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• LRU caches in C

  - by lazyconfabulator

  I need to cache a large (but variable) number of smallish (1 kilobyte to 10 megabytes) files in memory, for a C application (in a *nix environment). Since I don't want to eat all my memory, I'd like to set hard memory limit (say, 64 megabytes) and push files into a hash table with the file name as the key and dispose of the entries with the least use. What I believe I need is an LRU cache. Really, I'd rather not roll my own so if someone knows where I can find a workable library, please point the way? Failing that, can someone provide a simple example of an LRU cache in C? Related posts indicated that a hash table with a doubly-linked list, but I'm not even clear on how a doubly-linked list keeps LRU. Side note: I realize this is almost exactly the function of memcache, but it's not an option for me. I also took a look at the source hoping to enlighten myself on LRU caching, with no success.

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• MSP430 CMP operator

  - by Ludicrous

  Let's say I have the MSP430 assembly segment below: r15: 439c Memory map: 4390: 6045 0200 9c43 6400 8844 5044 363a 0000 Code: 448a: cmp #0x363a, 0x0(r15) 4490: jnz $+0x1c 4492: Code continues . . . 44ac: Jump to location The goal is to have the Z flag high. To do this with a cmp, both src and dst must be equal. If I have 363a in the memory location of r15, why is it that the resulting cmp does not trigger the Z flag? Through experimentation, I found that putting 3a36 in the memory location of r15 did in fact trigger the Z flag, but I don't understand why. If anyone could bring this to light, I would greatly appreciate it. If more information is needed, I will gladly provide it.

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• How *restrict / *__restrict__ works in C / C++?

  - by Moraru Lilian

  Here is some code I wrote: #include <iostream> using namespace std; int main(void) { int i = 7; int *__restrict__ a = &i; *a = 5; int *b = &i, *c = &i; *b = 8; *c = 9; cout << **&a << endl; //*a return 0; } From what I've read, if I do " *a = 5 ", it changes the value of the memory he, "a", is pointing to, after that the memory to which he is pointing to should not be modified by anyone else except "a", which means that these program is wrong because "b" and "c" modify it after that. Or, even if "b" modifies "i" first, after that only "a" should have access to that memory( "i" ). Am I getting it correctly?

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• Correct way to (re)launch a Java application with hardware-dependent VM parameters?

  - by LowLevelAbstraction

  EDIT I don't want to use Java Web Start I've got a Java application that I'd like to run with different VM parameters depending on the amount of memory the system it is launched on has. For example if the machine has 1 GB of memory or less I'd like to pass "-Xmx200m" and "-Xmx400m" if it has 2 GB and "-Xmx800m" if it has 8 GB (these are just examples). Is there a portable way to do this? I've tried having a first tiny Java app (hence portable) that determines the amount of memory available and then launches a new Java app but I don't think this is very clean. As of now I've written Bash shell scripts that invoke the Java app with the correct parameters depending on the config but it only works on Linux on OS X. What is the correct way to solve this? Would application packager package ;) help ?

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• Is it safe to catch an access violation in this scenario?

  - by Eloff

  I've read a lot, including here on SO that suggests this is a very bad idea in general and that the only thing you can do safely is exit the program. I'm not sure that this is true. This is for a pooling memory allocator that hands off large allocations to malloc. During pool_free() a pointer needs to be checked it it belongs to a pool or was allocated with malloc. By rounding the address down to the nearest 1MB boundary, I get a pointer to the beginning of a block of memory in the pool, or undefined if malloc was used. In the first case I can easily verify that the block of memory belongs to the pool, but, if it does not I will either fail this verification, or I will get an access violation (note that this is a read-only process). Could I not catch this with SEH (Windows) or handle the signal (POSIX) and simply treat it as a failed verification? (i.e. this is only possible if malloc was used, so pass the ptr to free())

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• Convert Decimal to ASCII

  - by Dan Snyder

  I'm having difficulty using reinterpret_cast. Before I show you my code I'll let you know what I'm trying to do. I'm trying to get a filename from a vector full of data being used by a MIPS I processor I designed. Basically what I do is compile a binary from a test program for my processor, dump all the hex's from the binary into a vector in my c++ program, convert all of those hex's to decimal integers and store them in a DataMemory vector which is the data memory unit for my processor. I also have instruction memory. So When my processor runs a SYSCALL instruction such as "Open File" my C++ operating system emulator receives a pointer to the beginning of the filename in my data memory. So keep in mind that data memory is full of ints, strings, globals, locals, all sorts of stuff. When I'm told where the filename starts I do the following: Convert the whole decimal integer element that is being pointed to to its ASCII character representation, and then search from left to right to see if the string terminates, if not then just load each character consecutively into a "filename" string. Do this until termination of the string in memory and then store filename in a table. My difficulty is generating filename from my memory. Here is an example of what I'm trying to do: C++ Syntax (Toggle Plain Text) 1.Index Vector NewVector ASCII filename 2.0 240faef0 128123792 'abc7' 'a' 3.0 240faef0 128123792 'abc7' 'ab' 4.0 240faef0 128123792 'abc7' 'abc' 5.0 240faef0 128123792 'abc7' 'abc7' 6.1 1234567a 243225 'k2s0' 'abc7k' 7.1 1234567a 243225 'k2s0' 'abc7k2' 8.1 1234567a 243225 'k2s0' 'abc7k2s' 9. //EXIT LOOP// 10.1 1234567a 243225 'k2s0' 'abc7k2s' Index Vector NewVector ASCII filename 0 240faef0 128123792 'abc7' 'a' 0 240faef0 128123792 'abc7' 'ab' 0 240faef0 128123792 'abc7' 'abc' 0 240faef0 128123792 'abc7' 'abc7' 1 1234567a 243225 'k2s0' 'abc7k' 1 1234567a 243225 'k2s0' 'abc7k2' 1 1234567a 243225 'k2s0' 'abc7k2s' //EXIT LOOP// 1 1234567a 243225 'k2s0' 'abc7k2s' Here is the code that I've written so far to get filename (I'm just applying this to element 1000 of my DataMemory vector to test functionality. 1000 is arbitrary.): C++ Syntax (Toggle Plain Text) 1.int i = 0; 2.int step = 1000;//top->a0; 3.string filename; 4.char *temp = reinterpret_cast<char*>( DataMemory[1000] );//convert to char 5.cout << "a0:" << top->a0 << endl;//pointer supplied 6.cout << "Data:" << DataMemory[top->a0] << endl;//my vector at pointed to location 7.cout << "Data(1000):" << DataMemory[1000] << endl;//the element I'm testing 8.cout << "Characters:" << &temp << endl;//my temporary char array 9. 10.while(&temp[i]!=0) 11.{ 12. filename+=temp[i];//add most recent non-terminated character to string 13. i++; 14. if(i==4)//when 4 chatacters have been added.. 15. { 16. i=0; 17. step+=1;//restart loop at the next element in DataMemory 18. temp = reinterpret_cast<char*>( DataMemory[step] ); 19. } 20. } 21. cout << "Filename:" << filename << endl; int i = 0; int step = 1000;//top-a0; string filename; char *temp = reinterpret_cast( DataMemory[1000] );//convert to char cout << "a0:" << top-a0 << endl;//pointer supplied cout << "Data:" << DataMemory[top-a0] << endl;//my vector at pointed to location cout << "Data(1000):" << DataMemory[1000] << endl;//the element I'm testing cout << "Characters:" << &temp << endl;//my temporary char array while(&temp[i]!=0) { filename+=temp[i];//add most recent non-terminated character to string i++; if(i==3)//when 4 chatacters have been added.. { i=0; step+=1;//restart loop at the next element in DataMemory temp = reinterpret_cast( DataMemory[step] ); } } cout << "Filename:" << filename << endl; So the issue is that when I do the conversion of my decimal element to a char array I assume that 8 hex #'s will give me 4 characters. Why isn't this this case? Here is my output: C++ Syntax (Toggle Plain Text) 1.a0:0 2.Data:0 3.Data(1000):4428576 4.Characters:0x7fff5fbff128 5.Segmentation fault

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• Application leaking Strings?

  - by Jörg B.

  My .net application does some heavy string loading/manipulation and unfortunately the memory consumption keeps rising and rising and when looking at it with a profiler I see alot of unreleased string instances. Now at one point of time or another I do need all objects t hat do have these string fields, but once done, I could get rid of e.g. the half of it and I Dispose() and set the instances to null, but the Garbage Collector does not to pick that up.. they remain in memory (even after half an hour after disposing etc). Now how do I get properly rid of unneeded strings/object instances in order to release them? They are nowhere referenced anymore (afaik) but e.g. aspose's memory profiler says their distance to the gc's root is '3'?

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• Criteria for selecting software for embedded device

  - by Suresh Kumar

  We are currently evaluating Web servers for an embedded device. We have laid down the evaluation criteria for things like HTTP version, Security, Compression etc. On the embeddable side, we have identified the following criteria: Memory footprint Memory management (support for plugging in a custom memory manager) CPU usage Thread usage (support for thread pool) Portability What I want inputs on is: Are there any other criteria that an embeddable software should meet? What exactly does it mean when someone says that a software is designed for embeddable use? We currently have zeroed in on two Web servers: AppWeb Lighttpd (lighty) Feature wise, both the above Web servers seem to be on par. However, it is claimed that AppWeb is designed for embedded use while Lighttpd is not. To choose between the above two Web servers, what criteria should I be looking at?

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• C# huge size 2-dim arrays

  - by 4eburek

  I need to declare square matrices in C# WinForms with more than 20000 items in a row. I read about 2GB .Net object size limit in 32bit and also the same case in 64bit OS. So as I understood the single answer - is using unsafe code or separate library built withing C++ compiler. The problem for me is worth because ushort[20000,20000] is smaller then 2GB but actually I cannot allocate even 700MB of memory. My limit is 650MB and I don't understand why - I have 32bit WinXP with 3GB of memory. I tried to use Marshal.AllocHGlobal(700<<20) but it throws OutOfMemoryException, GC.GetTotalMemory returns 4.5MB before trying to allocate memory. I found only that many people say use unsafe code but I cannot find example of how to declare 2-dim array in heap (any stack can't keep so huge amount of data) and how to work with it using pointers. Is it pure C++ code inside of unsafe{} brackets? Could you please provide a small example of working with matrices using pointers in unsafe code.

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• How to display .gif (with animation) on dc

  - by mukul sharma

  Hi All, in my application i am having a panel with associated a wxWindowDC and wxMemoryDC. i have to draw the various thing on that panel like bg color, on top of bg color bg image and on the top bg image i have to draw some text etc. I am storing all this thing into memory dc and finally in paint handler i m copying the memory dc to window dc. But i stuck in this process when i have a .gif (with multiple frames) and i m trying to bliting this gif image on DC that time it shows only a single frame of that gif image (its became a ordinary still image not an animated image). how i can store this whole gif image in memory dc and display full gif image on dc(with animation). I cant use wx.AnimateCrl() because i need that image in memoryDC. Any help really appreciable.

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• Apache Prefork Configuration

  - by user1618606

  I'm newbie on VPS configuration. So, I've installed apache, php and mysql and now I need to know how to configure Prefork to optimize Apache. The system configuration is: CPU Cores 2 x 2 Ghz @ 4 Ghz RAM Memory 2304 MB DDR3 Burst Memory 3 GB DDR3 Disk Space 30 GB SSD Bandwidth 3 TB SwitchPort 1 Gbps Actually, after linux, mysql, apache and php, there are 250 MB memory in use. Well, I don't have idea to calculate. I saw in some websistes, some vars like: KeepAlive On KeepAliveTimeout 1 MaxKeepAliveRequests 100 StartServers 15 MinSpareServers 15 MaxSpareServers 15 MaxClients 20 MaxRequestsPerChild 0 or StartServers 2 MaxClients 150 MinSpareThreads 25 MaxSpareThreads 75 ThreadsPerChild 25 MaxRequestsPerChild 0 How I could to do: Prefork or worker? Where and how the vars are placed? In httpd.conf? Big hug, Claudio.

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• Stopping pirates

  - by Pirate for Profit

  Okay, what do I do to stop pirates? Obviously a callhome to internet service. We are considering making some major aspects be dependent on a web service of some sort. Memory offsets and cracking. If I like rand randomly to allocate empty memory on the heap, would this throw off the crackers? I hacked some memory shit for EverQuest back in the dizzay but don't really know much about this. Registry on windows, etc., I know theres ways to identify the computer. That's easily spoofed with hex editor, but if I jumble up the strings in the program would that help? I need to know that + real ideas. I want the serials of their sound cards. Any other ideas?

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• Best way to reverse bitmap data that is upside down

  - by Wladimir

  Hello, I have a method that I call and it returns bitmap data from a capture device. It returns a pointer to the buffer data as an IntPtr and the buffer length as an int. I know in advance that this bitmap is a 24bpp and its width and height. The problem is that the buffer contains the bitmap data upside down and I need this data to be in the right order (reverse it). What I do is create a for loop and using CopyMemory, I copy each line (stride) of this data from bottom to up to a newly allocated memory space. Is there any way to make it faster than creating more memory each time I receive a new frame? It makes the application get a bit slow and consumes more memory as each bitmap is pretty big. I do this because I use another component that analyses the bitmaps and it doesn't work propertly if the bitmaps are upside down. I'm using .net, c# thanks!

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• What is the maximum number of controls that a VBA form can hold?

  - by Lunatik

  I'm currently building an Excel 2003 app that requires a horribly complex form and am worried about limitations on the number of controls. It currently has 154 controls (counted using Me.Controls.Count - this should be accurate, right?) but is probably only about a third complete. The workflow really fits a single form, but I guess I can split it up if I really have to. I see evidence in a Google search that VB6 (this usually includes VBA) has a hard limit of 254 controls in a form. However, I created a dummy form with well over 1200 controls which still loaded and appeared to work just fine. I did get some 'out of memory' errors when trying to add specific combinations of controls though, say 800 buttons and 150 labels, leading me to think that any limit might be affected by the memory requirements of each type of control. Does anyone have any information that might help ensure that I or, more importantly, other users with differing environments don't run into any memory issues with such a large form?

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• Task vs. process, is there really any difference?

  - by DASKAjA

  Hi there, I'm studying for my final exams in my CS major on the subject distributed systems and operating systems. I'm in the need for a good definition for the terms task, process and threads. So far I'm confident that a process is the representation of running (or suspended, but initiated) program with its own memory, program counter, registers, stack, etc (process control block). Processes can run threads which share memory, so that communication via shared memory is possible in contrast to processes which have to communicate via IPC. But what's the difference between tasks and process. I often read that they're interchangable and that the term task isn't used anymore. Is that really true?

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• How to initialise a STL vector/list with a class without invoking the copy constructor

  - by Warpspace

  I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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• High level audio crossfading library for python

  - by tcoopman

  I am looking for a high level audio library that supports crossfading for python (and that works in linux). In fact crossfading a song and saving it is about the only thing I need. I tried pyechonest but I find it really slow. Working with multiple songs at the same time is hard on memory too (I tried to crossfade about 10 songs in one, but I got out of memory errors and my script was using 1.4Gb of memory). So now I'm looking for something else that works with python. I have no idea if there exists anything like that, if not, are there good command line tools for this, I could write a wrapper for the tool.

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• Primary reasons why programming language runtimes use stacks?

  - by manuel aldana

  Many programming language runtime environments use stacks as their primary storage structure (e.g. see JVM bytecode to runtime example). Quickly recalling I see following advantages: Simple structure (pop/push), trivial to implement Most processors are anyway optimized for stack operations, so it is very fast Less problems with memory fragmentation, it is always about moving memory-pointer up and down for allocation and freeing complete blocks of memory by resetting the pointer to the last entry offset. Is the list complete or did I miss something? Are there programming language runtime environments which are not using stacks for storage at all?

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• How to free an Oracle Object-Type passed to an external procedure

  - by chila

  I'm using OTT to pass and load an Object Type from a C++ external procedure. The problem I have is that I don't know how to somehow mark the object for deallocation once extproc has done marshalling it. The object remains in extproc's memory forever making it grow in memory consumtion. Here's part of the code: void decodeFromBuffer(OCIExtProcContext *ctx, GPRS_GPRSCHARGINGRECORD *record, GPRS_GPRSCHARGINGRECORD_ind *recordInd, const unsigned char *buffer, int buffLen, OCIInd *bufferInd) { . . . assert(OCIExtProcGetEnv(ctx, &envh, &svch, &errh) == OCI_SUCCESS); recordInd->_atomic = OCI_IND_NOTNULL; // somehow I should mark the object for deallocation after extproc has done marshalling it // using OCINumberFromInt and OCIStringAssignText to load the object (this memory is never deallocated) . . . } How could I mark the object (and subobjects) for deallocation?

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• Efficient implementation of natural logarithm (ln) and exponentiation

  - by Donotalo

  Basically, I'm looking for implementation of log() and exp() functions provided in C library <math.h>. I'm working with 8 bit microcontrollers (OKI 411 and 431). I need to calculate Mean Kinetic Temperature. The requirement is that we should be able to calculate MKT as fast as possible and with as little code memory as possible. The compiler comes with log() and exp() functions in <math.h>. But calling either function and linking with the library causes the code size to increase by 5 Kilobytes, which will not fit in one of the micro we work with (OKI 411), because our code already consumed ~12K of available ~15K code memory. The implementation I'm looking for should not use any other C library functions (like pow(), sqrt() etc). This is because all library functions are packed in one library and even if one function is called, the linker will bring whole 5K library to code memory.

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• Caveats to be aware of when using threading in Python?

  - by knorv

  I'm quite new to threading in Python and have a couple of beginner questions. When starting more than say fifty threads using the Python threading module I start getting MemoryError. The threads themselves are very slim and not very memory hungry, so it seems like it is the overhead of the threading that causes the memory issues. Is there something I can do to increase the memory capacity or otherwise make Python allow for a larger number of threads? What is the maximum number of threads you've been able to run in your Python code using the threading module? Did you do any tricks to achieve that number? Are there any other caveats to be aware of when using the threading module?

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• java increase xmx dynamically at runtime

  - by Tomer

  Hi, I have a jvm server in my machine, now I want to have 2 apservers of mine sitting in same machine, however I want the standby one to have a really low amount of memory allocated with xmx because its passive, one the main server (active) goes down I want to allocate more memory to my passive server which is already up without restarting it (I have have them both having too much xmx - note they would consume memory at startup and I cant allow possibility of outOfMemory). So I want passive - low xmx once active goes down I want my passive to receive much more xmx. is there a way for me to achieve that. Thanks

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• Objective-c pointer assignment and reassignment dilema

  - by moshe

  Hi, If I do this: 1 NSMutableArray *near = [[NSMutableArray alloc] init]; 2 NSMutableArray *all = [[NSMutableArray alloc] init]; 3 NSMutableArray *current = near; 4 current = all; What happens to near? At line 3, am I setting current to point to the same address as near so that I now have two variables pointing to the same place in memory, or am I setting current to point to the location of near in memory such that I now have this structure: current - near - NSMutableArray The obvious difference would be the value of near at line 4. If the former is happening, near is untouched and still points to its initial place in memory. If the latter is happening,

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• malloc hangs in Linux

  - by Rahul

  I am using Linux on a 16 G with 2 quad core CPU. There are 8 processes which are doing some work (CPU intensive/network i/o). Out of which 4 have a memory leak (These are test conditions so no problem in having leaks here). Total space is occupied by all processes is around 15.4 G only 200 MB is free in system. Things are fine for some hours. But after that malloc hangs (for a process which doesn't have a memory leak). Its stuck for for more than 4 minutes (Note CPU is not 100% but io has gone up signficantly). Now there is no problem in the hanged process. (It has not corrupted the memory). What malloc is doing? (is it tryibg to defragment or builidng up swap space).I am using SUSE 10. Any pointers?

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• Creating a Dib by only specifying the size with GDI+ and DotNet...

  - by Kris Erickson

  I have just recently discovered the difference between different constructors in GDI+. Going: var bmp = new Bitmap(width, height, pixelFormat); creates a DDB (Device Dependent Bitmap) whereas: var bmp = new Bitmap(someFile); creates a DIB (Device Independent Bitmap). This is really not usually important, except when handling very large images (where a DDB will run out of memory, and run out of memory at different sizes depending on the machine and its video memory). I need to create a DIB rather than DDB, but specify the height, width and pixelformat. Does anyone know how to do this in DotNet. Also is there a guide to what type of Bitmap (DIB or DDB) is being created by which Bitmap constructor?

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