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• NedMalloc / DlMalloc experiences

  - by Suma

  I am currently evaluating a few of scalable memory allocators, namely nedmalloc and ptmalloc (both built on top of dlmalloc), as a replacement for default malloc / new because of significant contention seen in multithreaded environment. Their published performance seems to be good, however I would like to check what are experiences of other people who have really used them. Were your performance goals satisfied? Did you experience any unexpected or hard to solve issues (like heap corruption)? If you have tried both ptmaalloc and nedmalloc, which of the two would you recommend? Why (ease of use, performance)?

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• What causes a JRE 6 JVM code cache leak?

  - by Arturo Knight

  Since switching to JRE 6, my server's code cache usage (non-heap) keeps growing indefinitely. My application creates a lot of classes at runtime, BUT these classes are successfully unloaded during the GC process. I can see these classes getting unloaded in the gc logs and also the permGen usage stays constant. I specifically make sure in my code that these classes are orphaned once I am finished with them and so they correctly get garbage collected from permGen. The code cache however keeps growing. I only became aware of the code cache after switching to JRE 6. So I guess my questions are: Does GC include the code cache? What could cause a code cache memory leak, specifically. Is there a bug in JDK 6 in this area?

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• MapViewOfFile shared between 32bit and 64bit processes

  - by MK

  Hi, I'm trying to use MapViewOfFile in a 64 bit process on a file that is already mapped to memory of another 32 bit process. It fails and gives me an "access denied" error. Is this a known Windows limitation or am I doing something wrong? Same code works fine with 2 32bit processes. The code sort of looks like this: hMapFile = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, szShmName); if (NULL == hMapFile) { /* failed to open - create new (this happens in the 32 bit app) */ SECURITY_ATTRIBUTES sa; sa.nLength = sizeof(SECURITY_ATTRIBUTES); sa.bInheritHandle = FALSE; /* give access to members of administrators group */ BOOL success = ConvertStringSecurityDescriptorToSecurityDescriptor( "D:(A;OICI;GA;;;BA)", SDDL_REVISION_1, &(sa.lpSecurityDescriptor), NULL); HANDLE hShmFile = CreateFile(FILE_FAXCOM_SHM, FILE_ALL_ACCESS, 0, &sa, OPEN_ALWAYS, 0, NULL); hMapFile = CreateFileMapping(hShmFile, &sa, PAGE_READWRITE, 0, SHM_SIZE, szShmName); CloseHandle(hShmFile); } // this one fails in 64 bit app pShm = MapViewOfFile(hMapFile, FILE_MAP_ALL_ACCESS, 0, 0, SHM_SIZE);

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• Linux: page faults and network filesystems

  - by Alex B

  If a Linux system runs out of physical memory, does it drop inactive executable code pages? I assume the answer is yes, since there is no reason to keep them in swap, so they are simply discarded and re-loaded if necessary (as far as I know, that's what FreeBSD does). If the above is true for Linux, my question is, how does it handle executables run from network filesystems (e.g. NFS)? Does it go and fetch executable pages over the network if there is a page fault?

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• Is Private Bytes >> Working Set normal?

  - by Jacob

  OK, this may sound weird, but here goes. There are 2 computers, A (Pentium D) and B (Quad Core) with almost the same amount of RAM running Windows XP. If I run the same code on both computers, the allocated private bytes in A never goes down resulting in a crash later on. In B it looks like the private bytes is constantly deallocated and everything looks fine. In both computers, the working set is deallocated and allocated similarly. Could this be an issue with manifests or DLLs (system)? I'm clueless. Also, I compiled the executable on A and ran it on B and it worked. Note: I observed the utilized memory with Process Explorer. Question: During execution (where we have several allocations and deallocations) is it normal for the number of private bytes to be much bigger (1.5 GB vs 70 MB) than the working set?

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• The right way to manage subviews in a UIControl

  - by ed94133

  (iPhone SDK 3.x:) I have a UIControl subclass that creates a different number of subviews depending on the length of an NSArray property. Please take my word for it that this needs to be a UIControl rather than a UIView. Currently I implement subview management in drawRect, beginning by removing all subviews and then creating the appropriate number based on the property. I don't think this is very good memory management and I'm not sure if drawRect is really the appropriate place to add subviews. Any thoughts on the best way to handle this pattern? Thank you.

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• iPhone app: recover view after didReceiveMemoryWarning

  - by mga

  The app in question has a MainView->ModalView pair. The ModalView is shown via UIModalTransitionStyleFlipHorizontal. In case of didReceiveMemoryWarning, MainView is dumped (since it is not visible) and the app stays "alive" but when you flip back there is a (very) short period of time when the screen is blank (since the modal dialog is returning to a now-deallocated view). When the animation transition is over, MainView is regenerated and all is ok. I just would like to somehow regenerate MainView before returning from ModalView (in case of a memory warning). Is this a good idea? Am I doing something wrong as far as the warning is concerned? Thanks

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• OutOfMemoryException Processing Large File

  - by Krip

  We are loading a large flat file into BizTalk Server 2006 (Original release, not R2) - about 125 MB. We run a map against it and then take each row and make a call out to a stored procedure. We receive the OutOfMemoryException during orchestration processing, the Windows Service restarts, uses full 2 GB memory, and crashes again. The server is 32-bit and set to use the /3GB switch. Also I've separated the flow into 3 hosts - one for receive, the other for orchestration, and the third for sends. Anyone have any suggestions for getting this file to process wihout error? Thanks, Krip

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• Is the heap actually a heap?

  - by ElectricDialect

  In .NET (and Java as far as I know), the area where objects are dynamically allocated is referred to as the managed heap. However, most documentation that describes how the managed heap works depicts it as a linear data structure, such as a linked list or stack. So, is the managed heap actually a heap, or is it implemented with some other data structure? If it actually does not use a heap data structure, is seems like a significant failure of terminology to overload the meaning of this word. If it is in fact a heap data structure, what is the value that satisfies the heap property: the size of the allocated memory region?

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• Super wide, but not so tall, bitmap?

  - by Erik Karlsson

  Howdy folks. Is there any way to create a more space/resource efficient bitmap? Currently i try to render a file, approx 800 px high but around 720000px wide. It crashes my application, presumebly because of the share memory-size of the bitmap. Can i do it more efficient, like creating it as an gif directly and not later when i save it? I try to save a series of lines/rectangles from a real world reading, and i want it to be 1px per 1/100th of a second. Any input? And btw, i never manage to ogon using google open id : /

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• PerformSelectorInBackground leaking on device

  - by Oysio

  While it seems to not pose a problem on the simulator, using performSelectorInBackground on the device causes memory leaks. Or at least that's what Instruments indicates. Looking at the code I don't have a single clue what the cause could be. I tried to strip the affected code to a bare minimum but still strangely Instruments keeps showing a leak every time this piece of code is executed. Anything unusual going on here? //In viewcontrollerA: -(void)mainLoop { [self.viewControllerB performSelectorInBackground:@selector(calculateTotals) withObject:nil]; //This gives the same problem //[NSThread detachNewThreadSelector:@selector(calculateTotals) toTarget:self.viewControllerB withObject:nil]; //UI stuff ... } //viewControllerB: -(void)calculateTotals { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; //Heavy calculations ... [pool release]; }

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• Why does installing NVidia 9600GT graphics card, take 1GB of RAM away from Windows?

  - by Nick G

  Hi, I've changed graphics cards in my PC and now Windows 7 (32bit) is reporting that I have a whole gigabyte less physical RAM in my PC. Why is this? Firstly, the machine has 4GB of physical RAM. The old card was an ATI 2600XT with 256MB and the new card is an NVidia 9600GT with 512MB. With the ATI card windows sees 3326MB. With the NVidia card, windows sees 2558MB. I realise that due to address space restrictions I will not see all 4GB with 32bit windows, but why is there such a massive loss of RAM when simply changing cards (bearing in mind BOTH cards have their own RAM and borrow no main memory like some built on chipsets do). Would using 64 bit windows solve this? Thanks Nick.

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• How well do zippers perform in practice, and when should they be used?

  - by Rob

  I think that the zipper is a beautiful idea; it elegantly provides a way to walk a list or tree and make what appear to be local updates in a functional way. Asymptotically, the costs appear to be reasonable. But traversing the data structure requires memory allocation at each iteration, where a normal list or tree traversal is just pointer chasing. This seems expensive (please correct me if I am wrong). Are the costs prohibitive? And what under what circumstances would it be reasonable to use a zipper?

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• Should I typecast in PHP when defining my vars?

  - by Borislav

  I am sorry if this is more of a theory question then a real life problem but it is a real life situation for me. We were commenting on the way PHP works with vars and how memory heavy it is on the server due to its "mixed vars" and something occured to me - why not typecast right from the start? So I guess my quesion is: Whould it make any difference for the server load if all you PHP vars were"pre-casted"? Example: protected $_id; VS protected (int) $_id;

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• C String literals: Where do they go?

  - by Chris Cooper

  I have read a lot of posts about "string literals" on SO, most of which have been about best-practices, or where the literal is NOT located in memory. I am interested in where the string DOES get allocated/stored, etc. I did find one intriguing answer here, saying: Defining a string inline actually embeds the data in the program itself and cannot be changed (some compilers allow this by a smart trick, don't bother). but, it had to do with C++, not to mention that it says not to bother. I am bothering. =D So my question is, again, where and how is my string literal kept? Why should I not try to alter it? Does the implementation vary by platform? Does anyone care to elaborate on the "smart trick?" Thanks for any explanations.

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• .Net: Prevent an object from being paged out (VirtualLock equivalent)

  - by Gene

  How would one go about keep an object in memory such that it won't be paged out by the OS in .Net? i.e. Something similar to VirtualLock, but operating on an object, such that if compacting occurs and the object is moved it still would not be paged out, etc.. (I suppose one could pin the object's, determine what pages it belongs to, and then VirtualLock those pages, but that seems non-desireable for many reasons.) If possible, could you point me to a reference or working sample? (C# ideally) Many thanks in advance!

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• IPC speed and compare

  - by Lily

  I am trying to implement a real-time application which involves IPC across different modules. The modules are doing some data intensive processing. I am using message queue as the backbone(Activemq) for IPC in the prototype, which is easy(considering I am a totally IPC newbie), but it's very very slow. Here is my situation: I have isolated the IPC part so that I could change it other ways in future. I have 3 weeks to implement another faster version. ;-( IPC should be fast, but also comparatively easy to pick up I have been looking into different IPC approaches: socket, pipe, shared memory. However, I have no experience in IPC, and there is definitely no way I could fail this demo in 3 weeks... Which IPC will be the safe way to start with? Thanks. Lily

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• Why does this program crash: passing of std::string between DLLs

  - by msiemeri

  Hello together. I have some trouble figuring out why the following crashes (MSVC9): //// the following compiles to A.dll with release runtime linked dynamically //A.h class A { __declspec(dllexport) std::string getString(); }; //A.cpp #include "A.h" std::string A::getString() { return "I am a string."; } //// the following compiles to main.exe with debug runtime linked dynamically #include "A.h" int main() { A a; std::string s = A.getString(); return 0; } // crash on exit Obviously (?) this is due to the different memory models for the executable and DLL. Could it be that the string A::getString() returns is being allocated in A.dll and freed in main.exe? If so, why - and what would be a safe way to pass strings between DLLs (or executables, for that matter)? Without using wrappers like shared_ptr with a custom deleter.

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• Release objects before returning a value based on those object?

  - by Moshe

  Consider the following method, where I build a string and return it. I would like to release the building blocks of the sting, but then the string is based on values that no longer exists. Now what? Am I leaking memory and if so, how can I correct it? - (NSString) getMiddahInEnglish:(int)day{ NSArray *middah = [[NSArray alloc] initWithObjects:@"Chesed", @"Gevurah", @"Tiferes", @"Netzach", @"Hod", @"Yesod", @"Malchus"]; NSString *firstPartOfMiddah = [NSString stringWithFormat: @"%@", [middah objectAtIndex: ((int)day% 7)-1]]; NSString *secondPartOfMiddah = [NSString stringWithFormat: @"%@", [middah objectAtIndex: ((int)day / 7)]]; NSString *middahStr = [NSString string@"%@ She'bi@%", firstPartOfMiddah, secondPartOfMiddah]; [middah release]; [firstPartOfMiddah release]; [secondPartOfMiddah release]; return middahStr; }

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• A very basic auto-expanding list/array

  - by MainMa

  Hi, I have a method which returns an array of fixed type objects (let's say MyObject). The method creates a new empty Stack<MyObject>. Then, it does some work and pushes some number of MyObjects to the end of the Stack. Finally, it returns the Stack.ToArray(). It does not change already added items or their properties, nor remove them. The number of elements to add will cost performance. There is no need to sort/order the elements. Is Stack a best thing to use? Or must I switch to Collection or List to ensure better performance and/or lower memory cost?

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• Releasing NSData causes exception...

  - by badmanj

  Hi, Can someone please explain why the following code causes my app to bomb? NSData *myImage = UIImagePNGRepresentation(imageView.image); : [myImage release]; If I comment out the 'release' line, the app runs... but a few times calling the function containing this code and I get a crash - I guess caused by a memory leak. Even if I comment EVERYTHING else in the function out and just leave those two lines, when the release executes, the app crashes. I'm sure this must be a newbie "you don't know how to clean up your mess properly" kind of thing ;-) Cheers, Jamie.

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• iPhone: custom UITableViewCell with Interface Builder -> how to release cell objects?

  - by Stefan Klumpp

  The official documentation tells me I've to do these 3 things in order to manage the my memory for "nib objects" correctly. @property (nonatomic, retain) IBOutlet UIUserInterfaceElementClass *anOutlet; "You should then either synthesize the corresponding accessor methods, or implement them according to the declaration, and (in iPhone OS) release the corresponding variable in dealloc." - (void)viewDidUnload { self.anOutlet = nil; [super viewDidUnload]; } That makes sense for a normal view. However, how am I gonna do that for a UITableView with custom UITableViewCells loaded through a .nib-file? There the IBOutlets are in MyCustomCell.h (inherited from UITableViewCell), but that is not the place where I load the nib and apply it to the cell instances, because that happens in MyTableView.m So do I still release the IBOutlets in the dealloc of MyCustomCell.m or do I have to do something in MyTableView.m? Also MyCustomCell.m doesn't have a - (void)viewDidUnload {} where I can set my IBOutlets to nil, while my MyTableView.m does.

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• Efficient data structure design

  - by Sway

  Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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• Class members allocation on heap/stack? C++

  - by simplebutperfect

  If a class is declared as follows: class MyClass { char * MyMember; MyClass() { MyMember = new char[250]; } ~MyClass() { delete[] MyMember; } }; And it could be done like this: class MyClass { char MyMember[250]; }; How does a class gets allocated on heap, like if i do MyClass * Mine = new MyClass(); Does the allocated memory also allocates the 250 bytes in the second example along with the class instantiation? And will the member be valid for the whole lifetime of MyClass object? As for the first example, is it practical to allocate class members on heap?

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• Conceptual question about NSAutoreleasePools

  - by ryyst

  In my Cocoa program, wouldn't a really simple way of dealing with autoreleased objects be to just create a timer object inside the app delegate that calls the following method e.g. every 10 seconds: if (pool) { // Release & drain the current pool to free the memory. [pool release]; } // Create a new pool. pool = [[NSAutoreleasePool alloc] init]; The only problems I can imagine are: 1) If the above code runs in a separate thread, an object might get autoreleased between the release call to the old pool and the creation of the new pool - that seems highly unlikely though. 2) It's obviously not that efficient, because the pool might get released if there's nothing in it. Likewise, in the 10 second gap, many many objects might be autoreleased, causing the pool to grow a lot. Still, the above solution seems pretty suitable to small and simple projects. Why doesn't anybody use it? What's the best practice of using NSAutoreleasePools?

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