= "FF3, "; $bi2 .= "1, ";} else {$bi1 .= "FF3, "; $bi2 .= "NULL, ";} if (isset($_POST['SA3'])) {$bi1 .= "SA3, "; $bi2 .= "1, ";} else {$bi1 .= "SA3, "; $bi2 .= "NULL, ";} if (isset($_POST['SA4'])) {$bi1 .= "SA4, "; $bi2 .= "1, ";} else {$bi1 .= "SA4, "; $bi2 .= "NULL, ";} if (isset($_POST['CHR'])) {$bi1 .= "CHR, "; $bi2 .= "1, ";} else {$bi1 .= "CHR, "; $bi2 .= "NULL, ";} if (isset($_POST['OPE'])) {$bi1 .= "OPE, "; $bi2 .= "1, ";} else {$bi1 .= "OPE, "; $bi2 .= "NULL, ";} if (isset($_POST['OTH'])) {$bi1 .= "OTH, "; $bi2 .= "1, ";} else {$bi1 .= "OTH, "; $bi2 .= "NULL, ";} // $b1 is $bi1 without the last two characters (, ) which would cause a query error $b1 = substr($bi1, 0, -2); $b2 = substr($bi2, 0, -2); // :::::::::::THIS IS WHERE THE IMPORTANT STUFF IS, STACKOVERFLOW READERS:::::::::: // Split up all the words in $tags into individual variables - each tag is seperated with a space $pieces = explode(" ", $tags); // Usage: // echo $pieces[0]; // piece1 etc $ti1 = ""; $ti2 = ""; // Now we'll do similar to what we did with the compatible browsers to generate a bit of a query string if ($pieces[0]!=NULL) {$ti1 .= "tag1, "; $ti2 .= "$pieces[0], ";} else {$ti1 .= "tag1, "; $ti2 .= "NULL, ";} if ($pieces[1]!=NULL) {$ti1 .= "tag2, "; $ti2 .= "$pieces[1], ";} else {$ti1 .= "tag2, "; $ti2 .= "NULL, ";} if ($pieces[2]!=NULL) {$ti1 .= "tag3, "; $ti2 .= "$pieces[2], ";} else {$ti1 .= "tag3, "; $ti2 .= "NULL, ";} if ($pieces[3]!=NULL) {$ti1 .= "tag4, "; $ti2 .= "$pieces[3], ";} else {$ti1 .= "tag4, "; $ti2 .= "NULL, ";} if ($pieces[4]!=NULL) {$ti1 .= "tag5, "; $ti2 .= "$pieces[4], ";} else {$ti1 .= "tag5, "; $ti2 .= "NULL, ";} $t1 = substr($ti1, 0, -2); $t2 = substr($ti2, 0, -2); $sql = "INSERT INTO code (id, title, author, summary, code, date, $t1, $b1) VALUES ('', $title, $author, $summary, $codesanitised, NOW(), $t2, $b2)"; $this->db->query($sql); $this->load->view('subviews/template/headerview'); $this->load->view('subviews/template/menuview'); $this->load->view('subviews/template/sidebar'); $this->load->view('thanksforsubmission'); $this->load->view('subviews/template/footerview'); } } Sorry about that boring drivel of code there. I realise I probably have a few bad practises in there - please point them out if so. This is what the outputted query looks like (it results in an error and isn't queried at all): A Database Error Occurred Error Number: 1136 Column count doesn't match value count at row 1 INSERT INTO code (id, title, author, summary, code, date, tag1, tag2, tag3, tag4, tag5, IE6, IE7, IE8, FF2, FF3, SA3, SA4, CHR, OPE, OTH) VALUES ('', 'test2', 1, 'test2', 'test2 ', NOW(), 'test2, test2, test2, test2, test2', NULL, NULL, 1, 1, 1, 1, 1, 1, 1, NULL) You'll see at the bit after NOW(), 'test2, test2, test2, test2, test2' - I never asked it to put all that in apostrophes. Did I? What I could do is put each of those lines like this: if ($pieces[0]!=NULL) {$ti1 .= "tag1, "; $ti2 .= "'$pieces[0]', ";} else {$ti1 .= "tag1, "; $ti2 .= "NULL, ";} With single quotes around $pieces[0] etc. - but then my problem is that this kinda fails when the user only enters 4 tags, or 3, or whatever. Sorry if that's the worst phrased question in history, I tried, but my brain has turned to mush. Thanks for your help! Jack

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• javascript scope problem when lambda function refers to a variable in enclosing loop

  - by Stefan Blixt

  First question on stackoverflow :) Hope I won't embarrass myself... I have a javascript function that loads a list of albums and then it creates a list item for each album. The list item should be clickable, so I call jQuery's click() with a function that does stuff. I do this in a loop. My problem is that all items seem to get the same click function, even though I try to make a new one that does different stuff in each iteration. Another possibility is that the iteration variable is global somehow, and the function refers to it. Code below. debug() is just an encapsulation of Firebug's console.debug(). function processAlbumList(data, c) { for (var album in data) { var newAlbum = $('<li class="albumLoader">' + data[album].title + '</li>').clone(); var clickAlbum = function() { debug("contents: " + album); }; debug("Album: " + album + "/" + data[album].title); $('.albumlist').append(newAlbum); $(newAlbum).click(clickAlbum); } } Here is a transcript of what it prints when the above function runs, after that are some debug lines caused by me clicking on different items. It always prints "10", which is the last value that the album variable takes (there are 10 albums). Album: 0/Live on radio.electro-music.com Album: 1/Doodles Album: 2/Misc Stuff Album: 3/Drawer Collection Album: 4/Misc Electronic Stuff Album: 5/Odds & Ends Album: 6/Tumbler Album: 7/Bakelit 32 Album: 8/Film Album: 9/Bakelit Album: 10/Slow Zoom/Atomic Heart contents: 10 contents: 10 contents: 10 contents: 10 contents: 10 Any ideas? Driving me up the wall, this is. :) /Stefan

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• Non recursive way to position a genogram in 2D points for x axis. Descendant are below

  - by Nassign

  I currently was tasked to make a genogram for a family consisting of siblings, parents with aunts and uncles with grandparents and greatgrandparents for only blood relatives. My current algorithm is using recursion. but I am wondering how to do it in non recursive way to make it more efficient. it is programmed in c# using graphics to draw on a bitmap. Current algorithm for calculating x position, the y position is by getting the generation number. public void StartCalculatePosition() { // Search the start node (The only node with targetFlg set to true) Person start = null; foreach (Person p in PersonDic.Values) { if (start == null) start = p; if (p.Targetflg) { start = p; break; } } CalcPositionRecurse(start); // Normalize the position (shift all values to positive value) // Get the minimum value (must be negative) // Then offset the position of all marriage and person with that to make it start from zero float minPosition = float.MaxValue; foreach (Person p in PersonDic.Values) { if (minPosition > p.Position) { minPosition = p.Position; } } if (minPosition < 0) { foreach (Person p in PersonDic.Values) { p.Position -= minPosition; } foreach (Marriage m in MarriageList) { m.ParentsPosition -= minPosition; m.ChildrenPosition -= minPosition; } } } /// <summary> /// Calculate position of genogram using recursion /// </summary> /// <param name="psn"></param> private void CalcPositionRecurse(Person psn) { // End the recursion if (psn.BirthMarriage == null || psn.BirthMarriage.Parents.Count == 0) { psn.Position = 0.0f; if (psn.BirthMarriage != null) { psn.BirthMarriage.ParentsPosition = 0.0f; psn.BirthMarriage.ChildrenPosition = 0.0f; } CalculateSiblingPosition(psn); return; } // Left recurse if (psn.Father != null) { CalcPositionRecurse(psn.Father); } // Right recurse if (psn.Mother != null) { CalcPositionRecurse(psn.Mother); } // Merge Position if (psn.Father != null && psn.Mother != null) { AdjustConflict(psn.Father, psn.Mother); // Position person in center of parent psn.Position = (psn.Father.Position + psn.Mother.Position) / 2; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else { // Single mom or single dad if (psn.Father != null) { psn.Position = psn.Father.Position; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else if (psn.Mother != null) { psn.Position = psn.Mother.Position; psn.BirthMarriage.ParentsPosition = psn.Position; psn.BirthMarriage.ChildrenPosition = psn.Position; } else { // Should not happen, checking in start of function } } // Arrange the siblings base on my position (left younger, right older) CalculateSiblingPosition(psn); } private float GetRightBoundaryAncestor(Person psn) { float rPos = psn.Position; // Get the rightmost position among siblings foreach (Person sibling in psn.Siblings) { if (sibling.Position > rPos) { rPos = sibling.Position; } } if (psn.Father != null) { float rFatherPos = GetRightBoundaryAncestor(psn.Father); if (rFatherPos > rPos) { rPos = rFatherPos; } } if (psn.Mother != null) { float rMotherPos = GetRightBoundaryAncestor(psn.Mother); if (rMotherPos > rPos) { rPos = rMotherPos; } } return rPos; } private float GetLeftBoundaryAncestor(Person psn) { float rPos = psn.Position; // Get the rightmost position among siblings foreach (Person sibling in psn.Siblings) { if (sibling.Position < rPos) { rPos = sibling.Position; } } if (psn.Father != null) { float rFatherPos = GetLeftBoundaryAncestor(psn.Father); if (rFatherPos < rPos) { rPos = rFatherPos; } } if (psn.Mother != null) { float rMotherPos = GetLeftBoundaryAncestor(psn.Mother); if (rMotherPos < rPos) { rPos = rMotherPos; } } return rPos; } /// <summary> /// Check if two parent group has conflict and compensate on the conflict /// </summary> /// <param name="leftGroup"></param> /// <param name="rightGroup"></param> public void AdjustConflict(Person leftGroup, Person rightGroup) { float leftMax = GetRightBoundaryAncestor(leftGroup); leftMax += 0.5f; float rightMin = GetLeftBoundaryAncestor(rightGroup); rightMin -= 0.5f; float diff = leftMax - rightMin; if (diff > 0.0f) { float moveHalf = Math.Abs(diff) / 2; RecurseMoveAncestor(leftGroup, 0 - moveHalf); RecurseMoveAncestor(rightGroup, moveHalf); } } /// <summary> /// Recursively move a person and all his/her ancestor /// </summary> /// <param name="psn"></param> /// <param name="moveUnit"></param> public void RecurseMoveAncestor(Person psn, float moveUnit) { psn.Position += moveUnit; foreach (Person siblings in psn.Siblings) { if (siblings.Id != psn.Id) { siblings.Position += moveUnit; } } if (psn.BirthMarriage != null) { psn.BirthMarriage.ChildrenPosition += moveUnit; psn.BirthMarriage.ParentsPosition += moveUnit; } if (psn.Father != null) { RecurseMoveAncestor(psn.Father, moveUnit); } if (psn.Mother != null) { RecurseMoveAncestor(psn.Mother, moveUnit); } } /// <summary> /// Calculate the position of the siblings /// </summary> /// <param name="psn"></param> /// <param name="anchor"></param> public void CalculateSiblingPosition(Person psn) { if (psn.Siblings.Count == 0) { return; } List<Person> sibling = psn.Siblings; int argidx; for (argidx = 0; argidx < sibling.Count; argidx++) { if (sibling[argidx].Id == psn.Id) { break; } } // Compute position for each brother that is younger that person int idx; for (idx = argidx - 1; idx >= 0; idx--) { sibling[idx].Position = sibling[idx + 1].Position - 1; } for (idx = argidx + 1; idx < sibling.Count; idx++) { sibling[idx].Position = sibling[idx - 1].Position + 1; } }

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• Thread safe lazy contruction of a singleton in C++

  - by pauldoo

  Is there a way to implement a singleton object in C++ that is: Lazily constructed in a thread safe manner (two threads might simultaneously be the first user of the singleton - it should still only be constructed once). Doesn't rely on static variables being constructed beforehand (so the singleton object is itself safe to use during the construction of static variables). (I don't know my C++ well enough, but is it the case that integral and constant static variables are initialized before any code is executed (ie, even before static constructors are executed - their values may already be "initialized" in the program image)? If so - perhaps this can be exploited to implement a singleton mutex - which can in turn be used to guard the creation of the real singleton..) Excellent, it seems that I have a couple of good answers now (shame I can't mark 2 or 3 as being the answer). There appears to be two broad solutions: Use static initialisation (as opposed to dynamic initialisation) of a POD static varible, and implementing my own mutex with that using the builtin atomic instructions. This was the type of solution I was hinting at in my question, and I believe I knew already. Use some other library function like pthread_once or boost::call_once. These I certainly didn't know about - and am very grateful for the answers posted.

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• How to store a list in a column of a database table.

  - by John Berryman

  Howdy! So, per Mehrdad's answer to a related question, I get it that a "proper" database table column doesn't store a list. Rather, you should create another table that effectively holds the elements of said list and then link to it directly or through a junction table. However, the type of list I want to create will be composed of unique items (unlike the linked question's fruit example). Furthermore, the items in my list are explicitly sorted - which means that if I stored the elements in another table, I'd have to sort them every time I accessed them. Finally, the list is basically atomic in that any time I wish to access the list, I will want to access the entire list rather than just a piece of it - so it seems silly to have to issue a database query to gather together pieces of the list. AKX's solution (linked above) is to serialize the list and store it in a binary column. But this also seems inconvenient because it means that I have to worry about serialization and deserialization. Is there any better solution? If there is no better solution, then why? It seems that this problem should come up from time to time. ... just a little more info to let you know where I'm coming from. As soon as I had just begun understanding SQL and databases in general, I was turned on to LINQ to SQL, and so now I'm a little spoiled because I expect to deal with my programming object model without having to think about how the objects are queried or stored in the database. Thanks All! John

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• Best strategy for synching data in iPhone app

  - by iamj4de

  I am working on a regular iPhone app which pulls data from a server (XML, JSON, etc...), and I'm wondering what is the best way to implement synching data. Criteria are speed (less network data exchange), robustness (data recovery in case update fails), offline access and flexibility (adaptable when the structure of the database changes slightly, like a new column). I know it varies from app to app, but can you guys share some of your strategy/experience? For me, I'm thinking of something like this: 1) Store Last Modified Date in iPhone 2) Upon launching, send a message like getNewData.php?lastModifiedDate=... 3) Server will process and send back only modified data from last time. 4) This data is formatted as so: <+><data id="..."></data></+> // add this to SQLite/CoreData <-><data id="..."></data></-> // remove this <%><data id="..."><attribute>newValue</attribute></data></%> // new modified value I don't want to make <+, <-, <%... for each attribute as well, because it would be too complicated, so probably when receive a <% field, I would just remove the data with the specified id and then add it again (assuming id here is not some automatically auto-incremented field). 5) Once everything is downloaded and updated, I will update the Last Modified Date field. The main problem with this strategy is: If the network goes down when I am updating something = the Last Modified Date is not yet updated = next time I relaunch the app, I will have to go through the same thing again. Not to mention potential inconsistent data. If I use a temporary table for update and make the whole thing atomic, it would work, but then again, if the update is too long (lots of data change), the user has to wait a long time until new data is available. Should I use Last-Modified-Date for each of the data field and update data gradually?

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• (PHP) Validation, Security and Speed - Does my app have these?

  - by Devner

  Hi all, I am currently working on a building community website in PHP. This contains forms that a user can fill right from registration to lot of other functionality. I am not an Object-oriented guy, so I am using functions most of the time to handle my application. I know I have to learn OOPS, but currently need to develop this website and get it running soon. Anyway, here's a sample of what I let my app. do: Consider a page (register.php) that has a form where a user has 3 fields to fill up, say: First Name, Last Name and Email. Upon submission of this form, I want to validate the form and show the corresponding errors to the users: <form id="form1" name="form1" method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>"> <label for="name">Name:</label> <input type="text" name="name" id="name" /><br /> <label for="lname">Last Name:</label> <input type="text" name="lname" id="lname" /><br /> <label for="email">Email:</label> <input type="text" name="email" id="email" /><br /> <input type="submit" name="submit" id="submit" value="Submit" /> </form> This form will POST the info to the same page. So here's the code that will process the POST'ed info: <?php require("functions.php"); if( isset($_POST['submit']) ) { $errors = fn_register(); if( count($errors) ) { //Show error messages } else { //Send welcome mail to the user or do database stuff... } } ?> <?php //functions.php page: function sql_quote( $value ) { if( get_magic_quotes_gpc() ) { $value = stripslashes( $value ); } else { $value = addslashes( $value ); } if( function_exists( "mysql_real_escape_string" ) ) { $value = mysql_real_escape_string( $value ); } return $value; } function clean($str) { $str = strip_tags($str, '<br>,<br />'); $str = trim($str); $str = sql_quote($str); return $str; } foreach ($_POST as &$value) { if (!is_array($value)) { $value = clean($value); } else { clean($value); } } foreach ($_GET as &$value) { if (!is_array($value)) { $value = clean($value); } else { clean($value); } } function validate_name( $fld, $min, $max, $rule, $label ) { if( $rule == 'required' ) { if ( trim($fld) == '' ) { $str = "$label: Cannot be left blank."; return $str; } } if ( isset($fld) && trim($fld) != '' ) { if ( isset($fld) && $fld != '' && !preg_match("/^[a-zA-Z\ ]+$/", $fld)) { $str = "$label: Invalid characters used! Only Lowercase, Uppercase alphabets and Spaces are allowed"; } else if ( strlen($fld) < $min or strlen($fld) > $max ) { $curr_char = strlen($fld); $str = "$label: Must be atleast $min character &amp; less than $max char. Entered characters: $curr_char"; } else { $str = 0; } } else { $str = 0; } return $str; } function validate_email( $fld, $min, $max, $rule, $label ) { if( $rule == 'required' ) { if ( trim($fld) == '' ) { $str = "$label: Cannot be left blank."; return $str; } } if ( isset($fld) && trim($fld) != '' ) { if ( !eregi('^[a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.([a-zA-Z]{2,4})$', $fld) ) { $str = "$label: Invalid format. Please check."; } else if ( strlen($fld) < $min or strlen($fld) > $max ) { $curr_char = strlen($fld); $str = "$label: Must be atleast $min character &amp; less than $max char. Entered characters: $curr_char"; } else { $str = 0; } } else { $str = 0; } return $str; } function val_rules( $str, $val_type, $rule='required' ){ switch ($val_type) { case 'name': $val = validate_name( $str, 3, 20, $rule, 'First Name'); break; case 'lname': $val = validate_name( $str, 10, 20, $rule, 'Last Name'); break; case 'email': $val = validate_email( $str, 10, 60, $rule, 'Email'); break; } return $val; } function fn_register() { $errors = array(); $val_name = val_rules( $_POST['name'], 'name' ); $val_lname = val_rules( $_POST['lname'], 'lname', 'optional' ); $val_email = val_rules( $_POST['email'], 'email' ); if ( $val_name != '0' ) { $errors['name'] = $val_name; } if ( $val_lname != '0' ) { $errors['lname'] = $val_lname; } if ( $val_email != '0' ) { $errors['email'] = $val_email; } return $errors; } //END of functions.php page ?> OK, now it might look like there's a lot, but lemme break it down target wise: 1. I wanted the foreach ($_POST as &$value) and foreach ($_GET as &$value) loops to loop through the received info from the user submission and strip/remove all malicious input. I am calling a function called clean on the input first to achieve the objective as stated above. This function will process each of the input, whether individual field values or even arrays and allow only tags and remove everything else. The rest of it is obvious. Once this happens, the new/cleaned values will be processed by the fn_register() function and based on the values returned after the validation, we get the corresponding errors or NULL values (as applicable). So here's my questions: 1. This pretty much makes me feel secure as I am forcing the user to correct malicious data and won't process the final data unless the errors are corrected. Am I correct? Does the method that I follow guarantee the speed (as I am using lots of functions and their corresponding calls)? The fields of a form differ and the minimum number of fields I may have at any given point of time in any form may be 3 and can go upto as high as 100 (or even more, I am not sure as the website is still being developed). Will having 100's of fields and their validation in the above way, reduce the speed of application (say upto half a million users are accessing the website at the same time?). What can I do to improve the speed and reduce function calls (if possible)? 3, Can I do something to improve the current ways of validation? I am holding off object oriented approach and using FILTERS in PHP for the later. So please, I request you all to suggest me way to improve/tweak the current ways and suggest me if the script is vulnerable or safe enough to be used in a Live production environment. If not, what I can do to be able to use it live? Thank you all in advance.

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• What information should a SVN/Versioned file commit comment contain?

  - by RenderIn

  I'm curious what kind of content should be in a versioned file commit comment. Should it describe generally what changed (e.g. "The widget screen was changed to display only active widgets") or should it be more specific (e.g. "A new condition was added to the where clause of the fetchWidget query to retrieve only active widgets by default") How atomic should a single commit be? Just the file containing the updated query in a single commit (e.g. "Updated the widget screen to display only active widgets by default"), or should that and several other changes + interface changes to a screen share the same commit with a more general description like ("Updated the widget screen: A) display only active widgets by default B) added button to toggle showing inactive widgets") I see subversion commit comments being used very differently and was wondering what others have had success with. Some comments are as brief as "updated files", while others are many paragraphs long, and others are formatted in a way that they can be queried and associated with some external system such as JIRA. I used to be extremely descriptive of the reason for the change as well as the specific technical changes. Lately I've been scaling back and just giving a general "This is what I changed on this page" kind of comment.

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• Theory: "Lexical Encoding"

  - by _ande_turner_

  I am using the term "Lexical Encoding" for my lack of a better one. A Word is arguably the fundamental unit of communication as opposed to a Letter. Unicode tries to assign a numeric value to each Letter of all known Alphabets. What is a Letter to one language, is a Glyph to another. Unicode 5.1 assigns more than 100,000 values to these Glyphs currently. Out of the approximately 180,000 Words being used in Modern English, it is said that with a vocabulary of about 2,000 Words, you should be able to converse in general terms. A "Lexical Encoding" would encode each Word not each Letter, and encapsulate them within a Sentence. // An simplified example of a "Lexical Encoding" String sentence = "How are you today?"; int[] sentence = { 93, 22, 14, 330, QUERY }; In this example each Token in the String was encoded as an Integer. The Encoding Scheme here simply assigned an int value based on generalised statistical ranking of word usage, and assigned a constant to the question mark. Ultimately, a Word has both a Spelling & Meaning though. Any "Lexical Encoding" would preserve the meaning and intent of the Sentence as a whole, and not be language specific. An English sentence would be encoded into "...language-neutral atomic elements of meaning ..." which could then be reconstituted into any language with a structured Syntactic Form and Grammatical Structure. What are other examples of "Lexical Encoding" techniques? If you were interested in where the word-usage statistics come from : http://www.wordcount.org

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• volatile keyword seems to be useless?

  - by Finbarr

  import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; public class Main implements Runnable { private final CountDownLatch cdl1 = new CountDownLatch(NUM_THREADS); private volatile int bar = 0; private AtomicInteger count = new AtomicInteger(0); private static final int NUM_THREADS = 25; public static void main(String[] args) { Main main = new Main(); for(int i = 0; i < NUM_THREADS; i++) new Thread(main).start(); } public void run() { int i = count.incrementAndGet(); cdl1.countDown(); try { cdl1.await(); } catch (InterruptedException e1) { e1.printStackTrace(); } bar = i; if(bar != i) System.out.println("Bar not equal to i"); else System.out.println("Bar equal to i"); } } Each Thread enters the run method and acquires a unique, thread confined, int variable i by getting a value from the AtomicInteger called count. Each Thread then awaits the CountDownLatch called cdl1 (when the last Thread reaches the latch, all Threads are released). When the latch is released each thread attempts to assign their confined i value to the shared, volatile, int called bar. I would expect every Thread except one to print out "Bar not equal to i", but every Thread prints "Bar equal to i". Eh, wtf does volatile actually do if not this?

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• Using SQL dB column as a lock for concurrent operations in Entity Framework

  - by Sid

  We have a long running user operation that is handled by a pool of worker processes. Data input and output is from Azure SQL. The master Azure SQL table structure columns are approximated to [UserId, col1, col2, ... , col N, beingProcessed, lastTimeProcessed ] beingProcessed is boolean and lastTimeProcessed is DateTime. The logic in every worker role is: public void WorkerRoleMain() { while(true) { try { dbContext db = new dbContext(); // Read foreach (UserProfile user in db.UserProfile .Where(u => DateTime.UtcNow.Subtract(u.lastTimeProcessed) > TimeSpan.FromHours(24) & u.beingProcessed == false)) { user.beingProcessed = true; // Modify db.SaveChanges(); // Write // Do some long drawn processing here ... ... ... user.lastTimeProcessed = DateTime.UtcNow; user.beingProcessed = false; db.SaveChanges(); } } catch(Exception ex) { LogException(ex); Sleep(TimeSpan.FromMinutes(5)); } } // while () } With multiple workers processing as above (each with their own Entity Framework layer), in essence beingProcessed is being used a lock for MutEx purposes Question: How can I deal with concurrency issues on the beingProcessed "lock" itself based on the above load? I think read-modify-write operation on the beingProcessed needs to be atomic but I'm open to other strategies. Open to other code refinements too.

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• How can the Three-Phase Commit Protocol (3PC) guarantee atomicity?

  - by AndiDog

  I'm currently exploring worst case scenarios of atomic commit protocols like 2PC and 3PC and am stuck at the point that I can't find out why 3PC can guarantee atomicity. That is, how does it guarantee that if cohort A commits, cohort B also commits? Here's the simplified 3PC from the Wikipedia article: Now let's assume the following case: Two cohorts participate in the transaction (A and B) Both do their work, then vote for commit Coordinator now sends precommit messages... A receives the precommit message, acknowledges, and then goes offline for a long time B doesn't receive the precommit message (whatever the reason might be) and is thus still in "uncertain" state The results: Coordinator aborts the transaction because not all precommit messages were sent and acknowledged successfully A, who is in precommit state, is still offline, thus times out and commits B aborts in any case: He either stays offline and times out (causes abort) or comes online and receives the abort command from the coordinator And there you have it: One cohort committed, another aborted. The transaction is screwed. So what am I missing here? In my understanding, if the automatic commit on timeout (in precommit state) was replaced by infinitely waiting for a coordinator command, that case should work fine.

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