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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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• 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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• 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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• 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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• 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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• 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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• 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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• C++: Why don't I need to check if references are invalid/null?

  - by jbu

  Hi all, Reading http://www.cprogramming.com/tutorial/references.html, it says: In general, references should always be valid because you must always initialize a reference. This means that barring some bizarre circumstances (see below), you can be certain that using a reference is just like using a plain old non-reference variable. You don't need to check to make sure that a reference isn't pointing to NULL, and you won't get bitten by an uninitialized reference that you forgot to allocate memory for. My question is how do I know that the object's memory hasn't been freed/deleted AFTER you've initialized the reference. What it comes down to is that I can't take this advice on faith and I need a better explanation. Can anyone shed some light? Thanks, jbu

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• data structure for counting frequencies in a database table-like format

  - by user373312

  i was wondering if there is a data structure optimized to count frequencies against data that is stored in a database table-like format. for example, the data comes in a (comma) delimited format below. col1, col2, col3 x, a, green x, b, blue ... y, c, green now i simply want to count the frequency of col1=x or col1=x and col2=green. i have been storing the data in a database table, but in my profiling and from empirical observation, database connection is the bottle-neck. i have tried using in-memory database solutions too, and that works quite well; the only problem is memory requirements and quirky init/destroy calls. also, i work mainly with java, but have experience with .net, and was wondering if there was any api to work with "tabular" data in a linq way using java. any help is appreciated.

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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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• 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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• 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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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• Advice on "Invalid Pointer Operation" when using complex records

  - by Xaz

  Env: Delphi 2007 <JustificationI tend to use complex records quite frequently as they offer almost all of the advantages of classes but with much simpler handling.</Justification Anyhoo, one particularly complex record I have just implemented is trashing memory (later leading to an "Invalid Pointer Operation" error). This is an example of the memory trashing code: sSignature := gProfiles.Profile[_stPrimary].Signature.Formatted(True); On the second time i call it i get "Invalid Pointer Operation" It works OK if i call it like this: AProfile := gProfiles.Profile[_stPrimary]; ASignature := AProfile.Signature; sSignature := ASignature.Formatted(True); Background Code: gProfiles: TProfiles; TProfiles = Record private FPrimaryProfileID: Integer; FCachedProfile: TProfile; ... public < much code removed > property Profile[ProfileType: TProfileType]: TProfile Read GetProfile; end; function TProfiles.GetProfile(ProfileType: TProfileType): TProfile; begin case ProfileType of _stPrimary : Result := ProfileByID(FPrimaryProfileID); ... end; end; function TProfiles.ProfileByID(iID: Integer): TProfile; begin <snip> if LoadProfileOfID(iID, FCachedProfile) then begin Result := FCachedProfile; end else ... end; TProfile = Record private ... public ... Signature: TSignature; ... end; TSignature = Record private public PlainTextFormat : string; HTMLFormat : string; // The text to insert into a message when using this profile function Formatted(bHTML: boolean): string; end; function TSignature.Formatted(bHTML: boolean): string; begin if bHTML then result := HTMLFormat else result := PlainTextFormat; < SNIP MUCH CODE > end; OK, so I have a record within a record within a record, which is approaching Inception level confusion and I'm the first to admit is not really a good model. Clearly i am going to have to restructure it. What I would like from you gurus is a better understanding of why it is trashing the memory (something to do with the string object that is created then freed...) so that i can avoid making these kinds of errors in future. Thanks

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• java cannot reserver heap size error on windows server

  - by Prad

  HI, I have the following configuration: Server : windows 2003 server (32 bit) java version: 1.5_0_22 I get the following error when executing from command line ( my code is based off eclipse wihch gives the same error) java -XX:MaxPermSize=256m -Xmx512m Error occurred during initialization of VM Could not reserve enough space for object heap Could not create the Java virtual machine. The server has over 20GB physical memory with over 19 GB free right now. It does not give an error upto -Xmx486m I have read other articles about contiguous memory space. There is hardly anything running on this server. Can I validae this in any way? Thanks

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• PHP Fatal error on line number that doesn't exist

  - by alexantd

  Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 523800 bytes) in /Library/WebServer/Documents/XMLDataStore.class.php on line 981 The curious thing about this error is not the memory leak, which would be easy enough to troubleshoot. Rather, it is the fact that XMLDataStore.class.php is only 850 lines long, which I have verified in multiple text editors. This is with the PHP 5.3 bundled with Snow Leopard. I'm not using an opcode cache. Here is my php.ini: allow_url_fopen = Off error_reporting = -1 display_errors = 1 display_startup_errors = 1 date.timezone = 'America/Los_Angeles' output_buffering = Off realpath_cache_size = 0k XMLDataStore.class.php has recently been refactored and it used to be longer than 981 lines. It's almost as if PHP has cached a 2-week-old version and is reading that. I'm positive that the current version at /Library/WebServer/Documents/XMLDataStore.class.php is only 850 lines long, though.

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• SQL Stored Procedure

  - by Nathan

  I am trying to run a stored procedure with a while loop in it using Aqua Data Studio 6.5 and as soon as the SP starts Aqua Data starts consuming an increasing amount of my CPU's memory which makes absolutely no sense to me because everything should be off on the Sybase server I am working with. I have commented out and tested every piece of the SP and narrowed the issue down to the while loop. Can anyone explain to me what is going on? create procedure sp_check_stuff as begin declare @counter numeric (9), @max_id numeric (9), @exists numeric (1), @rows numeric (1) select @max_id = max(id) from my_table set @counter = 0 set @exists = 0 set @rows = 0 while @count <= @max_id begin //More logic which doesn't affect memory usage based //on commenting it out and running the SP set @counter = @counter + 1 set @exists = 0 set @rows = 0 end end return

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• Limitation for google sitemap.xml file size

  - by Chakrapani

  can any one please let me know the memory limitation(MB) of google sitemap.xml file size.

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• Switching from C++ (with a lot of STL use) to C for interpreter building

  - by wndsr

  I'm switching from C++ to C because I'm rebuilding my toy interpreter. I was used to vectors for dynamic allocation of objects like tokens or instructions of my programs, stacks and mainly strings with all their aspects. Now, in C I'm not going to have all these anymore. I know that I will have to use a lot of memory management, too. I'm completely new to C, I only know the high-level easy-life data structures from the STL, how can I get started with strings and dynamic memory allocation?

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• How to deal with large result sets with Linq to Entities?

  - by user169867

  I have a fairly complex linq to entities query that I display on a website. It uses paging so I never pull down more than 50 records at a time for display. But I also want to give the user the option to export the full results to Excel or some other file format. My concern is that there could potentially be a large # of records all being loaded into memory at one time to do this. Is there a way to process a linq result set 1 record at a time like you could w/ a datareader so only 1 record is really being kept in memory at a time? I'd appreciate any help. Thanks

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• App like default photo browser in iphone ?

  - by goeff27

  Hi All i am developing a app which contains feature like default photo browser in iphone. I done some what similar to that. but after loading some(near about 10-15) images from remote server,i am receiving memory warning.My requirement is loading image one by one. For this, on scroll view i am putting an images and increasing the contentSize of scroll view. it will work fine. but due to memory warning app quite. Guys, any have any idea to approach for this feature which work similar to photo app without problem? thanks in advance .

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• Sound Manager Classes for Windows (C# or C++ .Net 2.0)

  - by Yakov

  Hi guys! I need some classes for playing short wav sounds, this classes would load this wav files into memory when an instance created, play sounds in background when needed, release this wav files from memory when an instance disposed. How can I do this on C# for windows (.Net 2.0)? (Win API's sndPlaySound, OpenAL or may be any wrapper) Ideally I would love to find an exist solution that simple and able to solve my task. Do you know any solutions for this issue? Thankx for your time.

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• What is faster: multiple `send`s or using buffering?

  - by dauerbaustelle

  I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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• What would happen to GC if I run process with priority = RealTime?

  - by Bobb

  I have a C# app which runs with priority RealTime. It was all fine until I made few hectic changes in past 2 days. Now it runs out of memory in few hours. I am trying to find whether it is a memory leak I created of this is because I consume lot more objects than before and GC simply cant collect them because it runs with same priority. My question is - what could happen to GC when it tries to collect objects in application with RealTime priority (there is also at least one thread running with Highest thread priority)? (P.S. by realtime priority I mean Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.RealTime) Sorry forgot to tell. GC is in Server mode

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