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• Commited memory goes to physical RAM or reserves space in the paging file?

  - by Sil

  When I do VirtualAlloc with MEM_COMMIT this "Allocates physical storage in memory or in the paging file on disk for the specified reserved memory pages" (quote from MSDN article http://msdn.microsoft.com/en-us/library/aa366887%28VS.85%29.aspx). All is fine up until now BUT: the description of Commited Bytes Counter says that "Committed memory is the physical memory which has space reserved on the disk paging file(s)." I also read "Windows via C/C++ 5th edition" and this book says that commiting memory means reserving space in the page file.... The last two cases don't make sense to me... If you commit memory, doesn't that mean that you commit to physical storage (RAM)? The page file being there for swaping out currently unused pages of memory in case memory gets low. The book says that when you commit memory you actually reserve space in the paging file. If this were true than that would mean that for a committed page there is space reserved in the paging file and a page frame in physical in memory... So twice as much space is needed ?! Isn't the page file's purpose to make the total physical memory larger than it actually is? If I have a 1G of RAM with a 1G page file = 2G of usable "physical memory"(the book also states this but right after that it says what I discribed at point 2). What am I missing? Thanks.

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• Measuring the CPU frequency scaling effect

  - by Bryan Fok

  Recently I am trying to measure the effect of the cpu scaling. Is it accurate if I use this clock to measure it? template<std::intmax_t clock_freq> struct rdtsc_clock { typedef unsigned long long rep; typedef std::ratio<1, clock_freq> period; typedef std::chrono::duration<rep, period> duration; typedef std::chrono::time_point<rdtsc_clock> time_point; static const bool is_steady = true; static time_point now() noexcept { unsigned lo, hi; asm volatile("rdtsc" : "=a" (lo), "=d" (hi)); return time_point(duration(static_cast<rep>(hi) << 32 | lo)); } }; Update: According to the comment from my another post, I believe redtsc cannot use for measure the effect of cpu frequency scaling because the counter from the redtsc does not affected by the CPU frequency, am i right?

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• How to know who kills my threads

  - by mcabral

  I got a thread that is just banishing.. i'd like to know who is killing my thread and why. It occurs to me my thread is being killed by the OS, but i'd like to confirm this and if possible to know why it's killing it. As for the thread, i can assert it has at least 40 min of execution before dying, but it suddenly dies around 5 min. public void RunWorker() { Thread worker = new Thread(delegate() { DoSomethingForALongLongTime(); }); worker.IsBackground = true; worker.SetApartmentState(System.Threading.ApartmentState.STA); worker.Start(); }

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• A Question about dereferencing pointer to incomplete type In C programming

  - by user552279

  Hi, can you explain this error for me? Blockquote /////////////////////////////// In my A.h file: struct TreeNode; struct TreeHead; typedef struct TreeNode * Node; typedef struct TreeHead * Head; /////////////////////////////// In my A.c file: struct TreeNode { char* theData; Node Left; Node Right; } ; struct TreeHead{ int counter; char type; Node Root; }; Head Initialisation() { Head treeHead; treeHead = malloc(sizeof (struct TreeHead)); treeHead-Root = malloc(sizeof (struct TreeNode)); return treeHead; } /////////////////////////////// In my Main.c file: Head head; Node tree; int choose =5; head = Initialisation(); (head-Root) = tree; //When compiling, this line has an error: error: dereferencing pointer to incomplete type Blockquote haed-Root will return a Node pointer, tree is also a Node pointer. So why error is dereferencing pointer to "incomplete" type?

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• How can I seperate my TransactionScope so they don't interfere with each other?

  - by shenku

  I have some business logic that executes within a simple TransactionScope. using (var scope = new TransactionScope()) { // does some logic. // then some more... scope.Complete(); } During execution an ado exception ocurres and the transaction is on it's way to being disposed. In the mean time the exception is captured further upstream, and I try to log it to my database, via another connection. At this point I get another error saying The operation is not valid for the state of the transaction. Eeek! Now I can see I am able to use IsolationLevel, to change the way my transactions interact, but is this the right thing to do? And which should I use?

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• Confusion using MYSQLI

  - by user1020069

  I just started using mysqli API for PHP. Apparently, every time an object of the class MYSQLI is instantiated, it can setup a connection to the database as it connects to the server unlike mysql_connect, which connects to the server first and then you are required to specify the database to query. Now this is a good problem if the db exists, in my case, the db does not exist on the first ever connection to the server/execution of the problem, hence I must connect without specifying the database, which is fine, since the msyqli constructor does not make this database mandatory. My challenge is essentially, how do I check if the database exists before attempting the first connection. The only way to really do this would be to establish a conection to the server and then use the result of the following query to gauge if the database exists: SELECT COUNT(*) AS `exists` FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMATA.SCHEMA_NAME="dbname" ; If this returns true, then the database exists, but now the challenge is how do I get the mysqli object to query this database rather than having to prefix the name of the database in the query. Thanks much

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• How can I force the text go to the button of the panel?

  - by Roman

  At the moment I have the following code which works fine. label = new JLabel(panelLabel,SwingConstants.CENTER); outputPanel.add(label,BorderLayout.CENTER); I get the text in the center of the panel (in terms of the left-right position as well as in terms of the top-bottom). Now I want to set the position to the bottom (and center in terms of "left-right"). I tried to use SOUTH instead of the CENTER in the first line. Compiler does not complains but during the execution i get IllegalArgumentException: HorizontalAlignment. What is that?

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• Do MySQL Locked Tables affect related Views?

  - by CogitoErgoSum

  So after reading http://stackoverflow.com/questions/1415602/performance-in-pdo-php-mysql-transaction-versus-direct-execution in regards to performance issues I was thinking about I did some research on locking tables in MySQL. On http://dev.mysql.com/doc/refman/5.0/en/table-locking.html Table locking enables many sessions to read from a table at the same time, but if a session wants to write to a table, it must first get exclusive access. During the update, all other sessions that want to access this particular table must wait until the update is done. This part struck me particularly becuase most of our queries will be updates rather than inserts. I was wondering if one created a table called foo on which all updates/inserts were carried out and then a view called foo_view (A copy of foo, or perhaps foo and a linkage of several other tables plus foo) on which all selects occured, would this locking issue still occur? That is, would SELECT quries on foo_view still have to wait for an update to finish on foo?

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• How do I avoid a race condition in my Rails app?

  - by Cathal

  Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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• Trying to read keyboard input without blocking (Windows, C++)

  - by Adam E

  I'm trying to write a Windows console application (in C++ compiled using g++) that will execute a series of instructions in a loop until finished OR until ctrl-z (or some other keystroke) is pressed. The code I'm currently using to catch it isn't working (otherwise I wouldn't be asking, right?): if(kbhit() && getc(stdin) == 26) //The code to execute when ctrl-z is pressed If I press a key, it is echoed and the application waits until I press Enter to continue on at all. With the value 26, it doesn't execute the intended code. If I use something like 65 for the value to catch, it will reroute execution if I press A then Enter afterward. Is there a way to passively check for input, throwing it out if it's not what I'm looking for or properly reacting when it is what I'm looking for? ..and without having to press Enter afterward?

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• Minimizing Java Thread Context Switching Overhead

  - by binil

  I have a Java application running on Sun 1.6 32-bit VM/Solaris 10 (x86)/Nahelem 8-core(2 threads per core). A specific usecase in the application is to respond to some external message. In my performance test environment, when I prepare and send the response in the same thread that receives the external input, I get about 50 us advantage than when I hand off the message to a separate thread to send the response. I use a ThreadPoolExecutor with a SynchronousQueue to do the handoff. In your experience what is the acceptable delay between scheduling a task to a thread pool and it getting picked up for execution? What ideas had worked for you in the past to try improve this?

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• Exit Try/Catch to prevent code after from being run

  - by coffeeaddict

  I've got for example a try/catch in my method: } catch (OurCustomExceptionObject1 ex) { txtErrorMessage.InnerHtml = "test 1"; } catch(OurCustomExceptionObject2 ex) { txtErrorMessage.InnerHtml = "test 2"; } catch (OurCustomExceptionObject3 ex) { txtErrorMessage.InnerHtml = "test 3"; } ... rest of code here is being executed after the try/catch I do not want the rest of code to run if any of the exceptions are caught. I'm handling the exceptions. I heard do not use Exit Try for some reason. Is that true, it's bad to do this? Is this the right way to halt execution of code thereafter the catch statement?

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• java: assigning object reference IDs for custom serialization

  - by Jason S

  For various reasons I have a custom serialization where I am dumping some fairly simple objects to a data file. There are maybe 5-10 classes, and the object graphs that result are acyclic and pretty simple (each serialized object has 1 or 2 references to another that are serialized). For example: class Foo { final private long id; public Foo(long id, /* other stuff */) { ... } } class Bar { final private long id; final private Foo foo; public Bar(long id, Foo foo, /* other stuff */) { ... } } class Baz { final private long id; final private List<Bar> barList; public Baz(long id, List<Bar> barList, /* other stuff */) { ... } } The id field is just for the serialization, so that when I am serializing to a file, I can write objects by keeping a record of which IDs have been serialized so far, then for each object checking whether its child objects have been serialized and writing the ones that haven't, finally writing the object itself by writing its data fields and the IDs corresponding to its child objects. What's puzzling me is how to assign id's. I thought about it, and it seems like there are three cases for assigning an ID: dynamically-created objects -- id is assigned from a counter that increments reading objects from disk -- id is assigned from the number stored in the disk file singleton objects -- object is created prior to any dynamically-created object, to represent a singleton object that is always present. How can I handle these properly? I feel like I'm reinventing the wheel and there must be a well-established technique for handling all the cases.

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• What are the advantages and disadvantages of plug-in based architecture?

  - by RP

  I want to do the architectural design for a software that can be used integrate various third party software’s (executable) under one platform. Standard project types will be added to the platform by default. The project type defines the way in which the different software will be executed and their input and output files. The user can customize the available standard project type and that will be added to the platform as new project type which defines new custom execution flow. Also it should support easy extension and customization of the features. I read that plug-in based architecture supports both. What are the advantages and disadvantages of plug-in based architecture? Do we have any better architecture which can be used for this kind of scenario? Thanks in advance:)

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• Limiting object allocation over multiple threads

  - by John

  I have an application which retrieves and caches the results of a clients query. The client then requests different chunks of data and the application sends the relevant results and removes them from the cache. A new requirement for this application is that there needs to be a run-time configurable maximum number of results which may be cached. I've taken the naive approach and implemented this by using a counter under a lock which is incremented every time a result is cached and decremented whenever a result is removed from the cache. Unfortunately, this has drastically reduced the applications performance when processing a large number of concurrent requests. I have tried both a critical section lock and spin-lock; the performance improves a bit with a spin-lock, but is still unacceptably slow. Is there a better way to solve this problem which may improve performance? Right now I have a thread pool that services requests and each request is tied to a Request object which stores that cached results for that particular request. Here is a simplified pseudo code version of my current implementation: void ResultCallback( Result result, Request *request ) { lock totalResultsCached lock cachedLimit if( totalResultsCached + 1 > cachedLimit ) { unlock cachedLimit unlock totalResultsCached //cancel the request return; } ++totalResultsCached; unlock cachedLimit unlock totalResultsCached request.add(result) } void SendResults( int resultsToSend, Request *request ) { while ( resultsToSend > 0 ) { send(request.remove()) lock totalResultsCached --totalResultsCached unlock totalResultsCached --resultsToSend; } }

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• Get Data from Windows Form into C# program

  - by Jimmy

  I want my C# program to collect data. Then, when the OK button is clicked, I want this data to be loaded into my program -- such as into variables in Main(), or into data members of a class I have constructed, and I want the form to then go away -- not be hidden, but actually closed. Alas, read as I might in the book I have, the data collected by the form stays in the form, execution proceeds within the form, and the same form is used to display the result of the program's computations. Sheesh. All I want is to capture the form's information, close the form and proceed with my program. I would appreciate some tips on geting data from a form into Main() or into a class's data members. Thanks, Lucky

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• how to skip first 3 row of text file.

  - by Dilantha Chamal

  hey when i reading the text file using java, how can i skip first 3 rows of the text file. Show me how to do that. public class Reader { public static void main(String[] args) { BufferedReader reader; try { reader = new BufferedReader(new InputStreamReader( new FileInputStream("sample.txt"))); Map<String, Integer result = new LinkedHashMap<String, Integer(); Map<String, Integer result2 = new LinkedHashMap<String, Integer(); while (reader.ready()) { String line = reader.readLine(); /split a line with spaces/ String[] values = line.split("\s+"); /set a key date\tanimal/ String key = values[0] + "\t" + values[1]; int sum = 0; int count = 0; /get a last counter and sum/ if (result.containsKey(key)) { sum = result.get(key); count = result2.get(key); } else{ } /increment sum a count and save in the map with key/ result.put(key, sum + Integer.parseInt(values[2])); result2.put(key, count + 1); } /interate and print new output/ for (String key : result.keySet()) { Integer sum = result.get(key); Integer count = result2.get(key); System.out.println(key + " " + sum + "\t" + count); } reader.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } }

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• Profiling Java running by JNI calls

  - by Guy

  Hi, I have a C++ code that upon execution: Loads JVM (I have full control on how to load the JVM), and call Java methods (from loaded classes) using C JNI code. The Java code has no Main() and it is actually not a standard Java application. it is mainly a static code that compiled and compacted into Jar file, the code is being called by the C++ module. Is it possible to profile this Java code being executed by YourKit (have license for it)? If so I'll be glad to know how. Thanks, Guy

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• Objective-C: alloc of object within init of another object (memory management)

  - by Stefan Klumpp

  In my .h file I have: NSMutableArray *myArray; @property (nonatomic, retain) NSMutableArray *myArray; My .m file looks basically like this: @synthesize myArray; - (id) init { self = [super init]; if (self != nil) { self.myArray = .... ? // here I want to create an empty array } return self; } - (void) dealloc { [self.myArray release]; [super dealloc]; } What I'm not sure about is what do to in the init. 1) self.myArray = [[NSMutableArray alloc] init]; 2) NSMutableArray *tmp = [[NSMutableArray alloc] init]; self.myArray = tmp; [tmp release]; Solution 1 doesn't seem right to me, because of my @property (retain) setting I automatically increase the retain counter when setting self.myArray, but additionally I have already a "+1 retain" due to the [NSMutableArray alloc]. Thus the second solution seems more correct to me, even though it is cumbersome. Also am I wondering if self.myArray = ... is actually the same as [self setMyArray:...] and thus does increase the retain count.

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• Why use constants in programming?

  - by Adam N

  I've just been going back over a bit of C studying using Ivor Horton's Beginning C book. I got to the bit about declaring constants which seems to get mixed up with variables in the same sentence. Just to clarify, what is the difference in specifying constants and variables in C, and really, when do you need to use a constant instead of a variable? I know folks say to use a constant when the information doesn't change during program execution but I can't really think of a time when a variable couldn't be used instead. Thanks

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• mysql reference result from subquery

  - by iamrohitbanga

  this is what i am doing update t1 set x=a,y=b where a and b are obtained from (select query here) i know the select query the select query returns multiple results which are the same when i use group by or distinct query execution slows down considerably a and b are forward references so mysql reports an error i want to set a equal to the value obtained in the first row and b equal to the value obtained in the first row for the respective columns, to avoid group by. i don't know how to refer to the first result from the select query. how can i achieve all this?

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• How to Get the Method/Function Call Trace for a Specific Run?

  - by JackWM

  Given a Java or JavaScript program, after its execution, print out a sequence of calls. The calls are in invocation order. E.g. main() { A(); } A() { B(); C(); } Then the call trace should be: main -> A() -> B() -> C() Is there any tool that can profile and output this kind of information? It seems this is common a need for debugging or performance tuning. I noticed that some profilers can do this, but I prefer a simpler/easy-to-use one. Thanks!

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• Can I change the datsource of report model at runtime

  - by Manab De

  I've some adhoc reports developed on some report models which are published on Report Server (we're using SSRS 2008). Everything is running well. Now in our production environment we've near about forty (40) customers who have their own database (each have the same table structures and other database objects). Now the challenge is whenever a customer will log into the report server using windows authentication and trying to view those reports we need to get the SQL data from the proper database only. Reports are designed using the report model and each model has a valid data source which is connected to particular database. We can create forty separate data sources each will be connected to specific database. My question is, is there any way through which we can change the report model data source name dynamically or during runtime based on the customer name so that during execution of the report, SSRS would fetch the data from the correct database but not from any other database. Please help me.

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• Adding code to the beginning / end of methods in runtime dynamically

  - by Irchi

  I know instrumentation is a technique to add trace code dynamically into the methods to enable tracing and debugging. I was wondering if this is only a "Trace" option, hard coded into the CLR to add only trace code, or is there the ability to add any code to the methods? For example, I want to check for a condition in the beginning of every single method call in a certain class (say for permissions). Can I do this via adding dynamic code to the beginning of the methods in execution time? I'm not sure how this trace "instrumentation" thing works, but I'm wondering if this can be used for other goals too, or not.

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• The proccesses finished berfore they become completed

  - by Meysam Javadi

  suppose this scenario: i have a XML file that is uploaded, i read it to a DataTable with ReadXml method. now i want to insert this DataTable to database. i create a t-sql command to insert database(with StoredProcedure) for example var command =string.Format("exec SyncToDB '{0}','{1}", odatarow.ItemArray.GetValue(0), odatarow..ItemArray.GetValue(1)); Hitherto everything is ok but when i run this code ,all of rows not affected to DB, i think that a timeout occur the code execution. *note:*the number of rows is numerous.(25000). how to solve this?

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