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• Does MATLAB perform tail call optimization?

  - by Shea Levy

  I've recently learned Haskell, and am trying to carry the pure functional style over to my other code when possible. An important aspect of this is treating all variables as immutable, i.e. constants. In order to do so, many computations that would be implemented using loops in an imperative style have to be performed using recursion, which typically incurs a memory penalty due to the allocation a new stack frame for each function call. In the special case of a tail call (where the return value of a called function is immediately returned to the callee's caller), however, this penalty can be bypassed by a process called tail call optimization (in one method, this can be done by essentially replacing a call with a jmp after setting up the stack properly). Does MATLAB perform TCO by default, or is there a way to tell it to?

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• How to store images without taking up huge amounts of RAM

  - by Sheeo

  I'm working on a silverlight project where users get to create their own Collages. The problem When loading a bunch of images by using the BitmapImage class, Silverlight hogs up huge unreasonable amounts of RAM. 150 pictures where single ones fill up at most 4,5mb takes up about 1,6GB of RAM--thus ending up throwing memory exceptions. I'm loading them through streams, since the user selects their own photos. What I'm looking for A class, method or some process to eliminate the huge amount of RAM being sucked up. I've tried using a WriteableBitmap to render the images into, but I find this method forces me to reinvent the wheel when it comes to drag/drop and other things I want users to be able to do with the images.

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• So does Apple recommend to not use predicates and sort descriptors in an NSFetchRequest?

  - by dontWatchMyProfile

  From the docs: To summarize, though, if you execute a fetch directly, you should typically not add Objective-C-based predicates or sort descriptors to the fetch request. Instead you should apply these to the results of the fetch. If you use an array controller, you may need to subclass NSArrayController so you can have it not pass the sort descriptors to the persistent store and instead do the sorting after your data has been fetched. I don't get it. What's wrong with using them on fetch requests? Isn't it stupid to get back a whole big bunch of managed objects just to pick out a 1% of them in memory, leaving 99% garbage floating around? Isn't it much better to only fetch from the persistent store what you really need, in the order you need it? Probably I did get that wrong...

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• Linux Kernel - Slab Allocator Question

  - by Drex

  I am playing around with the kernel and am looking at the kmem_cache files_cachep belonging to fork.c. It detects the sizeof(files_struct). My question is this: I have altered files_struct and added a rb_root (red/black tree root) using the built-in functionality in linux/rbtree.h. I can properly insert values into this tree. However, at some point, a segfault occurs and GDB backtraces the following information: (gdb) backtrace 0 0x08066ad7 in page_ok (page=) at arch/um/os-Linux/sys-i386/task_size.c:31 1 0x08066bdf in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100 2 0x0804a216 in linux_main (argc=1, argv=0xbfb05f14) at arch/um/kernel/um_arch.c:277 3 0x0804acdc in main (argc=1, argv=0xbfb05f14, envp=0xbfb05f1c) at arch/um/os-Linux/main.c:150 I have spent many hours trying to figure out why there is a segfault given that the red/black tree inserts properly. I'm thinking it's a memory allocation issue with new processes made by fork() of a parent process. Could this be the case and could it have something to do with kmem_cache files_cachep?

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• Using C++, why can `throw` cause `terminate()`, and when are the stack variables to be freed?

  - by nbolton

  I'm pondering a question on Brainbench. I actually realised that I could answer my question easily by compiling the code, but it's an interesting question nonetheless, so I'll ask the question anyway and answer it myself shortly. Take a look at this snippet: The question considers what happens when we throw from a destructor (which causes terminate() to be called). It's become clear to me by asking the question that the memory is indeed freed and the destructor is called, but, is this before or after throw is called from foo? Perhaps the issue here is that throw is used while the stack is unwinding that is the problem... Actually this is slightly confusing.

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• Add bytes to binary file using only PHP?

  - by hurmans

  I am trying to add random bytes to binary (.exe) files to increase it size using php. So far I got this: function junk($bs) { // string length: 256 chars $tmp = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'; for($i=0;$i<=$bs;$i++) { $tmp = $tmp . $tmp; } return $tmp; } $fp = fopen('test.exe', 'ab'); fwrite($fp, junk(1)); fclose($fp); This works fine and the resulting exe is functional but if I want to do junk(100) to add more size to the file I get the php error "Fatal error: Allowed memory size..." In which other way could I achieve this without getting an error? Would it be ok to loop the fwrite xxx times?

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• C# "Could not find a part of the path" - Creating Local File

  - by Pyronaut

  I am trying to write to a folder that is located on my C:\ drive. I keep getting the error of : Could not find a part of the path .. etc My filepath looks basically like this : C:\WebRoot\ManagedFiles\folder\thumbs\5c27a312-343e-4bdf-b294-0d599330c42d\Image\lighthouse.jpg And I am writing to it like so : using (MemoryStream memoryStream = new MemoryStream()) { thumbImage.Save(memoryStream, ImageFormat.Jpeg); using (FileStream diskCacheStream = new FileStream(cachePath, FileMode.CreateNew)) { memoryStream.WriteTo(diskCacheStream); } memoryStream.WriteTo(context.Response.OutputStream); } Don't worry too much about the memory stream. It is just outputting it (After I save it). Since I am creating a file, I am a bit perplexed as to why it cannot find the file (Shouldn't it just write to where I tell it to, regardless?). The strange thing is, It has no issue when I'm testing it above using File.Exists. Obviously that is returning false, But it means that atleast my Filepath is semi legit. Any help is much appreciated.

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• Javascript clears a variable after there is no further reference it

  - by Praveen Prasad

  It is said, javascript clears a variable from memory after its being referenced last. just for the sake of this question i created a JS file with only one variable; //file start //variable defined var a=["Hello"] //refenence to that variable alert(a[0]); // //file end no further reference to that variable, so i expect javascript to clear varaible 'a' Now i just ran this page and then opened firebug and ran this code alert(a[0]); Now this alerts the value of variable, If the statement "Javascript clears a variable after there is no further reference it" is true how come alert() shows its value. Is it because all variable defined in global context become properties of window object, and since even after the execution file window objects exist so does it properties.

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• [C++]Advantage of using a static member function instead of an equivalent non-static member function

  - by jonathanasdf

  I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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• How to scroll and zoom in/out large images on iPhone?

  - by Horace Ho

  I have a large image, size around 30000 (w) x 6000 (h) pixels. You may consider it's like a big map. I assume I need to crop it up into smaller tiles. Questions: what are the right ViewControllers to use? (link) what is the tile strategy? (I put this in another question, as it's not iPhone specific) Requirements: whole image (though cropped) can be scrolled up/down/left/right by swipes zoom in (up to pixel-to-pixel) out (down to screen-fit-by-height) by the 2-finger operation memory efficiency by lazy loading tiles Bonus requirements: automatic scroll, say from left to right slowly and smoothly Thanks!

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• How to use a dialog in an Excel shared addin

  - by user169867

  I'm writing a shared addin for Excel. It adds a CommandBarButton that when clicked opens a WPF window to collect some information from the user. I wanted to keep the same WPF dialog in memory and reuse it so that if the user clicks the CommandBarButton again their previous values would still be there. So I made a reference to my WPD as a private member of my addin object that implements Extensibility.IDTExtensibility2. I created the window during OnStartupComplete(), but for some reason when I run Excel the window immediately opens even though I never called ShowDialog() and when I do call ShowDialog() when the CommandBarButton is clicked to reOpen the window it fails to load. Does anyone know why this happens and what the correct way to handle this is? Thanks very much for any help.

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• Beagleboard: How do I send/receive data to/from the DSP?

  - by snakile

  I have a beagleboard with TMS320C64x+ DSP. I'm working on an image processing beagleboard application. Here's how it's going to work: The ARM reads an image from a file and put the image in a 2D array. The arm sends the matrix to the DSP. The DSP receives the matrix. The DSP performs the image processing algorithm on the received matrix (the algorithm code uses about 5MB of dynamically allocated memory). The DSP sends the processed image (matrix) to the ARM. The arm received the matrix. The arm saved the processed image to a file. I'v already written the code for steps 1,3,5. What is the easiest way to do steps 3+4 (sending the data)? Code examples are welcome.

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• Are there Python ORMs out there that support multiple independent databases concurrently in use?

  - by sdt

  I'm writing an application in Python where I wish to use sqlite as the backing store for documents edited by the app, with documents generally living in memory, but being saved to disk-based databases when the application saves. Ideally I'd like to use something like an ORM to make access to the data from my Python application code simple. Unfortunately it seems like the majority of Python ORMs, including SQLAlchemy, SQLObject, Django, and Storm, associate the database connection (or engine or whatever) with the classes representing table data, rather than instances of those classes. This restricts these ORMs to working with a single database connection across all instances. Since I'd like to support having multiple documents open simultaneously, this isn't going to work for me. Are there any ORMs out there that support this usage model in Python? Bazaar seems to support this, but it's quite out of date, and at first glance appears to have some other shortcomings. Thanks for any suggestions!

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• How can I integrate graphs and JPEG images with RAVE Reports?

  - by JonDave of the Philippines

  I really love RAVE Reports in creating multiple reports especially with formulas and accounting systems... but recently I am having problems with integrating JPEG Pictures and Graphs with my newly Delphi Language developed Little ERP System. I bought some JPEG Components but it seems problematic. I also experienced some irregularities with my RAVE Reports now. When I run my program then try to preview some reports, it seems to be running fine, but when I close the program, the EXE file is still in the taskbar. I need to ctrl-alt-delete first for me to use Report Previews normally. If I don't, RAVE REPORT ERROR message will appear everytime I click the PRINT button; it says "STREAM READ ERROR" even though I used to "FreeAndNil" to free the memory stream when Report Preview Form closes. When I tried to run the My Applications without previewing RAVE reports, the program closes perfectly. Any suggestions and recommendations will be an enormous help. Thank you.

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• Passing arguments to java vm from NSIS script

  - by CodeBuddy

  I'm developing my first java application using Eclipse. I've recently needed to adjust the amount of memory allocated by passing -Xmx256M to the JVM. The application is currently package up as a runnable jar and installed using the NSIS. I'm having a problem passing arguments to the jar file once its installed. What is the common practice for doing this? Here is what I'm currently doing in my nsi file: CreateShortcut "$SMPROGRAMS\$StartMenuGroup\$(^Name).lnk" "$SYSDIR\javaw.exe" "-jar -Xmx256M $INSTDIR\Foo.jar" This results in the following being created as the shortcut Target on windows: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M C:\Program Files\Foo\Foo.jar Unfortunately this does not work due to the space in C:\Program Files, If I change the link created manually to include quotes all is well: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M "C:\Program Files\Foo\Foo.jar"

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• How is a new programming language actually formed/created ?

  - by hory.incpp

  Fortran-Algol-Cpl-Bcpl-C-C++-Java ..... Seems like every language is built upon an ancestor language. My question : New languages extend parent ones or there is some kind of a trick? e.g. System.out.print() in Java ; is it actually printf() in C, and so on (printf is actually .. in Cpl)? If so, doesn't this make every further language be slower and need more memory? What separates a new language from a framework?

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• Java multi-threading - what is the best way to monitor the activity of a number of threads?

  - by MalcomTucker

  I have a number of threads that are performing a long runing task. These threads themselves have child threads that do further subdivisions of work. What is the best way for me to track the following: How many total threads my process has created What the state of each thread currently is What part of my process each thread has currently got to I want to do it in as efficient a way as possible and once threads finish, I don't want any references to them hanging around becasuse I need to be freeing up memory as early as possible. Any advice?

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• How does c# type safety affect the garbage collection?

  - by Indeera

  I'm dealing with code that handles large buffers ( 100MB) and manipulation of these is done in unsafe blocks. I'd like to refactor these to avoid unsafe code. I'm wondering about the likely memory performance gains (positive/negative/neutral) before I embark on that. I assert that if the compiler can verify types, it could possibly generate better code and that could also mean good GC performance. Is this a valid assertion? What is your experience? Thanks.

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• Fatal error with php code

  - by basma

  hello i have a problem in my php code that use recursion: <?php solveTowers(5, "A", "B", "C"); function solveTowers($count, $src, $dest, $spare) { if (count == 1) { echo "Move a disk from ".$src." to ".$dest ; } else { solveTowers($count - 1, $src, $spare, $dest); solveTowers(1, $src, $dest, $spare); solveTowers($count - 1, $spare, $dest, $src); } } ?> but it doesnt run !! this error accures : Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 261904 bytes) in C:\xampp\htdocs\cap492\towers.php on line 13 line 13 is the first call to the function in the else statment can you please help me with that ?!

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• Socket ping-pong performance

  - by Kamil_H

  I have written two simple programs (tried it in C++ and C#). This is pseudo code: -------- Client --------------- for(int i = 0; i < 200.000; i++) { socket_send("ping") socket_receive(buff) } --------- Server ------------- while(1) { socket_receive(buff) socket_send("pong") } I tried it on Windows. Execution time of client is about 45 seconds. Can somebody explain me why this takes so long? I understand that if there were real network connection between client and server the time of one 'ping-pong' would be: generate_ping + send_via_network + generate_pong + send_via_network but here everything is done in 'local' mode. Is there any way to make this inter process ping-pong faster using network sockets (I'm not asking about shared memory for example :) )

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• What is the best possible technology for pulling huge data from 4 remote servers

  - by Habib Ullah Bahar

  Hello, For one of our project, we need to pull huge real time stock data from 4 remote servers across two countries. The trivial process here, check the sources for a regular interval and save the update to database. But as these are real time stock data of more than 1000 companies, I have to pull every second, which isn't good in case of memory, bandwidth I think. Please give me suggestion on which technology/platform [We are flexible here. PHP, Python, Java, PERL - anyone of them will be OK for us] we should choose, it can be achieved easily and with better performance.

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• Alternate way to create a clone of a UNIX System

  - by Spirit

  THE STORY: (If you don't like to read much, down below is the question :) ) Where I work we have two HP RP2470 servers same hardware same number of hard drives same everything :). One of them is a production server and runs HP-UX 11.00. The poor ba***rd hasn't been turned off for years and now I have to make a clone of it on the other server - just in case, for redundancy. The problem is simple (or not simple) as I have to make the the other server exactly the same. However the old version of OS (UX 11.00 is a history now) and the old software running on it, have made my task almost impossible. On the production server there is also a cloning/recover utility Ignite-UX. I tried many times to create a recovery tape with it. Then when I load the tape on the backup server, it succeeds with the loading of the tape (no errors no warnings) but on the next restart it fails to load the OS :S and drops into HP`s ISL prompt. --- THE QUESTION: Is there an alternate way to create a clone of the Unix System? The environment is: 1. 2x HP RP2470 Servers (non-Intel), same hardware, same number od HDDs (two each of them) same everything. 2. OS running: HP-UX 11.00 The production server has to be cloned without downtime - sadly :( as I hope that they will reconsider on this one For example (like on Windows platforms), if you try to copy an entire HDD with Windows inside on another HDD, and then put that HDD on another PC it will still work, as long as the hardware is the same. Can I do something like that with a Unix system? Can I somehow COPY the contents of the entire HDD, put those on another HDD, and then just load the HDD into the other server? (If you haven't read the story the servers are exactly the same) Will it work? Can it be done with ordinary commands like cp or dump or something like that? Does any one have a similar experience? --- UPDATE: 26.01.2012 NOTE: The update is related to "The Story". If you haven't read that part then you can skip this update. This is just a short update on the recover logs from the Ignite Tape.. someone with more exp. might notice something.. ... --- READING CONTENTS OF THE IGNITE TAPE --- --- OUTPUT OMITED --- ... ... x ./configure3, 413696 bytes, 808 tape blocks x ./monitor_bpr, 20480 bytes, 40 tape blocks * Download_mini-system: Complete * Loading_software: Begin * Installing boot area on disk. * Enabling swap areas. * Backing up LVM configuration for "vg00". * Processing the archive source (Recovery Archive). * Wed Jan 25 15:27:32 EST 2012: Starting archive load of the source (Recovery Archive). * Positioning the tape (/dev/rmt/0mn). * Archive extraction from tape is beginning. Please wait. * Wed Jan 25 15:39:52 EST 2012: Completed archive load of the source (Recovery Archive). * Executing user specified script: "/opt/ignite/data/scripts/os_arch_post_l". * Running in recovery mode (os_arch_post_l). * Running the ioinit command ("/sbin/ioinit -c") * Creating device files via the insf command. insf: Installing special files for sdisk instance 0 address 0/0/1/1.15.0 insf: Installing special files for sdisk instance 1 address 0/0/2/0.1.0 insf: Installing special files for sdisk instance 2 address 0/0/2/1.15.0 insf: Installing special files for stape instance 0 address 0/0/1/0.3.0 insf: Installing special files for btlan instance 0 address 0/0/0/0 insf: Installing special files for btlan instance 1 address 0/2/0/0 insf: Installing special files for pseudo driver dlpi insf: Installing special files for pseudo driver kepd insf: Installing special files for pseudo driver framebuf insf: Installing special files for pseudo driver sad * Running "/opt/upgrade/bin/tlinstall -v" and correcting transition link permissions. * Constructing the bootconf file. * Setting primary boot path to "0/0/1/1.15.0". * Executing: "/var/adm/sw/products/PHSS_20146/pfiles/iux_postload". * Executing: "/var/adm/sw/products/PHSS_25982/pfiles/iux_postload". NOTE: tlinstall is searching filesystem - please be patient NOTE: Successfully completed * Loading_software: Complete * Build_Kernel: Begin NOTE: Since the /stand/vmunix kernel is already in place, the kernel will not be re-built. Note that no mod_kernel directives will be processed. * Build_Kernel: Complete * Boot_From_Client_Disk: Begin * Rebooting machine as expected. NOTE: Rebooting system. sync'ing disks (0 buffers to flush): 0 buffers not flushed 0 buffers still dirty Closing open logical volumes... Done Console reset done. Boot device reset done. ********** VIRTUAL FRONT PANEL ********** System Boot detected ***************************************** LEDs: RUN ATTENTION FAULT REMOTE POWER FLASH OFF OFF ON ON LED State: Running non-OS code. (i.e. Boot or Diagnostics) ... ... ... --- SERVER IS PERFORMING POST SEQUENCE HERE --- --- OUTPUT OMITED --- ... ... ... ***************************************** ************ EARLY BOOT VFP ************* End of early boot detected ***************************************** Firmware Version 43.50 Duplex Console IO Dependent Code (IODC) revision 1 ------------------------------------------------------------------------------ (c) Copyright 1995-2002, Hewlett-Packard Company, All rights reserved ------------------------------------------------------------------------------ Processor Speed State CoProcessor State Cache Size Number State Inst Data --------- -------- --------------------- ----------------- ------------ 0 650 MHz Active Functional 750 KB 1.5 MB 1 650 MHz Idle Functional 750 KB 1.5 MB Central Bus Speed (in MHz) : 120 Available Memory : 2097152 KB Good Memory Required : 16140 KB Primary boot path: 0/0/1/1.15 Alternate boot path: 0/0/2/1.15 Console path: 0/0/4/1.643 Keyboard path: 0/0/4/0.0 Processor is starting autoboot process. To discontinue, press any key within 10 seconds. 10 seconds expired. Proceeding... Trying Primary Boot Path ------------------------ Booting... Boot IO Dependent Code (IODC) revision 1 HARD Booted. ISL Revision A.00.38 OCT 26, 1994 ISL booting hpux ISL>

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• VS2010's "Public Property <PropertyName> As <DataType> vs. Public var

  - by Velika2

  In VS2008, I used to type Public Property <PropName> As <dataType> and hit the Enter key and the IDE editor would automatically expand it out to a full blown property block. Now, from what I understand, a new feature of 2010 is that the compiler automatically "expands" the short syntax above into the same IL code that you would get with the full property GET AND SET sub methods that were are accustomed to seeing before in the editor. But functionality, how the heck is this any different than just having a Public class level variable? If the only diff is what it compiles to and if otehrwise there is no functional difference, isn't the new way less efficient than the old since it involves more code than just having a class level memory variable? Public as I thought that if you weren't going to have code behind your properties that they were essentially the same. I guess the diffrenece is that they just added the keyword "Property" but functionality, their is no diff, eh?

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• What is your favourite Windbg tip/trick?

  - by user15071

  I have come to realize that Windbg is a very powerful debugger for the Windows platform & I learn something new about it once in a while. Can fellow Windbg users share some of their mad skills? ps: I am not looking for a nifty command, those can be found in the documentation. How about sharing tips on doing something that one couldn't otherwise imagine could be done with windbg? e.g. Some way to generate statistics about memory allocations when a process is run under windbg.

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