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• F# performance in scientific computing

  - by aaa

  hello. I am curious as to how F# performance compares to C++ performance? I asked a similar question with regards to Java, and the impression I got was that Java is not suitable for heavy numbercrunching. I have read that F# is supposed to be more scalable and more performant, but how is this real-world performance compares to C++? specific questions about current implementation are: How well does it do floating-point? Does it allow vector instructions how friendly is it towards optimizing compilers? How big a memory foot print does it have? Does it allow fine-grained control over memory locality? does it have capacity for distributed memory processors, for example Cray? what features does it have that may be of interest to computational science where heavy number processing is involved? Are there actual scientific computing implementations that use it? Thanks

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• Question on Pointer Arithmetic

  - by pws5068

  Heyy Everybody! I am trying to create a memory management system, so that a user can call myMalloc, a method I created. I have a linked list keeping track of my free memory. My problem is when I am attempting to find the end of a free bit in my linked list. I am attempting to add the size of the memory free in that section (which is in the linked list) to the pointer to the front of the free space, like this. void *tailEnd = previousPlace->head_ptr + ((previousPlace->size+1)*(sizeof(int)); I was hoping that this would give me a pointer to the end of that segment. However, I keep getting the warning: "pointer of type 'void*' used in arithmetic" Is there a better way of doing this? Thanks!

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• Why is thread local storage so slow?

  - by dsimcha

  I'm working on a custom mark-release style memory allocator for the D programming language that works by allocating from thread-local regions. It seems that the thread local storage bottleneck is causing a huge (~50%) slowdown in allocating memory from these regions compared to an otherwise identical single threaded version of the code, even after designing my code to have only one TLS lookup per allocation/deallocation. This is based on allocating/freeing memory a large number of times in a loop, and I'm trying to figure out if it's an artifact of my benchmarking method. My understanding is that thread local storage should basically just involve accessing something through an extra layer of indirection, similar to accessing a variable via a pointer. Is this incorrect? How much overhead does thread-local storage typically have? Note: Although I mention D, I'm also interested in general answers that aren't specific to D, since D's implementation of thread-local storage will likely improve if it is slower than the best implementations.

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• .NET and 64-bit application

  - by user54064

  I want to make existing .NET applications (WinForms and WebForms) run on 64-bit machines, optimized to take advantage of more memory available on 64-bit machines. What do I need to do to the applications to take advantage of the memory? Do I just select the target CPU as 64-bit? What is the advantage of selecting the target versus just compiling the app for All CPUs and have the .NET optimize the app locally? Will Crystal Reports (in VS 2008) run optimized for 64-bit and take advantage of the upper memory?

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• What is the difference among NSString alloc:initWithCString versus stringWithUTF8String?

  - by mobibob

  I thought these two methods were (memory allocation-wise) equivalent, however, I was seeing "out of scope" and "NSCFString" in the debugger if I used what I thought was the convenient method (commented out below) and when I switched to the more explicit method my code stopped crashing! Notice that I am getting the string that is being stored in my container from sqlite3 query. p = (char*) sqlite3_column_text (queryStmt, 1); // GUID = (NSString*) [NSString stringWithUTF8String: (p!=NULL) ? p : ""]; GUID = [[NSString alloc] initWithCString:(p!=NULL) ? p : "" encoding:NSUTF8StringEncoding]; Also note, that if I looked at the values in the debugger and printed them with NSLog they looked correct, however, I don't think new memory was allocated and the value copied. Instead the memory pointer was stored - went out of scope - referenced later - crash!

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• OutOfMemoryError trying to upload to Blobstore locally

  - by jeanh

  Hi all, I am trying to set up a basic file upload to blobstore, but I get this OutOfMemoryError: WARNING: Error for /_ah/upload/ aghvbWdkcmVzc3IcCxIVX19CbG9iVXBsb2FkU2Vzc2lvbl9fGMACDA java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:2786) at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:71) at javax.mail.internet.MimeMultipart.readTillFirstBoundary(MimeMultipart.java: 316) at javax.mail.internet.MimeMultipart.parse(MimeMultipart.java:186) at javax.mail.internet.MimeMultipart.getCount(MimeMultipart.java:109) at com.google.appengine.api.blobstore.dev.UploadBlobServlet.handleUpload(UploadBlobServlet.java: 135) at com.google.appengine.api.blobstore.dev.UploadBlobServlet.access $000(UploadBlobServlet.java:72) at com.google.appengine.api.blobstore.dev.UploadBlobServlet $1.run(UploadBlobServlet.java:100) at java.security.AccessController.doPrivileged(Native Method) at com.google.appengine.api.blobstore.dev.UploadBlobServlet.doPost(UploadBlobServlet.java: 98) at javax.servlet.http.HttpServlet.service(HttpServlet.java:713) at javax.servlet.http.HttpServlet.service(HttpServlet.java:806) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java: 511); I used the Memory Analyzer on Eclipse and it said that the memory leak suspect is QueuedThreadPool. I found this information about a memory leak bug: http://jira.codehaus.org/browse/JETTY-1188 Has anyone else had this issue? Thanks, Jean

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• if cookies are disabled, does asp.net store the cookie as a session cookie instead or not?

  - by Erx_VB.NExT.Coder

  basically, if cookeis are disabled on the client, im wondering if this... dim newCookie = New HttpCookie("cookieName", "cookieValue") newCookie.Expires = DateTime.Now.AddDays(1) response.cookies.add(newCookie) notice i set a date, so it should be stored on disk, if cookies are disabled does asp.net automatically store this cookie as a session cookie (which is a cookie that lasts in browser memory until the user closes the browser, if i am not mistaken).... OR does asp.net not add the cookie at all (anywhere) in which case i would have to re-add the cookie to the collection without the date (which stores as a session cookie)... of course, this would require me doing the addition of a cookie twice... perhaps the second time unnecessarily if it is being stored in browsers memory anyway... im just trying not to store it twice as it's just bad code!! any ideas if i need to write another line or not? (which would be)... response.cookies.add(New HttpCookie("cookieName", "cookieValue") ' session cookie in client browser memory thanks guys

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• How to prevent DOS attacks using image resizing in an ASP.NET application?

  - by Waleed Eissa

  I'm currently developing a site where users can upload images to use as avatars, I know this makes me sound a little paranoid but I was wondering what if a malicious user uploads an image with incredibly large dimensions that will eat the server memory (as a DOS attack), I already have a limit on the file size that can be uploaded (250 k) but even that size can allow for an image with incredibly large dimensions if the image for example is a JPEG that contains one color and created with a very low quality setting. Taking into consideration that the image is uploaded as a bitmap in memory when being resized (ie. not compressed), I wonder if such DOS attacks occur, even to check the image dimensions it has to be uploaded in memory first, did you hear about any attacks that exploited this? Am I too worried?

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• Multithreaded program in C: calculating thread stack space

  - by SlappyTheFish

  Situation: I am writing a program in C that maintains a number of threads. Once a thread ends, a new one is created. Each thread forks - the child runs a PHP process via exec() and the parent waits for it to finish. Each PHP process takes the next item from a queue, processes it and exits. Basic code: http://www.4pmp.com/2010/03/multitasking-php-in-parallel/ Problem: The PHP processes are Symfony tasks and Symfony requires a fairly huge amount of memory. How can I safely calculate the required stack space for each thread so that PHP processes will have enough memory? The memory limit set in php.ini is 128Mb so should I allocate this much space in the stack?

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• GC.AddMemoryPressure in C#

  - by ssheldon

  I am writing an application in C# that makes use of a 3rd party COM DLL, this dll creates a lot of resources (like bitmaps, video, data structures) in unmanaged memory. While digging around I came across the following call for the Garbage Collector: GC.AddMemoryPressure(long long bytesAllocated) It is documented in MSDN here: http://msdn.microsoft.com/en-us/library/system.gc.addmemorypressure.aspx This sounds like something I should be calling since this external dll is createing a lot of resources the CLR is unaware of. I guess I have two questions... How do I know how much memory pressure to add when the dll is 3rd party and it's not possible for me to know exactly how much memory this dll is allocating. How important is it to do this?

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• How to debug unreleased COM references from managed code?

  - by Marek

  I have been searching for a tool to debug unreleased COM references, that usually cause e.g. Word/Outlook processes to hang in memory in case the code does not call Marshal.ReleaseCOMObject on all COM instances correctly. (Outlook 2007 partially fixes this for outlook addins, but this is a generic question). Is there a tool that would display at least a list of COM references (by type) held by managed code? Ideally, it would also display memory profiler-style object trees helping to debug where the reference increment occured. Debugging at runtime is not that important as being able to attach to a hung process - because the problem typically occurs when the code is done with the COM interface and someone forgot to release something - the application (e.g. winword) hangs in memory even after the calling managed application quits. If such tool does not exist, what is the (technical?) reason? It would be very useful for debugging a lot of otherwise very hard to find problems when working with COM interop.

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• resource acquisition is initialization "RAII"

  - by hitech

  in the example below class X{ int *r; public: X(){cout<< X is created ; r new int[10]; } ~X(){cout<< X is destroyed ; delete [] r; } }; class Y { public: Y(){ X x; throw 44; } ~Y(){cout<< Y is destroyed ;} }; I got this example of RAII from one site and ave some doubts. please help. in the contructor of x we are not considering the scenation "if the memory allocation fails" . Here for the destructor of Y is safe as in y construcotr is not allocating any memory. what if we need to do some memory allocation also in y constructor?

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• How do I find out what objects points to another object i Xcode Instruments

  - by Arlaharen

  I am trying to analyze some code of mine, looking for memory leaks. My problem is that some of my objects are leaking (at least as far as I can see), but the Leaks tool doesn't detect the leaks. My guess is that some iPhone OS object still holds pointers to my leaked objects. The objects I am talking about are subclasses of UIViewController that I use like this: MyController *controller = [[MyController alloc] initWithNibName:@"MyController" bundle:nil]; [self.navigationController pushViewController:controller animated:YES]; When these objects are no longer needed I do: [self.navigationController popViewControllerAnimated:YES]; Without a [controller release] call right now. Now when I look at what objects that gets created I see a lot of MyController instances that never gets destroyed. To me these are memory leaks, but to the Leaks tool they are not. Can someone here tell me if there is some way Instruments can tell me what objects are pointing to my MyController instances and thereby making them not count as memory leaks?

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• VS2010 profiler/leak detection

  - by Noah Roberts

  Anyone know of a profiler and leak detector that will work with VS2010 code? Preferably one that runs on Win7. I've searched here and in google. I've found one leak detector that works (Memory Validator) but I'm not too impressed. For one thing it shows a bunch of menu leaks and stuff which I'm fairly confident are not real. I also tried GlowCode but it's JUST a profiler and refuses to install on win7. I used to use AQtime. It had everything I needed, memory/resource leak detection, profiling various things, static analysis, etc. Unfortunately it gives bogus results now. My main immediate issue is that VS2010 is saying there are leaks in a program that had none in VS2005. I'm almost certain it's false positives but I can't seem to find a good tool to verify this. Memory Validator doesn't show the same ones and the reporting of leaks from VS doesn't seem rational.

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• Legacy Database, Fluent NHibernate, and Testing my mappings

  - by sdanna

  As the post title implies, I have a legacy database (not sure if that matters), I'm using Fluent NHibernate and I'm attempting to test my mappings using the Fluent NHibernate PersistenceSpecification class. My question is really a process one, I want to test these when I build locally in Visual Studio using the built in Unit Testing framework for now. Obviously this implies (I think) that I'm going to need a database. What are some options for getting this into the build? If I use an in memory database does NHibernate or Fluent NHibernate have some some mechanism for sucking the database schema from a target database or maybe the in memory database can do this? Will I need to manually get the schema to feed to an in memory database? Ideally I would like to get this this setup to where the other developers don't really have to think about it other than when they break the build because the tests don't pass.

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• GDB hardware watchpoint very slow - why?

  - by Laurynas Biveinis

  On a large C application, I have set a hardware watchpoint on a memory address as follows: (gdb) watch *((int*)0x12F5D58) Hardware watchpoint 3: *((int*)0x12F5D58) As you can see, it's a hardware watchpoint, not software, which would explain the slowness. Now the application running time under debugger has changed from less than ten seconds to one hour and counting. The watchpoint has triggered three times so far, the first time after 15 minutes when the memory page containing the address was made readable by sbrk. Surely during those 15 minutes the watchpoint should have been efficient since the memory page was inaccessible? And that still does not explain, why it's so slow afterwards. The GDB is $ gdb --version GNU gdb (GDB) 7.0-ubuntu [...] Thanks in advance for any ideas as what might be the cause or how to fix/work around it.

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• Garbage collection of Strings returned from C# method calls in ascx pages

  - by Icarus

  Hi, For a web application developed on ASP.NET, we are finding that for user control files (ascx) we are returning long strings as a result of method calls. These are embedded in the ascx pages using the special tags <% %> When performing memory dump analysis for the application, we find that many of those strings are not being garbage collected. Also, the ascx pages are compiled to temporary DLLs and they are held in memory. Is this responsible for causing the long strings to remain in memory and not be garbage collected ? Note : The strings are larger than 85K in size.

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• Parallelism in Python

  - by fmark

  What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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• LRU caches in C

  - by lazyconfabulator

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

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

  - by Moraru Lilian

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

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• MSP430 CMP operator

  - by Ludicrous

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

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

  - by LowLevelAbstraction

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

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

  - by Eloff

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

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• Convert Decimal to ASCII

  - by Dan Snyder

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

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• Application leaking Strings?

  - by Jörg B.

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

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