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• Getting deadlocks in MySQL

  - by at

  We're very frustratingly getting deadlocks in MySQL. It isn't because of exceeding a lock timeout as the deadlocks happen instantly when they do happen. Here's the SQL code that is executing on 2 separate threads (with 2 separate connections from the connection pool) that produces a deadlock: UPDATE Sequences SET Counter = LAST_INSERT_ID(Counter + 1) WHERE Sequence IS NULL Sequences table has 2 columns: Sequence and Counter The LAST_INSERT_ID allows us to retrieve this updated counter value as per MySQL's recommendation. That works perfect for us, but we get these deadlocks! Why are we getting them and how can we avoid them?? Thanks so much for any help with this.

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• Why Do try ... catch Blocks Require Braces?

  - by Bidou

  Hello. While in other statements like if ... else you can avoid braces if there is only one instruction in a block, you cannot do that with try ... catch blocks: the compiler doesn't buy it. For instance: try do_something_risky(); catch (...) std::cerr << "Blast!" << std::endl; With the code above, g++ simply says it expects a '{' before do_something_risky(). Why this difference of behavior between try ... catch and, say, if ... else ? Thanks!

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• What does a mercurial revision with no parent mean?

  - by Wilka

  I have a Mercurial repository that is in a strange state now. This is what it looks like in TortoiseHG: I didn't think this would be possible. Revision 54 has a parent of "-1 (000000000000)" (i.e. nothing). There's clearly something I don't understand yet about Mercurial, can anyone let me know what this means - and what must have happened for it to get into this state. As far as I know, it's only had stuff pushed and pulled from it - and nobody has been using any wacky extensions. Revisions 54 and 55 were just adding tags, but if I 'update -C' to revision 54 I end up with ONLY the .hgtags file. I've made a clone from revision 53 to fix this. But I'd rather understand what happened here, so I can avoid it happening again.

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• Facebook login within an iframe (but outside FB)

  - by Cystack

  At some point in my application, I use an iframe. In this iframe, some Facebook stuff could be useful and for that, I use the graph API a lot. Problem is : when someone isn't logged in to facebook or hasn't allowed my application yet, they are prompted to click the "connect with facebook" button. But as soon as they click it, the iframe gets destroyed and the top page is replaced with the Facebook login page. Eventually the top page is redireccted to the previous iframe URL, but the former parent page is lost forever. Is this the intended behaviour of FB connect ? Is there a way to avoid it or to hack around it ? (maybe using a popup instead of an iframe, but that sounds ugly (uglier than an iframe)). I am currently using the PHP SDK Thanks a lot

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• nested has_many

  - by Nick Vanderbilt

  I am using Rails 2.3.5. Class User < ActiveRecord::Base has_many :phones end class Phone < ActiveRecord::Base has_many :frequency_bands end I want to get all the frequency_bands for a user. I know I can write a method def freq_bands for User but I would like to know if it is possible to have has_many freq_bands for a User. In this way I can chain the call. What I would like to have is class User < ActiveRecor::Base has_many :frequence_bands, :through => phones end I think it is possible to have nested has_many using this plugin http://github.com/ianwhite/nested_has_many_through However if possible I would like to avoid using another plugin and rely solely on rails.

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• access a property via string with array in php?

  - by sprugman

  (This is in drupal, but I don't really think that matters.) I have a big list of properties that I need to map between two objects, and in one, the value that I need to map is buried inside an array. I'm hoping to avoid hard-coding the property names in the code. If I have a class like this: class Product { public $colors, $sizes; } I can access the properties like this: $props = array('colors', 'sizes'); foreach ($props as $p) { $this->$p = $other_object->$p; } As far as I can tell, if each of the properties on the left are an array, I can't do this: foreach ($props as $p) { $this->$p[0]['value'] = $other_object->$p; } Is that correct, or am I missing some clever way around this?

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• CSS: reposition element on hover state but maintain clickable area position

  - by abirduphigh

  I'm trying to create the effect of a button that 'lifts' from the page when rolled over. Using CSS, I have a block style <a> element that, when hovered, re-positions itself up and to the left 5px, and a shadow is left behind: a { display: inline-block; position: relative; } a:hover { top: -5px; left: -5px; box-shadow: rgba(0,0,0,.2) 5px 5px 2px; } The problem: When the <a> block jumps 5px away from the cursor during the hover, the cursor is no longer actually hovering over the block and the block then jumps back when the cursor is moved only slightly thereafter. How can I maintain the original hover area so that the element doesn't keep jumping back and forth when the cursor is only slightly moved? I'd like to avoid adding superfluous container elements to my code if at all possible.

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• Get a property value with only the object and the name of the property (but not the type)

  - by Vaccano

  Suppose I have a method that passes in the name of a property (as a string) and the object that the property is on (as object). How could I get the value of the property? Here is some code to make it a bit more concrete: protected override void Paint(Graphics g, Rectangle bounds, CurrencyManager source, int rowNum, Brush backBrush, Brush foreBrush, bool alignToRight) { // The next line is made up code var currentValue = source.Current.CoolMethodToTakePropertyNameAndReturnValue(MappingName); // Paint out the retrieved value g.DrawString(currentValue.ToString() , _gridFont, new SolidBrush(Color.Black), bounds.Left + 1, bounds.Top); } MappingName is the name of the property I want to get the value for. What I need is CoolMethodToTakePropertyNameAndReturnValue. Any ideas? I am running on the Compact Framework. I would also prefer to avoid reflection (but if that is my only recourse then so be it). Thanks for any help.

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• Make SQL query more efficient

  - by Webnet

  I currently have this query which runs 2 of the exact same sub queries but pull different data. When I make the values comma separated it throws an SQL error saying the sub query can return only one value. Is there anything else I can do to avoid running multiple sub queries? SELECT product_id, ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id) as listing_count, sku, type_id, ( SELECT AVG(ebay_archive_listing.current_price), AVG(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing WHERE id IN ( SELECT listing_id FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id ) AND ebay_archive_listing.start_time >= '.$startTimestamp.' AND ebay_archive_listing.start_time <= '.$endTimestamp.' AND ebay_archive_listing.current_price > 0 ) as average_bid_price, ( SELECT FROM ebay_archive_listing WHERE id IN ( SELECT listing_id FROM ebay_archive_product_listing_assoc WHERE product_id = product_master.product_id ) AND ebay_archive_listing.start_time >= '.$startTimestamp.' AND ebay_archive_listing.start_time <= '.$endTimestamp.' AND ebay_archive_listing.buy_it_now_price > 0 ) as average_buyout_price FROM product_master I'm aware of the syntax error... I'm selecting 2 seperate averages and am wondering if I can do it any simpler way.

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• Does C# 4's covariance support nesting of generics?

  - by Scott Bilas

  I don't understand why 'x' below converts, but 'y' and 'z' do not. var list = new List<List<int>>(); IEnumerable<List<int>> x = list; List<IEnumerable<int>> y = list; IEnumerable<IEnumerable<int>> z = list; Does the new covariance feature simply not work on generics of generics or am I doing something wrong? (I'd like to avoid using .Cast< to make y and z work.)

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• How to manage memory for ios with large csv files?

  - by Pell000

  I'm new to ios development, and I'm running into issues relating to memory management and my approaches to dealing with large datasets. Right now, I am loading the csv files and storing the relevant data as objects in memory at app initialization. Some of the csv files are larger than 1MB, and in total, my app uses about 180MB of memory. This is obviously way too high of a number (unless the info I found is wrong and this is an acceptable number, then please let me know). I feel as though there is a fundamental flaw in my approach: is there a way I can avoid storing the csv files in the project itself? Or, is there a kind of "lazy" loading I can do so that I can simply look up info in the csv file, as opposed to loading all of the data from it at once? Any help would do. I think that I need a new perspective in how to manage this more efficiently.

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• Simplifying CASE WHEN SQL statement

  - by kateroh

  Im trying to improve the following CASE statement to calculate the difference only once. I do it to avoid negative numbers: SELECT (CASE WHEN ((SELECT 100 - (SELECT COUNT(CustomerId) FROM Customers)) > 0) THEN (SELECT 100 - (SELECT COUNT(CustomerId) FROM Customers)) ELSE (0) END) This not only looks stupid, but also is not thread-safe. I tried the following, but I get an error message "Invalid column name 'diff'." SELECT (CASE WHEN ((SELECT 100 - (SELECT COUNT(CustomerId) FROM Customers) as diff) > 0) THEN (diff) ELSE (0) END) How can this be simplified? Is there an in-built SQL function that already does this job? EDIT: Sorry, forgot to mention that the select statement is inside of a view declaration, so I cant declare variables.

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• XCode Project Code Changes Not Updating 100% After Save-Build-Run

  - by Greg

  When I make code changes to my iPhone game project in XCode, and then do CMD-B + Enter, I expect the project to be saved, build and run on the simulator with the latest. What is happening though, sometimes, is that it doesn't pick up a small change I make unless I clean the project and then build. I'm a long time Java person and newish to C-based languages and it's compiler. Can someone explain to me what is cached after each build that does this and how to change my project settings to avoid having to clean everytime? Or tell me the bad news that this is part of C development? Not trying to bash it - I get compiled JSPs stuck in the working cache often in Java, too. :P

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• Is it OK to have HTML tags inside an array (is there risk of hacking)?

  - by janoChen

  I have the following array: 'tagline_p' => "I'm a <a href='#showcase'>multilingual web</a> developer, designer and translator. I'm here to <a href='#contact'>help you</a> reach a worldwide audience.", Should I escape the HTML tags inside the array to avoid hackings to my site? (How to escape them?) or is OK to have HTML tags inside an array?

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• Select distinct ... inner join vs. select ... where id in (...)

  - by Tonio

  I'm trying to create a subset of a table (as a materialized view), defined as those records which have a matching record in another materialized view. For example, let's say I have a Users table with user_id and name columns, and a Log table, with entry_id, user_id, activity, and timestamp columns. First I create a materialized view of the Log table, selecting only those rows with timestamp some_date. Now I want a materliazed view of the Users referenced in my snapshot of the Log table. I can either create it as select * from Users where user_id in (select user_id from Log_mview), or I can do select distinct u.* from Users u inner join Log_mview l on u.user_id = l.user_id (need the distinct to avoid multiple hits from users with multiple log entries). The former seems cleaner and more elegant, but takes much longer. Am I missing something? Is there a better way to do this?

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• memory management question -- releasing an object which has to be returned

  - by ulag

  Hi, I have an NSMutableArray called playlist. This is in a method called getAllPlaylists. The code is something like this: -(NSMutableArray *)getAllPlaylists { //playlist is an instance variable playlist = [[NSMutableArray alloc] init]; //memory leak here . . //some code here which populates the playlist array [playlist addObject: object1]; . . return playlist; } The array allocation step of playlist is causing a memory leak. In such a scenario where can i release this array? Or can i avoid allocation n initialization of playlist here by doing something else?

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• how to use javascript to download a file on Chrome without Chrome auto renaming file to "download"? [duplicate]

  - by user3688566

  This question already has an answer here: Is there any way to specify a suggested filename when using data: URI? 11 answers I use javascript to generate a file and download. It seems that depending on the version of chrome, the download file names can be auto renamed to 'download'. is there a way to avoid it? this is my code: var link = document.createElement("a"); link.setAttribute("href", 'data:application/octet-stream,' + 'file content here'); link.setAttribute("download", 'file1.txt'); link.click(); This is not a duplicated question because i am using the latest chrome and the previously suggested hyperlink is exactly what i am using. I think chrome v34 works fine. but once my chrome autoupdated to v35, it went back to 'download' file name.

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• C#: Using as bool? instead of object something = ViewState["hi"]

  - by Programmin Tool

  So I'm going through old code (2.0) and I came across this: object isReviewingValue = ViewState["IsReviewing"]; if (isReviewingValue is bool) { return (bool)isReviewingValue; } My first thought was to us the "as" keyword to avoid the unneeded (bool)isReviewingValue; But "as" only works with non value types. No problem, I just went ahead and did this: bool? isReviewingValue= ViewState["IsReviewing"] as bool?; if (isReviewingValue.HasValue) { return isReviewingValue.Value; } Question is: Besides looking a bit more readable, is this in fact better?

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• iOS: Releasing Object Thats In Use (ARC)

  - by RileyE

  I have an object that I have created that subscribes to some NSNotificationCenter notifications, but it is being released, since I don't have a pointer to the instantiation. The instantiation has a delegate that will call a method back to another class I have, so I felt it unnecessary to also have a pointer to it, since the pointer doesn't serve any purpose. Basically, I have an instantiation of a class, DelegateListener (name is just for example purposes), which subscribes to some of the default NSNotificationCeneter's notifications. This instantiation isn't assigned to any pointer after the instantiation ends. The instantiation, however, has a property, delegate. I assign a value to that delegate during the instantiation. That delegate implements methods that I want the DelegateListener to call when the notifications that it subscribed to fire. The problem with this is that the instantiation of DelegateListener that I create gets released, unless if I assign it to a retained pointer. Is there a way to avoid this automatic release of my DelegateListener instantiation within ARC?

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• C++ vector that *doesn't* initialize its members?

  - by Mehrdad

  I'm making a C++ wrapper for a piece of C code that returns a large array, and so I've tried to return the data in a vector<unsigned char>. Now the problem is, the data is on the order of megabytes, and vector unnecessarily initializes its storage, which essentially turns out to cut down my speed by half. How do I prevent this? Or, if it's not possible -- is there some other STL container that would avoid such needless work? Or must I end up making my own container? (Pre-C++11) Note: I'm passing the vector as my output buffer. I'm not copying the data from elsewhere.

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• Shoud a method that waits for a change of state be const?

  - by Space_C0wb0y

  In a multithreaded scenario, I have a method like this: bool WaitForChange( time_duration WaitTime ) const; This method waits either until the state of the object has changed and returns true, or until the timeout times out (how do you say that?) and returns false. My intuition is, that const is to protect against unwanted side-effects of the method itself, so this is fine. But then again, some user might think that the state of the could not have changed, since the method is declared const. Is that user stupid, or should I make the method non-const in order to avoid confusion?

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• Why do dicts of defaultdict(int)'s use so much memory? (and other simple python performance question

  - by dukhat

  import numpy as num from collections import defaultdict topKeys = range(16384) keys = range(8192) table = dict((k,defaultdict(int)) for k in topKeys) dat = num.zeros((16384,8192), dtype="int32") print "looping begins" #how much memory should this use? I think it shouldn't use more that a few #times the memory required to hold (16384*8192) int32's (512 mb), but #it uses 11 GB! for k in topKeys: for j in keys: dat[k,j] = table[k][j] print "done" What is going on here? Furthermore, this similar script takes eons to run compared to the first one, and also uses an absurd quantity of memory. topKeys = range(16384) keys = range(8192) table = [(j,0) for k in topKeys for j in keys] I guess python ints might be 64 bit ints, which would account for some of this, but do these relatively natural and simple constructions really produce such a massive overhead? I guess these scripts show that they do, so my question is: what exactly is causing the high memory usage in the first script and the long runtime and high memory usage of the second script and is there any way to avoid these costs?

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• nested has_many

  - by dorelal

  I am using Rails 2.3.5. Class User < ActiveRecord::Base has_many :phones end class Phone < ActiveRecord::Base has_many :frequency_bands end I want to get all the frequency_bands for a user. I know I can write a method def freq_bands for User but I would like to know if it is possible to have has_many freq_bands for a User. In this way I can chain the call. What I would like to have is class User < ActiveRecor::Base has_many :frequence_bands, :through => phones end I think it is possible to have nested has_many using this plugin http://github.com/ianwhite/nested_has_many_through However if possible I would like to avoid using another plugin and rely solely on rails.

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• How can a Perl force its caller to return? [closed]

  - by JS Bangs

  Possible Duplicate: Is it possible for a Perl subroutine to force its caller to return? I want to write a subroutine which causes the caller to return under certain conditions. This is meant to be used as a shortcut for validating input to a function. What I have so far is: sub needs($$) { my ($condition, $message) = @_; if (not $condition) { print "$message\n"; # would like to return from the *parent* here } return $condition; } sub run_find { my $arg = shift @_; needs $arg, "arg required" or return; needs exists $lang{$arg}, "No such language: $arg" or return; # etc. } The advantage of returning from the caller in needs would then be to avoid having to write the repetitive or return inside run_find and similar functions.

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• C++ Reading and Editing pixels of a bitmap image

  - by BettyD

  I'm trying to create a program which reads an image in (starting with bitmaps because they're the easiest), searches through the image for a particular parameter (i.e. one pixel of (255, 0, 0) followed by one of (0, 0, 255)) and changes the pixels in some way (only within the program, not saving to the original file.) and then displays it. I'm using Windows, simple GDI for preference and I want to avoid custom libraries just because I want to really understand what I'm doing for this test program. Can anyone help? In any way? A website? Advice? Example code? Thanks

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