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  • How are a session identifiers generated?

    - by Asaf R
    Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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  • How to solve this problem with lists?

    - by osabri
    what i don't understand in my task here what kind of list i can use, and if it should have 2 attributes key and value ? or only value? with pointers to another node ofc the task: "design a function which create a list using input from the keyboard _ the prefered solution. Assume that some magic stops the input; so the length of a list is not known in advance.(alternative solution: a function which creates explicitly a fixed list. However, all other function can not assume any knowledge about the length of lists). Necessary utilities( additional functions to be created): a function which deallocates the memory used for lists and a function which prints the content of the list. let the element of lists contain a letter. Design a function which create a copy of such list. can't also understand the list line !!!!!???

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  • In C, as free() knows an array size, why isn't there a function that gets the array size? [closed]

    - by user354959
    Possible Duplicate: If free() knows the length of my array, why can’t I ask for it in my own code? Searching around (including here at stackoverflow), I got that malloc() allocates an array and also creates a header to control the array info. In this header, there's also the array size. free() use such information to know how to deallocate that array. So, if the array size info is "there" (somewhere in the memory), why there isn't a function that returns an array size, looking for this at the array header? Or am I missing something?

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  • What are the ways to create draw data structures for latex?

    - by alicephacker
    I tried tikz/pgf a bit but have not had much luck creating a nice diagram to visualize bitfields or byte fields of packed data structures (i.e. in memory). Essentially I want a set of rectangles representing ranges of bits with labels inside, and offsets along the top. There should be multiple rows for each word of the data structure. This is similar to most of the diagrams in most processor manuals labeling opcode encoding etc. Has anyone else tried to do this using latex or is there a package for this?

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  • Creating additional Window by a thread - C

    - by Jamie Keeling
    Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a separate thread so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate thread 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I hope it makes sense. Thanks!

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  • How do I view how many concurrent long polling requests there are on my server?

    - by Pascal
    My host is Joyent. My host says I have 15 process limit and prstat -J shows those processes but that doesn't tell me how many long polling requests are currently being served. I could record it myself but that would add alot of performance overhead. I need to know when the server is at its long polling limits. I know this limit occurs far before the memory or CPU is used up. From experimentation, I've already verified that the number of long polls open is NOT equivalant to the number of processes running, probably because each process has multiple threads, each serving a request. thanks.

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  • Splitting a string into new rows in R

    - by user3703195
    I have a data set like below: Country Region Molecule Item Code IND NA PB102 FR206985511 THAI AP PB103 BA-107603 / F000113361 / 107603 LUXE NA PB105 1012701 / SGP-1012701 / F041701000 IND AP PB106 AU206985211 / CA-F206985211 THAI HP PB107 F034702000 / 1010701 / SGP-1010701 BANG NA PB108 F000007970/25781/20009021 I want to split based the string values in ITEMCODE column on / and create a new row for each entry. For instance, the desired output will be: Country Region Molecule Item Code New row IND NA PB102 FR206985511 FR206985511 THAI AP PB103 BA-107603 / F000113361 / 107603 F000113361 107603 BA-107603 LUXE NA PB105 1012701 / SP-1012701 / F041701000 1012701 SP-1012701 F041701000 IND AP PB106 AU206985211 / CA-F206985211 AU206985211 CA-F206985211 THAI HP PB107 F034702000 / 1010701 / SP-1010701 F034702000 1010701 SP-1010701 BANG NA PB108 F000007970/25781/20009021 F000007970 25781 20009021 I tried the below code library(splitstackshape) df2=concat.split.multiple(df1,"Plant.Item.Code","/", direction="long") but got the Error "Error: memory exhausted (limit reached?)" When i tried strsplit() i got the below error message. Error in strsplit(df1$Plant.Item.Code, "/") : non-character argument Any help from you will be appreciated.

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  • Is it possible to find out what FlashBuilder is doing during compilation?

    - by justkevin
    I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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  • Double indirection and structures passed into a function

    - by ZPS
    I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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  • Easiest way to combine a dataset and other data in a single file?

    - by Tim Gradwell
    I have a dataset in C# which I can serialise using dataset.WriteXml(filename); but I want the file to contain other data as well (essentially some meta data about the dataset). I could add another table to the dataset which contained the metadata, but I'd prefer to keep it separate, if at all possible. Essentially I think I want to create a 'combination of files' file, that looks something like this: size_of_file1 file1 size_of_file2 file2 ... etc Then, I'd like to load the file into memory, and split the file into separate streams, so that I can feed the dataset into dataset.ReadXml(stream); and the metadata into something else. Sound possible? Can anyone tell me how I can do it? Thanks Tim

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  • Clojure closures and GC

    - by Ralph
    It is my understanding that the default ClassLoader used in Java (and thus, Clojure) holds on to pointers to any anonymous classes created, and thus, onto lambdas and closures. These are never garbage collected, and so represent a "memory leak". There is some investigation going on for Java 7 or 8 to adding an anonymous ClassLoader that will not retain references to these functions. In the mean time how are people dealing with writing long-running applications in languages like Clojure and Scala, that encourage the use of these constructs? Is there any possibility that Clojure could provide its own anonymous ClassLoader, extending the system one, but not holding onto created classes?

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  • Ruby: Read large data from stdout and stderr of an external process on Windows

    - by BinaryMuse
    Greetings, all, I need to run a potentially long-running process from Ruby on Windows and subsequently capture and parse the data from the external process's standard output and error. A large amount of data can be sent to each, but I am only necessarily interested in one line at a time (not capturing and storing the whole of the output). After a bit of research, I found that the Open3 class would take care of executing the process and giving me IO objects connected to the process's standard output and error (via popen3). Open3.popen3("external-program.bat") do |stdin, out, err, thread| # Step3.profit() ? end However, I'm not sure how to continually read from both streams without blocking the program. Since calling IO#readlines on out or err when a lot of data has been sent results in a memory allocation error, I'm trying to continuously check both streams for available input, but not having much luck with any of my implementations. Thanks in advance for any advice!

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  • Objective-C: Initializing char with char at index of string.

    - by Mr. McPepperNuts
    unichar myChar = [myString characterAtIndex:0]; [myNSMutableArray addObject:myChar]; I am trying to insert the first char of a string into an array, to create an array of chars. the first line does not give me an error. The second line however, provides the following error: warning: passing argument 1 of 'addObject:' makes pointer from integer without a cast This also crashes the application with a "bad address" error. I thought this error was due to a problem with memory allocation. Can someone shed some light on this.

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  • Is there any significant benefit to reading string directly from control instead of moving it into a

    - by Kevin
    sqlInsertFrame.Parameters.AddWithValue("@UserName", txtUserName.txt); Given the code above...if I don't have any need to move the textbox data into a string variable, is it best to read the data directly from the control? In terms of performance, it would seem smartest to not create any unnecessary variables which use up memory if its not needed. Or is this a situation where its technically true but doesn't yield any real world results due to the size of the data in question. Forgive me, I know this is a very basic question.

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  • Why does this script work in the current directory but fail when placed in the path?

    - by kiloseven
    I wish to replace my failing memory with a very small shell script. #!/bin/sh if ! [ –a $1.sav ]; then mv $1 $1.sav cp $1.sav $1 fi nano $1 is intended to save the original version of a script. If the original has been preserved before, it skips the move-and-copy-back (and I use move-and-copy-back to preserve the original timestamp). This works as intended if, after I make it executable with chmod I launch it from within the directory where I am editing, e.g. with ./safe.sh filename However, when I move it into /usr/bin and then I try to run it in a different directory (without the leading ./) it fails with: *-bash: /usr/bin/safe.sh: /bin/sh: bad interpreter: Text file busy* My question is, when I move this script into the path (verified by echo $PATH) why does it then fail? D'oh? Inquiring minds want to know how to make this work.

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  • ContextSwitchDeadlock Was Detected error in C#

    - by assassin
    Hi, I am running a C# application, and during run-time I get the following error: The CLR has been unable to transition from COM context 0x20e480 to COM context 0x20e5f0 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. Can anyone please help me out with the problem here? Thanks a lot.

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  • Book resources for x86/x64 assembly programming on Win platform

    - by Scott Davies
    Hello, I ran a search for assembly language resources on stackoverflow.com and found some interesting results, but they seemed to boil down to two groups: 1) Assembly references to old ia32 architecture, such as the 80386 to Pentium 2) Windows agnostic books. Most of the commenters make the point that assembler is CPU dependent and that the OS is irrelevant, but it seems pointless to me to pick a book that has assembly examples that refer to MS-DOS interrupts and memory layouts. Likewise, learning assembler on Linux would seem to produce Linux executables Are there any: 1) Modern 2) x86/x64 3) on Windows platform - book resources available ? The reason I am targeting the Win platform is I would like to do low-level, OS internals programming, to supplement my Win C/C++ work. Thanks

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  • [Ruby] How can I randomly iterate through a large Range?

    - by void
    I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: (0..9).sort_by{rand}.map{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle could be used to increase efficiency, but this code is sufficient for many purposes. My problem is that sort_by will transform the range into an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do?

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  • [CA_COLOR_OPAQUE] things that make a layer non-opaque. scaled CAGradientLayer?

    - by mahal tertin
    i spent some time with the environment variable CA_COLOR_OPAQUE = 1 and have my findings to share. things that make a CALayer non-opaque (slow, more memory, ...): * contents with alpha (like an NSImage with an icon) * NSImage/CGImage from a pdf as contents (even when the pdf does not contain any alpha and opaque=YES) * backgroundColor = nil * CATextLayer with text in a (because it is contents with alpha) * rounded corners? maybe/sometimes * masksToBounds? not necessarily as we scale most of tree with CATransform3DScale on sublayerTransform i found also these rather irritating non-opaque: * CAGradientLayer that is somewhere down in this scaled tree (even when set all the gradient colors without alpha) * edgeAntialiasingMask != 0 of a layer that is somewhere down in this scaled tree the last two do not make sense to me. why should it be non opaque? what do i see? if anyone has any thoughts on these findings, i'm happy to learn as i couldn't find such a list yet.

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  • Excel workbooks produced by POI don't work when linked

    - by Eric Nicolas
    Here is what I'm doing : Create a workbook in memory (book = new HSSFWorkbook(), ...) Save it to disk (book.write(...)) Open in Excel (ok) Create another workbook in Excel, which links to the first one (=PoiWorkbook?xls!A1) Close Excel Then everytime I open the second workbook again, all the links are #N/A, unless I also open the POI-generated workbook at the same time. I never saw this behaviour with standard workbooks created in Excel. Anyone has seen this and found a workaround ? Thanks.

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  • Transferring data from 2d Dynamic array in C to CUDA and back

    - by Soumya
    I have a dynamically declared 2D array in my C program, the contents of which I want to transfer to a CUDA kernel for further processing. Once processed, I want to populate the dynamically declared 2D array in my C code with the CUDA processed data. I am able to do this with static 2D C arrays but not with dynamically declared C arrays. Any inputs would be welcome! I mean the dynamic array of dynamic arrays. The test code that I have written is as below. #include "cuda_runtime.h" #include "device_launch_parameters.h" #include <stdio.h> #include <conio.h> #include <math.h> #include <stdlib.h> const int nItt = 10; const int nP = 5; __device__ int d_nItt = 10; __device__ int d_nP = 5; __global__ void arr_chk(float *d_x_k, float *d_w_k, int row_num) { int index = (blockIdx.x * blockDim.x) + threadIdx.x; int index1 = (row_num * d_nP) + index; if ( (index1 >= row_num * d_nP) && (index1 < ((row_num +1)*d_nP))) //Modifying only one row data pertaining to one particular iteration { d_x_k[index1] = row_num * d_nP; d_w_k[index1] = index; } } float **mat_create2(int r, int c) { float **dynamicArray; dynamicArray = (float **) malloc (sizeof (float)*r); for(int i=0; i<r; i++) { dynamicArray[i] = (float *) malloc (sizeof (float)*c); for(int j= 0; j<c;j++) { dynamicArray[i][j] = 0; } } return dynamicArray; } /* Freeing memory - here only number of rows are passed*/ void cleanup2d(float **mat_arr, int x) { int i; for(i=0; i<x; i++) { free(mat_arr[i]); } free(mat_arr); } int main() { //float w_k[nItt][nP]; //Static array declaration - works! //float x_k[nItt][nP]; // if I uncomment this dynamic declaration and comment the static one, it does not work..... float **w_k = mat_create2(nItt,nP); float **x_k = mat_create2(nItt,nP); float *d_w_k, *d_x_k; // Device variables for w_k and x_k int nblocks, blocksize, nthreads; for(int i=0;i<nItt;i++) { for(int j=0;j<nP;j++) { x_k[i][j] = (nP*i); w_k[i][j] = j; } } for(int i=0;i<nItt;i++) { for(int j=0;j<nP;j++) { printf("x_k[%d][%d] = %f\t",i,j,x_k[i][j]); printf("w_k[%d][%d] = %f\n",i,j,w_k[i][j]); } } int size1 = nItt * nP * sizeof(float); printf("\nThe array size in memory bytes is: %d\n",size1); cudaMalloc( (void**)&d_x_k, size1 ); cudaMalloc( (void**)&d_w_k, size1 ); if((nP*nItt)<32) { blocksize = nP*nItt; nblocks = 1; } else { blocksize = 32; // Defines the number of threads running per block. Taken equal to warp size nthreads = blocksize; nblocks = ceil(float(nP*nItt) / nthreads); // Calculated total number of blocks thus required } for(int i = 0; i< nItt; i++) { cudaMemcpy( d_x_k, x_k, size1,cudaMemcpyHostToDevice ); //copy of x_k to device cudaMemcpy( d_w_k, w_k, size1,cudaMemcpyHostToDevice ); //copy of w_k to device arr_chk<<<nblocks, blocksize>>>(d_x_k,d_w_k,i); cudaMemcpy( x_k, d_x_k, size1, cudaMemcpyDeviceToHost ); cudaMemcpy( w_k, d_w_k, size1, cudaMemcpyDeviceToHost ); } printf("\nVerification after return from gpu\n"); for(int i = 0; i<nItt; i++) { for(int j=0;j<nP;j++) { printf("x_k[%d][%d] = %f\t",i,j,x_k[i][j]); printf("w_k[%d][%d] = %f\n",i,j,w_k[i][j]); } } cudaFree( d_x_k ); cudaFree( d_w_k ); cleanup2d(x_k,nItt); cleanup2d(w_k,nItt); getch(); return 0;

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  • what practical proofs are there about the Turing completeness of neural nets? what nns can execute c

    - by Albert
    I'm interested in the computational power of neural nets. It is generally accepted that recurrent neural nets are Turing complete. Now I was searching for some papers which proofs this. What I found so far: Turing computability with neural nets, Hava T. Siegelmann and Eduardo D. Sontag, 1991 I think this is only interesting from a theoretical point of view because it needs to have the neuron activity of infinite exactness (to encode the state somehow as a rational number). S. Franklin and M. Garzon, Neural computability This needs an unbounded number of neurons and also doesn't really seem to be that much practical. (Note that another question of mine tries to point out this kind of problem between such theoretical results and the practice.) I'm searching mostly for some neural net which really can execute some code which I can also simulate and test in practice. Of course, in practice, they would have some kind of limited memory. Does anyone know something like this?

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  • Forcing a templated object to construct from a pointer

    - by SalamiArmi
    I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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  • RSA encrypted data block size

    - by calccrypto
    how do you store an rsa encrypted data block? the output might be significantly greater than the original input data block size, and i dont think people waste memory by padding bucket loads of 0s in front of each data block. besides, how would they be removed? or is each block stored on new lines within the file? if that is the case, how would you tell the difference between legitimate new line and a '\n' char written into the file? what am i missing? im writing the "write to file" part in python, so maybe its one of the differences between: open(file,'w') open(file,'w+b') open(file,'wb') that i dont know. or is it something else?

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