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• What's a way for a client to automatically resolve the ip address of a server?

  - by zooropa

  The project I am working on is a client/server architecture. In a LAN environment, I want the client's to be able to automatically determine the server's address. I want to avoid having to manually configure each client with the ip address of the server. What is the best way to do this? Some alternatives I have thought about doing are: The server could listen for broadcast packets from the clients. The message from the client would be a request for the IP address of the server. The server would respond with its address. The machine running my project's server could also have a bind server running. The LAN's router could be configured to use it as one of its DNS servers. I think I saw that there is a bind library. Does that mean I can build the bind service into my server so that bind doesn't have to be installed on the server? Any other ideas? What have you done in the past? What are the pros/cons of these approaches and others that might be suggested? Thanks for your help!

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• jQuery event "looping"

  - by Deryck

  Hi I´m trying to code a tooltip (Yes I know, I have my reasons to avoid plugins in this case) in jQuery. Whe I show the tooltip and leave the mouse in the same place the show and hide repeats forever. It´s like the element triggers the hover event again and again and again. I try unbind for the event but it does not work neither. $("td.with-tooltip").mouseover( function() { var offset = $(this).offset(); var baseX = offset.left; var baseY = offset.top; var inputWidth = $(this).width(); var baseX = baseX + 50; var baseY = baseY - $(".desc").height(); $(".desc div").html($(this).attr("title")); $(".desc").css({"position":"absolute", "left": baseX, "top": baseY }).fadeIn(); $(this).unbind("mouseover"); }).mouseleave( function() { $(".desc").fadeOut(); }); What can I do? thanks.

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• How to detect changing directory size in Perl

  - by materiamage

  Hello, I am trying to find a way of monitoring directories in Perl, in particular the size of a directory, and upon detecting a change in directory size, perform a particular action. The issue I have is with large files that require a noticeable amount of time to copy into this directory, i.e. 100MB. What happens (in Windows, not Unix) is the system reserves enough disk space for the entire file, even though the file is still copying in progress. This causes problems for me, because my script will try to perform an action on this file that has not finished copying over. I can easily detect directory size changes in Unix via 'du', but 'du' in Windows does not behave the same way. Are there any accurate methods of detecting directory size changes in Perl? Edit: Some points to clarify: - My Perl script is only monitoring a particular directory, and upon detecting a new file or a new directory, perform an action on this new file or directory. It is not copying any files; users on the network will be copying files into the directory I am monitoring. - The problem occurs when a new file or directory appears (copied, not moved) that is significantly large ( 100MB, but usually a couple GB) and my program fires before this copy completes - In Unix I can easily 'du' to see that the file/directory in question is growing in size, and take the appropriate action - In Windows the size is static, so I cannot detect this change - opendir/readdir/closedir is not feasible, as some of the directories that appear may contain thousands of files, and I want to avoid the overhead of Ideally I would like my program to be triggered on change, but I am not sure how to do this. As of right now it busy waits until it detects a change. The change in file/directory size is not in my control.

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• asp.net 4.0 webforms - how to keep ContentPlaceHolder1_ out of client id's in a simple way?

  - by James Manning

  I'm attempting to introduce master pages to an existing webforms site that's avoided using them because of client id mangling in the past (and me not wanting to deal with the mangling and doing <% foo.ClientID % everywhere :) GOAL: use 'static' id values (whatever is in the server control's id attribute) except for data-bound / repeating controls which would break for those cases and therefore need suffixes or whatever to differentiate (basically, Predictable) Now that the site migrated to ASP.NET 4.0, I first attempted to use ClientIDMode of Static (in the web.config) but that broke too many places doing repeating controls (checkboxes inside gridviews, for instance) since they all resulted with the same id. So, I then tried Predictable (again, just in the web.config) so that the repeating controls wouldn't have conflicting id's, and it works well except that the master page content placeholder (which is indeed a naming container) is still reflecting in the resulting client id's (for instance, ContentPlaceHolder1_someCheckbox). Certainly I could leave the web.config setting as static and then go through all the databound/repeating controls switch them to Predictable, but I'm hoping there's some easier/simpler way to get that effect without having to scatter ClientIDMode attributes in those N number of places (or extend all those databound controls with my own usercontrol that just sets clientidmode, or whatever). I even thought of leaving web.config set to static and doing a master or basepage handler (preinit? not sure if that would work or not) that would go walk Controls with OfType<INamingContainer() (might be a better choice on the type, but that seems like a good starting choice looking at repeater and gridview) and then set those to Predictable so I'd get static for all my 'normal' things outside of repeating controls but not have to deal with static inside things like gridview/repeater/etc. I don't see any way to mark the content placeholder such that it 'opts out' of being included in child id's - setting the ID of the placeholder to empty/blank doesn't work as it's a required attribute :) At that point I figured there was a better/simpler way that I was missing and decided to ask on SO :) Edit: I thought about changing all my 'fetch by id' jquery calls from $('#foo') to fetch_by_id('foo') and then having that function return the 'right one' by checking $('#foo').length and then $('#ContentPlaceHolder1_foo').length (and maybe other patterns) or even just have it return $('#foo, #ContentPlaceHolder1_foo') (again, potentially other patterns) but changing all the places I fetch elements by id seemed pretty ugly too, and I'd like to avoid that abstraction layer if possible to do so easily :)

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• HTML + CSS: fixed background image and body width/min-width (including fiddle)

  - by insertusernamehere

  So, here is my problem. I'm kinda stuck at the moment. I have a huge background image and content in the middle with those attributes: content is centered with margin auto and has a fixed width the content is related to the image (like the image is continued within the content) this relation is only horizontally (vertically scrolling moves everything around) This works actually fine (I'm only talking desktop, not mobile here :) ) with a position fixed on the huge background image. The problem that occurs is the following: When I resize the window to "smaller than the content" the background image gets it width from the body instead of the viewport. So the relation between content and image gets lost. Now I have this little JavaScript which does the trick, but this is of course some overhead I want to avoid: $(window).resize(function(){ img.css('left', (body.width() - img.width()) / 2 ); }); This works with a fixed positioned image, but can get a litty jumpy while calculating. I also tried things like that: <div id="test" style=" position: absolute; z-index: 0; top: 0; left: 0; width: 100%: height: 100%; background: transparent url(content/dummy/brand_backgroud_1600_1.jpg) no-repeat fixed center top; "></div> But this gets me back to my problem described. Is there any "script-less", elegant solution for this problem? UPDATE: now with Fiddle The one I'm trying to solve: http://jsfiddle.net/insertusernamehere/wPmrm/ The one with Javascript that works: http://jsfiddle.net/insertusernamehere/j5E8z/ NOTE The image size is always fixed. The image never gets scaled by the browser. In the JavaScript example it get's blown. So don't care about the size.

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• ProtoInclude for fields ?

  - by Big

  I have a simple object [ProtoContract] public class DataChangedEventArgs<T> : EventArgs { private readonly object key; private readonly T data; private readonly DataChangeType changeType; ///<summary> /// Key to identify the data item ///</summary> public object Key { get { return key; } } [ProtoMember(2, IsRequired = true)] public T Data { get { return data; } } [ProtoMember(3, IsRequired = true)] public DataChangeType ChangeType { get { return changeType; } } and I have a problem with the key. Its type is object, but it can be either int, long or string. I would intuitively use a ProtoInclude attribute to say "expect these types" but unfortunately they are class only attribute. Does anybody has any idea how I could work around this ? For background, the public object Key is here for historical reasons (and all over the place) so I would very much like to avoid the mother of all refactorings ;-) Any chance I could get this to Serialize, even force it to Serialize as a string ?

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• How to create instances of a class from a static method?

  - by Pierre

  Hello. Here is my problem. I have created a pretty heavy readonly class making many database calls with a static "factory" method. The goal of this method is to avoid killing the database by looking in a pool of already-created objects if an identical instance of the same object (same type, same init parameters) already exists. If something was found, the method will just return it. No problem. But if not, how may I create an instance of the object, in a way that works with inheritance? >>> class A(Object): >>> @classmethod >>> def get_cached_obj(self, some_identifier): >>> # Should do something like `return A(idenfier)`, but in a way that works >>> class B(A): >>> pass >>> A.get_cached_obj('foo') # Should do the same as A('foo') >>> A().get_cached_obj('foo') # Should do the same as A('foo') >>> B.get_cached_obj('bar') # Should do the same as B('bar') >>> B().get_cached_obj('bar') # Should do the same as B('bar') Thanks.

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• C# DynamicMethod prelink

  - by soywiz

  I'm the author of a psp emulator made in C#. I'm generating lots of "DynamicMethod" using ILGenerator. I'm converting assembly code into an AST, and then generating IL code and building that DynamicMethod. I'm doing this in another thread, so I can generate new methods while the program is executing others so it can run smoothly. My problem is that the native code generation is lazy, so the machine code is generated when the function is called, not when the IL is generated. So it generates in the program executing thread, native code generation is prettly slow as it is the asm-ast-il step. I have tried the Marshal.Prelink method that it is suposed to generate the machine code before executing the function. It does work on Mono, but it doesn't work on MS .NET. Marshal.Prelink(MethodInfo); Is there a way of prelinking a DynamicMethod on MS .NET? I thought adding a boolean parameter to the function that if set, exits the function immediately so no code is actually executed. I could "prelink" that way, but I think that's a nasty solution I want to avoid. Any idea?

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• Generic FSM for game in C++ ?

  - by Mr.Gando

  Hello, I was wondering if there's a way I could code some kind of "generic" FSM for a game with C++?. My game has a component oriented design, so I use a FSM Component. my Finite State Machine (FSM) Component, looks more or less this way. class gecFSM : public gecBehaviour { public: //Constructors gecFSM() { state = kEntityState_walk; } gecFSM(kEntityState s) { state = s; } //Interface void setRule(kEntityState initialState, int inputAction, kEntityState resultingState); void performAction(int action); private: kEntityState fsmTable[MAX_STATES][MAX_ACTIONS]; }; I would love to hear your opinions/ideas or suggestions about how to make this FSM component, generic. With generic I mean: 1) Creating the fsmTable from an xml file is really easy, I mean it's just a bunch of integers that can be loaded to create an MAX_STATESxMAX_ACTION matrix. void gecFSM::setRule(kEntityState initialState, int inputAction, kEntityState resultingState) { fsmTable[initialState][inputAction] = resultingState; } 2) But what about the "perform Action" method ? void gecFSM::performAction(int action) { switch( smTable[ ownerEntity->getState() ][ action ] ) { case WALK: /*Walk action*/ break; case STAND: /*Stand action*/ break; case JUMP: /*Jump action*/ break; case RUN: /*Run action*/ break; } } What if I wanted to make the "actions" and the switch generic? This in order to avoid creating a different FSM component class for each GameEntity? (gecFSMZombie, gecFSMDryad, gecFSMBoss etc ?). That would allow me to go "Data Driven" and construct my generic FSM's from files for example. What do you people suggest?

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• Is there any reason to use C instead of C++ for embedded development?

  - by Piotr Czapla

  Question I have two compilers on my hardware C++ and C89 I'm thinking about using C++ with classes but without polymorphism (to avoid vtables). The main reasons I’d like to use C++ are: I prefer to use “inline” functions instead of macro definitions. I’d like to use namespaces as I prefixes clutter the code. I see C++ a bit type safer mainly because of templates, and verbose casting. I really like overloaded functions and constructors (used for automatic casting). Do you see any reason to stick with C89 when developing for very limited hardware (4kb of RAM)? Conclusion Thank you for your answers, they were really helpful! I though the subject through and I will stick with C mainly because: It is easier to predict actual code in C and this is really important if you have only 4kb of ram. My team consists of C developers mainly so advance features of C++ won't be frequently used. I've found a way to inline functions in my C compiler (C89). It is hard to accept one answer as you provided so many good answers. Unfortunately I can't create a wiki and accept it so I will choose one answer that made me think most.

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• Moving from a non-clustered PK to a clustered PK in SQL 2005

  - by adaptr

  HI all, I recently asked this question in another thread, and thought I would reproduce it here with my solution: What if I have an auto-increment INT as my non-clustered primary key, and there are about 15 foreign keys defined to it ? (snide comment about original designer being braindead in the original :) ) This is a 15M row table, on a live database, SQL Standard, so dropping indexes is out of the question. Even temporarily dropping the foreign key constraints will be difficult. I'm curious if anybody has a solution that causes minimal downtime. I tested this in our testing environment and finally found that the downtime wasn't as severe as I had originally feared. I ended up writing a script that drops all FK constraints, then drops the non-clustered key, re-creates the PK as a clustered index, and finally re-created all FKs WITH NOCHECK to avoid trawling through all FKs to check constraint compliance. Then I just enable the CHECK constraints to enable constraint checking from that point onwards, and all is dandy :) The most important thing to realize is that during the time the FKs are absent, there MUST NOT be any INSERTs or DELETEs on the parent table, as this may break the constraints and cause issues in the future. The total time taken for clustering a 15M row, 800MB index was ~4 minutes :)

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• Pump Messages During Long Operations + C# (it is urgent)

  - by Newbie

  Hi I have a web service that is doing huge computation and is taking more than a minute. I have generated the proxy file of the web service and then from my client end I am using the dll(of course I generated the proxy dll). My client side code is TimeSeries3D t = new TimeSeries3D(); int portfolioId = 4387919; string[] str = new string[2]; str[0] = "MKT_CAP"; DateRange dr = new DateRange(); dr.mStartDate = DateTime.Today; dr.mEndDate = DateTime.Today; Service1 sc = new Service1(); t = sc.GetAttributesForPortfolio(portfolioId, true, str, dr); But since it is taking to much time for the server to compute, after 1 minute I am receiving an error message The CLR has been unable to transition from COM context 0x33caf30 to COM context 0x33cb0a0 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. Kindly guide me what to do? It is very urgent. Thanks

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• Immutable classes in C++

  - by ereOn

  Hi, In one of my projects, I have some classes that represent entities that cannot change once created, aka. immutable classes. Example : A class RSAKey that represent a RSA key which only has const methods. There is no point changing the existing instance: if you need another one, you just create one. My objects sometimes are heavy and I enforced the use of smart pointers to avoid copy. So far, I have the following pattern for my classes: class RSAKey : public boost::noncopyable, public boost::enable_shared_from_this<RSAKey> { public: /** * \brief Some factory. * \param member A member value. * \return An instance. */ static boost::shared_ptr<const RSAKey> createFromMember(int member); /** * \brief Get a member. * \return The member. */ int getMember() const; private: /** * \brief Constructor. * \param member A member. */ RSAKey(int member); /** * \brief Member. */ const int m_member; }; So you can only get a pointer (well, a smart pointer) to a const RSAKey. To me, it makes sense, because having a non-const reference to the instance is useless (it only has const methods). Do you guys see any issue regarding this pattern ? Are immutable classes something common in C++ or did I just created a monster ? Thank you for your advices !

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• Are Dynamic Prepared Statements Bad? (with php + mysqli)

  - by John

  I like the flexibility of Dynamic SQL and I like the security + improved performance of Prepared Statements. So what I really want is Dynamic Prepared Statements, which is troublesome to make because bind_param and bind_result accept "fixed" number of arguments. So I made use of an eval() statement to get around this problem. But I get the feeling this is a bad idea. Here's example code of what I mean // array of WHERE conditions $param = array('customer_id'=>1, 'qty'=>'2'); $stmt = $mysqli->stmt_init(); $types = ''; $bindParam = array(); $where = ''; $count = 0; // build the dynamic sql and param bind conditions foreach($param as $key=>$val) { $types .= 'i'; $bindParam[] = '$p'.$count.'=$param["'.$key.'"]'; $where .= "$key = ? AND "; $count++; } // prepare the query -- SELECT * FROM t1 WHERE customer_id = ? AND qty = ? $sql = "SELECT * FROM t1 WHERE ".substr($where, 0, strlen($where)-4); $stmt->prepare($sql); // assemble the bind_param command $command = '$stmt->bind_param($types, '.implode(', ', $bindParam).');'; // evaluate the command -- $stmt->bind_param($types,$p0=$param["customer_id"],$p1=$param["qty"]); eval($command); Is that last eval() statement a bad idea? I tried to avoid code injection by encapsulating values behind the variable name $param. Does anyone have an opinion or other suggestions? Are there issues I need to be aware of?

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• Python's asyncore to periodically send data using a variable timeout. Is there a better way?

  - by Nick Sonneveld

  I wanted to write a server that a client could connect to and receive periodic updates without having to poll. The problem I have experienced with asyncore is that if you do not return true when dispatcher.writable() is called, you have to wait until after the asyncore.loop has timed out (default is 30s). The two ways I have tried to work around this is 1) reduce timeout to a low value or 2) query connections for when they will next update and generate an adequate timeout value. However if you refer to 'Select Law' in 'man 2 select_tut', it states, "You should always try to use select() without a timeout." Is there a better way to do this? Twisted maybe? I wanted to try and avoid extra threads. I'll include the variable timeout example here: #!/usr/bin/python import time import socket import asyncore # in seconds UPDATE_PERIOD = 4.0 class Channel(asyncore.dispatcher): def __init__(self, sock, sck_map): asyncore.dispatcher.__init__(self, sock=sock, map=sck_map) self.last_update = 0.0 # should update immediately self.send_buf = '' self.recv_buf = '' def writable(self): return len(self.send_buf) > 0 def handle_write(self): nbytes = self.send(self.send_buf) self.send_buf = self.send_buf[nbytes:] def handle_read(self): print 'read' print 'recv:', self.recv(4096) def handle_close(self): print 'close' self.close() # added for variable timeout def update(self): if time.time() >= self.next_update(): self.send_buf += 'hello %f\n'%(time.time()) self.last_update = time.time() def next_update(self): return self.last_update + UPDATE_PERIOD class Server(asyncore.dispatcher): def __init__(self, port, sck_map): asyncore.dispatcher.__init__(self, map=sck_map) self.port = port self.sck_map = sck_map self.create_socket(socket.AF_INET, socket.SOCK_STREAM) self.bind( ("", port)) self.listen(16) print "listening on port", self.port def handle_accept(self): (conn, addr) = self.accept() Channel(sock=conn, sck_map=self.sck_map) # added for variable timeout def update(self): pass def next_update(self): return None sck_map = {} server = Server(9090, sck_map) while True: next_update = time.time() + 30.0 for c in sck_map.values(): c.update() # <-- fill write buffers n = c.next_update() #print 'n:',n if n is not None: next_update = min(next_update, n) _timeout = max(0.1, next_update - time.time()) asyncore.loop(timeout=_timeout, count=1, map=sck_map)

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• zoomfactor value in CGAffineTransformMakeScale in iPhone

  - by suse

  Hello, 1) I'm doing pinch zoom on the UIImageView , how should i decide upon the zoomfactor value, because when the zoomfactor value goes beyond 0[i.e negative value]the image is gettig tilted, which i dont want it to happen. how to avoid this situation. 2) Y is the flickring kind of rotationis happening, Y not the smooth rotation? ll this be taken care by CGAffineTransformMakeScale(zoomfactor,zoomfactor);method? This is what i'm doing in my code: zoomFactor = 0;// Initially zoomfactor is set to zero - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{ NSLog(@" Inside touchesBegan .................."); NSArray *twoTouches = [touches allObjects]; UITouch *first = [twoTouches objectAtIndex:0]; OPERATION = [self identifyOperation:touches :first]; NSLog(@"OPERATION : %d",OPERATION); if(OPERATION == OPERATION_PINCH){ //double touch pinch UITouch *second = [twoTouches objectAtIndex:1]; f_G_initialDistance = distanceBetweenPoints([first locationInView:self.view],[second locationInView:self.view]); } NSLog(@" leaving touchesBegan .................."); } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { NSLog(@" Inside touchesMoved ................."); NSArray *twoTouchPoints = [touches allObjects]; if(OPERATION == OPERATION_PINCH){ CGFloat currentDistance = distanceBetweenPoints([[twoTouchPoints objectAtIndex:0] locationInView:self.view],[[twoTouchPoints objectAtIndex:1] locationInView:self.view]); int pinchOperation = [self identifyPinchOperation:f_G_initialDistance :currentDistance]; G_zoomFactor = [self calculateZoomFactor:pinchOperation :G_zoomFactor]; [uiImageView_G_obj setTransform:CGAffineTransformMakeScale(G_zoomFactor, G_zoomFactor)]; [self.view bringSubviewToFront:resetButton]; [self.view bringSubviewToFront:uiSlider_G_obj]; f_G_initialDistance = currentDistance; } NSLog(@" leaving touchesMoved .................."); } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { NSLog(@" Inside touchesEnded .................."); NSArray *twoTouches = [touches allObjects]; UITouch *first = [twoTouches objectAtIndex:0]; if(OPERATION == OPERATION_PINCH){ //do nothing } NSLog(@" Leaving touchesEnded .................."); } Thank You.

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• create an independent hidden process

  - by Jessica

  I'm creating an application with its main window hidden by using the following code: STARTUPINFO siStartupInfo; PROCESS_INFORMATION piProcessInfo; memset(&siStartupInfo, 0, sizeof(siStartupInfo)); memset(&piProcessInfo, 0, sizeof(piProcessInfo)); siStartupInfo.cb = sizeof(siStartupInfo); siStartupInfo.dwFlags = STARTF_USESHOWWINDOW | STARTF_FORCEOFFFEEDBACK | STARTF_USESTDHANDLES; siStartupInfo.wShowWindow = SW_HIDE; if(CreateProcess(MyApplication, "", 0, 0, FALSE, 0, 0, 0, &siStartupInfo, &piProcessInfo) == FALSE) { // blah return 0; } Everything works correctly except my main application (the one calling this code) window loses focus when I open the new program. I tried lowering the priority of the new process but the focus problem is still there. Is there anyway to avoid this? furthermore, is there any way to create another process without using CreateProcess (or any of the API's that call CreateProcess like ShellExecute)? My guess is that my app is losing focus because it was given to the new process, even when it's hidden. To those of you curious out there that will certainly ask the usual "why do you want to do this", my answer is because I have a watchdog process that cannot be a service and it gets started whenever I open my main application. Satisfied? Thanks for the help. Code will be appreciated. Jess.

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• Trap SIGPIPE when trying to write without reader

  - by Matt

  I am trying to implement a named-pipe communication solution in BASH between two processes. The first process runs a script which echo something in a named-pipe: send(){ echo 'something' > $NAMEDPIPE } And the second script is supposed to read the named-pipe via another script which contains: while true;do if read line < $NAMEDPIPE;do someCommands fi done Not that the named pipe has been previously created using the traditional command mkfifo $NAMEDPIPE My problem is that the reader script is not always running so that if the writer script try to write in the named-pipe it stay blocked until a reader connect the pipe. I want to avoid this behavior, and a solution would be to trap a SIGPIPE signal. Indeed, according to man 7 signal is supposed to be send when trying to write in a pipe with no reader. So I changed my red function by: read(){ trap 'echo "SIGPIPE received"' SIGPIPE echo 'something' > $NAMEDPIPE } But when I run the reader script, the script stay blocked, and not "SIGPIPE received" appears... Am I mistaking on the signal mechanism or is there any better solution to my problem ? Thank you for your help.

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• Is it possible for a function called from within an object to have access to that object's scope?

  - by Elliot Bonneville

  I can't think of a way to explain what I'm after more than I've done in the title, so I'll repeat it. Is it possible for an anonymous function called from within an object to have access to that object's scope? The following code block should explain what I'm trying to do better than I can: function myObj(testFunc) { this.testFunc = testFunc; this.Foo = function Foo(test) { this.test = test; this.saySomething = function(text) { alert(text); }; }; var Foo = this.Foo; this.testFunc.apply(this); } var test = new myObj(function() { var test = new Foo(); test.saySomething("Hello world"); }); When I run this, I get an error: "Foo is not defined." How do I ensure that Foo will be defined when I call the anonymous function? Here's a jsFiddle for further experimentation. Edit: I am aware of the fact that adding the line var Foo = this.Foo; to the anonymous function I pass in to my instance of myObj will make this work. However, I'd like to avoid having to expose the variable inside the anonymous function--do I have any other options?.

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• MySql Query lag time?

  - by Click Upvote

  When there are multiple PHP scripts running in parallel, each making an UPDATE query to the same record in the same table repeatedly, is it possible for there to be a 'lag time' before the table is updated with each query? I have basically 5-6 instances of a PHP script running in parallel, having been launched via cron. Each script gets all the records in the items table, and then loops through them and processes them. However, to avoid processing the same item more than once, I store the id of the last item being processed in a seperate table. So this is how my code works: function getCurrentItem() { $sql = "SELECT currentItemId from settings"; $result = $this->db->query($sql); return $result->get('currentItemId'); } function setCurrentItem($id) { $sql = "UPDATE settings SET currentItemId='$id'"; $this->db->query($sql); } $currentItem = $this->getCurrentItem(); $sql = "SELECT * FROM items WHERE status='pending' AND id > $currentItem'"; $result = $this->db->query($sql); $items = $result->getAll(); foreach ($items as $i) { //Check if $i has been processed by a different instance of the script, and if so, //leave it untouched. if ($this->getCurrentItem() > $i->id) continue; $this->setCurrentItem($i->id); // Process the item here } But despite of all the precautions, most items are being processed more than once. Which makes me think that there is some lag time between the update queries being run by the PHP script, and when the database actually updates the record. Is it true? And if so, what other mechanism should I use to ensure that the PHP scripts always get only the latest currentItemId even when there are multiple scripts running in parrallel? Would using a text file instead of the db help?

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• C# Fun with Generics - Mutual Dependencies

  - by Kenneth Cochran

  As an experiment I'm trying to write a generic MVP framework. I started with: public interface IPresenter<TView> where TView: IView<IPresenter<... { TView View { get; set;} } public interface IView<TPresenter> where TPresenter:IPresenter<IView<... { TPresenter Presenter { get; set; } } Obviously this can't work because the types of TView and TPresenter can't be resolved. You'd be writing Type<Type<... forever. So my next attempt looked like this: public interface IView<T> where T:IPresenter { ... } public interface IView:IView<IPresenter> { } public interface IPresenter<TView> where TView: IView { ... } public interface IPresenter: IPresenter<IView> { ... } This actually compiles and you can even inherit from these interfaces like so: public class MyView : IView, IView<MyPresenter> { ... } public class MyPresenter : IPresenter, IPresenter<MyView> { ... } The problem is in the class definition you have to define any members declared in the generic type twice. Not ideal but it still compiles. The problem's start creeping up when you actually try to access the members of a Presenter from a View or vice versa. You get an Ambiguous reference when you try to compile. Is there any way to avoid this double implementation of a member when you inherit from both interfaces? Is it even possible to resolve two mutually dependent generic types at compile time?

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• Transitioning from desktop app written in C++ to a web-based app

  - by Karim

  We have a mature Windows desktop application written in C++. The application's GUI sits on top of a windows DLL that does most of the work for the GUI (it's kind of the engine). It, too, is written in C++. We are considering transitioning the Windows app to be a web-based app for various reasons. What I would like to avoid is having to writing the CGI for this web-based app in C++. That is, I would rather have the power of a 4G language like Python or a .NET language for creating the web-based version of this app. So, the question is: given that I need to use a C++ DLL on the backend to do the work of the app what technology stack would you recommend for sitting between the user's browser and are C++ dll? We can assume that the web server will be Windows. Some options: Write a COM layer on top of the windows DLL which can then be access via .NET and use ASP.NET for the UI Access the export DLL interface directly from .NET and use ASP.NET for the UI. Write a custom Python library that wraps the windows DLL so that the rest of the code can be written. Write the CGI using C++ and a C++-based MVC framework like Wt Concerns: I would rather not use C++ for the web framework if it can be avoided - I think languages like Python and C# are simply more powerful and efficient in terms of development time. I'm concerned that my mixing managed and unmanaged code with one of the .NET solutions I'm asking for lots of little problems that are hard to debug (purely anecdotal evidence for that) Same is true for using a Python layer. Anything that's slightly off the beaten path like that worries me in that I don't have much evidence one way or the other if this is a viable long term solution.

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• How to correctly waitFor() a saveScreenShot() end of execution.

  - by Alain

  Here is my full first working test: var expect = require('chai').expect; var assert = require('assert'); var webdriverjs = require('webdriverjs'); var client = {}; var webdriverOptions = { desiredCapabilities: { browserName: 'phantomjs' }, logLevel: 'verbose' }; describe('Test mysite', function(){ before(function() { client = webdriverjs.remote( webdriverOptions ); client.init(); }); var selector = "#mybodybody"; it('should see the correct title', function(done) { client.url('http://localhost/mysite/') .getTitle( function(err, title){ expect(err).to.be.null; assert.strictEqual(title, 'My title page' ); }) .waitFor( selector, 2000, function(){ client.saveScreenshot( "./ExtractScreen.png" ); }) .waitFor( selector, 7000, function(){ }) .call(done); }); after(function(done) { client.end(done); }); }); Ok, it does not do much, but after working many hours to get the environement correctly setup, it passed. Now, the only way I got it working is by playing with the waitFor() method and adjust the delays. It works, but I still do not understand how to surely wait for a png file to be saved on disk. As I will deal with tests orders, I will eventually get hung up from the test script before securely save the file. Now, How can I improve this screen save sequence and avoid loosing my screenshot ? Thanks.

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• MySQL: Get average of time differences?

  - by Nebs

  I have a table called Sessions with two datetime columns: start and end. For each day (YYYY-MM-DD) there can be many different start and end times (HH:ii:ss). I need to find a daily average of all the differences between these start and end times. An example of a few rows would be: start: 2010-04-10 12:30:00 end: 2010-04-10 12:30:50 start: 2010-04-10 13:20:00 end: 2010-04-10 13:21:00 start: 2010-04-10 14:10:00 end: 2010-04-10 14:15:00 start: 2010-04-10 15:45:00 end: 2010-04-10 15:45:05 start: 2010-05-10 09:12:00 end: 2010-05-10 09:13:12 ... The time differences (in seconds) for 2010-04-10 would be: 50 60 300 5 The average for 2010-04-10 would be 103.75 seconds. I would like my query to return something like: day: 2010-04-10 ave: 103.75 day: 2010-05-10 ave: 72 ... I can get the time difference grouped by start date but I'm not sure how to get the average. I tried using the AVG function but I think it only works directly on column values (rather than the result of another aggregate function). This is what I have: SELECT TIME_TO_SEC(TIMEDIFF(end,start)) AS timediff FROM Sessions GROUP BY DATE(start) Is there a way to get the average of timediff for each start date group? I'm new to aggregate functions so maybe I'm misunderstanding something. If you know of an alternate solution please share. I could always do it ad hoc and compute the average manually in PHP but I'm wondering if there's a way to do it in MySQL so I can avoid running a bunch of loops. Thanks.

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• Use queried json data in a function

  - by SztupY

  I have a code similar to this: $.ajax({ success: function(data) { text = ''; for (var i = 0; i< data.length; i++) { text = text + '<a href="#" id="Data_'+ i +'">' + data[i].Name + "</a><br />"; } $("#SomeId").html(text); for (var i = 0; i< data.length; i++) { $("#Data_"+i).click(function() { alert(data[i]); RunFunction(data[i]); return false; }); } } }); This gets an array of some data in json format, then iterates through this array generating a link for each entry. Now I want to add a function for each link that will run a function that does something with this data. The problem is that the data seems to be unavailable after the ajax success function is called (although I thought that they behave like closures). What is the best way to use the queried json data later on? (I think setting it as a global variable would do the job, but I want to avoid that, mainly because this ajax request might be called multiple times) Thanks.

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