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• C++'s std::string pools, debug builds? std::string and valgrind problems

  - by Den.Jekk

  Hello, I have a problem with many valgrind warnings about possible memory leaks in std::string, like this one: 120 bytes in 4 blocks are possibly lost in loss record 4,192 of 4,687 at 0x4A06819: operator new(unsigned long) (vg_replace_malloc.c:230) by 0x383B89B8B0: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C3B4: (within /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C4A9: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) I'm wondering: does std::string (GCC 4.1.2) use any memory pools? if so, is there any way to disable the pools (in form of a debug build etc.)? Regards, Den

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• Can my app arrange a gdb breakpoint or watch?

  - by Larry Gritz

  Is there a way for my code to be instrumented to insert a break point or watch on a memory location that will be honored by gdb? (And presumably have no effect when gdb is not attached.) I know how to do such things as gdb commands within the gdb session, but for certain types of debugging it would be really handy to do it "programmatically", if you know what I mean -- for example, the bug only happens with a particular circumstance, not any of the first 11,024 times the crashing routine is called, or the first 43,028,503 times that memory location is modified, so setting a simple break point on the routine or watch point on the variable is not helpful -- it's all false positives. I'm concerned mostly about Linux, but curious about if similar solutions exist for OS X (or Windows, though obviously not with gdb).

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• Speed-up of readonly MyISAM table

  - by Ozzy

  We have a large MyISAM table that is used to archive old data. This archiving is performed every month, and except from these occasions data is never written to the table. Is there anyway to "tell" MySQL that this table is read-only, so that MySQL might optimize the performance of reads from this table? I've looked at the MEMORY storage engine, but the problem is that this table is so large that it would take a large portion of the servers memory, which I don't want. Hope my question is clear enough, I'm a novice when it comes to db administration so any input or suggestions are welcome.

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• POC of take screenshot from XP virtual machine of windows 7 main machine.

  - by Svisstack

  Hello, I searching any ideas of take screenshot of main machine on windows 7 from virtual machine on windows XP, have any ideas or proof on concept to can do this? Maybe from integration drivers or something? I don't require any code snipets, must have only POC of can't do this. EDIT: Can be process integration idea? (dump any process memory on main machine from virtualized)

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• How to return a string literal from a function

  - by skydoor

  Hi I am always confused about return a string literal or a string from a function. I was told that there might be memory leak because you don't know when the memory will be deleted? For example, in the code below, how to implement foo() so that make the output of the code is "Hello World"? void foo ( ) // you can add parameters here. { } int main () { char *c; foo ( ); printf ("%s",c); return 0; } Also if the return type of foo() is not void, but you can return char*, what should it be.

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• Type Declaration - Pointer Asterisk Position

  - by sahs

  Hello, in C++, the following means "allocate memory for an int pointer": int* number; So, the asterisk is part of the variable type; without it, that would mean something else (that's why I usually don't separate the asterisk from the variable type). Then what is the reason the asterisk is considered something else, instead of being part of the type? For example, it seems better, if the following meant "allocate memory for two int pointers": int* number1, number2; Am I wrong?

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• is ROBOCOPY a good form of backup as a tool?

  - by dasko

  seeing how it does not do a write verify unless scripted (or is it needed?) is it a decent option to dump a few folders to another server? i am just worried about whether the data, after being copied, might be corrupted but you would not be aware of it being buggy? i have used it in the past without issue but am seeking feedback in case i missed something obvious.

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• How to write a datatable to excel work book at client side

  - by senthilkumar

  Hi Guys Currently i am doing one project in that we need to generate report from database. Since my server memory is too low im getting 'Out of Memory' Exception when im writing it at serverside and also when i write directly to a excel file using http header as excel file im not able to create multiple sheets since my database table is huge more than 65536 rows. I saw many solution using a third party tool but i cant use those into mine..If anyone already worked on this please give me some direction. Also i tried using javascript but for that i need to use datagrid at server side?? but in my project i m not allowed to use like this.

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• How Flask loads blueprint internaly?

  - by Ignas B.

  I'm just interested how Flask's blueprints gets imported. It still imports the python module at the end of all the stuff done by Flask and if I'm right python does two things when importing: registers the module name in the namespace and then initialize it if needed. So if Flask blueprint is initialized when it gets registered, so all the module then is in memory and if there are lots of blueprints to register, the memory just gets wasted, because in one request basically you use one blueprint. Not a big loss but still... But if it is only registered in the namespace and initialized only when needed (when the real request reaches it), then it make sense to register them all at once (as is the recommended way I understood). This is I guess the case here :) But just wanted to ask and understand a bit deeper.

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• iptables intercept local traffic

  - by Anonymous

  i hope someone can help me out with somewhat simple task. I'm trying to redirect a client in my router through my desktop PC, so i can dump the traffic and analyze it (its potential source of poisoning the network with malicious packets). However i don't have a second NIC on my hands and i was hoping i can redirect all the traffic from that IP through my PC. In essence to become MITM for the client. Does anyone have any idea where to start: Current state: (localip)-(router)-(internet) And what i want to do: (localip)-(pc)-(router)-(internet)

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• Given a function which produces a random integer in the range 1 to 5, write a function which produce

  - by praveen

  what is simple solution what is effective solution to less minimum memory and(or) cpu speed?

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• C++ conditional compilation

  - by Shaown

  I have the following code snippet #ifdef DO_LOG #define log(p) record(p) #else #define log(p) #endif void record(char *data){ ..... ..... } Now if I call log("hello world") in my code and DO_LOG isn't defined, will the line be compiled, in other words will it eat up the memory for the string "hello world"? P.S. There are a lot of record calls in the program and it is memory sensitive, so is there any other way to conditionally compile so that it only depends on the #define DO_LOG? Thanks in advance.

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• Side effects of reordering columns in PostgreSQL

  - by Summer

  I sometimes re-order the columns in my Postgres DB. Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. My question is: what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did beforehand? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• are runtime linking library globals shared among plugins loaded with dlopen?

  - by conejoroy

  I've a C++ program that links at runtime with, lets say, mylib.so. then, the same program uses dlopen()/dlsym() to load a function from myplugin.so, dynamic library that in turn has dependencies to mylib.so. My question is: will the program AND the function in the plugin access the same globals defined in mydlib.so in the same memory area reserved for the program, or each will be assigned different, unrelated copies in its own memory space? if the latter is the default behaviour, is it possible to change that? Thanks in advance =)!

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• thread management in nbody code of cuda-sdk

  - by xnov

  When I read the nbody code in Cuda-SDK, I went through some lines in the code and I found that it is a little bit different than their paper in GPUGems3 "Fast N-Body Simulation with CUDA". My questions are: First, why the blockIdx.x is still involved in loading memory from global to share memory as written in the following code? for (int tile = blockIdx.y; tile < numTiles + blockIdx.y; tile++) { sharedPos[threadIdx.x+blockDim.x*threadIdx.y] = multithreadBodies ? positions[WRAP(blockIdx.x + q * tile + threadIdx.y, gridDim.x) * p + threadIdx.x] : //this line positions[WRAP(blockIdx.x + tile, gridDim.x) * p + threadIdx.x]; //this line __syncthreads(); // This is the "tile_calculation" function from the GPUG3 article. acc = gravitation(bodyPos, acc); __syncthreads(); } isn't it supposed to be like this according to paper? I wonder why sharedPos[threadIdx.x+blockDim.x*threadIdx.y] = multithreadBodies ? positions[WRAP(q * tile + threadIdx.y, gridDim.x) * p + threadIdx.x] : positions[WRAP(tile, gridDim.x) * p + threadIdx.x]; Second, in the multiple threads per body why the threadIdx.x is still involved? Isn't it supposed to be a fix value or not involving at all because the sum only due to threadIdx.y if (multithreadBodies) { SX_SUM(threadIdx.x, threadIdx.y).x = acc.x; //this line SX_SUM(threadIdx.x, threadIdx.y).y = acc.y; //this line SX_SUM(threadIdx.x, threadIdx.y).z = acc.z; //this line __syncthreads(); // Save the result in global memory for the integration step if (threadIdx.y == 0) { for (int i = 1; i < blockDim.y; i++) { acc.x += SX_SUM(threadIdx.x,i).x; //this line acc.y += SX_SUM(threadIdx.x,i).y; //this line acc.z += SX_SUM(threadIdx.x,i).z; //this line } } } Can anyone explain this to me? Is it some kind of optimization for faster code?

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• How can I position QDockWidgets as the screen shot shows using code?

  - by Nathan

  I want a Qt window to come up with the following arrangement of dock widgets on the right. Qt allows you to provide an argument to the addDockWidget method of QMainWindow to specify the position (top, bottom, left or right) but apparently not how two QDockWidgets placed on the same side will be arranged. Here is the code that adds the dock widgets. this uses PyQt4 but it should be the same for Qt with C++ self.memUseGraph = mem_use_widget(self) self.memUseDock = QDockWidget("Memory Usage") self.memUseDock.setObjectName("Memory Usage") self.memUseDock.setWidget(self.memUseGraph) self.addDockWidget(Qt.DockWidgetArea(Qt.RightDockWidgetArea),self.memUseDock) self.diskUsageGraph = disk_usage_widget(self) self.diskUsageDock = QDockWidget("Disk Usage") self.diskUsageDock.setObjectName("Disk Usage") self.diskUsageDock.setWidget(self.diskUsageGraph) self.addDockWidget(Qt.DockWidgetArea(Qt.RightDockWidgetArea),self.diskUsageDock) When this code is used to add both of them to the right side, one is above the other, not like the screen shot I made. The way I made that shot was to drag them there with the mouse after starting the program, but I need it to start that way.

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• Efficient alternatives to merge for larger data.frames R

  - by Etienne Low-Décarie

  I am looking for an efficient (both computer resource wise and learning/implementation wise) method to merge two larger (size1 million / 300 KB RData file) data frames. "merge" in base R and "join" in plyr appear to use up all my memory effectively crashing my system. Example load test data frame and try test.merged<-merge(test, test) or test.merged<-join(test, test, type="all") - The following post provides a list of merge and alternatives: How to join data frames in R (inner, outer, left, right)? The following allows object size inspection: https://heuristically.wordpress.com/2010/01/04/r-memory-usage-statistics-variable/ Data produced by anonym

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• Maximum executable size on the iPhone?

  - by Sirp

  Is there a maximum size of executables or executables + shared objects on the iPhone? I've been developing an app that has been crashing on startup or early in execution with SIGSYS. Removing code from the program has helped, though structuring data so the code is simply not executed does not. This could be memory corruption, of some kind, however when I compiled with -Os rather than -O2 or -O3 the size of my executable goes down from 5.15MB to 3.60MB and the application runs perfectly. I also have a bunch of libraries I use, of course. I'm wondering, is there a limit on the size of executable code on the iPhone? Or am I just 'getting lucky' and masking memory corruption when I use -Os?

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• Read random lines from huge CSV file in Python

  - by jbssm

  I have this quite big CSV file (15 Gb) and I need to read about 1 million random lines from it. As far as I can see - and implement - the CSV utility in Python only allows to iterate sequentially in the file. It's very memory consuming to read the all file into memory to use some random choosing and it's very time consuming to go trough all the file and discard some values and choose others, so, is there anyway to choose some random line from the CSV file and read only that line? I tried without success: import csv with open('linear_e_LAN2A_F_0_435keV.csv') as file: reader = csv.reader(file) print reader[someRandomInteger] A sample of the CSV file: 331.093,329.735 251.188,249.994 374.468,373.782 295.643,295.159 83.9058,0 380.709,116.221 352.238,351.891 183.809,182.615 257.277,201.302 61.4598,40.7106

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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• What the best approach to iterate and "store" files over a directory in C (Linux) ?

  - by Andrei Ciobanu

  I have written a function that checks if to files are duplicates or not. This function signature is: int check_dup_memmap(char *f1_name, char *f2_name) It returns: (-1) - If something went wrong; (0) - If the two files are similar; (+1) - If the two files are different; The next step is to write a function that iterates through all the files in a certain directory,apply the previous function, and gives a report on every existing duplicates. Initially I've thought to write a function that generates a file with all the filenames in a certain directory and then, read that file again and gain and compare every two files. Here is that version of the function, that gets all the filenames in a certain directory. void *build_dir_tree(char *dirname, FILE *f) { DIR *cdir = NULL; struct dirent *ent = NULL; struct stat buf; if(f == NULL){ fprintf(stderr, "NULL file submitted. [build_dir_tree].\n"); exit(-1); } if(dirname == NULL){ fprintf(stderr, "NULL dirname submitted. [build_dir_tree].\n"); exit(-1); } if((cdir = opendir(dirname)) == NULL){ char emsg[MFILE_LEN]; sprintf(emsg, "Cannot open dir: %s [build_dir_tree]\t",dirname); perror(emsg); } chdir(dirname); while ((ent = readdir(cdir)) != NULL) { lstat(ent->d_name, &buf); if (S_ISDIR(buf.st_mode)) { if (strcmp(".", ent->d_name) == 0 || strcmp("..", ent->d_name) == 0) { continue; } build_dir_tree(ent->d_name, f); } else{ fprintf(f, "/%s/%s\n",util_get_cwd(),ent->d_name); } } chdir(".."); closedir(cdir); } Still I consider this approach a little inefficient, as I have to parse the file again and again. In your opinion what are other approaches should I follow: Write a datastructure and hold the files instead of writing them in the file ? I think for a directory with a lot of files, the memory will become very fragmented. Hold all the filenames in auto-expanding array, so that I can easy access every file by their index, because they will in a contiguous memory location. Map this file in memory using mmap() ? But mmap may fail, as the file gets to big. Any opinions on this. I want to choose the most efficient path, and access as few resources as possible. This is the requirement of the program... EDIT: Is there a way to get the numbers of files in a certain directory, without iterating through it ?

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• Best practices for displaying large number of images as thumbnails in c#

  - by andySF

  I got to a point where it's very difficult to get answers by debugging and tracing object, so i need some help. What I'm trying to do: A history form for my screen capture pet project. The history must list all images as thumbnails (ex: picasa). What I've done: I created a HistoryItem:UserControl. This history item has a few buttons, a check box, a label and a picture box. The buttons are for delete/edit/copy image. The check box is used for selecting one or more images and the label is for some info text. The picture box is getting the image from a public property that is a path and a method creates a proportional thumbnail to display it when the control has been loaded. This user control has two public events. One for deleting the image and one for bubbling the events for mouse enter and mouse leave trough all controls. For this I use EventBroadcastProvider. The bubbling is useful because wherever I move the mouse over the control, the buttons appear. The dispose method has been extended and I manually remove the events. All images are loaded by looping a xml file that contains the path of all images. For each image in this XML I create a new HitoryItem that is added (after a little coding to sort and limit the amount of images loaded) to a flow layout panel. The problem: When I lunch the history form, and the flow layout panel is populated with my HistoryItem custom control, my memory usage increases drastically.From 14Mb to around 100MB with 100 images loaded. By closing the history form and disposing whatever I could dispose and even trying to call GC.Collect() the memory increase remain. I search for any object that could not be disposed properly like an image or event but wherever I used them they are disposed. The problem seams to be from multiple sources. One is that the events for bubbling are not disposing properly, and the other is from the picture box itself. All of this i could see by commenting all the code to a limited version when only the custom control without any image processing and even events is loaded. Without the events the memory consumption is reduced by axiomatically 20%. So my real question is if this logic, flow layout panels and custom controls with picture boxes, is the best solution for displaying large amounts of images as thumbnails. Thank you!

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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• What are the pros and cons of using manual list iteration vs recursion through fail

  - by magus

  I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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• Tomcat application: Frequent OutOfMemory PermGen exception while image uploads

  - by rabbit

  Hi, I have a tomcat 6 application which I have set parameters of -Xms512m -Xmx1024m. I thought 1 GB of memory in a 4 GB RAM would be enough, but that is not the case. On application stop/start multiple times (from tomcat manager) and also on image uploads (sometimes) I run into the OutOfMemory PermGen space error and the site stops responding. Should I increase the memory still some more? Is there anything else that I can do to from the tomcat side so that it does not run into the PermGen space issue? Thanks in advance for pointers/tips etc.

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