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  • How do I prevent a tar pipe from causing swapping?

    - by Jeff Shattock
    I have a rather large filesystem that I need to transfer from one Linux server to another. I figured the best way to do this was via a tar/netcat pipe arrangment, something like tar c . | pv | nc blah blah blah And it works great, the network stays fairly saturated, life is good. Until the source machine starts swapping. The files are on a raid on the source system, so the read speed is much faster than the write speed on the other end. Since the dest machine hasnt picked up the data yet, the source machine needs to stick it somewhere, so into RAM it goes, until there is no more free RAM. It then starts swapping, which is horribly painful since that machine has its OS installed on a somewhat slow CF card. Both machines have 4GB of physical ram, 64 bit Ubuntu 9.04 server. GigE link between them. How do I prevent this swapping? Can I put a "speed-limit" on the tar or netcat process so that the transfer speed doesn't overwhelm the write throughput on the destination end? The man pages didn't list anything, but there might be something I'm overlooking.

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  • Objective-C classes, pointers to primitive types, etc.

    - by Toby Wilson
    I'll cut a really long story short and give an example of my problem. Given a class that has a pointer to a primitive type as a property: @interface ClassOne : NSObject { int* aNumber } @property int* aNumber; The class is instantiated, and aNumber is allocated and assigned a value, accordingly: ClassOne* bob = [[ClassOne alloc] init]; bob.aNumber = malloc(sizeof(int)); *bob.aNumber = 5; It is then passed, by reference, to assign the aNumber value of a seperate instance of this type of class, accordingly: ClassOne* fred = [[ClassOne alloc] init]; fred.aNumber = bob.aNumber; Fred's aNumber pointer is then freed, reallocated, and assigned a new value, for example 7. Now, the problem I'm having; Since Fred has been assigned the same pointer that Bob had, I would expect that Bob's aNumber will now have a value of 7. It doesn't, because for some reason it's pointer was freed, but not reassigned (it is still pointing to the same address it was first allocated which is now freed). Fred's pointer, however, has the allocated value 7 in a different memory location. Why is it behaving like this? What am I minsunderstanding? How can I make it work like C++ does?

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  • Handler invocation speed: Objective-C vs virtual functions

    - by Kerido
    I heard that calling a handler (delegate, etc.) in Objective-C can be even faster than calling a virtual function in C++. Is it really correct? If so, how can that be? AFAIK, virtual functions are not that slow to call. At least, this is my understanding of what happens when a virtual function is called: Compute the index of the function pointer location in vtbl. Obtain the pointer to vtbl. Dereference the pointer and obtain the beginning of the array of function pointers. Offset (in pointer scale) the beginning of the array with the index value obtained on step 1. Issue a call instruction. Unfortunately, I don't know Objective-C so it's hard for me to compare performance. But at least, the mechanism of a virtual function call doesn't look that slow, right? How can something other than static function call be faster?

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • C++ this as thread parameter, variables unavailable

    - by brecht
    I have three classes: class Rtss_Generator { int mv_transfersize; } class Rtss_GenSine : Rtss_Generator class Rtss_GenSineRpm : Rtss_GenSine Rtss_GenSine creates a thread in his constructer, it is started immediatly and the threadfunction is off-course declared static, waiting for an event to start calculating. the problem: all the variables that are accessed through the gen-pointer are 0, but it does not fail. Also, this-address in the constructer and the gen-pointer-address in the thread are the same, so the pointer is ok. this code is created and compile in visual studio 6.0 service pack 2003 ORIGINAL CODE no thread Rtss_GenSine::getNextData() { //[CALCULATION] //mv_transferSize is accessible and has ALWAYS value 1600 which is ok } NEW CODE Rtss_GenSine::Rtss_GenSine() { createThread(NULL, threadFunction, (LPVOID) this,0,0); } Rtss_GenSine::getNextData() { SetEvent(startCalculating); WaitForSingleObject(stoppedCalculaing, INFINITE); } DWORD Rtss_GenSine::threadFunction(LPVOID pParam) { Rtss_GenSine* gen = (Rtss_GenSine*) pParam; while(runThread) { WaitForSingleObject(startCalculating, INFINITE); ResetEvent(startCalculating) //[CALCULATION] //gen->mv_transferSize ---> it does not fail, but is always zero //all variables accessed via the gen-pointer are 0 setEvent(stoppedCalculaing) } }

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  • Using a Function returning apointer as LValue

    - by Amrish
    Why cant I used a function returning a pointer as a lvalue? For example this one works int* function() { int* x; return x; } int main() { int* x = function(); x = new int(9); } but not this int* function() { int* x; return x; } int main() { int* x; function() = x; } While I can use a pointer variable as a lvalue, why can't I use a function returning a pointer as a lvalue? Also, when the function returns a refernce, instead of a pointer, then it becomes a valid lvalue.

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  • C++: Pointers and scope

    - by oh boy
    int* test( ) { int a = 5; int* b = &a; return b; } Will the result of test be a bad pointer? As far as I know a should be deleted and then b would become a messed up pointer, right? How about more complicated things, not an int pointer but the same with a class with 20 members or so?

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  • Slow Browsing/Direct Download, but Fast Bittorrent Download

    - by Dr Haisook
    I'm using Windows XP SP2. I have a 1 MB connection via a SpeedTouch 585, and my internet speed registers at 0.3 MB, with a maximum download of 30kbps. Not to mention a terrible ping at 500-1500. On the other hand, I get full speed in uTorrent - a bittorrent program - reaching up to 100 kbps; the way it should be. I haven't made any changes to anything. And it has been functioning well until the last month. I waited in hope that it could be an ISP issue and that it would be resolved, but their support crew did not help me with this problem either. I've tried disabling all firewalls, and all wireless connections, using different browsers, and disabling QoS. But it did not work. Me thinks it's an ISP issue, but if so, how am I getting full speed in uTorrent? Could somebody help me out with this? Thanks.

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  • Function Pointer

    - by Shaista Naaz
    How is that function pointer better than if-else or switch case? Is it because function pointer helps callback functions and thus promotes asynchronous implementation?

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  • PHP array pointer craziness

    - by JMan
    I'm trying to create a "GetCurrentLevel" method that takes a point value as an input and returns what "Level" that corresponds to. I'm storing the Level = Points mapping in an array, but the array pointer is not moving logically when I use it a foreach loop. I've added echo statements for debugging. Here's my class definition: class Levels extends Model { protected $_map = array ( 'None' => 0, 'Bronze' => 50, 'Silver' => 200, 'Gold' => 500 ); public function __construct() { parent::__construct(); } public function GetCurrentLevel($points) { foreach ($this->_map as $name => $threshold) { echo "Level Name: $name<br/>"; echo "Level Threshold: $threshold<br/>"; echo "Current Level: " . key($this->_map) . "<br/>"; echo "Current Threshold: " . current($this->_map) . "<br/>"; if ($points < $threshold) /* Threshold is now above the points, so need to go back one level */ { $previousThreshold = prev($this->_map); echo "Previous Threshold: $previousThreshold<br/>"; echo "Final Level: " . key($this->_map) . "<br/>"; return key($this->_map); } echo "Go to next level <br/>"; } } And here is what I see when I call GetCurrentLevel(60): Level Name: None Level Threshold: 0 Current Level: Bronze //* Looks like foreach immediately moves the array pointer *// Current Threshold: 50 Go to next level Level Name: Bronze Level Threshold: 50 Current Level: Bronze //* WTF? Why hasn't the array pointer moved? *// Current Threshold: 50 Go to next level Level Name: Silver Level Threshold: 200 Current Level: Bronze //* WTF? Why hasn't the array pointer moved? *// Current Threshold: 50 Previous Threshold: 0 Final Level: None But the "Final Level" should be 'Bronze' since 60 points is above the 50 points needed for a Bronze medal, but below the 200 points needed for a Silver medal. Sorry for the long post. Thanks for your help!

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  • question regarding pointer in c language

    - by din
    char *sample = "String Value"; &sample is a pointer to the pointer of "String Value" is the above statement right? If the above statement right, what is the equivalent of &sample if my declaration is char sample[] = "String Value"

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  • python object to native c++ pointer

    - by Lodle
    Im toying around with the idea to use python as an embedded scripting language for a project im working on and have got most things working. However i cant seem to be able to convert a python extended object back into a native c++ pointer. So this is my class: class CGEGameModeBase { public: virtual void FunctionCall()=0; virtual const char* StringReturn()=0; }; class CGEPYGameMode : public CGEGameModeBase, public boost::python::wrapper<CGEPYGameMode> { public: virtual void FunctionCall() { if (override f = this->get_override("FunctionCall")) f(); } virtual const char* StringReturn() { if (override f = this->get_override("StringReturn")) return f(); return "FAILED TO CALL"; } }; Boost wrapping: BOOST_PYTHON_MODULE(GEGameMode) { class_<CGEGameModeBase, boost::noncopyable>("CGEGameModeBase", no_init); class_<CGEPYGameMode, bases<CGEGameModeBase> >("CGEPYGameMode", no_init) .def("FunctionCall", &CGEPYGameMode::FunctionCall) .def("StringReturn", &CGEPYGameMode::StringReturn); } and the python code: import GEGameMode def Ident(): return "Alpha" def NewGamePlay(): return "NewAlpha" def NewAlpha(): import GEGameMode import GEUtil class Alpha(GEGameMode.CGEPYGameMode): def __init__(self): print "Made new Alpha!" def FunctionCall(self): GEUtil.Msg("This is function test Alpha!") def StringReturn(self): return "This is return test Alpha!" return Alpha() Now i can call the first to functions fine by doing this: const char* ident = extract< const char* >( GetLocalDict()["Ident"]() ); const char* newgameplay = extract< const char* >( GetLocalDict()["NewGamePlay"]() ); printf("Loading Script: %s\n", ident); CGEPYGameMode* m_pGameMode = extract< CGEPYGameMode* >( GetLocalDict()[newgameplay]() ); However when i try and convert the Alpha class back to its base class (last line above) i get an boost error: TypeError: No registered converter was able to extract a C++ pointer to type class CGEPYGameMode from this Python object of type Alpha I have done alot of searching on the net but cant work out how to convert the Alpha object into its base class pointer. I could leave it as an object but rather have it as a pointer so some non python aware code can use it. Any ideas?

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  • Converting a pointer C# type to F#??

    - by Brendon
    Hello all I am just a beginner in programing i wish covert some code from C# to F#, I have encotered this code: "float[] v1=new float[10]" I need to use this pointer to pass to the function: "ComputeBuffer bufV1 = new ComputeBuffer(Context, ComputeMemoryFlags.ReadWrite | ComputeMemoryFlags.UseHostPointer, v1);" If i creat an array in F# like this: "let v1 = [| 1.0..10.0 |]" and call now the funaction like this: "let bufV1 = new ComputeBuffer(Context, ComputeMemoryFlags.ReadWrite ||| ComputeMemoryFlags.UseHostPointer, v1)" Is it an error?? How do i pass a pointer??

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  • How to cast a pointer of memory block to std stream

    - by Shahrooz Kia
    I have programed an application on windows XP and in Visual Studio with c++ language. In that app I used LoadResource() API to load a resource for giving a file in the resource memory. It returned a pointer of memory block and I wanna cast the pointer to the std stream to use for compatibility. Could anyone help me?

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  • Call c++ function pointer from c#

    - by Sam
    Is it possible to call a c(++) static function pointer like this typedef int (*MyCppFunc)(void* SomeObject); from c#? void CallFromCSharp(MyCppFunc funcptr, IntPtr param) { funcptr(param); } I need to be able to callback from c# into some old c++ classes. C++ is managed, but the classes are not ref classes (yet). So far I got no idea how to call a c++ function pointer from c#, is it possible?

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  • C++ class pointer

    - by JHollanti
    I know that you can get a reference to a static method like this: typedef void (*pointer)(); pointer p = &MyClass::MyMethod; But is there a way to get a reference to the class itself?

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  • pointer&dynamic memory

    - by gcc
    how many methods are there taking input by using with pointer and dynamic memory input 3 1 2 n k l 2 1 2 p 4 55 62 * # x x is stop character and first input 3 is for another variable int hakko; only hakko use first input the others will be hold in one pointer and input size not determined

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  • NFS and KVM. Slow Speed

    - by Javier Martinez
    I have a KVM virtualization in Debian with 2 guests (Debian and Windows 2008). I want to have a 'mount point' shared that can be accessed by the 3 system (host and 2 guests) at the same time. So the only thing that I found was a NFS/SMB network storage. I picked NFS Due to my Ethernet network (10/100), the speed average that I get between accessing/transfering files between the 3 system is always 8~10MB/s. The point is if is there any chance of get a boost system for sharing files between 3 system (at the same time) without wasting the speed of my SATA disks. I mean, without the Ethernet limitation of 10 MB/s

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  • In search of a network file system with extended caching to speed up file access

    - by Brecht Machiels
    I'm running a small home server that stores my documents. The disks in this server are in a RAID 1 configuration (using Linux md) and it's also periodically being backup up to an external hard drive to make sure I don't lose them. However, I'm always accessing the files from other computers on the home network using an SMB share, and this results in a considerable speed penalty (especially when connected over WLAN). This is quite annoying when editing large files, such as digital camera RAWs, for example. I've been looking for a solution to this problem. It would have to offer some kind of local caching to speed up the file access. The client would preferably not keep a copy of all data on the server, as it consists of a very large collection of photographs, most of which I will not access frequently. Instead, it should only cache the accessed files and sync the changes back in the background. Ideally, it would also do some smart read-ahead (cache the files that are in the same directory as the currently opened file, for examples), but I suppose that's asking a bit much. Synchronization should be automatic (on file change). Conflicting file changes (at the same time on different clients) are unlikely to happen in my use case, but I would prefer if they are handled properly (notification to the user). I've come across the following options, so far: something similar to Dropbox. iFolder seems to be the only thing that comes close, but its reputation (stability) and requirements put me off. A distributed file system such as OpenAFS. I'm not sure this will speed up file access. It is probably overkill for what I need. Maybe NFS or even Samba offer these possibilities. I read a bit about Windows' Offline Files, but its operation seems limited (at least on Windows XP). As this is just for personal use, I'm not willing to spend a lot of money. A free solution would be preferred. Also, the server needs to run on Linux, and I need a client for at least Windows.

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  • how I can Specifying tcpreplay speed

    - by herzl shemuelian
    I am tring to Specify tcpreplay speed but I can't do it this is my detail of test: $tcpreplay -V tcpreplay version: 3.4.4 (build 2450) 1)$ tcpreplay -i %0 -p 100 -L 500 _udp_only.pcap Actual: 500 packets (42247 bytes) sent in 5.05 seconds.Rated: 8365.7 bps, 0.06 Mbps, 99.01 pps s 2)$ tcpreplay -i %0 -p 1000 -L 5000 _udp_only.pcap Actual: 5000 packets (427710 bytes) sent in 5.19 seconds. Rated: 82410.4 bps, 0.63 Mbps, 963.39 pps //here is problem I stay in 966.00 pps 3)$ tcpreplay -i %0 -p 10000 -L 50000 _udp_only.pcap Actual: 50000 packets (4322559 bytes) sent in 51.76 seconds.Rated: 83511.6 bps, 0.64 Mbps, 966.00 pps I have same problem when I try to Specify --mbps for 8600 packets 86 byte avg for each packet -M0.086 -L 860 ---- Rated: 10812.9 bps, 0.08 Mbps, 127.22 pps -M0.86 -L 860 ---- Rated: 83062.5 bps, 0.63 Mbps, 977.27 pps -M0.86 -L 8600 ---- Rated: 82554.9 bps, 0.63 Mbps, 965.21 pps why and how I can to Specify speed? I use OS windows7

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  • my torrent speed is slower all of the sudden

    - by nazmi98
    Last year when I tried to download torrent the speed was around 120 kb/s, but now it's only 10 kbs/s. I'm really confused here. I have been trying everything that I could find on the internet but nothing seems to work, so I'm really desperate for help. One more thing: I don't know if this will help, but i'm from Malaysia. My internet speed is 1 mb. I tried using all the PCs that I own and all seems to produce the same result.

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