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• are simultaneous reads of a variable thread-safe?

  - by Dasuraga

  Assuming that the variable isn't in any risk of being modified during the reads, are there any inherent problems in a variable being read by 2 or more threads at the same time?

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• Why thread started by ScheduledExecutorService.schedule() never quits?

  - by moonese

  If I create a scheduled task by calling ScheduledExecutorService.schedule(), it never quits after execution, is it a JDK bug, or I just miss something? note: doSomething() is empty method below. public static void doSomething() { } public static void main(String[] args) { ScheduledFuture scheduleFuture = Executors.newSingleThreadScheduledExecutor().schedule(new Callable() { public Void call() { try { doSomething(); } catch (Exception e) { e.printStackTrace(); } return null; } }, 1, TimeUnit.SECONDS); }

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• jquery ui - making dialogs more "dynamic" ?

  - by mike

  Hello, I have a page that uses multiple dialogs for different things. Some dialogs may have buttons that others do not while other may need to be a different height than another... All of them have a set of params that will not change. My question, can I have a default like: $('.someElement').dialog({ width: 999, show: 'slide', hide: 'slide', ETC: 'some other option' }); and use it for all of my dialogs, then pass buttons or height to it dynamically when I open a dialog? It just seems wrong to have something like the above for every dialog I need... Thanks!

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• static method and thread safety

  - by Anthos

  Is the following code threadsafe ? public static Entity getInstance(){ //the constructor below is a default one. return new Entity(); }

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• Sidescrolling UI on iPhone

  - by Michael

  Please lead me in the right direction. I need to provide user with small text centered on the iPhone screen. User can make quick scroll left or right in order to get the next or previous text. There can be hundreds of such text pieces. The process itself is similar to Photo application sidescrolling but much simple, no zoom. As far as I can understand I need to use UIScrollView class, then call hundreds of addSubviews? Is it the optimal way or I should always keep 3 subviews and replace them on the fly? What kind of tricks should be used to achieve the "scroll and center" effect? Thanks

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• Partition tool with console UI (as in server installation)?

  - by lepe

  Back in 2006, Ray (3DLover) posted the same question in: http://ubuntuforums.org/showthread.php?t=309680 but none of the answers were really useful. Now with a little help from AskUbuntu community, I would like to repeat his question again to see if this time it can be answered correctly. So this is the question (and what I wish too): I'm looking for a UI tool for managing partitions in a console. I have installed Ubuntu Server, so I don't have X Windows at all. fdisk and sfdisk are entirely command line. parted is slightly better, but it's not really a UI. cfdisk has somewhat of a UI, but it only works on one disk at a time, and there's no advanced options like configuring LVM or RAID. Just partitioning. I love the partition tool that is available during the OS install procedure. You can partition, configure RAID's and LMV sets. It can format the partitions with several different file systems, it can set labels, mount options and it can insert your volumes into your fstab. Is this tool available as a stand-alone program? I can't find it anywhere. I think it's called parted_server, but I can't find much information about where to get it. In the past, I have run the Ubuntu install procedure just to use the partition manager that comes with it. (canceling the install after making my partition edits) Anyone help me on this? Thanks -Ray Thanks in advance.

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• how do you make a "concurrent queue safe" lazy loader (singleton manager) in objective-c

  - by Rich

  Hi, I made this class that turns any object into a singleton, but I know that it's not "concurrent queue safe." Could someone please explain to me how to do this, or better yet, show me the code. To be clear I want to know how to use this with operation queues and dispatch queues (NSOperationQueue and Grand Central Dispatch) on iOS. Thanks in advance, Rich EDIT: I had an idea for how to do it. If someone could confirm it for me I'll do it and post the code. The idea is that proxies make queues all on their own. So if I make a mutable proxy (like Apple does in key-value coding/observing) for any object that it's supposed to return, and always return the same proxy for the same object/identifier pair (using the same kind of lazy loading technique as I used to create the singletons), the proxies would automatically queue up the any messages to the singletons, and make it totally thread safe. IMHO this seems like a lot of work to do, so I don't want to do it if it's not gonna work, or if it's gonna slow my apps down to a crawl. Here's my non-thread safe code: RMSingletonCollector.h // // RMSingletonCollector.h // RMSingletonCollector // // Created by Rich Meade-Miller on 2/11/11. // Copyright 2011 Rich Meade-Miller. All rights reserved. // #import <Foundation/Foundation.h> #import "RMWeakObjectRef.h" struct RMInitializerData { // The method may take one argument. // required SEL designatedInitializer; // data to pass to the initializer or nil. id data; }; typedef struct RMInitializerData RMInitializerData; RMInitializerData RMInitializerDataMake(SEL initializer, id data); @interface NSObject (SingletonCollector) // Returns the selector and data to pass to it (if the selector takes an argument) for use when initializing the singleton. // If you override this DO NOT call super. + (RMInitializerData)designatedInitializerForIdentifier:(NSString *)identifier; @end @interface RMSingletonCollector : NSObject { } + (id)collectionObjectForType:(NSString *)className identifier:(NSString *)identifier; + (id<RMWeakObjectReference>)referenceForObjectOfType:(NSString *)className identifier:(NSString *)identifier; + (void)destroyCollection; + (void)destroyCollectionObjectForType:(NSString *)className identifier:(NSString *)identifier; @end // ==--==--==--==--==Notifications==--==--==--==--== extern NSString *const willDestroySingletonCollection; extern NSString *const willDestroySingletonCollectionObject; RMSingletonCollector.m // // RMSingletonCollector.m // RMSingletonCollector // // Created by Rich Meade-Miller on 2/11/11. // Copyright 2011 Rich Meade-Miller. All rights reserved. // #import "RMSingletonCollector.h" #import <objc/objc-runtime.h> NSString *const willDestroySingletonCollection = @"willDestroySingletonCollection"; NSString *const willDestroySingletonCollectionObject = @"willDestroySingletonCollectionObject"; RMInitializerData RMInitializerDataMake(SEL initializer, id data) { RMInitializerData newData; newData.designatedInitializer = initializer; newData.data = data; return newData; } @implementation NSObject (SingletonCollector) + (RMInitializerData)designatedInitializerForIdentifier:(NSString *)identifier { return RMInitializerDataMake(@selector(init), nil); } @end @interface RMSingletonCollector () + (NSMutableDictionary *)singletonCollection; + (void)setSingletonCollection:(NSMutableDictionary *)newSingletonCollection; @end @implementation RMSingletonCollector static NSMutableDictionary *singletonCollection = nil; + (NSMutableDictionary *)singletonCollection { if (singletonCollection != nil) { return singletonCollection; } NSMutableDictionary *collection = [[NSMutableDictionary alloc] initWithCapacity:1]; [self setSingletonCollection:collection]; [collection release]; return singletonCollection; } + (void)setSingletonCollection:(NSMutableDictionary *)newSingletonCollection { if (newSingletonCollection != singletonCollection) { [singletonCollection release]; singletonCollection = [newSingletonCollection retain]; } } + (id)collectionObjectForType:(NSString *)className identifier:(NSString *)identifier { id obj; NSString *key; if (identifier) { key = [className stringByAppendingFormat:@".%@", identifier]; } else { key = className; } if (obj = [[self singletonCollection] objectForKey:key]) { return obj; } // dynamic creation. // get a class for Class classForName = NSClassFromString(className); if (classForName) { obj = objc_msgSend(classForName, @selector(alloc)); // if the initializer takes an argument... RMInitializerData initializerData = [classForName designatedInitializerForIdentifier:identifier]; if (initializerData.data) { // pass it. obj = objc_msgSend(obj, initializerData.designatedInitializer, initializerData.data); } else { obj = objc_msgSend(obj, initializerData.designatedInitializer); } [singletonCollection setObject:obj forKey:key]; [obj release]; } else { // raise an exception if there is no class for the specified name. NSException *exception = [NSException exceptionWithName:@"com.RMDev.RMSingletonCollector.failed_to_find_class" reason:[NSString stringWithFormat:@"SingletonCollector couldn't find class for name: %@", [className description]] userInfo:nil]; [exception raise]; [exception release]; } return obj; } + (id<RMWeakObjectReference>)referenceForObjectOfType:(NSString *)className identifier:(NSString *)identifier { id obj = [self collectionObjectForType:className identifier:identifier]; RMWeakObjectRef *objectRef = [[RMWeakObjectRef alloc] initWithObject:obj identifier:identifier]; return [objectRef autorelease]; } + (void)destroyCollection { NSDictionary *userInfo = [singletonCollection copy]; [[NSNotificationCenter defaultCenter] postNotificationName:willDestroySingletonCollection object:self userInfo:userInfo]; [userInfo release]; // release the collection and set it to nil. [self setSingletonCollection:nil]; } + (void)destroyCollectionObjectForType:(NSString *)className identifier:(NSString *)identifier { NSString *key; if (identifier) { key = [className stringByAppendingFormat:@".%@", identifier]; } else { key = className; } [[NSNotificationCenter defaultCenter] postNotificationName:willDestroySingletonCollectionObject object:[singletonCollection objectForKey:key] userInfo:nil]; [singletonCollection removeObjectForKey:key]; } @end RMWeakObjectRef.h // // RMWeakObjectRef.h // RMSingletonCollector // // Created by Rich Meade-Miller on 2/12/11. // Copyright 2011 Rich Meade-Miller. All rights reserved. // // In order to offset the performance loss from always having to search the dictionary, I made a retainable, weak object reference class. #import <Foundation/Foundation.h> @protocol RMWeakObjectReference <NSObject> @property (nonatomic, assign, readonly) id objectRef; @property (nonatomic, retain, readonly) NSString *className; @property (nonatomic, retain, readonly) NSString *objectIdentifier; @end @interface RMWeakObjectRef : NSObject <RMWeakObjectReference> { id objectRef; NSString *className; NSString *objectIdentifier; } - (RMWeakObjectRef *)initWithObject:(id)object identifier:(NSString *)identifier; - (void)objectWillBeDestroyed:(NSNotification *)notification; @end RMWeakObjectRef.m // // RMWeakObjectRef.m // RMSingletonCollector // // Created by Rich Meade-Miller on 2/12/11. // Copyright 2011 Rich Meade-Miller. All rights reserved. // #import "RMWeakObjectRef.h" #import "RMSingletonCollector.h" @implementation RMWeakObjectRef @dynamic objectRef; @synthesize className, objectIdentifier; - (RMWeakObjectRef *)initWithObject:(id)object identifier:(NSString *)identifier { if (self = [super init]) { NSString *classNameForObject = NSStringFromClass([object class]); className = classNameForObject; objectIdentifier = identifier; objectRef = object; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(objectWillBeDestroyed:) name:willDestroySingletonCollectionObject object:object]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(objectWillBeDestroyed:) name:willDestroySingletonCollection object:[RMSingletonCollector class]]; } return self; } - (id)objectRef { if (objectRef) { return objectRef; } objectRef = [RMSingletonCollector collectionObjectForType:className identifier:objectIdentifier]; return objectRef; } - (void)objectWillBeDestroyed:(NSNotification *)notification { objectRef = nil; } - (void)dealloc { [[NSNotificationCenter defaultCenter] removeObserver:self]; [className release]; [super dealloc]; } @end

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• Metro apps crash on startup, driver or permissions issue?

  - by Vee

  After installing Win8 x64 RC, Metro apps worked correctly, but desktop OpenGL apps were slow and unresponsive. I installed the latest Win8 nVidia drivers, and the OpenGL apps started working correctly. At the same time, because of annoying permission messages, I changed the C:\ drive and all its files ownerships to my user, and gave it full permission. I restarted my pc after installing the drivers, and now Metro apps only show the splash screen, then crash. I tried installing other versions of the nVidia drivers, with the same result. My GPU is a GeForce GTX275. Is this a known problem with nVidia drivers? Or maybe changing the ownership of C:\ is the real problem? Thank you. More information (after looking in the event viewer) I've managed to find the problem and the error in the Event Viewer. I still cannot solve it. Here's the information I found by opening the Mail app and letting it crash: Log Name: Microsoft-Windows-TWinUI/Operational Source: Microsoft-Windows-Immersive-Shell Date: 07/06/2012 15.54.17 Event ID: 5961 Task Category: (5961) Level: Error Keywords: User: VEE-PC\Vittorio Computer: vee-pc Description: Activation of the app microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail for the Windows.Launch contract failed with error: The app didn't start.. Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="Microsoft-Windows-Immersive-Shell" Guid="{315A8872-923E-4EA2-9889-33CD4754BF64}" /> <EventID>5961</EventID> <Version>0</Version> <Level>2</Level> <Task>5961</Task> <Opcode>0</Opcode> <Keywords>0x4000000000000000</Keywords> <TimeCreated SystemTime="2012-06-07T13:54:17.472416600Z" /> <EventRecordID>6524</EventRecordID> <Correlation /> <Execution ProcessID="3008" ThreadID="6756" /> <Channel>Microsoft-Windows-TWinUI/Operational</Channel> <Computer>vee-pc</Computer> <Security UserID="S-1-5-21-2753614643-3522538917-4071044258-1001" /> </System> <EventData> <Data Name="AppId">microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail</Data> <Data Name="ContractId">Windows.Launch</Data> <Data Name="ErrorCode">-2144927141</Data> </EventData> </Event> Found other stuff, this is another error that appears when opening a Metro app: Log Name: Application Source: ESENT Date: 07/06/2012 16.01.00 Event ID: 490 Task Category: General Level: Error Keywords: Classic User: N/A Computer: vee-pc Description: svchost (1376) SRUJet: An attempt to open the file "C:\Windows\system32\SRU\SRU.log" for read / write access failed with system error 5 (0x00000005): "Access is denied. ". The open file operation will fail with error -1032 (0xfffffbf8). Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="ESENT" /> <EventID Qualifiers="0">490</EventID> <Level>2</Level> <Task>1</Task> <Keywords>0x80000000000000</Keywords> <TimeCreated SystemTime="2012-06-07T14:01:00.000000000Z" /> <EventRecordID>11854</EventRecordID> <Channel>Application</Channel> <Computer>vee-pc</Computer> <Security /> </System> <EventData> <Data>svchost</Data> <Data>1376</Data> <Data>SRUJet: </Data> <Data>C:\Windows\system32\SRU\SRU.log</Data> <Data>-1032 (0xfffffbf8)</Data> <Data>5 (0x00000005)</Data> <Data>Access is denied. </Data> </EventData> </Event> After changing permissions again (adding Everyone and Creator Owner to System32), the "access denied to sru.log" error disappears, but this one appears in its place: Log Name: Application Source: Microsoft-Windows-Immersive-Shell Date: 07/06/2012 16.16.34 Event ID: 2486 Task Category: (2414) Level: Error Keywords: (64),Process Lifetime Manager User: VEE-PC\Vittorio Computer: vee-pc Description: App microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail did not launch within its allotted time. Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="Microsoft-Windows-Immersive-Shell" Guid="{315A8872-923E-4EA2-9889-33CD4754BF64}" /> <EventID>2486</EventID> <Version>0</Version> <Level>2</Level> <Task>2414</Task> <Opcode>0</Opcode> <Keywords>0x2000000000000042</Keywords> <TimeCreated SystemTime="2012-06-07T14:16:34.616499600Z" /> <EventRecordID>11916</EventRecordID> <Correlation /> <Execution ProcessID="3008" ThreadID="6996" /> <Channel>Application</Channel> <Computer>vee-pc</Computer> <Security UserID="S-1-5-21-2753614643-3522538917-4071044258-1001" /> </System> <EventData> <Data Name="ApplicationId">microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail</Data> </EventData> </Event> Now I'm stuck. It tells me "Activation of app microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail failed with error: The app didn't start. See the Microsoft-Windows-TWinUI/Operational log for additional information." but I can't find the Microsoft-Windows-TWinUI/Operational log. I'm starting a bounty. I found the TWinUI/Operational log. It only tells me: Log Name: Microsoft-Windows-TWinUI/Operational Source: Microsoft-Windows-Immersive-Shell Date: 07/06/2012 16.28.57 Event ID: 5961 Task Category: (5961) Level: Error Keywords: User: VEE-PC\Vittorio Computer: vee-pc Description: Activation of the app microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail for the Windows.BackgroundTasks contract failed with error: The app didn't start.. Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="Microsoft-Windows-Immersive-Shell" Guid="{315A8872-923E-4EA2-9889-33CD4754BF64}" /> <EventID>5961</EventID> <Version>0</Version> <Level>2</Level> <Task>5961</Task> <Opcode>0</Opcode> <Keywords>0x4000000000000000</Keywords> <TimeCreated SystemTime="2012-06-07T14:28:57.238140800Z" /> <EventRecordID>6536</EventRecordID> <Correlation /> <Execution ProcessID="3008" ThreadID="2624" /> <Channel>Microsoft-Windows-TWinUI/Operational</Channel> <Computer>vee-pc</Computer> <Security UserID="S-1-5-21-2753614643-3522538917-4071044258-1001" /> </System> <EventData> <Data Name="AppId">microsoft.windowscommunicationsapps_8wekyb3d8bbwe!Microsoft.WindowsLive.Mail</Data> <Data Name="ContractId">Windows.BackgroundTasks</Data> <Data Name="ErrorCode">-2144927141</Data> </EventData> </Event> I need to go deeper. I found a forum thread that told me to look for "DCOM" errors. I found this one related to the app crash "The server Microsoft.WindowsLive.Mail.wwa did not register with DCOM within the required timeout." Log Name: System Source: Microsoft-Windows-DistributedCOM Date: 07/06/2012 16.46.45 Event ID: 10010 Task Category: None Level: Error Keywords: Classic User: VEE-PC\Vittorio Computer: vee-pc Description: The server Microsoft.WindowsLive.Mail.wwa did not register with DCOM within the required timeout. Event Xml: <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"> <System> <Provider Name="Microsoft-Windows-DistributedCOM" Guid="{1B562E86-B7AA-4131-BADC-B6F3A001407E}" EventSourceName="DCOM" /> <EventID Qualifiers="0">10010</EventID> <Version>0</Version> <Level>2</Level> <Task>0</Task> <Opcode>0</Opcode> <Keywords>0x8080000000000000</Keywords> <TimeCreated SystemTime="2012-06-07T14:46:45.586943800Z" /> <EventRecordID>2763</EventRecordID> <Correlation /> <Execution ProcessID="804" ThreadID="2364" /> <Channel>System</Channel> <Computer>vee-pc</Computer> <Security UserID="S-1-5-21-2753614643-3522538917-4071044258-1001" /> </System> <EventData> <Data Name="param1">Microsoft.WindowsLive.Mail.wwa</Data> </EventData> </Event>

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• Wpf progressbar not updating during method calculation

  - by djerry

  Hey guys, In my app, i have an import option, to read info from a .csv or .txt file and write it to a database. To test, i"m just using 200-300 lines of data. At the beginning of the method, i calculate number of objects/lines to be read. Every time an object is written to the database, i want to update my progressbar. This is how i do it : private void Update(string path) { double lines = 0; using (StreamReader reader = new StreamReader(path)) while ((reader.ReadLine()) != null) lines++; if (lines != 0) { double progress = 0; string lijn; double value = 0; List<User> users = new List<User>(); using (StreamReader reader = new StreamReader(path)) while ((line = reader.ReadLine()) != null) { progress++; value = (progress / lines) * 100.0; updateProgressBar(value); try { User user = ProcessLine(lijn); } catch (ArgumentOutOfRangeException) { continue; } catch (Exception) { continue; } } return; } else { //non relevant code } } To update my progressbar, i'm checking if i can change the ui of the progressbar like this : delegate void updateProgressbarCallback(double value); private void updateProgressBar(double value) { if (pgbImportExport.Dispatcher.CheckAccess() == false) { updateProgressbarCallback uCallBack = new updateProgressbarCallback(updateProgressBar); pgbImportExport.Dispatcher.Invoke(uCallBack, value); } else { Console.WriteLine(value); pgbImportExport.Value = value; } } When i!m looking at the output, the values are calculated correctly, but the progressbar is only showing changes after the method has been called completely, so when the job is done. That's too late to show feedback to the user. Can anyone help me solve this. EDIT : I'm also trying to show some text in labels to tell te user what is being done, and those aren't udpated till after the method is complete. Thanks in advance.

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• glitchy stuttery iphone game loop

  - by Adam

  This is a problem I've been trying to solve for a few days now, and I've looked at the various solutions on stackoverflow and nothing has really seemed to work for me. I'm making an iPhone game with OpenGLES graphics and accelerometer input, at this point it's very simple, but the rendering is already pretty bad... it stutters and seems to jump back or forward in time. It doesn't happen a lot, but it happens enough to be a problem. I mean, who wants to play a game where a bullet gets magically transported into the player, and then it's game over? No one. I've tried using NSTimer for the game loop, I've tried using a separate thread (with a frame rate and continuously) I've tried using different frame rates, from 30FPS to 60FPS (It seems to have a max frame rate around 45FPS, but no problems at 30FPS) I've tried using timeIntervalSince1970 and CFGetAbsoluteTime to measure loop time, with no noticeable diffence Anyone have any ideas on what is the best way to get this looking better? One of the posts I've read suggested running the simulation at a fixed frame rate and then just render as fast as possible, does that seem like a good idea?

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• PHP database simulation

  - by Emdiesse

  I have a PHP script that works by calling items from a database based upon the time they were placed in there and it deletes them if they are older than 5 minutes. Basically, I want to now simulate what would happen if this database was being updated regularly. So I was considering sticking in some code that loads an XML file then goes through and parses that into the database based upon the time data located within a node of the xml data... but the problem there is I want it to continually loop through an enter this data so it'll never actually run the other processes So I was thinking of having another PHP script do that that could do this independantly of the php script that is going to display this data... In theory: I am looking to have a button that I can press and it will then run some php code to load up an XML file from a directory on my web server and then iterate though the data sending the data, to a database, based upon the time within a node in the PHP script and when the script was first called So back to my page that displayed the data... if I continually hit refresh it will contain different results each time because data is being added by the other process and this php script removes the older data when it is refreshed Any information on this? Is there a way I can silently, and safely, run a php script without it being loaded into a browser... like a thread!?

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• Boost::Mutex & Malloc

  - by M. Tibbits

  Hi all, I'm trying to use a faster memory allocator in C++. I can't use Hoard due to licensing / cost. I was using NEDMalloc in a single threaded setting and got excellent performance, but I'm wondering if I should switch to something else -- as I understand things, NEDMalloc is just a replacement for C-based malloc() & free(), not the C++-based new & delete operators (which I use extensively). The problem is that I now need to be thread-safe, so I'm trying to malloc an object which is reference counted (to prevent excess copying), but which also contains a mutex pointer. That way, if you're about to delete the last copy, you first need to lock the pointer, then free the object, and lastly unlock & free the mutex. However, using malloc to create a boost::mutex appears impossible because I can't initialize the private object as calling the constructor directly ist verboten. So I'm left with this odd situation, where I'm using new to allocate the lock and nedmalloc to allocate everything else. But when I allocate a large amount of memory, I run into allocation errors (which disappear when I switch to malloc instead of nedmalloc ~ but the performance is terrible). My guess is that this is due to fragmentation in the memory and an inability of nedmalloc and new to place nice side by side. There has to be a better solution. What would you suggest?

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• How to use boost::bind with non-copyable params, for example boost::promise ?

  - by zhengxi

  Some C++ objects have no copy constructor, but have move constructor. For example, boost::promise. How can I bind those objects using their move constructors ? #include <boost/thread.hpp> void fullfil_1(boost::promise<int>& prom, int x) { prom.set_value(x); } boost::function<void()> get_functor() { // boost::promise is not copyable, but movable boost::promise<int> pi; // compilation error boost::function<void()> f_set_one = boost::bind(&fullfil_1, pi, 1); // compilation error as well boost::function<void()> f_set_one = boost::bind(&fullfil_1, std::move(pi), 1); // PS. I know, it is possible to bind a pointer to the object instead of // the object itself. But it is weird solution, in this case I will have // to take cake about lifetime of the object instead of delegating that to // boost::bind (by moving object into boost::function object) // // weird: pi will be destroyed on leaving the scope boost::function<void()> f_set_one = boost::bind(&fullfil_1, boost::ref(pi), 1); return f_set_one; }

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• notify listener inside or outside inner synchronization

  - by Jary Zeels

  Hello all, I am struggling with a decision. I am writing a thread-safe library/API. Listeners can be registered, so the client is notified when something interesting happens. Which of the two implementations is most common? class MyModule { protected Listener listener; protected void somethingHappens() { synchronized(this) { ... do useful stuff ... listener.notify(); } } } or class MyModule { protected Listener listener; protected void somethingHappens() { Listener l = null; synchronized(this) { ... do useful stuff ... l = listener; } l.notify(); } } In the first implementation, the listener is notified inside the synchronization. In the second implementation, this is done outside the synchronization. I feel that the second one is advised, as it makes less room for potential deadlocks. But I am having trouble to convince myself. A downside of the second imlementation is that the client might receive 'incorrect' notifications, which happens if it accessed the module prior to the l.notify() statement. thanks a lot

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• Java problem with multiple threads when executing a runnable jar file

  - by Spi1988

  I have developed a Java Swing application, which uses the SwingWorker class to perform some long running tasks. When the application is run from the IDE (Netbeans), I can start multiple long running tasks simultaneously without any problem. I created a runnable jar file for the application, in order to be able to run it from outside the IDE. The application when run from this jar file works well with the only exception that it doesn't allow me to start 2 long running tasks simultaneously. When I start the first task (assume it takes 2 minitues to complete), every thing works fine, the UI does not freeze (it never freezes). However, when I try to run another task (assume it takes just 10 seconds, therefore it should finish before the first task) while the first task has not yet completed, nothing seems to happen. In reality, the second task would have started, and also finished its processing, however its results are only displayed once the first task completes. I dunno why this is happening. Is there some restriction on the number of threads which could run simultaneously on the JVM? Are there any jvm arguments which i could try to solve this problem. I hope i explained my problem well. Thanks in advance, Peter Bartolo

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• Impossible to be const-correct when combining data and it's lock?

  - by Graeme

  I've been looking at ways to combine a piece of data which will be accessed by multiple threads alongside the lock provisioned for thread-safety. I think I've got to a point where I don't think its possible to do this whilst maintaining const-correctness. Take the following class for example: template <typename TType, typename TMutex> class basic_lockable_type { public: typedef TMutex lock_type; public: template <typename... TArgs> explicit basic_lockable_type(TArgs&&... args) : TType(std::forward<TArgs...>(args)...) {} TType& data() { return data_; } const TType& data() const { return data_; } void lock() { mutex_.lock(); } void unlock() { mutex_.unlock(); } private: TType data_; mutable TMutex mutex_; }; typedef basic_lockable_type<std::vector<int>, std::mutex> vector_with_lock; In this I try to combine the data and lock, marking mutex_ as mutable. Unfortunately this isn't enough as I see it because when used, vector_with_lock would have to be marked as mutable in order for a read operation to be performed from a const function which isn't entirely correct (data_ should be mutable from a const). void print_values() const { std::lock_guard<vector_with_lock>(values_); for(const int val : values_) { std::cout << val << std::endl; } } vector_with_lock values_; Can anyone see anyway around this such that const-correctness is maintained whilst combining data and lock? Also, have I made any incorrect assumptions here?

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• C# struct with object as data member

  - by source-energy

  As we know, in C# structs are passed by value, not by reference. So if I have a struct with the following data members: private struct MessageBox { // data members private DateTime dm_DateTimeStamp; // a struct type private TimeSpan dm_TimeSpanInterval; // also a struct private ulong dm_MessageID; // System.Int64 type, struct private String dm_strMessage; // an object (hence a reference is stored here) // more methods, properties, etc ... } So when a MessageBox is passed as a parameter, a COPY is made on the stack, right? What does that mean in terms of how the data members are copied? The first two are struct types, so copies should be made of DateTime and TimeSpan. The third type is a primitive, so it's also copied. But what about the dm_strMessage, which is a reference to an object? When it's copied, another reference to the same String is created, right? The object itself resides in the heap, and is NOT copied (there is only one instance of it on the heap.) So now we have to references to the same object of type String. If the two references are accessed from different threads, it's conceivable that the String object could be corrupted by being modified from two different directions simultaneously. The MSDN documentation says that System.String is thread safe. Does that mean that the String class has a built-in mechanism to prevent an object being corrupted in exactly the type of situation described here? I'm trying to figure out if my MessageBox struct has any potential flaws / pitfalls being a structure vs. a class. Thanks for any input. Source.Energy.

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• problem with implementing a simple work queue

  - by John Deerikio

  Hi all, I am having troubles with implementing a simple work queue. Doing some analysis, I am facing a subtle problem. The work queue is backed by a regular linked list. The code looks like this (simplified): 0. while (true) 1. while (enabled == true) 2. acquire lock on the list and get the next action to be executed (blocking operation) (store it in a local variable) 3. execute the action (outside the lock on the list on previous line) 4. get lock on this work queue 5. wait until this work queue has been notified (triggered when setEnabled(true) has been callled) The setEnabled(e) operation looks like this (simplified): enabled = e if (enabled == true) acquire lock on this work queue and do notify() Although this works, there is a condition in which a deadlock occurs. It happens in the following rare situation: while an action is being executed, setEnabled(false) is called just before step (4) is entered, setEnabled(true) is called now step (5) keeps waiting forever, because this work queue has already been notified How do I solve this? I have been looking at this for some time, but I cannot come up with a solution. Please note I am fairly new to thread synchronization. Thanks a lot.

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• Is locking on the requested object a bad idea?

  - by Quick Joe Smith

  Most advice on thread safety involves some variation of the following pattern: public class Thing { private static readonly object padlock = new object(); private string stuff, andNonsense; public string Stuff { get { lock (Thing.padlock) { if (this.stuff == null) this.stuff = "Threadsafe!"; } return this.stuff; } } public string AndNonsense { get { lock (Thing.padlock) { if (this.andNonsense == null) this.andNonsense = "Also threadsafe!"; } return this.andNonsense; } } // Rest of class... } In cases where the get operations are expensive and unrelated, a single locking object is unsuitable because a call to Stuff would block all calls to AndNonsense, degrading performance. And rather than create a lock object for each call, wouldn't it be better to acquire the lock on the member itself (assuming it is not something that implements SyncRoot or somesuch for that purpose? For example: public string Stuff { get { lock (this.stuff) { // Pretend that this is a very expensive operation. if (this.stuff == null) this.stuff = "Still threadsafe and good?"; } return this.stuff; } } Strangely, I have never seen this approach recommended or warned against. Am I missing something obvious?

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• Does Interlocked guarantee visibility to other threads in C# or do I still have to use volatile?

  - by Lirik

  I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Interlocked. This is needed in scenarios where other libraries, interfaces or hardware can access your variable and update it anytime, or need the most recent version. Does Interlocked guarantee visibility of the atomic operation to all threads, or do I still have to use the volatile keyword on the value in order to guarantee visibility of the change? Here is my example: public class CountDownLatch { private volatile int m_remain; // <--- do I need the volatile keyword there since I'm using Interlocked? private EventWaitHandle m_event; public CountDownLatch (int count) { Reset(count); } public void Reset(int count) { if (count < 0) throw new ArgumentOutOfRangeException(); m_remain = count; m_event = new ManualResetEvent(false); if (m_remain == 0) { m_event.Set(); } } public void Signal() { // The last thread to signal also sets the event. if (Interlocked.Decrement(ref m_remain) == 0) m_event.Set(); } public void Wait() { m_event.WaitOne(); } }

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• Timer in java ,time difference problem

  - by javatechi

  I want to create a timer for my app. The sample code is shown below. When the method datetwo() is called the same time in milliseconds is shown as there in the main method. Please help me out with this import java.util.Date; import java.util.Timer; public class TimerChe { Timer timer; static Date date = new Date(); static Date date2 = new Date(); public static void timerMethod(){ new Thread() { public void run() { try { while (true) { sleep(10000); datetwo(); } } catch (InterruptedException ex) { } } }.start(); } public static void datetwo() { System.out.println ("OK, It's time to do something!") ; System.out.println("The Time is " + date2.getTime() + " milliseconds since 1970/01/01"); } public static void main(String args[]) throws Exception { System.out.println("The Time is " + date.getTime() + " milliseconds since 1970/01/01" ); System.out.println ("Schedule something to do in the mean time.") ; timerMethod(); } }

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• Noise with multi-threaded raytracer

  - by herber88

  This is my first multi-threaded implementation, so it's probably a beginners mistake. The threads handle the rendering of every second row of pixels (so all rendering is handled within each thread). The problem persists if the threads render the upper and lower parts of the screen respectively. Both threads read from the same variables, can this cause any problems? From what I've understood only writing can cause concurrency problems... Can calling the same functions cause any concurrency problems? And again, from what I've understood this shouldn't be a problem... The only time both threads write to the same variable is when saving the calculated pixel color. This is stored in an array, but they never write to the same indices in that array. Can this cause a problem? Multi-threaded rendered image (Spam prevention stops me from posting images directly..) Ps. I use the exactly same implementation in both cases, the ONLY difference is a single vs. two threads created for the rendering.

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• java Sockets and Threads Problem

  - by vs4vijay

  I am doin a Some Socket Programing Stuff in Java.. Here i have created a button(Create Server)..and when i click it ,it starts server...but i want to change the button name to (Stop Server) after Starting the server... so i did this.. but when i press start server it starts and the button name remains the same... and when a client gets connected to it ,then it change the name to stop server... tell me whats the wrong with this code?? Here is My a SomePart Of Code... public void actionPerformed(ActionEvent ex) { if(ex.getActionCommand() == "CreateServer") { bt1.setText("Stop Server"); bt2.setEnabled(false); b5.setText("Server Started On Port " + tf2.getText()); System.out.println("Server started 1"); create(Integer.parseInt(tf2.getText())); //my func. to create server System.out.println("Server started 2"); } } and my create() fucn. contains some sockets and thread...so tell me what the problem...

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• Why is UITableView not reloading (even on the main thread)?

  - by radesix

  I have two programs that basically do the same thing. They read an XML feed and parse the elements. The design of both programs is to use an asynchronous NSURLConnection to get the data then to spawn a new thread to handle the parsing. As batches of 5 items are parsed it calls back to the main thread to reload the UITableView. My issue is it works fine in one program, but not the other. I know that the parsing is actually occuring on the background thread and I know that [tableView reloadData] is executing on the main thread; however, it doesn't reload the table until all parsing is complete. I'm stumped. As far as I can tell... both programs are structured exactly the same way. Here is some code from the app that isn't working correctly. - (void)startConnectionWithURL:(NSString *)feedURL feedList:(NSMutableArray *)list { self.feedList = list; // Use NSURLConnection to asynchronously download the data. This means the main thread will not be blocked - the // application will remain responsive to the user. // // IMPORTANT! The main thread of the application should never be blocked! Also, avoid synchronous network access on any thread. // NSURLRequest *feedURLRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:feedURL]]; self.bloggerFeedConnection = [[[NSURLConnection alloc] initWithRequest:feedURLRequest delegate:self] autorelease]; // Test the validity of the connection object. The most likely reason for the connection object to be nil is a malformed // URL, which is a programmatic error easily detected during development. If the URL is more dynamic, then you should // implement a more flexible validation technique, and be able to both recover from errors and communicate problems // to the user in an unobtrusive manner. NSAssert(self.bloggerFeedConnection != nil, @"Failure to create URL connection."); // Start the status bar network activity indicator. We'll turn it off when the connection finishes or experiences an error. [UIApplication sharedApplication].networkActivityIndicatorVisible = YES; } - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { self.bloggerData = [NSMutableData data]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { [bloggerData appendData:data]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { self.bloggerFeedConnection = nil; [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; // Spawn a thread to fetch the link data so that the UI is not blocked while the application parses the XML data. // // IMPORTANT! - Don't access UIKit objects on secondary threads. // [NSThread detachNewThreadSelector:@selector(parseFeedData:) toTarget:self withObject:bloggerData]; // farkData will be retained by the thread until parseFarkData: has finished executing, so we no longer need // a reference to it in the main thread. self.bloggerData = nil; } If you read this from the top down you can see when the NSURLConnection is finished I detach a new thread and call parseFeedData. - (void)parseFeedData:(NSData *)data { // You must create a autorelease pool for all secondary threads. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; self.currentParseBatch = [NSMutableArray array]; self.currentParsedCharacterData = [NSMutableString string]; self.feedList = [NSMutableArray array]; // // It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not desirable // because it gives less control over the network, particularly in responding to connection errors. // NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data]; [parser setDelegate:self]; [parser parse]; // depending on the total number of links parsed, the last batch might not have been a "full" batch, and thus // not been part of the regular batch transfer. So, we check the count of the array and, if necessary, send it to the main thread. if ([self.currentParseBatch count] > 0) { [self performSelectorOnMainThread:@selector(addLinksToList:) withObject:self.currentParseBatch waitUntilDone:NO]; } self.currentParseBatch = nil; self.currentParsedCharacterData = nil; [parser release]; [pool release]; } In the did end element delegate I check to see that 5 items have been parsed before calling the main thread to perform the update. - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { if ([elementName isEqualToString:kItemElementName]) { [self.currentParseBatch addObject:self.currentItem]; parsedItemsCounter++; if (parsedItemsCounter % kSizeOfItemBatch == 0) { [self performSelectorOnMainThread:@selector(addLinksToList:) withObject:self.currentParseBatch waitUntilDone:NO]; self.currentParseBatch = [NSMutableArray array]; } } // Stop accumulating parsed character data. We won't start again until specific elements begin. accumulatingParsedCharacterData = NO; } - (void)addLinksToList:(NSMutableArray *)links { [self.feedList addObjectsFromArray:links]; // The table needs to be reloaded to reflect the new content of the list. if (self.viewDelegate != nil && [self.viewDelegate respondsToSelector:@selector(parser:didParseBatch:)]) { [self.viewDelegate parser:self didParseBatch:links]; } } Finally, the UIViewController delegate: - (void)parser:(XMLFeedParser *)parser didParseBatch:(NSMutableArray *)parsedBatch { NSLog(@"parser:didParseBatch:"); [self.selectedBlogger.feedList addObjectsFromArray:parsedBatch]; [self.tableView reloadData]; } If I write to the log when my view controller delegate fires to reload the table and when cellForRowAtIndexPath fires as it's rebuilding the table then the log looks something like this: parser:didParseBatch: parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: parser:didParseBatch: parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: parser:didParseBatch: parser:didParseBatch: parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath Clearly, the tableView is not reloading when I tell it to every time. The log from the app that works correctly looks like this: parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath parser:didParseBatch: tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath tableView:cellForRowAtIndexPath

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• WPF: Updating visibility of controls not updating the screen

  - by Brad McBride

  I will preface this by stating that I am new to WPF programming and may be making multiple errors. Any insight that can be provided to help me improve in my skills are greatly appreciated. I am working with a WPF application and am looping through a list of objects that contain properties that describe a document that should be built on the fly and automatically printed. I am attempting to display a small grid in the interface that shows the document being built before it is printed. This serves two purposes: one, it allows the user to see work being done by the application. Two, it renders the items on the screen so that I can then have something to actually print since WPF appears to not be able to load an image for printing dynamicaly without displaying it on the screen. In my code, I am setting the various elements in the grid and setting the visibility to visible. However, the UI is not updating and the printed document doesn't look as intended since the image never shows up on the screen. Here is the XAML that I have set up <Grid x:Name="LayoutRoot" Background="Black"> <Grid Name="previewGrid" Grid.Row="1" Grid.Column="1" Background="White" Visibility="Hidden"> <Canvas Name="pageCanvas" HorizontalAlignment="Center" VerticalAlignment="Center"> <Grid Name="pageGrid" Width="163" Height="211"> <Grid.ColumnDefinitions> <ColumnDefinition Width="81.5"></ColumnDefinition> <ColumnDefinition Width="81.5"></ColumnDefinition> </Grid.ColumnDefinitions> <TextBlock Grid.Column="0" Name="copyright" TextAlignment="Center" HorizontalAlignment="Center" VerticalAlignment="Bottom"></TextBlock> <Image Name="pageImage" Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Center"></Image> </Grid> </Canvas> .....canvas for pages 2-4 not shown but structure is the same as for pageGrid..... </Grid> </Grid> </Window> Here is the code behind that is supposed to set the elements. previewGrid.Visibility = Windows.Visibility.Visible pageURI = New Uri(pageCollection(i).iamgeURL, UriKind.Absolute) pageGrid.Visibility = Windows.Visibility.Visible bmp.BeginInit() bmp.StreamSource = getCachedURLStream(cardURI) bmp.EndInit() pageImage.Source = bmp copyright.Text = copyrightText cardPreviewGrid.UpdateLayout() ' More code that prints the visual element pageGrid previewGrid.Visibility = Windows.Visibility.Hidden The code in codebehind loops through a number of times depending on how many different documents the user prints. Basically it builds a visual element for a page, prints an XPS version of it and then builds the next page and prints it, etc. Once all pages have been processed, the job is actually sent to the printer. The only purpose of this application is to let the user print these documents so there is not other task that they can do in the application while the documents print. I thought that putting this task in a background thread would help to update the UI but since I am trying to manipulate items directly on the UI thread it would appear that this option won't work for me. What am I doing wrong here and how can I improve the code so that I can get the behavior that I am trying to achieve?

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