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  • Lock free multiple readers single writer

    - by dummzeuch
    I have got an in memory data structure that is read by multiple threads and written by only one thread. Currently I am using a critical section to make this access threadsafe. Unfortunately this has the effect of blocking readers even though only another reader is accessing it. There are two options to remedy this: use TMultiReadExclusiveWriteSynchronizer do away with any blocking by using a lock free approach For 2. I have got the following so far (any code that doesn't matter has been left out): type TDataManager = class private FAccessCount: integer; FData: TDataClass; public procedure Read(out _Some: integer; out _Data: double); procedure Write(_Some: integer; _Data: double); end; procedure TDataManager.Read(out _Some: integer; out _Data: double); var Data: TDAtaClass; begin InterlockedIncrement(FAccessCount); try // make sure we get both values from the same TDataClass instance Data := FData; // read the actual data _Some := Data.Some; _Data := Data.Data; finally InterlockedDecrement(FAccessCount); end; end; procedure TDataManager.Write(_Some: integer; _Data: double); var NewData: TDataClass; OldData: TDataClass; ReaderCount: integer; begin NewData := TDataClass.Create(_Some, _Data); InterlockedIncrement(FAccessCount); OldData := TDataClass(InterlockedExchange(integer(FData), integer(NewData)); // now FData points to the new instance but there might still be // readers that got the old one before we exchanged it. ReaderCount := InterlockedDecrement(FAccessCount); if ReaderCount = 0 then // no active readers, so we can safely free the old instance FreeAndNil(OldData) else begin /// here is the problem end; end; Unfortunately there is the small problem of getting rid of the OldData instance after it has been replaced. If no other thread is currently within the Read method (ReaderCount=0), it can safely be disposed and that's it. But what can I do if that's not the case? I could just store it until the next call and dispose it there, but Windows scheduling could in theory let a reader thread sleep while it is within the Read method and still has got a reference to OldData. If you see any other problem with the above code, please tell me about it. This is to be run on computers with multiple cores and the above methods are to be called very frequently. In case this matters: I am using Delphi 2007 with the builtin memory manager. I am aware that the memory manager probably enforces some lock anyway when creating a new class but I want to ignore that for the moment. Edit: It may not have been clear from the above: For the full lifetime of the TDataManager object there is only one thread that writes to the data, not several that might compete for write access. So this is a special case of MREW.

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  • Mapping an Array to a Single Row

    - by João Bragança
    I have the following classes: public class InventoryItem { private Usage[] usages = new Usage[12]; virtual public Usage[] Usages { get { return usages; }} virtual public string Name{get;set;} } public class Usage { virtual public double Quantity{get;set;} virtual public string SomethingElse{get;set;} } I know that Usages.Length will always be 12. I think it would be best to store it in the DB like so: Name nvarchar(64), Usage_Quantity_0 float, Usage_SomethingElse_0 nvarchar(16), Usage_Quantity_1 float, Usage_SomethingElse_1 nvarchar(16), ... Usage_Quantity_11 float, Usage_SomethingElse_11 nvarchar(16), How can I get this done?

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  • Reverting single file in SVN to a particular revision

    - by Gökhan Sever
    Hello, I have a file as shown below in an SVN repo that I would like to revert to a previous version. What is the way to do this in SVN? I want only downgrade this particular file to an older version, not the whole repo. Thanks. $ svn log myfile.py ---------------------- r179 | xx | 2010-05-10 Change 3 ---------------------- r175 | xx | 2010-05-08 Change 2 ---------------------- r174 | xx | 2010-05-04 Initial

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  • How to automatically split git commits to separate changes to a single file

    - by Hercynium
    I'm just plain stuck as to how to accomplish this, or if it's even possible. Even it it can be done, I wonder if it could be setting us up for a messed-up, unmanageable repository. I have set up two branches of the code-base. One is "master" and the other is "prod". The HEAD of prod is always the latest code in production, and master is the main development branch. Here's the problem, though: We're converting from CVS here at $work and most of the developers are still getting used to git. Their CVS workflow involved tagging versions of individual files for production, then updating the servers using the tag. Unfortunately, this has let to sloppy practices like committing unrelated changes together and then tagging the files after-the-fact... and the devs want to know how they can do the following: In their local repos, they hack and commit to their hearts' delight, then at the end of the day, be able to run a command that takes a list of files whose commits over the day get merged with their local prod - and only those files - even if those commits combine changes to other files. I know how to split commits with git rebase --interactive, but I have no clue how I would automate splitting commits at all, never mind the way I want to. I do realize the simplest thing would be to just tell them to switch the their prod branches, checkout the files from their master branches into the working tree then commit to prod. My problem with that is losing the history of their commits over the day.

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  • Best way to store 3 pieces of data as a single entry

    - by Matt
    For a game server, I want to record details when a player makes a kill, store this, and then at intervals update to a sql database. The part i'm interested in right now is the best method of storing the kill information. What i'd like to pass to the sql server on update would be {PlayerName, Kills, Deaths}, where the kills and deaths are a sum for the period between updates. So i'm assuming i'd build a list along the lines of {bob, 1, 0} {frank, 0, 1} {tom, 1, 0} {frank, 0, 1} then on update, consolidate the list to {frank, 14, 3}etc Can someone offer some advice please?

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  • Updating a single file in a compressed tar

    - by Phil
    Given a compressed archive file such as application.tar.gz which has a folder application/x/y/z.jar among others, I'd like to be able to take my most recent version of z.jar and update/refresh the archive with it. Is there a way to do this other than something like the following? tar -xzf application.tar.gz cp ~/myupdatedfolder/z.jar application/x/y tar -czf application application.tar.gz I understand the -u switch in tar may be of use to avoid having to untar the whole thing, but I'm unsure how to use it exactly.

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  • How to call different methods from single webservices class

    - by pointer
    I have a following RESTful webservice, I have two methods for http get. One function signs in and other function signs out a user from an application. Following is the code: import javax.ws.rs.core.Context; import javax.ws.rs.core.UriInfo; import javax.ws.rs.PathParam; import javax.ws.rs.Consumes; import javax.ws.rs.PUT; import javax.ws.rs.Path; import javax.ws.rs.GET; import javax.ws.rs.POST; import javax.ws.rs.Produces; import javax.ws.rs.QueryParam; /** * REST Web Service * * @author Pointer */ @Path("generic") public class GenericResource { @Context private UriInfo context; /** * Creates a new instance of GenericResource */ public GenericResource() { } /** * Retrieves representation of an instance of * com.ef.apps.xmpp.ws.GenericResource * * @return an instance of java.lang.String */ @GET @Produces("text/html") public String SignIn(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } @GET @Produces("text/html") public String SignOut(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } } Now, where would I specify that which function I want to call for http get?

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  • Import a Single Field Text File into MySQL

    - by Kirk
    I have a text file that looks like this: value1 value2 value3 There are 32 million lines. Each line is terminated by a \n. The fields are not enclosed or delimited with any characters. I'm trying to import it into MySQL using this code, but it is not working: LOAD DATA LOCAL INFILE 'data.txt' INTO TABLE `table` FIELDS TERMINATED BY '' ENCLOSED BY '' LINES TERMINATED BY '\n' (`column1`) Can anyone tell me what I'm doing wrong?

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  • Struts2 Converting Enum Array fills array with single null value

    - by Kyle Partridge
    For a simple action class with these member variables: ... private TestConverterEnum test; private TestConverterEnum[] tests; private List<TestConverterEnum> tList; ... And a simple enum: public enum TestConverterEnum { A, B, C; } Using the default struts2 enum conversion, when I send the request like so: TestConterter.action?test=&tests=&tList=&b=asdf For test I get a null value, which is expected. For the Array and List, however, I get and Array (or list) with one null element. Is this what is expected? Is there a way to prevent this. We recently upgraded our struts2 version, and we had our own converters, which also don't work in this case, so I was hoping to use the default conversion method. We already have code that is validating these arrays for null and length, and I don't want to have to add another condition to these branches. Is there a way to prevent this bevavior?

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  • Join a single row in one table to n random rows in another

    - by Einar Egilsson
    Is it possible to make a join in SQL server that joins each row from table A to n random rows in another? For example, say I have a Customer table, a Product table and an Order table. I want to join each customer to 5 random products and insert these rows into the order table. (And each customer should be joined to 5 random rows of his own, I don't want all customers joining to the same 5 rows). Is this possible? I'm using SQL Server 2005 and it's fine if the solution is specific to that. This is a weird requirement but I'm basically making a small data generator to generate some random data.

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  • Source control system for single developer

    - by kaiz.net
    What's the recommended source control system for a very small team (one developer)? Price does not matter. Customer would pay :-) I'm working on Vista32 with VS 2008 in C++ and later in C# and with WPF. Setting up an extra (physical) server for this seems overkill to me. Any opinions?

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  • Turn a single partylist field into multiple

    - by dsabater
    Is there a way to transform a partylist field like Customer in a Campaign Response to allow for multiple Contacts/Accounts/Leads? Although unsupported, I now from Jian Wang that some attributes of the lookup can be modified in the onload() event like this: crmForm.all.customer.setAttribute("lookuptypes", "1,2"); Is there a similiar attribute that would turn this into a field that allows multiple participants like the To field in an e-mail? Thank you

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  • How to mark empty in a single element in a float array

    - by Vineeth Mohan
    I have a large float (primitive) array and not every element in the array is filled. How can i mark a particular element as EMPTY. I understand this can be achieved by some special symbols but still i would like to know the standard way. Even if i am using some special symbol , how will i handle a situation where the actual data item is the value of special symbol. In short my question is how to implement the NULL feature in a primitive type array in java. PS - The reason why i am not using Float object is to achieve a high memory and speed performance. Thanks Vineeth

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  • Can this be done with single SQL query

    - by Ghostrider
    I'm using MySQL. I have a table Type SubType 1 1 1 5 1 6 1 8 2 2 2 3 3 1 3 2 3 3 For each type there is some number of subtypes. For every subtype in a type there is a corresponding subtype in the next type: (1,1) => (2,2) (1,5) => (2,3) (1,6) => (2,2) (1,8) => (2,3) (2,2) => (3,1) (2,3) => (3,2) In case you haven't seen the pattern, here it is: you sort both current and next types by subtype, then in the next type you get subtype in the same position as your current subtype in current type is. If there are more subtypes in the current type that in the next one, you warp around and start from the first subtype in the next type. Is it possible to construct a query that takes current type and subtype and returns corresponding subtype in the next type?

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  • WPF, Setting property with single value on multiple subcontrols

    - by Andre van Heerwaarde
    I have a parent contentcontrol which displays data via a datatemplate. The datatemplate contains a stackpanel with several usercontols of the same type. I like to set the property only once on the parent control, it must set the value of the property on all the subcontrols. But if there is a way to do it on the stackpanel it's also OK. The template can be changed at runtime and the values need also to be propagated to the new template. My current solution is to implement the property on both parent and subcontrol and use code to propagate the value from the parent to all the subcontrols. My question is: is there a better or other ways of doing this?

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  • Best practice with respect to NPE and multiple expressions on single line

    - by JRL
    I'm wondering if it is an accepted practice or not to avoid multiple calls on the same line with respect to possible NPEs, and if so in what circumstances. For example: getThis().doThat(); vs Object o = getThis(); o.doThat(); The latter is more verbose, but if there is an NPE, you immediately know what is null. However, it also requires creating a name for the variable and more import statements. So my questions around this are: Is this problem something worth designing around? Is it better to go for the first or second possibility? Is the creation of a variable name something that would have an effect performance-wise? Is there a proposal to change the exception message to be able to determine what object is null in future versions of Java ?

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  • How to group a database write and spreadsheet write in single "transaction"

    - by WhyGeeEx
    I have a Java program that writes results to both a DB (SQL Server) and a spreadsheet (POI), and it would be best if neither is written to if there's an error with either. It would be a lot worse if the spreadsheet was produced and then an error happened while saving to the DB, so I'm doing the DB-write first. Even so, I'm wondering if someone knows of a way to guarantee they both succeed or fail as a unit. Thanks!

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  • Single Large v/s Multiple Small MySQL tables for storing Options

    - by Prasad
    Hi there, I'm aware of several question on this forum relating to this. But I'm not talking about splitting tables for the same entity (like user for example) Suppose I have a huge options table that stores list options like Gender, Marital Status, and many more domain specific groups with same structure. I plan to capture in a OPTIONS table. Another simple option is to have the field set as ENUM, but there are disadvantages of that as well. http://www.brandonsavage.net/why-you-should-replace-enum-with-something-else/ OPTIONS Table: option_id <will be referred instead of the name> name value group Query: select .. from options where group = '15' - Since this table is expected to be multi-tenant, the no of rows could grow drastically. - I believe splitting the tables instead of finding by the group would be easier to write & faster to execute. - or perhaps partitioning by the group or tenant? Pl suggest. Thanks

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  • Nhibernate - getting single column from other table

    - by Muhammad Akhtar
    I have following tables Employee: ID,CompanyID,Name //CompanyID is foriegn key of Company Table Company: CompanyID, Name I want to map this to the following class: public class Employee { public virtual Int ID { get; set; } public virtual Int CompanyID { get; set; } public virtual string Name { get; set; } public virtual string CompanyName { get; set; } protected Employee() { } } here is my xml class <class name="Employee" table="Employee" lazy="true"> <id name="Id" type="Int32" column="Id"> <generator class="native" /> </id> <property name="CompanyID" column="CompanyID" type="Int32" not-null="false"/> <property name="Name" column="Name" type="String" length="100" not-null="false"/> What I need to add in xml class to map CompanyName in my result? here is my code... public ArrayList getTest() { ISession session = NHibernateHelper.GetCurrentSession(); string query = "select Employee.*,(Company.Name)CompanyName from Employee inner join Employee on Employee.CompanyID = Company.CompanyID"; ArrayList document = (ArrayList)session.CreateSQLQuery(query, "Employee", typeof(Document)).List(); return document; } but in the returned result, I am getting CompanyName is null is result set and other columns are fine. Note:In DB, tables don't physical relation Please suggest my solution ------ Thanks

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  • Table rows with identifying parameter in each row SQL SERVER 2008 into single row

    - by LiverpoolsNumber9
    Sorry - my question title is probably as inept at my attempt to do this. I have the following (well, similar) in a table in a CMS pageID key value 201 title Page 201's title 201 description This is 201 201 author Dave 301 title Page 301's title 301 description This is 301 301 author Bob As you've probably guessed, what I need is a query that will produce: pageID title description author 201 Page 201's title This is page 201 Dave 301 Page 301's title This is page 301 Bob If anybody could help, i'd be eternally grateful - I know this is "please send me the code" but I'm absolutely stuck. Thanks in advance.

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  • Android 2.1: Muliple Handlers in a Single Activity

    - by Soumya Simanta
    Hi, I've more than one Handlers in an Activity. I create all the handlers in the onCreate() of the main activity. My understanding is the handlerMessage() method of each handler will never be called at the same time because all messages are put in the same queue (the Activity thread MessageQueue). Therefore, they will be executed in the order in which are put into the Queue. They will also be executed in the main activity thread. Is this correct ? public void onCreate() { this.handler1 = new Handler() { @Override public void handleMessage(Message msg) { //operation 1 : some operation with instanceVariable1 super.handleMessage(msg); } }; this.handler2 = new Handler() { @Override public void handleMessage(Message msg) { //Operation 2: some operation with instanceVariable1 super.handleMessage(msg); } }; this.handler3 = new Handler() { @Override public void handleMessage(Message msg) { //Operation 3: some operation with instanceVariable1 super.handleMessage(msg); } }; }

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  • SendTo menu and single instance program.

    - by Semas
    Hello. Making a program trough witch i will be able to send files to FTP server just by right clicking "SendTo". Problem is that every time i click "SendTo" it opens new exe file and it works as separate program. I need to make it somehow to send file with already open program. Thank you.

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  • Multiple inputs on a single line with Twitter Bootstrap and Simple Form 2.0

    - by noel_g
    I am using simple_form 2.0 with twitter bootstrap. I am trying to determine what is the proper wrapper format in order to get something like [city] [State] [Zip] I believe my form needs to be <div class="control-group"> <%= f.input :city,:wrapper => :small, :placeholder => "City", :input_html => { :class=>"span2", :maxlength => 10},:label => false %> <%= f.input :region, :wrapper => :small , :placeholder => "Region", :input_html => { :class=>"span1", :maxlength => 5}, :label => false %> <%= f.input :postal_code, :wrapper => :small, :placeholder => "Postal Code",:input_html => { :class=>"span2", :maxlength => 10},:label => false %> </div> I tried this wrapper config.wrappers :small, :tag => 'div', :class => 'controls inline-inputs', :error_class => 'error' do |b| b.use :placeholder b.use :label_input end I believe I would need to define the CSS as well, but before I go down a rabbit hole I thought I would ask if this is built in somewhere.

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