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  • OSX Weak Linking - check if a class exists and use that class

    - by psychotik
    I'm trying to create a universal iPhone app, but it uses a class defined only in a newer version of the SDK. The framework exists on older systems, but a class defined in the framework doesn't. I know I want to use some kind of weak linking, but any documentation I can find talks about runtime checks for function existence - how do I check that a class exists?

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  • Simple Data Caching using Weak References in WCF

    - by Tawani
    Given that I have the following WCF service: class LookUpService { public List<County> GetCounties(string state) { var db = new LookUpRepository(); return db.GetCounties(state); } } class County { public string StateCode{get;set;} public string CountyName{get;set;} public int CountyCode{get;set;} } What will be the most efficient (or best) way to cache a state's counties using weak references (or any other approach) so that we don't hit the database every time we need to look up data. Note that we will not have access to the HttpRuntime (and HttpContext).

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  • Static/Dynamic vs Strong/Weak

    - by Dan Revell
    I see these terms banded around all over the place in programming and I have a vague notion of what they mean. A search shows me that such things have been asked all over stack overflow in fact. As far as I'm aware Static/Dynamic typing in languages is subtly different to Strong/Weak typing but what that difference is eludes me. Different sources seem to use different different meanings or even use the terms interchangeably. I can't find somewhere that talks about both and actually spells out the difference. What would be nice is if someone could please spell this out clearly here for me and the rest of the world.

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  • AS3: Weak Listener References Not Appropriate During Initialization?

    - by TheDarkIn1978
    as i currently understand, if an event listener is added to an object with useWeakReference set to true, then it is eligible for garbage collection and will be removed if and when the garbage collection does a sweep. public function myCustomSpriteClass() //constructor { this.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownListener, false, 0, true); this.addEventListener(MouseEvent.MOUSE_UP, mouseUpListener, false, 0, true); } in this case, is it not appropriate to initialize an object with weak references event listeners, incase the garbage collector does activate a sweep removing the objects event listeners since they were added during initialization of the object? in this case, would it only be appropriate to create a type of deallocate() method which removes the event listeners before the object is nullified?

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  • How to avoid XCode framework weak-linking problems?

    - by Frank R.
    Hi, I'm building an application that takes advantage of Mac OS X 10.6-only technologies, but without giving up backwards compatibility to 10.5 Leopard. The way I do this is by setting the 10.6 SDK as the base SDK, weak-linking all frameworks and setting the deployment target to 10.5 as described in: http://developer.apple.com/mac/library/DOCUMENTATION/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html This works fine; before making a call that is Snow Leopard-only I need to check that the selector or indeed the class actually exist. Or I can just check the OS version before making the call. The problem is that this is incredibly fragile. If I make a single call that is 10.6 only I blow Leopard-compatibility. So using even the normal code code completion feature can be dangerous. My question: is there any way of checking which calls are not defined on 10.5 before doing a release build? Some kind of static analysis, or even just a trick (a target set the other SDK?) would do. I obviously should test on a Leopard machine before releasing anything, but even so I can't possibly go through all paths of the program before every release. Any advice would be appreciated. Best regards, Frank

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  • Weak linking on iPhone refuses to work

    - by Jonathan Grynspan
    I've got an iPhone app that's mainly targetting 3.0, but which takes advantage of newer APIs when they're available. Code goes something like this: if (UIApplicationDidEnterBackgroundNotification != NULL) [nc addObserver: self selector: @selector(irrelelvantCallbackName:) name: UIApplicationDidEnterBackgroundNotification object: nil]; Now, according to everything Apple's ever said, if the relevant APIs are weakly linked, that will work fine because the dynamic linker will evaluate UIApplicationDidEnterBackgroundNotification to NULL. Except that it doesn't. The application compiles, but as soon as it hits "if (UIApplicationDidEnterBackgroundNotification != NULL)" it crashes with EXC_BAD_ACCESS. Is this simply a matter of a compiler flag I need to set? Or am I going about this the wrong way?

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  • Python - how to check if weak reference is still available

    - by Alex
    Hi all, I am passing some weakrefs from Python into C++ class, but C++ destructors are actively trying to access the ref when the real object is already dead, obviously it crashes... Is there any Python C/API approach to find out if Python reference is still alive or any other known workaround for this ? Thanks

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  • Maddening Linked List problem

    - by Mike
    This has been plaguing me for weeks. It's something really simple, I know it. Every time I print a singly linked list, it prints an address at the end of the list. #include <iostream> using namespace std; struct node { int info; node *link; }; node *before(node *head); node *after(node *head); void middle(node *head, node *ptr); void reversep(node *head, node *ptr); node *head, *ptr, *newnode; int main() { head = NULL; ptr = NULL; newnode = new node; head = newnode; for(int c1=1;c1<11;c1++) { newnode->info = c1; ptr = newnode; newnode = new node; ptr->link = newnode; ptr = ptr->link; } ptr->link=NULL; head = before(head); head = after(head); middle(head, ptr); //reversep(head, ptr); ptr = head; cout<<ptr->info<<endl; while(ptr->link!=NULL) { ptr=ptr->link; cout<<ptr->info<<endl; } system("Pause"); return 0; } node *before(node *head) { node *befnode; befnode = new node; cout<<"What should go before the list?"<<endl; cin>>befnode->info; befnode->link = head; head = befnode; return head; } node *after(node *head) { node *afnode, *ptr2; afnode = new node; ptr2 = head; cout<<"What should go after the list?"<<endl; cin>>afnode->info; ptr2 = afnode; afnode->link=NULL; ptr2 = head; return ptr2; } void middle(node *head, node *ptr) { int c1 = 0, c2 = 0; node *temp, *midnode; ptr = head; while(ptr->link->link!=NULL) { ptr=ptr->link; c1++; } c1/=2; c1-=1; ptr = head; while(c2<c1) { ptr=ptr->link; c2++; } midnode = new node; cout<<"What should go in the middle of the list?"<<endl; cin>>midnode->info; cout<<endl; temp=ptr->link; ptr->link=midnode; midnode->link=temp; } void reversep(node *head, node *ptr) { node *last, *ptr2; ptr=head; ptr2=head; while(ptr->link!=NULL) ptr = ptr->link; last = ptr; cout<<last->info; while(ptr!=head) { while(ptr2->link!=ptr) ptr2=ptr2->link; ptr = ptr2; cout<<ptr->info; } } I'll admit that this is class work, but even the professor can't figure it out, and says that its probably something insignificant that we're overlooking, but I can't put my mind to rest until I find out what it is.

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  • .NET Weak Event Handlers – Part II

    - by João Angelo
    On the first part of this article I showed two possible ways to create weak event handlers. One using reflection and the other using a delegate. For this performance analysis we will further differentiate between creating a delegate by providing the type of the listener at compile time (Explicit Delegate) vs creating the delegate with the type of the listener being only obtained at runtime (Implicit Delegate). As expected, the performance between reflection/delegate differ significantly. With the reflection based approach, creating a weak event handler is just storing a MethodInfo reference while with the delegate based approach there is the need to create the delegate which will be invoked later. So, at creating the weak event handler reflection clearly wins, but what about when the handler is invoked. No surprises there, performing a call through reflection every time a handler is invoked is costly. In conclusion, if you want good performance when creating handlers that only sporadically get triggered use reflection, otherwise use the delegate based approach. The explicit delegate approach always wins against the implicit delegate, but I find the syntax for the latter much more intuitive. // Implicit delegate - The listener type is inferred at runtime from the handler parameter public static EventHandler WrapInDelegateCall(EventHandler handler); public static EventHandler<TArgs> WrapInDelegateCall<TArgs>(EventHandler<TArgs> handler) where TArgs : EventArgs; // Explicite delegate - TListener is the type that defines the handler public static EventHandler WrapInDelegateCall<TListener>(EventHandler handler); public static EventHandler<TArgs> WrapInDelegateCall<TArgs, TListener>(EventHandler<TArgs> handler) where TArgs : EventArgs;

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  • B.S.in Computer Science, weak eyes => career change

    - by Prometheus
    So I am going to earn B.S. in Computer Science soon. I like computers. I like programming. The problem is that my eyes are very weak. Depending on their condition, I can only put in about 6 hours in front of computer a day. If I push myself, I have trouble even keeping my eyes open because of soreness/pain, consequently headaches. My eyes do not have medical conditions. I was just born with weak eyes. I tried many different approaches to work around this problem - better monitor, breaks every 10 minutes, supplements... I even memorized a lot of shortcuts to reduce my time on computers! But I am finally giving up. I do not think I can be a programmer for the rest of my life. I was the top of my class in high school because all works were paper-based, I did average in college due to the nature of my eyes and the difficulty of the material. So what do you recommend I do? Or, Is there a career that is similar to programming but requires interacting with computers less?

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  • How is precedence determined in C pointers?

    - by ankur.trapasiya
    I've come across two pointer declarations that I'm having trouble understanding. My understanding of precedence rules goes something like this: Operator Precedence Associativity (), [ ] 1 Left to Right *, identifier 2 Right to Left Data type 3 But even given this, I can't seem to figure out how to evaluate the following examples correctly: First example float * (* (*ptr)(int))(double **,char c) My evaluation: *(ptr) (int) *(*ptr)(int) *(*(*ptr)(int)) Then, double ** char c Second example unsigned **( * (*ptr) [5] ) (char const *,int *) *(ptr) [5] *(*ptr)[5] *(*(*ptr)[5]) **(*(*ptr)[5]) How should I read them?

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  • does ping command to a dns name uses DNS PTR type messages?

    - by TiagoM
    Okay I cant understand this, when I try to ping to a machine on my network using the name associated I get a response from that machine, thats normal.. But there are messages that the sender sends to the top machine (SOA) that I dont understand.. First he sends a type A and gets a response with the IP associated to the name used on the ping command, but after that.. the sender only sends (before each ping) messages of type PTR to the (SOA) Saying this: Standar query 0xf66c PTR 12.45.168.192.in-addr.arpa and SOA respond with: Standard query response 0xf66c No such name And before each ping they do this, I dont know why... I notice this using wireshark, thanks alot again for accept me here, being able to get some answer :)

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  • Cost to GC of using weak references in C#?

    - by Scott Bilas
    In another question, Stephen C says: A second concern is that there are runtime overheads with using weak references. The obvious costs are those of creating weak references and calling get on them. A less obvious cost is that significant extra work needs to be done each time the GC runs. So what exactly is the cost to the GC of a weak ref? What extra work does it need to do, and how big of a deal is it? I can make some educated guesses, but am interested in the actual mechanics.

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  • Multi-IP address zimbra server DNS PTR records and spam

    - by David Fraser
    We have a mail server running Zimbra (ZCS 6.0.8). The server has 5 active public IP addresses in the same subnet. (.226-.230). I currently have A records for each of these (host0.domain.com..host4.domain.com), with the main host.domain.com of the machine pointing to .226. Our host has ended up being listed on the SORBS DUHL list (even though it's in a server farm). According to them you can get removed quickly by checking that your host has an MX record, an A record, and a PTR record that points back to the hostname given in the MX record. I tried setting the PTR records so that each of these addresses resolved back to their A record (i.e. .228 had a PTR to host2.domain.com). However, I then got mail being rejected from other servers because when Postfix (under Zimbra control) sends out mail, it uses the main hostname for the HELO - there doesn't seem to be any way to override it. So the PTR records currently say host.domain.com for all 5 IP addresses. What's the correct way to handle this? Should I have an A record for the domain that points to all the IP addresses (for round-robin handling)? I'm nervous of changes that could cause problems, so I'm wondering what the standard way to handle a multiple-IP-address mail server is.

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  • how to add a REverse PTR Record on Amazon Route 53?

    - by Oscar Cabrero
    if i have the below ip 168.144.254.X and i would like to add a ptr record in amazon in the form of X.254.144.168.in-addr.arpa what should be in the name field and what should be in the value field i have a zone created with a name like mydomain.com which host the DNS records for my ip. amazon wont let me add a value of X.254.144.168.in-addr.arpa in the name field do i need to create a new zone for the ip in order to allow this?

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  • Great Debugging skills weak problem solving

    - by Mahmoud
    For the 5 years I worked for various companies, I worked in large software like computer vision kits, embedded, games. I found myself very good at debuggins skills, I've even found and fixed bugs in frameworks and I solved them. The problem is that I'm very weak at problem solving. I got interview with Qualcomm, and they said you're fine at software, but you have a limited problem solving, I also had the same results with Google. I'm very bad at solving puzzles and brain teasers. During the interviews I solve all of the software related problems on the blackboard, but when I went to the GM and face math problems and probabilities, I struggle. How can I improve my problem solving skills? Edit Some of the problems: A cake that is cut from anywhere and needs just one cut to halved in equal. I told him cut it horizontally, he said No, consider it as a 2D Problem!. Consider a concenteric 3 circles, each one can get a color, but not matched with the other circle, how many blobs you can make out of those circles ? this was with the GM ( Augmented Reality SDK) Consider a train, an infinite one, and you looked at the window, and there are two cars, one big, and one small, what is the probability of having only a big car, I said 50%, he said, what if that two cars you dont know their length, and you want to get the probability of getting the biggest one, I struggled, didn't solve it... I was really exahusted after long day of interviews prob of having a number divisible by 5 in numbers from 1 to 100.. struggled!! All coding questions I solved them like reverse a string, detect a cycle in a linked list,..etc.

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  • ath9k driver does not weak up

    - by shantanu
    I know this is common question but i found no suitable answer, so i am asking this again. I installed ubuntu 11.10. I found the bug for ath9k, so set first network boot from BIOS menu. That's worked. I have upgraded to 12.04 yesterday. Now ath9k is creating problem again. First network boot is still enable. ath9k works at start. But failed(connect again and again) after couple of minutes. dmesg show error that it can not weak up in 500us. So i tried #compat-wireless-3.5.1-1. But result is same. I have also added #nohwcrypt=1 option in /etc/modeprob.d/ath9k.conf. Still no luck. I tried #rmmod and then modprobe sudo modprobe ath9k nohwcrypt=1 dmesg shows me error: [ 400.690086] ath9k: Driver unloaded [ 406.214329] ath9k 0000:06:00.0: enabling device (0000 -> 0002) [ 406.214348] ath9k 0000:06:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17 [ 406.214368] ath9k 0000:06:00.0: setting latency timer to 64 [ 406.428517] ath9k 0000:06:00.0: Failed to initialize device [ 406.428852] ath9k 0000:06:00.0: PCI INT A disabled [ 406.428887] ath9k: probe of 0000:06:00.0 failed with error -5 dmesg error when driver fail: 355.023521] ath: Chip reset failed [ 355.023524] ath: Unable to reset channel, reset status -22 [ 355.023556] ath: Unable to set channel [ 355.088569] ath: Failed to stop TX DMA, queues=0x10f! [ 355.122708] ath: DMA failed to stop in 10 ms AR_CR=0xffffffff AR_DIAG_SW=0xffffffff DMADBG_7=0xffffffff [ 355.122714] ath: Could not stop RX, we could be confusing the DMA engine when we start RX up [ 355.263962] ath: Chip reset failed [ 355.263966] ath: Unable to reset channel (2437 MHz), reset status -22 [ 358.996063] ath: Failed to wakeup in 500us [ 364.004182] ath: Failed to wakeup in 500us I can not install fresh ubuntu because i have lots of application installed. System : Acer Aspire 4250 AMD dual core 1.6GHZ Atheros Communications Inc. AR9485 Wireless Network Adapter (rev 01) EDITED Now i am in serious problem. No wifi device is not showing in ifconfig or lshw commands. Only ether-net interface shows. I tried (FN + WIFI) several times to enable the device but nothing helps. Now I have installed fresh ubuntu 12.04. Please help lshw -c network: *-network description: Ethernet interface product: 82566DC Gigabit Network Connection vendor: Intel Corporation physical id: 19 bus info: pci@0000:00:19.0 logical name: eth0 version: 02 serial: 00:19:d1:7a:8e:f9 size: 100Mbit/s capacity: 1Gbit/s width: 32 bits clock: 33MHz capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=2.0.0-k duplex=full firmware=1.1-0 ip=192.168.1.114 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s resources: irq:45 memory:90300000-9031ffff memory:90324000-90324fff ioport:20c0(size=32) rfkill command does not show anything but no error.

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  • Weak reference and Strong reference

    - by theband
    package uk.co.bigroom.utils { import flash.utils.Dictionary; /** * Class to create a weak reference to an object. A weak reference * is a reference that does not prevent the object from being * garbage collected. If the object has been garbage collected * then the get method will return null. */ public class WeakRef { private var dic:Dictionary; /** * The constructor - creates a weak reference. * * @param obj the object to create a weak reference to */ public function WeakRef( obj:* ) { dic = new Dictionary( true ); dic[obj] = 1; } /** * To get a strong reference to the object. * * @return a strong reference to the object or null if the * object has been garbage collected */ public function get():* { for ( var item:* in dic ) { return item; } return null; } } } In this Class, how they denote one as Weak Reference and one as Strong reference.

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  • Do I have to use a DNS PTR?

    - by JrSysAdmin
    I am currently working on a site in my free time with a few other guys and we are wanting to redirect xxx.com to our new site, yyy.com. So we have xxx.com set to redirect the 216.111.11.1 which is the IP for yyy.com. However, this just says the website is unavailable so it seems as though we need a DNS PTR to redirect 216.111.11.1 to yyy.com. Is there any way to do this without a DNS PTR? The pointer will cost us $15 and it just seems like there should be some better way to go about doing this. Any ideas?

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