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  • Limiting object allocation over multiple threads

    - by John
    I have an application which retrieves and caches the results of a clients query. The client then requests different chunks of data and the application sends the relevant results and removes them from the cache. A new requirement for this application is that there needs to be a run-time configurable maximum number of results which may be cached. I've taken the naive approach and implemented this by using a counter under a lock which is incremented every time a result is cached and decremented whenever a result is removed from the cache. Unfortunately, this has drastically reduced the applications performance when processing a large number of concurrent requests. I have tried both a critical section lock and spin-lock; the performance improves a bit with a spin-lock, but is still unacceptably slow. Is there a better way to solve this problem which may improve performance? Right now I have a thread pool that services requests and each request is tied to a Request object which stores that cached results for that particular request. Here is a simplified pseudo code version of my current implementation: void ResultCallback( Result result, Request *request ) { lock totalResultsCached lock cachedLimit if( totalResultsCached + 1 > cachedLimit ) { unlock cachedLimit unlock totalResultsCached //cancel the request return; } ++totalResultsCached; unlock cachedLimit unlock totalResultsCached request.add(result) } void SendResults( int resultsToSend, Request *request ) { while ( resultsToSend > 0 ) { send(request.remove()) lock totalResultsCached --totalResultsCached unlock totalResultsCached --resultsToSend; } }

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  • Dynamic allocation in C

    - by Kerby82
    I'm writing a program and I have the following problem: char *tmp; sprintf (tmp,"%ld",(long)time_stamp_for_file_name); Could someone explain how much memory allocate for the string tmp. How many chars are a long variable? Thank you, I would appreciate also a link to an exahustive resource on this kind of information. Thank you

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  • dynamic memory allocation [closed]

    - by gcc
    i wanna write a program that creates (allocating memory) and manipulates (adding elements and increasing memory etc.) integer arrays dynamically according to given input sequences. input sequence which starts with the maximum number of arrays, includes integers to be put into arrays and some one letter characters which are commands to carry out some tasks (activating next array, deleting an array etc). also, i wanna create *c_arrays which is the address of the array whose elements are the actual capacities (How many integer slots are already allocated for an array?) of arrays how should i organize(set up) the algorithm?

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  • Dynamic memory allocation with default values

    - by viswanathan
    class A { private: int m_nValue; public: A() { m_nValue = 0; } A(int nValue) { m_nValue = nValue); ~A() {} } Now in main if i call A a(2);// 2 will be assigned for m_nValue of object A. Now how do we do this if i want to define an array of objects. Also how do we do this if i dynamically create objects using operator new like A *pA; pA = new A[5];// while creating the object i want the parameterised constructor to be //called I hope the question is clear. Do let me know if more explanation is needed

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  • MMGR Questions, code use and thread-saftey

    - by chadb
    1) Is MMGR thread safe? 2) I was hoping someone could help me understand some code. I am looking at something where a macro is used, but I don't understand the macro. I know it contains a function call and an if check, however, the function is a void function. How does wrapping "(m_setOwner (FILE,_LINE_,FUNCTION),false)" ever change return types? #define someMacro (m_setOwner(__FILE__,__LINE__,__FUNCTION__),false) ? NULL : new ... void m_setOwner(const char *file, const unsigned int line, const char *func); 3) What is the point of the reservoir? 4) On line 770 ("void *operator new(size_t reportedSize)" there is the line "// ANSI says: allocation requests of 0 bytes will still return a valid value" Who/what is ANSI in this context? Do they mean the standards? 5) This is more of C++ standards, but where does "reportedSize" come from for "void *operator new(size_t reportedSize)"? 6) Is this the code that is actually doing the allocation needed? "au-actualAddress = malloc(au-actualSize);"

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  • SQL Scenario of allocating ids to user

    - by Enjoy coding
    Hi, I have an sql scenario as follows which I have been trying to improve. There is a table 'Returns' which is having ids of the returned goods against a shop for an item. Its structure is as below. Returns ------------------------- Return ID | Shop | Item ------------------------- 1 Shop1 Item1 2 Shop1 Item1 3 Shop1 Item1 4 Shop1 Item1 5 Shop1 Item1 There is one more table Supplier with Shop, supplier and Item as shown below. Supplier --------------------------------- Supplier | Shop | Item | Volume --------------------------------- supp1 Shop1 Item1 20% supp2 Shop1 Item1 80% Now as you see supp1 is supplying 20 % of total item1 volume and supp2 is supplying 80% of Item1 to shop1. And there were 5 return of items against the same Item1 for same Shop1. Now I need to allocate any four return IDs to Supp1 and remaining one return Id to supp2. This allocation of numbers is based on the ratio of the supplied volume percentage of the supplier. This allocation varies depending on the ratio of volume of supplied items. Now I have tried a method of using RANKs as shown below by use of temp tables. temp table 1 will have Shop, Return Id, Item, Total count of return IDs and Rank of the return id. temp table 2 will have shop, Supplier, Item and his proportion and rank of proportion. Now I am facing the difficulty in allocating top return ids to top supplier as illustrated above. As SQL doesnt have loops how can I achieve this. I have been tying several ways of doing this. Please advice. My environment is Teradata (ANSI SQL is enough). Thanks in advance.

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  • What to throw in a C++ class wrapping a C library ?

    - by ereOn
    I have to create a set of wrapping C++ classes around an existing C library. For many objects of the C library, the construction is done by calling something like britney_spears* create_britney_spears() and the opposite function void free_britney_spears(britney_spears* brit). If the allocation of a britney_spears fails, create_britney_spears() returns NULL. This is, as far as I know, a very common pattern. Now I want to wrap this inside a C++ class. //britney_spears.hpp class BritneySpears { public: BritneySpears(); private: boost::shared_ptr<britney_spears> m_britney_spears; }; And here is the implementation: // britney_spears.cpp BritneySpears::BritneySpears() : m_britney_spears(create_britney_spears(), free_britney_spears) { if (!m_britney_spears) { // Here I should throw something to abort the construction, but what ??! } } So the question is in the code sample: What should I throw to abort the constructor ? I know I can throw almost anything, but I want to know what is usually done. I have no other information about why the allocation failed. Should I create my own exception class ? Is there a std exception for such cases ? Many thanks.

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  • XCode and Instruments for memory leaks

    - by coure06
    I have tested my iphone app using XCode and instrument. I am watching the memory allocation tables, its showing me that every things is increasing i.e Bytes, Live Bytes and so on. What does it means? Am i not deallocating the objects? Can i find which objects are not deallocating using instruments?

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  • Drawable advantage over bitmap for memory in android

    - by Tabish
    This question is linked with the answers in the following question: Error removing Bitmaps[Android] Is there any advantage of using Drawable over Bitmap in Android in terms of memory de-allocation ? I was looking at Romain Guy project Shelves and he uses SoftReference for images caches but I'm unable to search where is the code which is de-allocating these Drawables when SoftReference automatically reclaims the memory for Bitmap. As far as I know .recycle() has to be explicitly called on the Bitmap for it to be de-allocated.

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  • Memory ReAllocation

    - by davispuh
    What is the right and best way to reallocate memory? for example I allocate 100 bytes with WinAPI function HeapAlloc then I fill 100 bytes of that memory with some data and now I want to add more new data at end of previous... What Should I do? Make a new allocation with more bytes and then copy old+new to new location and free old memory? Or there is some way to allocate new memory at end of old data and then copy only new data?

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  • .NET allocations profiling

    - by nimoraca
    I need a way to track all allocations in a .NET application that happen during a single step in the process of debugging my application. I mean, when I'm in the debugger, stepping through code, I would like to see for a single step what allocation took place. Is there a tool or a way to do it? I tried several memory profilers including CLR profiler, JetBrains and .NET Memory Profiler 3.5 and none of them seems to provide this kind of funcionality.

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  • In plesk 9.3.0, which php.ini is in use?

    - by Gaia
    I have 3 (actually 4, but the 4th one is for installatron) php.ini files in my Virtuozzo Container running RHEL 5.x /vz/root/1003/usr/local/psa/admin/conf/php.ini /vz/root/1003/etc/php.ini /vz/root/1003/etc/etc/php.ini which one do I use to change the MEMORY_LIMIT for a wordpress app running in the container 1003? Thanks!

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  • Would SSD drives benefit from a non-default allocation unit size?

    - by davebug
    The default allocation unit size recommended when formatting a drive in our current set-up is 4096 bytes. I understand the basics of the pros and cons of larger and smaller sizes (performance boost vs. space preservation) but it seems the benefits of a solid state drive (seek times massively lower than hard disks) may create a situation where a much smaller allocation size is not detrimental. Were this the case it would at least partially help to overcome the disadvantage of SSD (massively higher prices per GB). Is there a way to determine the 'cost' of smaller allocation sizes specifically related to seek times? Or are there any studies or articles recommending a change from the default based on this newer tech? (Assume the most average scattering of sizes program files, OS files, data, mp3s, text files, etc.)

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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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  • 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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  • Efficient algorithm for creating an ideal distribution of groups into containers?

    - by Inshim
    I have groups of students that need to be allocated into classrooms of a fixed capacity (say, 100 chairs in each). Each group must only be allocated to a single classroom, even if it is larger than the capacity (ie there can be an overflow, with students standing up) I need an algorithm to make the allocations with minimum overflows and under-capacity classrooms. A naive algorithm to do this allocation is horrendously slow when having ~200 groups, with a distribution of about half of them being under 20% of the classroom size. Any ideas where I can find at least some good starting point for making this algorithm lightning fast? Thanks!

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  • Can you tune C runtime heap segment reservation size on XP?

    - by Jason
    When the VC6 C runtime on XP can't serve an allocation request within an existing heap segment, it reserves a new segment. The size of these new segments increase by factors of 2 (until there are not large enough free areas to do that, at which point it falls down to smaller segments.) In any case, is there any way to control this behavior on XP with the VC6 runtime? For example, doubling up to a point, but capping at 64MB segments. If there is no way on XP but there is on 7, that would be good to know too. Or if there is no way on VC6 but there is on VC8 or up would be interesting.

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  • Embedded Linux: Memory Fragmentation

    - by waffleman
    In many embedded systems, memory fragmentation is a concern. Particularly, for software that runs for long periods of time (months, years, etc...). For many projects, the solution is to simply not use dynamic memory allocation such as malloc/free and new/delete. Global memory is used whenever possible and memory pools for types that are frequently allocated and deallocated are good strategies to avoid dynamic memory management use. In Embedded Linux how is this addressed? I see many libraries use dynamic memory. Is there mechanism that the OS uses to prevent memory fragmentation? Does it clean up the heap periodically? Or should one avoid using these libraries in an embedded environment?

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  • Where does memory dynamically allocated reside?

    - by Summer_More_More_Tea
    Hello everyone: We know that malloc() and new operation allocate memory from heap dynamically, but where does heap reside? Does each process have its own private heap in the namespace for dynamic allocation or the OS have a global one shared by all the processes. What's more, I read from a textbook that once memory leak occurs, the missing memory cannot be reused until next time we restart our computer. Is this thesis right? If the answer is yes, how can we explain it? Thanks for your reply. Regards.

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  • strategy to allocate/free lots of small objects

    - by aaa
    hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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  • Is there any danger in calling free() or delete instead of delete[]? [closed]

    - by Matt Joiner
    Possible Duplicate: ( POD )freeing memory : is delete[] equal to delete ? Does delete deallocate the elements beyond the first in an array? char *s = new char[n]; delete s; Does it matter in the above case seeing as all the elements of s are allocated contiguously, and it shouldn't be possible to delete only a portion of the array? For more complex types, would delete call the destructor of objects beyond the first one? Object *p = new Object[n]; delete p; How can delete[] deduce the number of Objects beyond the first, wouldn't this mean it must know the size of the allocated memory region? What if the memory region was allocated with some overhang for performance reasons? For example one could assume that not all allocators would provide a granularity of a single byte. Then any particular allocation could exceed the required size for each element by a whole element or more. For primitive types, such as char, int, is there any difference between: int *p = new int[n]; delete p; delete[] p; free p; Except for the routes taken by the respective calls through the delete-free deallocation machinery?

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  • Boost::Mutex & Malloc

    - by M. Tibbits
    Hi all, I'm trying to use a faster memory allocator in C++. I can't use Hoard due to licensing / cost. I was using NEDMalloc in a single threaded setting and got excellent performance, but I'm wondering if I should switch to something else -- as I understand things, NEDMalloc is just a replacement for C-based malloc() & free(), not the C++-based new & delete operators (which I use extensively). The problem is that I now need to be thread-safe, so I'm trying to malloc an object which is reference counted (to prevent excess copying), but which also contains a mutex pointer. That way, if you're about to delete the last copy, you first need to lock the pointer, then free the object, and lastly unlock & free the mutex. However, using malloc to create a boost::mutex appears impossible because I can't initialize the private object as calling the constructor directly ist verboten. So I'm left with this odd situation, where I'm using new to allocate the lock and nedmalloc to allocate everything else. But when I allocate a large amount of memory, I run into allocation errors (which disappear when I switch to malloc instead of nedmalloc ~ but the performance is terrible). My guess is that this is due to fragmentation in the memory and an inability of nedmalloc and new to place nice side by side. There has to be a better solution. What would you suggest?

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