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• Browser timing out attempting to load images

  - by notJim

  I've got a page on a webapp that has about 13 images that are generated by my application, which is written in the Kohana PHP framework. The images are actually graphs. They are cached so they are only generated once, but the first time the user visits the page, and the images all have to be generated, about half of the images don't load in the browser. Once the page has been requested once and images are cached, they all load successfully. Doing some ad-hoc testing, if I load an individual image in the browser, it takes from 450-700 ms to load with an empty cache (I checked this using Google Chrome's resource tracking feature). For reference, it takes around 90-150 ms to load a cached image. Even if the image cache is empty, I have the data and some of the application's startup tasks cached, so that after the first request, none of that data needs to be fetched. My questions are: Why are the images failing to load? It seems like the browser just decides not to download the image after a certain point, rather than waiting for them all to finish loading. What can I do to get them to load the first time, with an empty cache? Obviously one option is to decrease the load times, and I could figure out how to do that by profiling the app, but are there other options? As I mentioned, the app is in the Kohana PHP framework, and it's running on Apache. As an aside, I've solved this problem for now by fetching the page as soon as the data is available (it comes from a batch process), so that the images are always cached by the time the user sees them. That feels like a kludgey solution to me, though, and I'm curious about what's actually going on.

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• Animate screen while loading textures

  - by Omega

  My RPG-like game has random battles. When the player enters a random battle, it is necessary for my game to load the textures used within that battle (animated monsters, animations, etc). The textures are quite a lot, and rather big (the battles are very graphical intensive). Such process consumes significant time. And while it is loading, the whole screen freezes. The game's map freezes, and the wait time is significant - I personally find it annoying. I can't afford to preload the textures because, after doing some math, I realized: If I preload all the textures at the beginning of the game, the application will definitely crash. If I preload the textures that are used in a specific map when the player enters the map, the application is very likely to crash as well. I can only afford to load the textures when I need them, and dispose of them as soon as the battle ends. I'd prefer to not use a "loading screen" image because it affects my game's design and concept. I want to avoid this approach. If I could do some kind of animation while loading the textures, it would be great, which leads to my question: is that possible? What kind of animation, you ask? Well, how about... you remember when Final Fantasy used to distort the screen while apparently loading the textures? Something like that. But well, distorting is quite a time-consuming process as well, so maybe just a cool frame-by-frame animation or something. While writing this, I realized that I could make small pauses between textures (there are multiple textures), and during such pauses, I update the screen to represent the animation's state. However, this is very unlikely to happen, because each texture is 2048x2048, so the animation would be refreshed at a rather laggy (and annoying) rate. I'd prefer to avoid this as well.

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• Use of extern in C++ dll

  - by dom_beau

  I declare then instantiate a static variable in a DLL. // DLL.h class A { //... }; static A* a; // DLL.cpp A* a = new A; So far, so good... I was suggested to use extern rather than static. extern A* a; // in DLL.h No problem with that but the extern variable must be declared somewhere. I got Invalid storage class member. In other words, what I was used to do is to declare a variable in a source file like this: // In src.cpp A a; then extern declare it in another source file in the same project: // In src2.cpp extern A a; so it is the same object a at link time. Maybe it is not the right thing to do? So, where to declare the variable that is now extern? Note that I used static declaration in order to see the variable instantiated as soon as the dll is loaded. Note that the current use of static works most of the time but I think I observe a delay or something like this in the variable instantiation while it should always be instantiated at load time. I'm investigating this problem for a week now and I can't find no solution.

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• MySQL query paralyzes site

  - by nute

  Once in a while, at random intervals, our website gets completely paralyzed. Looking at SHOW FULL PROCESSLIST;, I've noticed that when this happens, there is a specific query that is "Copying to tmp table" for a loooong time (sometimes 350 seconds), and almost all the other queries are "Locked". The part I don't understand is that 90% of the time, this query runs fine. I see it going through in the process list and it finishes pretty quickly most of the time. This query is being called by an ajax call on our homepage to display product recommendations based your browsing history (a la amazon). Just sometimes, randomly (but too often), it gets stuck at "copying to tmp table". Here is a caught instance of the query that was up 109 seconds when I looked: SELECT DISTINCT product_product.id, product_product.name, product_product.retailprice, product_product.imageurl, product_product.thumbnailurl, product_product.msrp FROM product_product, product_xref, product_viewhistory WHERE ( (product_viewhistory.productId = product_xref.product_id_1 AND product_xref.product_id_2 = product_product.id) OR (product_viewhistory.productId = product_xref.product_id_2 AND product_xref.product_id_1 = product_product.id) ) AND product_product.outofstock='N' AND product_viewhistory.cookieId = '188af1efad392c2adf82' AND product_viewhistory.productId IN (24976, 25873, 26067, 26073, 44949, 16209, 70528, 69784, 75171, 75172) ORDER BY product_xref.hits DESC LIMIT 10 Of course the "cookieId" and the list of "productId" changes dynamically depending on the request. I use php with PDO.

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• Concurrent Threads in C# using BackgroundWorker

  - by Jim Fell

  My C# application is such that a background worker is being used to wait for the acknowledgement of some transmitted data. Here is some psuedo code demonstrating what I'm trying to do: UI_thread { TransmitData() { // load data for tx // fire off TX background worker } RxSerialData() { // if received data is ack, set ack received flag } } TX_thread { // transmit data // set ack wait timeout // fire off ACK background worker // wait for ACK background worker to complete // evaluate status of ACK background worker as completed, failed, etc. } ACK_thread { // wait for ack received flag to be set } What happens is that the ACK BackgroundWorker times out, and the acknowledgement is never received. I'm fairly certain that it is being transmitted by the remote device because that device has not changed at all, and the C# application is transmitting. I have changed the ack thread from this (when it was working)... for( i = 0; (i < waitTimeoutVar) && (!bAckRxd); i++ ) { System.Threading.Thread.Sleep(1); } ...to this... DateTime dtThen = DateTime.Now(); DateTime dtNow; TimeSpan stTime; do { dtNow = DateTime.Now(); stTime = dtNow - dtThen; } while ( (stTime.TotalMilliseconds < waitTimeoutVar) && (!bAckRxd) ); The latter generates a very acurate wait time, as compared to the former. However, I am wondering if removal of the Sleep function is interferring with the ability to receive serial data. Does C# only allow one thread to run at a time, that is, do I have to put threads to sleep at some time to allow other threads to run? Any thoughts or suggestions you may have would be appreciated. I am using Microsoft Visual C# 2008 Express Edition. Thanks.

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• Isn't an Iterator in c++ a kind of a pointer?

  - by Bilthon

  Ok this time I decided to make a list using the STL. I need to create a dedicated TCP socket for each client. So everytime I've got a connection, I instantiate a socket and add a pointer to it on a list. list<MyTcp*> SocketList; //This is the list of pointers to sockets list<MyTcp*>::iterator it; //An iterator to the list of pointers to TCP sockets. Putting a new pointer to a socket was easy, but now every time the connection ends I should disconnect the socket and delete the pointer so I don't get a huge memory leak, right? well.. I thought I was doing ok by setting this: it=SocketList.begin(); while( it != SocketList.end() ){ if((*it)->getClientId() == id){ pSocket = it; // <-------------- compiler complains at this line SocketList.remove(pSocket); pSocket->Disconnect(); delete pSocket; break; } } But the compiler is saying this: error: invalid cast from type ‘std::_List_iterator<MyTcp*>’ to type ‘MyTcp*’ Can someone help me here? i thought I was doing things right, isn't an iterator at any given time just pointing to one of the elements of the set? how can I fix it?

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• How to put reminder in Blackberry calendar

  - by anta40

  I need to put several reminders in the BB calendar. The idea is several hours, or days before a promo expires, the alarm will remind it for you. Here's my code so far: long ONE_HOUR = 3600; long ONE_DAY = 24 * 3600; try { EventList eventList = (EventList)PIM.getInstance().openPIMList(PIM.EVENT_LIST, PIM.READ_WRITE); BlackBerryEvent bbEvent = (BlackBerryEvent) eventList.createEvent(); FavoritePromo promo; if (eventList.isSupportedField(BlackBerryEvent.ALARM)){ for (int x = 0; x < promos.size(); x++){ promo = (FavoritePromo) promos.elementAt(x); time = (StringUtil.strToDate(promo.getExpireDate())).getTime() - value; bbEvent.addString(BlackBerryEvent.SUMMARY, BlackBerryEvent.ATTR_NONE, promo.getTitle()); bbEvent.addDate(BlackBerryEvent.ALARM,0,time); bbEvent.commit(); } } } catch (PIMException e){ } Every time i run it, an "IllegalArgumentException" is always thrown. I'm not really sure what goes wrong here...

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• Determing if an unordered vector<T> has all unique elements

  - by Hooked

  Profiling my cpu-bound code has suggested I that spend a long time checking to see if a container contains completely unique elements. Assuming that I have some large container of unsorted elements (with < and = defined), I have two ideas on how this might be done: The first using a set: template <class T> bool is_unique(vector<T> X) { set<T> Y(X.begin(), X.end()); return X.size() == Y.size(); } The second looping over the elements: template <class T> bool is_unique2(vector<T> X) { typename vector<T>::iterator i,j; for(i=X.begin();i!=X.end();++i) { for(j=i+1;j!=X.end();++j) { if(*i == *j) return 0; } } return 1; } I've tested them the best I can, and from what I can gather from reading the documentation about STL, the answer is (as usual), it depends. I think that in the first case, if all the elements are unique it is very quick, but if there is a large degeneracy the operation seems to take O(N^2) time. For the nested iterator approach the opposite seems to be true, it is lighting fast if X[0]==X[1] but takes (understandably) O(N^2) time if all the elements are unique. Is there a better way to do this, perhaps a STL algorithm built for this very purpose? If not, are there any suggestions eek out a bit more efficiency?

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• File name containing more than 16 characters inside parentheses failing

  - by Tom anMoney

  I am generating file names that contain a timestamp in the following format: "base_name (yyyy-mm-dd hhmmss).ext" This seems to cause a problem on Android. Here's my log: /storage/sdcard0/anMoney/transfer/Net worth over time _ Forecast (2012-11-19 110550).pdf E/Gmail (11802): java.io.FileNotFoundException: /storage/sdcard0/myapp/transfer/Net worth over time _ Forecast (2012-11-19 110550).pdf: open failed: ENOENT (No such file or directory) E/Gmail (11802): at libcore.io.IoBridge.open(IoBridge.java:416) E/Gmail (11802): at java.io.FileInputStream.<init>(FileInputStream.java:78) E/Gmail (11802): at java.io.FileInputStream.<init>(FileInputStream.java:105) E/Gmail (11802): at android.content.ContentResolver.openInputStream(ContentResolver.java:445) E/Gmail (11802): at com.google.android.gm.provider.MailEngine.cacheAttachment(MailEngine.java:3054) E/Gmail (11802): at com.google.android.gm.provider.MailEngine.sendOrSaveDraft(MailEngine.java:2746) E/Gmail (11802): at com.google.android.gm.provider.MailProvider.sendOrSaveDraft(MailProvider.java:477) E/Gmail (11802): at com.google.android.gm.provider.MailProvider.insert(MailProvider.java:534) E/Gmail (11802): at android.content.ContentProvider$Transport.insert(ContentProvider.java:201) E/Gmail (11802): at android.content.ContentResolver.insert(ContentResolver.java:864) E/Gmail (11802): at com.google.android.gm.provider.Gmail$MessageModification.sendOrSaveNewMessage(Gmail.java:3576) E/Gmail (11802): at com.google.android.gm.ComposeActivity$SendOrSaveTask$1.onInitializationComplete(ComposeActivity.java:1765) E/Gmail (11802): at com.google.android.gm.provider.MailEngine$5.run(MailEngine.java:1006) E/Gmail (11802): at android.os.Handler.handleCallback(Handler.java:615) E/Gmail (11802): at android.os.Handler.dispatchMessage(Handler.java:92) E/Gmail (11802): at android.os.Looper.loop(Looper.java:137) E/Gmail (11802): at android.os.HandlerThread.run(HandlerThread.java:60) E/Gmail (11802): Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory) Now, if I trim the file name to have only 16 characters within the parentheses, everything is working as expected. I am able to send the file as a GMail attachment. The following file name is working fine: /storage/sdcard0/myapp/transfer/Net worth over time _ Forecast (2012-11-19 11070).pdf I tried the following troubleshooting: It's not the overall length of the file name, as if I shorten the base name, the same behavior remains It's not GMail, uploading the file to Google Drive fails similarly 16 characters inside the parentheses work, but not 17 It's not the space character inside the parentheses that causes the issue, as I replaced it with a dash and it's the same problem. Anybody has any ideas on what's going on here?

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• Android: How to periodically check current location without draining the battery

  - by uyahalom

  I have a background service which works periodically by timer.scheduleAtFixedRate. It wakes up every amount of time (let's say 60 seconds for example) and checks for the location. The location is checked by locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 60000, 5, listener); and the actual location is collected from the listener's onLocationChanged. Now, when the phone is outside and GPS reception is good, this works fine. But, if the phone is inside, the GPS is almost always active - looking for a signal, and the battery is drained rapidly. I created another thread using a Handler and a Runnable in order to conrol the GPS active time accurately: I used locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener); and locManager.removeUpdates(listener); so I can open and close the GPS as I want. In this case, I can open the GPS for the exact amount of time, but found out that it doesn't lock in an area with good reception even after 10 seconds. So here I'm draining the battery again... I'm using API level 7, hence I cannot use locationManager.requestSingleUpdate. I have two questions: Is there any way to optimize this process? Will upgrading to API level 9 (and use locationManager.requestSingleUpdate) improve the process significantly? I mean, does it worth upgrading?

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• Algorithm to determine if array contains n...n+m?

  - by Kyle Cronin

  I saw this question on Reddit, and there were no positive solutions presented, and I thought it would be a perfect question to ask here. This was in a thread about interview questions: Write a method that takes an int array of size m, and returns (True/False) if the array consists of the numbers n...n+m-1, all numbers in that range and only numbers in that range. The array is not guaranteed to be sorted. (For instance, {2,3,4} would return true. {1,3,1} would return false, {1,2,4} would return false. The problem I had with this one is that my interviewer kept asking me to optimize (faster O(n), less memory, etc), to the point where he claimed you could do it in one pass of the array using a constant amount of memory. Never figured that one out. Along with your solutions please indicate if they assume that the array contains unique items. Also indicate if your solution assumes the sequence starts at 1. (I've modified the question slightly to allow cases where it goes 2, 3, 4...) edit: I am now of the opinion that there does not exist a linear in time and constant in space algorithm that handles duplicates. Can anyone verify this? The duplicate problem boils down to testing to see if the array contains duplicates in O(n) time, O(1) space. If this can be done you can simply test first and if there are no duplicates run the algorithms posted. So can you test for dupes in O(n) time O(1) space?

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• How can I read a continuously updating log file in Perl?

  - by Octopus

  I have a application generating logs in every 5 sec. The logs are in below format. 11:13:49.250,interface,0,RX,0 11:13:49.250,interface,0,TX,0 11:13:49.250,interface,1,close,0 11:13:49.250,interface,4,error,593 11:13:49.250,interface,4,idle,2994215 and so on for other interfaces... I am working to convert these into below CSV format: Time,interface.RX,interface.TX,interface.close.... 11:13:49,0,0,0,.... Simple as of now but the problem is, I have to get the data in CSV format online, i.e as soon the log file updated the CSV should also be updated. What I have tried to read the output and make the header is: #!/usr/bin/perl -w use strict; use File::Tail; my $head=["Time"]; my $pos={}; my $last_pos=0; my $current_event=[]; my $events=[]; my $file = shift; $file = File::Tail->new($file); while(defined($_=$file->read)) { next if $_ =~ some filters; my ($time,$interface,$count,$eve,$value) = split /[,\n]/, $_; my $key = $interface.".".$eve; if (not defined $pos->{$eve_key}) { $last_pos+=1; $pos->{$eve_key}=$last_pos; push @$head,$eve; } print join(",", @$head) . "\n"; } Is there any way to do this using Perl?

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• How to get timestamp of tick precision in .NET / C#?

  - by Hermann

  Up until now I used DateTime.Now for getting timestamps, but I noticed that if you print DateTime.Now in a loop you will see that it increments in descrete jumps of approx. 15 ms. But for certain scenarios in my application I need to get the most accurate timestamp possible, preferably with tick (=100 ns) precision. Any ideas? Update: Apparently, StopWatch / QueryPerformanceCounter is the way to go, but it can only be used to measure time, so I was thinking about calling DateTime.Now when the application starts up and then just have StopWatch run and then just add the elapsed time from StopWatch to the initial value returned from DateTime.Now. At least that should give me accurate relative timestamps, right? What do you think about that (hack)? NOTE: StopWatch.ElapsedTicks is different from StopWatch.Elapsed.Ticks! I used the former assuming 1 tick = 100 ns, but in this case 1 tick = 1 / StopWatch.Frequency. So to get ticks equivalent to DateTime use StopWatch.Elapsed.Ticks. I just learned this the hard way. NOTE 2: Using the StopWatch approach, I noticed it gets out of sync with the real time. After about 10 hours, it was ahead by 5 seconds. So I guess one would have to resync it every X or so where X could be 1 hour, 30 min, 15 min, etc. I am not sure what the optimal timespan for resyncing would be since every resync will change the offset which can be up to 20 ms.

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• Mootools Form Post Problem, Abort increasingly+1 with each request

  - by Naresh

  Hi all, i'm using Mootools 1.2. Ihave 15 Forms with same name only change in their id's like form1, form2, form3, ... ,form15 same with their elements. i need to submit all forms by ajax. For that purpos i make a function and call them on each functions onClick event. function is function addStepConfiguration(id,mystrip,comment,error,submitid,i) { $(id).addEvent('submit', function(e) { e.stop(); $(submitid).setStyle('display','none'); loading_Img(i); this.set('send', { onComplete: function(responseText) { $('loading_img'+i).innerHTML = ''; SplittedResText = responseText.split("|"); if(SplittedResText[1]=='undefined') { $(error).innerHTML=SplittedResText[0]; } else { $(comment).innerHTML=SplittedResText[0]; $(mystrip).set('class',SplittedResText[1]); removeMsg.delay(20,'',error); removeMsg.delay(1500,'',comment); } $(submitid).setStyle('display','block'); } }); this.send(); }); } When i submit a form say first one then it submitted and give response normally, but in second time without page refresh, it abort the request one time. in third attempt it abort 2 times..then go on +1 each time. It gives no error, just abort and again request automatically. i can't understand what is the problem. please any one can help me.

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• unbuffered I/O in Linux

  - by stuck

  I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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• VB6 ActiveX exe - what is the proper registration sequence?

  - by Timbuck

  I have recently updated a Visual Basic 6 application that is an ActiveX exe, running on Windows XP. I have a couple of testers for this application who have received a copy of the exe and are attempting to run it. However, they are getting an error message "Unexpected error;quitting" when trying to do so. A key difference between their testing and my testing is that on the machines I tested on, I have admin rights and was able to register the application using the appname.exe /regserver command line. Reading the details at MS Support about file registration appears unclear: Visual Basic ActiveX EXE files register themselves the first time you run the EXE. However, you cannot use the EXE as a COM server until it is registered. So does this mean that after the first time the users run the exe that the application should be correctly registered, and the error I am receiving is sign of something other than an incorrectly registered application? Or does this mean that the application will not work properly until such time as the file is explicitly registered using the appname.exe /regserver command line? nb - during a production distribution, the software would be sent out to client PCs using Systems Management Server, which isn't an option for this testing.

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• How to end a thread in perl

  - by user1672190

  I am new to perl and i have a question about perl thread. I am trying to create a new thread to check if the running function is timed out, and my way of doing it is as below. Logic is 1.create a new thread 2.run the main function and see if it is timed out, if ture, kill it Sample code: $exit_tread = false; # a flag to make sure timeout thread will run my $thr_timeout = threads->new( \&timeout ); execute main function here; $exit_thread = true # set the flag to true to force thread ends $thr_timeout->join(); #wait for the timeout thread ends Code of timeout function sub timeout { $timeout = false; my $start_time = time(); while (!$exit_thread) { sleep(1); last if (main function is executed); if (time() - $start_time >= configured time ) { logmsg "process is killed as request timed out"; _kill_remote_process(); $timeout = true; last; } } } now the code is running as i expected, but i am just not very clear if the code $exit_thread = true works because there is a "last" at the end of while loop. Can anybody give me a answer? Thanks

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• unicode convertion problem

  - by bhoomi-nature

  Hai frnds i am bhoomi new to php,i am having having below problem in my coding please can you help anyone 1.first i want to open one word document which is having content and i wann to edit it 2.for that i am opening word document from the server and at that time its opening with garbage value(i thing its not converting to utf8 format) 3.wen i delete that garbage value and insert something from textarea to that file it is going to insert and next time onwords its its getting open properly. 4.actually i wann that doc file should open with english words wats there in that doc instead of garbage value..first time opening only its giving problem. i am using below code for that please do the needful $filename = 'test.doc'; if(isset($_REQUEST['Submit'])){ $somecontent = stripslashes($_POST['somecontent']); // Let's make sure the file exists and is writable first. if (is_writable($filename)) { // In our example we're opening $filename in append mode. // The file pointer is at the bottom of the file hence // that's where $somecontent will go when we fwrite() it. if (!$handle = fopen($filename, 'w')) { echo "Cannot open file ($filename)"; exit; } // Write $somecontent to our opened file. if (fwrite($handle, $somecontent) === FALSE) { echo "Cannot write to file ($filename)"; exit; } echo "Success, wrote ($somecontent) to file ($filename) - Continue - "; fclose($handle); } else { echo "The file $filename is not writable"; } } else{ // get contents of a file into a string $handle = fopen($filename, 'r'); $somecontent = fread($handle, filesize($filename)); ? Edit file

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• Which of these methods provides for the fastest page loading?

  - by chromedude

  I am building a database in MySQL that will be accessed by PHP scripts. I have a table that is the activity stream. This includes everything that goes on on the website (following of many different things, liking, upvoting etc.). From this activity stream I am going to run an algorithm for each user depending on their activity and display relevant activity. Should I create another table that stores the activity for each user once the algorithm has been run on the activity or should I run the algorithm on the activity table every time the user accesses the site? UPDATE:(this is what is above except rephrased hopefully in an easier to understand way) I have a database table called activity. This table creates a new row every time an action is performed by a user on the website. Every time a user logs in I am going to run an algorithm on the new rows (since the users last login) in the table (activity) that apply to them. For example if the user is following a user who upvoted a post in the activity stream that post will be displayed when the user logs in. I want the ability for the user to be able to access previous content applying to them. Would it be easiest to create another table that saved the rows that have already been run over with the algorithm except attached to individual users names? (a row can apply to multiple different users)

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• How do I determine when two moving points become visible to each other?

  - by Devin Jeanpierre

  Suppose I have two points, Point1 and Point2. At any given time, these points may be at different positions-- they are not necessarily static. Point1 is located at some position at time t, and its position is defined by the continuous functions x1(t) and y1(t) giving the x and y coordinates at time t. These functions are not differentiable, they are constructed piecewise from line segments. Point2 is the same, with x2(t) and y2(t), each function having the same properties. The obstacles that might prevent visibility are simple (and immobile) polygons. How can I find the boundary points for visibility? i.e. there are two kinds of boundaries: where the points become visible, and become invisible. For a become-visible boundary i, there exists some ?0, such that for any real number a, a ? (i-?, i) , Point1 and Point2 are not visible (i.e. the line segment that connects (x1(a), y1(a)) to (x2(a), y2(x)) crosses some obstacles). For b ? (i, i+?) they are visible. And it is the other way around for becomes-invisible. But can I find such a precise boundary, and if so, how?

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• sql queries slower than expected

  - by neubert

  Before I show the query here are the relevant table definitions: CREATE TABLE phpbb_posts ( topic_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, poster_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, KEY topic_id (topic_id), KEY poster_id (poster_id), ); CREATE TABLE phpbb_topics ( topic_id mediumint(8) UNSIGNED NOT NULL auto_increment ); Here's the query I'm trying to do: SELECT p.topic_id, p.poster_id FROM phpbb_topics AS t LEFT JOIN phpbb_posts AS p ON p.topic_id = t.topic_id AND p.poster_id <> ... WHERE p.poster_id IS NULL; Basically, the query is an attempt to find all topics where the number of times someone other than the target user has posted in is zero. In other words, the topics where the only person who has posted is the target user. Problem is that query is taking a super long time. My general assumption when it comes to SQL is that JOINs of any are super fast and can be done in no time at all assuming all relevant columns are primary or foreign keys (which in this case they are). I tried out a few other queries: SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id; That returns 353340 pretty quickly. I then do these: SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id AND p.poster_id <> 77198; SELECT COUNT(1) FROM phpbb_topics AS t JOIN phpbb_posts AS p ON p.topic_id = t.topic_id WHERE p.poster_id <> 77198; And both of those take quite a while (between 15-30 seconds). If I change the < to a = it takes no time at all. Am I making some incorrect assumptions? Maybe my DB is just foobar'd?

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• C++ Iterator Pipelining Designs

  - by Kirakun

  Suppose we want to apply a series of transformations, int f1(int), int f2(int), int f3(int), to a list of objects. A naive way would be SourceContainer source; TempContainer1 temp1; transform(source.begin(), source.end(), back_inserter(temp1), f1); TempContainer2 temp2; transform(temp1.begin(), temp1.end(), back_inserter(temp2), f2); TargetContainer target; transform(temp2.begin(), temp2.end(), back_inserter(target), f3); This first solution is not optimal because of the extra space requirement with temp1 and temp2. So, let's get smarter with this: int f123(int n) { return f3(f2(f1(n))); } ... SourceContainer source; TargetContainer target; transform(source.begin(), source.end(), back_inserter(target), f123); This second solution is much better because not only the code is simpler but more importantly there is less space requirement without the intermediate calculations. However, the composition f123 must be determined at compile time and thus is fixed at run time. How would I try to do this efficiently if the composition is to be determined at run time? For example, if this code was in a RPC service and the actual composition--which can be any permutation of f1, f2, and f3--is based on arguments from the RPC call.

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• Updating a C# 2.0 events example to be idiomatic with C# 3.5?

  - by Damien Wildfire

  I have a short events example from .NET 2.0 that I've been using as a reference point for a while. We're now upgrading to 3.5, though, and I'm not clear on the most idiomatic way to do things. How would this simple events example get updated to reflect idioms that are now available in .NET 3.5? // Args class. public class TickArgs : EventArgs { private DateTime TimeNow; public DateTime Time { set { TimeNow = value; } get { return this.TimeNow; } } } // Producer class that generates events. public class Metronome { public event TickHandler Tick; public delegate void TickHandler(Metronome m, TickArgs e); public void Start() { while (true) { System.Threading.Thread.Sleep(3000); if (Tick != null) { TickArgs t = new TickArgs(); t.Time = DateTime.Now; Tick(this, t); } } } } // Consumer class that listens for events. public class Listener { public void Subscribe(Metronome m) { m.Tick += new Metronome.TickHandler(HeardIt); } private void HeardIt(Metronome m, TickArgs e) { System.Console.WriteLine("HEARD IT AT {0}",e.Time); } } // Example. public class Test { static void Main() { Metronome m = new Metronome(); Listener l = new Listener(); l.Subscribe(m); m.Start(); } }

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• Can a second stored procedure doing the same thing finish before first one?

  - by evanmortland

  Hello, I have an audit record table that I am writing to. I am connecting to MyDb, which has a stored procedure called 'CreateAudit', which is a passthrough stored procedure to another database on the same machine called 'CreatedAudit' as well. I call the CreateAudit stored procedure from my application, using subsonic as the DAL. The first time I call it, I call it with the following (pseudocode): Result = CreateAudit(recordId, "Opened") Right after that, I call: Result2 = CreateAudit(recordId, "Closed") In my second stored procedure it is supposed to mark the record that was created by the CreateAudit(recordId, "Opened") with a status of closed. It works great if I run them independently of one another, but when they run in sequence in the application, the record is not marked as "Closed". When I run SQL profiler I see that both queries ran, and if I copy the queries out and run them from query analyzer the record gets marked as closed 100% of the time! When I run it from the application, about once every 20 times or so, the record is successfully marked closed - the other 19 times nothing happens, but I do not get an error! Is it possible for the .NET app to skip over the ouput from the first stored procedure and start executing the second stored procedure before the record in the first is created? When I add a "WAITFOR DELAY '00:00:00:003'" to the top of my stored procedure, the record is also closed 100% of the time. My head is spinning, any ideas why this is happening! Thanks for any responses, very interested in hearing how this can happen.

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• Can't open COM1 from application launched at startup

  - by n0rd

  I'm using WinLIRC with IR receiver connected to serial port COM1 on Windows 7 x64. WinLIRC is added to Startup folder (Start-All applications-Startup) so it starts every time I log in. Very often (but not all the time) I see initialization error messages from WinLIRC, which continue for some time (couple of minutes) if I retry initialization, and after some retries it initializes correctly and works fine. If I remove it from Startup and start manually at any other moment it starts without errors. I've downloaded WinLIRC sources and added MessageBox calls here and there so I can see what happens during initialization and found out that CreateFile call fails: if((hPort=CreateFile( settings.port,GENERIC_READ | GENERIC_WRITE, 0,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0))==INVALID_HANDLE_VALUE) { char buffer[256]; sprintf_s(buffer, "CreateFile(%s) failed with %d", settings.port, GetLastError()); MessageBox(NULL, buffer, "debug", MB_OK); hPort=NULL; return false; } I see message box saying "CreateFile(COM1) failed with 5", and 5 is an error code for "Access denied" error according to this link. So the question is why opening COM-port can fail with such error right after booting Windows and proceed normally few seconds or minutes later?

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