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• Java concurrency - Should block or yield?

  - by teto

  Hi, I have multiple threads each one with its own private concurrent queue and all they do is run an infinite loop retrieving messages from it. It could happen that one of the queues doesn't receive messages for a period of time (maybe a couple seconds), and also they could come in big bursts and fast processing is necessary. I would like to know what would be the most appropriate to do in the first case: use a blocking queue and block the thread until I have more input or do a Thread.yield()? I want to have as much CPU resources available as possible at a given time, as the number of concurrent threads may increase with time, but also I don't want the message processing to fall behind, as there is no guarantee of when the thread will be reescheduled for execution when doing a yield(). I know that hardware, operating system and other factors play an important role here, but setting that aside and looking at it from a Java (JVM?) point of view, what would be the most optimal?

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• Adding characters to string

  - by Jamza

  I am currently trying to build a very basic serial shell with my arduino. I am able to get an output from the device using Serial.read() and can get the character it has outputted, but I cannot work out how to then add that character to a longer to form the full command. I tried the logical thing but it doesn't work: char Command[]; void loop(){ if(Serial.available() > 0){ int clinput = Serial.read(); Command = Command + char(clinput); } Can anybody help? Thank You.

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• Queues And Wait Handles in C#

  - by Michael Covelli

  I've had the following code in my application for some years and have never seen an issue from it. while ((PendingOrders.Count > 0) || (WaitHandle.WaitAny(CommandEventArr) != 1)) { lock (PendingOrders) { if (PendingOrders.Count > 0) { fbo = PendingOrders.Dequeue(); } else { fbo = null; } } // Do Some Work if fbo is != null } Where CommandEventArr is made up of the NewOrderEvent (an auto reset event) and the ExitEvent (a manual reset event). But I just realized today that its not thread safe at all. If this thread gets interrupted right after the first (PendingOrder.Count 0) check has returned false. And then the other thread both enqueues an order and sets the NewOrderEvent before I get a chance to wait on it, the body of the while loop will never run. What's the usual pattern used with a Queue and an AutoResetEvent to fix this and do what I'm trying to do with the code above?

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• How to identify each parameter type in a C# method?

  - by user465876

  I have a C# method say: MyMethod(int num, string name, Color color, MyComplexType complex) Using reflection, how can I distinctly identify each of the parameter types of any method? I want to perform some task by parameter type. If the type is simple int, string or boolean then I do something, if it is Color, XMLDocument, etc I do something else and if it is user defined type like MyComplexType or MyCalci etc then I want to do certain task. I am able to retrieve all the parameters of a method using ParameterInfo and can loop through each parameter and get their types. But how can I identify each data type? foreach (var parameter in parameters) { //identify primitive types?? //identify value types //identify reference types } Edit: this is apart of my code to create a propert grid sort of page where I want to show the parameter list with data types for the selected method. If the parameter has any userdefined type/reference type then I want to expand it further to show all the elements under it with datatypes.

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• Parsing timestamps - do it in MySQL or in PHP?

  - by Andrew Heath

  Let's say you've got a table with a timestamp column, and you want to parse that column into two arrays - $date and $time. Do you, personally: a) query like this DATE(timestamp), TIME(timestamp) , or perhaps even going as far as HOUR(timestamp), MINUTE(timestamp b) grab the timestamp column and parse it out as needed with a loop in PHP I feel like (a) is easier... but I know that I don't know anything. And it feels a little naughty to make my query hit the same column 2 or 3 times for output... Is there a best-practice for this?

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• get look up a string given a func<T,object> param

  - by Sammy

  given this code namespace GridTests { public class Grid<T> { IEnumerable<T> DataSource { get; set; } IList<Column> Columns = new List<Column>(); class Column { public string DisplayText { get; set; } Func<T, object> Rowdata { get; set; } } } } I need to be able to loop through the columns collection and get the Rowdata's object value using the DisplayText. Thanks

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• Difference between local and instance variables in ruby

  - by fflyer05

  I am working on a script that creates several fairly complex nested hash datastructures and then iterates through them conditionally creating database records. This is a standalone script using active record. After several minutes of running I noticed a significant lag in server responsiveness and discovered that the script, while being set to be nice +19, was enjoying a steady %85 - %90 total server memory. In this case I am using instance variables simply for readability. It helps knowing what is going to be re-used outside of the loop vs. what won't. Is there a reason to not use instance variables when they are not needed? Are there differences in memory allocation and management between local and instance variables? Would it help setting @variable = nil when its no longer needed?

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• How to assign variable dynamically to php list function

  - by ravisoni

  What I am doing that I want to generate a list based on how many items are in an array, so I have counted the items and loop over them, create a number based var and construct a string $var which contains $a1,$a2.... and assigns the $var to list list($var) and tried to access $a1 but it gives me the error "Undefined variable: a1" Is there any other way to do it? Here is my code: $arr = array('1','2','3'); $listsize = count($arr); $var=''; for($i=1;$i<=$listsize;$i++){ $var.='$a'.$i; if($i!=$listsize){ $var.=','; } } list($var) = $arr; echo $a1;

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• RoR: Condition Always False - Why?

  - by Matt Hollingsworth

  Working in RoR 2.3.x. My quiz_results table has a row for user_id (3907) and result (0.1), and two users I'm looking at with no rows in the quiz_results table. This line keeps returining false: -if QuizResult.find_by_user_id(@user_id).present? But if I change it to anything that returns true, the next line reports an error on the * method: ="#{(QuizResult.average('score', :conditions => 'user_id = #{@user.id}') * 100).round}%" The beginning of the code is a loop: [email protected] do |user| Any ideas how to fix? Have tried unsuccessfully all day.

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• Shall I optimize or let compiler to do that?

  - by Knowing me knowing you

  What is the preferred method of writing loops according to efficiency: Way a) /*here I'm hoping that compiler will optimize this code and won't be calling size every time it iterates through this loop*/ for (unsigned i = firstString.size(); i < anotherString.size(), ++i) { //do something } or maybe should I do it this way: Way b) unsigned first = firstString.size(); unsigned second = anotherString.size(); and now I can write: for (unsigned i = first; i < second, ++i) { //do something } the second way seems to me like worse option for two reasons: scope polluting and verbosity but it has the advantage of being sure that size() will be invoked once for each object. Looking forward to your answers.

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• Minimizing distance to a weighted grid

  - by Andrew Tomazos - Fathomling

  Lets suppose you have a 1000x1000 grid of positive integer weights W. We want to find the cell that minimizes the average weighted distance.to each cell. The brute force way to do this would be to loop over each candidate cell and calculate the distance: int best_x, best_y, best_dist; for x0 = 1:1000, for y0 = 1:1000, int total_dist = 0; for x1 = 1:1000, for y1 = 1:1000, total_dist += W[x1,y1] * sqrt((x0-x1)^2 + (y0-y1)^2); if (total_dist < best_dist) best_x = x0; best_y = y0; best_dist = total_dist; This takes ~10^12 operations, which is too long. Is there a way to do this in or near ~10^8 or so operations?

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• JQuery get height of each previous element

  - by Jk_

  I'm trying to find a good solution to get the height of all the element above my target. So loop the prev() function ! Any ideas on how I could deal with that ? <div> <div style="height:50px;width:100%"></div> <div style="height:12px;width:100%"></div> <div style="height:23px;width:100%"></div> <div style="height:56px;width:100%"></div> <div id="#mytarget"><p>HERE</p></div> </div> $('#mytarget').prev().each(function() { alert($(this).outerHeight()); }); and it will fires ["56","23","12","50"].

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• dabbledb + iPhone

  - by user193545

  I have been using DabbbleDB online database for storing/retrieving values for one of my iPhone applications. I am using their JSON response for retrieving the records. The problem that I am facing is that if there are a large number of records in the database, it takes a long time to get the response from the server and then to parse the JSON response. Instead I would like to to get a set of records at a time and run a loop to fetch all the records in background. I do not know whether we can query for a set of records at a time from online databases like DabbleDB. Anybody having an idea, please help.

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• Any way to break if statement in PHP?

  - by Usman

  Is there any command in PHP to stop executing the current or parent if statement, same as break or break(1) for switch/loop. For example $arr=array('a','b'); foreach($arr as $val) { break; echo "test"; } echo "finish"; in the above code PHP will not do echo "test"; and will go to echo "finish"; I need this for if $a="test"; if("test"==$a) { break; echo "yes"; // I don't want this line or lines after to be executed, without using another if } echo "finish"; I want to break the if statement above and stop executing echo "yes"; or such codes which are no longer necessary to be executed, there may be or may not be an additional condition, is there way to do this?

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• How to do something after effect animation ends in Flex?

  - by Chobicus

  I'm a beginner in Flex so there must be more elegant way of doing this. //move effect private var m:Move = new Move(); //this function creates labels with some text and starts move effect on them public function moveText(i:int):void { var myLabel:Label = new Label(); myLabel.text = "some text"; m.target = myLabel; ... m.play(); } Method moveText is called in a loop so I guess that labels don't get "garbage collected". What I want to do is to remove Labels created in moveText method after play animation ends. Another way of doing this is maybe creating some kind of "pool" of labels which I would use to move arround text. I don't know how would I return labels in to "pool". The question is how to do something after effect animation ends?

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• Birthday effect - clarification needed plz.

  - by Mark

  Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: 1) Pick any message m and compute h(m). 2) Update list L. Check if h(m) is in the list L. 3) if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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• PHP from database and query

  - by Kyle R

  I have a table: id, affiliate Each time somebody clicks a link, a new row is inserted, ID being the ID of the page, and affiliate being the ID of the affiliate. For example: Page ID: 9 Affiliate ID: 1 Page ID: 9 Affiliate ID: 2 Page ID: 9 Affiliate ID: 3 I only have 3 affiliates. I want to select this information, and group them by affiliate, for the ID. I have tried this query: SELECT COUNT(*) FROM table WHERE id = '9' GROUP BY affiliate It works fine when I do it in php my admin, how do I get the info in PHP? I have tried: $q = mysql_query("SELECT COUNT(*) FROM table WHERE id = '" . $id . "' GROUP BY affiliate"); $r = mysql_fetch_array($q); When trying to print the data onto the page, I am only getting one result. Do I need to use a foreach/while loop to get all 3? How would I go about doing this? Thank you!

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• Ojective C Class or struct?

  - by Scott Pendleton

  I have a class Song with properties Title, Key, Artist, etc. There are no methods. I loop through a database of song information and create a Song object for each, populating the properties, and then store the Song objects in an NSArray. Then I thought, why not just have a struct Song with all those same properties instead of a class Song. Doing so would eliminate the class files, the #import Song line in the using class's .m file, and the need to alloc, init, release. On the other hand, I'd have to put the struct definition in every class that might need it. (Unless there's some globally accessible location -- is there?) Also, can a struct be stored in an NSArray?

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• How to initialize std::vector from C-style array?

  - by dehmann

  What is the cheapest way to initialize a std::vector from a C-style array? Example: In the following class, I have a vector, but due to outside restrictions, the data will be passed in as C-style array: class Foo { std::vector<double> w_; public: void set_data(double* w, int len){ // how to cheaply initialize the std::vector? } Obviously, I can call w_.resize() and then loop over the elements, or call std::copy(). Are there any better methods?

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• Create MVC 5 Combo Box from CRM Entities?

  - by SpaceCowboy74

  I am working on an MVC 5 App that pulls data from Dynamics CRM 5. The Data I am getting back is an IQueryable of type Account (The CRM Entity class auto generated by CrmSvcUtil). I am retrieving all of the items and can loop through them with code like this: @foreach (var item in Model.ToList()) { <tr> <td> @item.AccountId </td> <td> @Html.DisplayFor(modelItem => item.Name) </td> </tr> } The problem is, I would like to instead put them in a drop down list. I can't figure out what the syntax is to put these in a DropDown is. Any suggestions?

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• Visual Basic 2013 String Replacement

  - by user3707612

  I found this code that replaces a string in a text file. But, I am trying to make it so that it replaces several strings in a text file. My.Computer.FileSystem.WriteAllText("C:\windows\PrinterList2.txt", My.Computer.FileSystem.ReadAllText("C:\windows\PrinterList.txt").Replace("IT", "ADM-IT"), False) For example, I need it to replace "IT" with "ADM-IT" and "AR" with "ADM-AR" and possibly a hundred or so more. How can I get it to loop to do them all? Running this line of code over and over just overwrites the file with the last item for replacement. Thanks in advance.

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• Implementing an iterator over binary tree using C++ 11

  - by user1459339

  I would like to create an iterator over the binary tree so as to be able to use range-based for loop. I understand I ought to implement the begin() and end() function first. Begin should probably point to the root. According to the specification, however, the end() functions returns "the element following the last valid element". Which element (node) is that? Would it not be illegal to point to some "invalid" place? The other thing is the operator++. What is the best way to return "next" element in tree? I just need some advice to begin with this programming.

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• How to get the set events of a control?

  - by Jack

  It's possible via C# code get an list of methods/delegates that was set to Control? let me explain better.. For example. Assuming some definitions like this: foo.Click += (a, b) => { ... } //.. foo.Click += (A,B) => { ... } And a megic method: var baa = foo.GetEvents("Click"); Returns baa[0] points to (a, b) => { ... } baa[1] points to (A,B) => { ... } My scenery: I make and add dynamically event to some controls inside a loop. I want depending to a boolean value a event of control of index one,will removed by using control.Click -= baa[1] or something like this. I hope this is clear for your. Thanks in advance.

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• Is there a limitation to the length of the query in mysql?

  - by Bakhtiyor

  I am asking this question because I need to know this limitation as I am generating SELECT query in my PHP script and the part of WHERE in this query is generated inside the loop. Precisely it looks like this $query="SELECT field_names FROM table_name WHERE "; $condition="metadata like \"%$uol_metadata_arr[0]%\" "; for($i=1; $i<count($uol_metadata_arr); $i++){ $condition.=" OR metadata like \"%$uol_metadata_arr[$i]%\" "; } $query.=$condition; $result=mysql_query($query); So, that's why I need to know how long my $query string can be, because the array *$uol_metadata_arr* could contain many items.

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• Help needed in pivoting (SQL Server 2005)

  - by Newbie

  I have a table like ID Grps Vals --- ---- ----- 1 1 1 1 1 3 1 1 45 1 2 23 1 2 34 1 2 66 1 3 10 1 3 17 1 3 77 2 1 144 2 1 344 2 1 555 2 2 11 2 2 22 2 2 33 2 3 55 2 3 67 2 3 77 The desired output being ID Record1 Record2 Record3 --- ------- ------- ------- 1 1 23 10 1 3 34 17 1 45 66 77 2 144 11 55 2 344 22 67 2 555 33 77 I have tried(using while loop) but the program is running slow. I have been asked to do so by using SET based approach. My approach so far is SELECT ID,[1] AS [Record1], [2] AS [Record2], [3] as [Record3] FROM ( Select Row_Number() Over(Partition By ID Order By Vals) records ,* From myTable)x PIVOT (MAX(vals) FOR Grps IN ([1],[2],[3])) p But it is not working. Can any one please help to solve this.(SQL SERVER 2005)

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