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• APC decreasing php performance??? (php 5.3, apache 2.2, windows vista 64bit)

  - by M.M.

  Hi, I have an Apache/2.2.15 (VC9) and PHP/5.3.2 (VC9 thread safe) running as an apache module on Vista 64bit machine. All running fine. Project that I'm benchmarking (with apache's ab utility) is basically standard Zend Framework project with no db connection involved. Average (median) apache response is about 0.15 seconds. After I've installed APC (3.1.4-dev VC9 thread safe) with standard settings suddenly the request response time raised to 1.3 seconds (!), which is unacceptable... All apc settings looked always good (through the apc.php script: enough shm memory, no cache full, fragmentation 0%). Only difference was to disable the stats lookup (apc.stat = 0). Then the response dropped to 0.09 seconds which was finally better than without the apc. IIRC, it's expected and obvious that the stat lookup creates some overhead, but shouldn't it still be far more performant compared to running wihout the apc extension at all? Or put it differently why is the apc.stat creating so much overhead? Apparently, something is not working as it should, I don't really know where to start looking. Thank you for your time/answers/direction in advance. Cheers, m.

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• Any workarounds for non-static member array initialization?

  - by TomiJ

  In C++, it's not possible to initialize array members in the initialization list, thus member objects should have default constructors and they should be properly initialized in the constructor. Is there any (reasonable) workaround for this apart from not using arrays? [Anything that can be initialized using only the initialization list is in our application far preferable to using the constructor, as that data can be allocated and initialized by the compiler and linker, and every CPU clock cycle counts, even before main. However, it is not always possible to have a default constructor for every class, and besides, reinitializing the data again in the constructor rather defeats the purpose anyway.] E.g. I'd like to have something like this (but this one doesn't work): class OtherClass { private: int data; public: OtherClass(int i) : data(i) {}; // No default constructor! }; class Foo { private: OtherClass inst[3]; // Array size fixed and known ahead of time. public: Foo(...) : inst[0](0), inst[1](1), inst[2](2) {}; }; The only workaround I'm aware of is the non-array one: class Foo { private: OtherClass inst0; OtherClass inst1; OtherClass inst2; OtherClass *inst[3]; public: Foo(...) : inst0(0), inst1(1), inst2(2) { inst[0]=&inst0; inst[1]=&inst1; inst[2]=&inst2; }; }; Edit: It should be stressed that OtherClass has no default constructor, and that it is very desirable to have the linker be able to allocate any memory needed (one or more static instances of Foo will be created), using the heap is essentially verboten. I've updated the examples above to highlight the first point.

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• Peculiar JRE behaviour running RMI server under load, should I worry?

  - by darri

  I've been developing a minimalistic Java rich client CRUD application framework for the past few years, mostly as a hobby but also actively using it to write applications for my current employer. The framework provides database access to clients either via a local JDBC based connection or a lightweight RMI server. Last night I started a load testing application, which ran 100 headless clients, bombarding the server with requests, each client waiting only 1 - 2 seconds between running simple use cases, consisting of selecting records along with associated detail records from a simple e-store database (Chinook). This morning when I looked at the telemetry results from the server profiling session I noticed something which to me seemed strange (and made me keep the setup running for the remainder of the day), I don't really know what conclusions to draw from it. Here are the results: Memory GC activity Threads CPU load Interesting, right? So the question is, is this normal or erratic? Is this simply the JRE (1.6.0_03 on Windows XP) doing it's thing (perhaps related to the JRE configuration) or is my framework design somehow causing this? Running the server against MySQL as opposed to an embedded H2 database does not affect the pattern. I am leaving out the details of my server design, but I'll be happy to elaborate if this behaviour is deemed erratic.

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• Reading and writing to files simultaneously?

  - by vipersnake005

  Moved the question here. Suppose, I want to store 1,000,000,000 integers and cannot use my memory. I would use a file(which can easily handle so much data ). How can I let it read and write and the same time. Using fstream file("file.txt', ios::out | ios::in ); doesn't create a file, in the first place. But supposing the file exists, I am unable to use to do reading and writing simultaneously. WHat I mean is this : Let the contents of the file be 111111 Then if I run : - #include <fstream> #include <iostream> using namespace std; int main() { fstream file("file.txt",ios:in|ios::out); char x; while( file>>x) { file<<'0'; } return 0; } Shouldn't the file's contents now be 101010 ? Read one character and then overwrite the next one with 0 ? Or incase the entire contents were read at once into some buffer, should there not be atleast one 0 in the file ? 1111110 ? But the contents remain unaltered. Please explain. Thank you.

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• DB optimization to use it as a queue

  - by anony

  We have a table called worktable which has some columns(key(primary key), ptime, aname, status, content) we have something called producer which puts in rows in this table and we have consumer which does an order-by on the key column and fetches the first row which has status as 'pending'. The consumer does some processing on this row: 1. updates status to "processing" 2. does some processing using content 3. deletes the row we are facing contention issues when we try to run multiple consumers(probably due to the order-by which does a full table scan)... using Advanced queues would be our next step but before we go there we want to check what is the max throughput we can achieve with multiple consumers and producer on the table. What are the optimizations we can do to get the best numbers possible? Can we do an in-memory processing where a consumer fetches 1000 rows at a time processes and deletes? will that improve? What are other possibilities? partitioning of table? parallelization? Index organized tables?...

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• The best way to predict performance without actually porting the code?

  - by ardiyu07

  I believe there are people with the same experience with me, where he/she must give a (estimated) performance report of porting a program from sequential to parallel with some designated multicore hardwares, with a very few amount of time given. For instance, if a 10K LoC sequential program was given and executes on Intel i7-3770k (not vectorized) in 100 ms, how long would it take to run if one parallelizes the code to a Tesla C2075 with NVIDIA CUDA, given that all kinds of parallelizing optimization techniques were done? (but you're only given 2-4 days to report the performance? assume that you didn't know the algorithm at all. Or perhaps it'd be safer if we just assume that it's an impossible situation to finish the job) Therefore, I'm wondering, what most likely be the fastest way to give such performance report? Is it safe to calculate solely by the hardware's capability, such as GFLOPs peak and memory bandwidth rate? Is there a mathematical way to calculate it? If there is, please prove your method with the corresponding problem description and the algorithm, and also the target hardwares' specifications. Or perhaps there already exists such tool to (roughly) estimate code porting? (Please don't the answer: 'kill yourself is the fastest way.')

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• Rotate a linked list

  - by user408041

  I want to rotate a linked list that contains a number. 123 should be rotated to 231. The function created 23 but the last character stays empty, why? typedef struct node node; struct node{ char digit; node* p; }; void rotate(node** head){ node* walk= (*head); node* prev= (*head); char temp= walk->digit; while(walk->p!=NULL){ walk->digit=walk->p->digit; walk= walk->p; } walk->digit=temp; } How I create the list: node* convert_to_list(int num){ node * curr, * head; int i=0,length=0; char *arr=NULL; head = NULL; length =(int) log10(((double) num))+1; arr =(char*) malloc((length)*sizeof(char)); //allocate memory sprintf (arr, "%d" ,num); //(num, buf, 10); for(i=length;i>=0;i--) { curr = (node *)malloc(sizeof(node)); (curr)->digit = arr[i]; (curr)->p = head; head = curr; } curr = head; return curr; }

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• Aliasing `T*` with `char*` is allowed. Is it also allowed the other way around?

  - by StackedCrooked

  Note: This question has been renamed and reduced to make it more focused and readable. Most of the comments refer to the old text. According to the standard objects of different type may not share the same memory location. So this would not be legal: int i = 0; short * s = reinterpret_cast<short*>(&i); // BAD! The standard however allows an exception to this rule: any object may be accessed through a pointer to char or unsigned char: int i = 0; char * c = reinterpret_cast<char*>(&i); // OK However, it is not clear to me if this is also allowed the other way around. For example: char * c = read_socket(...); unsigned * u = reinterpret_cast<unsigned*>(c); // huh? Summary of the answers The answer is NO for two reasons: You an only access an existing object as char*. There is no object in my sample code, only a byte buffer. The pointer address may not have the right alignment for the target object. In that case dereferencing it would result in undefined behavior. On the Intel and AMD platforms it will result performance overhead. On ARM it will trigger a CPU trap and your program will be terminated! This is a simplified explanation. For more detailed information see answers by @Luc Danton, @Cheers and hth. - Alf and @David Rodríguez.

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• NSManagedObject How To Reload

  - by crissag

  I have a view that consists of a table of existing objects and an Add button, which allows the user to create a new object. When the user presses Add, the object is created in the list view controller, so that the object will be part of that managed object context (via the NSEntityDescription insertNewObjectForEntityForName: method). The Add view has a property for the managed object. In the list view controller, I create an Add view controller, set the property to the managed object I created, and then push the Add view on to the navigation stack. In the Add view, I have two buttons for save and cancel. In the save, I save the managed object and pass the managed object back to the list view controller via a delegate method. If the user cancels, then I delete the object and pass nil back to the list view controller. The complication I am having in the add view is related to a UIImagePickerController. In the Add view, I have a button which allows the user to take a photo of the object (or use an existing photo from the photo library). However, the process of transferring to the UIImagePickerController and having the user use the camera, is resulting in a didReceiveMemoryWarning in the add view controller. Further, the view was unloaded, which also caused my NSManagedObject to get clobbered. My question is, how to you go about reloading the NSManagedObject in the case where it was released because of the low memory situation?

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• C++: Vector of objects vs. vector of pointers to new objects?

  - by metamemetics

  Hello, I am seeking to improve my C++ skills by writing a sample software renderer. It takes objects consisting of points in a 3d space and maps them to a 2d viewport and draws circles of varying size for each point in view. Which is better: class World{ vector<ObjectBaseClass> object_list; public: void generate(){ object_list.clear(); object_list.push_back(DerivedClass1()); object_list.push_back(DerivedClass2()); or... class World{ vector<ObjectBaseClass*> object_list; public: void generate(){ object_list.clear(); object_list.push_back(new DerivedClass1()); object_list.push_back(new DerivedClass2()); ?? Would be using pointers in the 2nd example to create new objects defeat the point of using vectors, because vectors automatically call the DerivedClass destructors in the first example but not in the 2nd? Are pointers to new objects necessary when using vectors because they handle memory management themselves as long as you use their access methods? Now let's say I have another method in world: void drawfrom(Viewport& view){ for (unsigned int i=0;i<object_list.size();++i){ object_list.at(i).draw(view); } } When called this will run the draw method for every object in the world list. Let's say I want derived classes to be able to have their own versions of draw(). Would the list need to be of pointers then in order to use the method selector (-) ?

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• Using the read function to read in a file.

  - by robUK

  Hello, gcc 4.4.1 I am using the read function to read in a wave file. However, when it gets to the read function. Execution seems to stop and freezes. I am wondering if I am doing anything wrong with this. The file size test-short.wave is: 514K. What I am aiming for is to read the file into the memory buffer chunks at a time. Currently I just testing this. Many thanks for any suggestions, #include <stdio.h> #include <stdlib.h> #include <errno.h> #include <fcntl.h> #include <string.h> #include <unistd.h> int main(void) { char buff = malloc(10240); int32_t fd = 0; int32_t bytes_read = 0; char *filename = "test-short.wav"; /* open wave file */ if((fd = (open(filename, O_RDWR)) == -1)) { fprintf(stderr, "open [ %s ]\n", strerror(errno)); return 1; } printf("Opened file [ %s ]\n", filename); printf("sizeof(buff) [ %d ]\n", sizeof(buff)); printf("strlen(buff) [ %d ]\n", strlen(buff)); bytes_read = read(fd, buff, sizeof(buff)); printf("Bytes read [ %d ]\n", bytes_read); return 0; }

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• Sparc Assembly Call currupts data

  - by Sigge

  I am at the moment working with some assembler code for the Sparc processor family, and i am having some truble with a piece of code.. I think the code and output explains more, but in the short.. When i do a call to the function println my varaibels that i have written to the %fp - 8 memory location is destoryed.. here is my assembler code that i am trying to run !PROCEDURE main .section ".text" .global main .align 4 main: save %sp, -96, %sp L1: set 96, %l0 mov %l0, %o0 call initObject ; nop mov %o0, %l0 mov %l0, %o0 call Test$go ; nop mov %o0, %l0 mov %l0, %o0 call println ; nop L0: ret restore !END main !PROCEDURE Test$go .section ".text" .global Test$go .align 4 Test$go: save %sp, -96, %sp L3: mov %i0, %l0 set 0, %l0 set -8, %l1 add %fp,%l1, %l1 st %l0, [%l1] set 1, %l0 mov %l0, %o0 call println ; nop set -8, %l0 add %fp,%l0, %l0 ld [%l0], %l0 mov %l0, %o0 call println ; nop set 1, %l0 mov %l0, %i0 L2: ret restore !END Test$go Here is the assembler code for the println code .global println .type println,#function println: save %sp,-96,%sp ! block 1 .L193: ! File runtime.c: ! 42 } ! 43 ! 45 /** ! 46 Prints an integer to the standard output stream. ! 47 ! 48 @param i The integer to be printed. ! 49 */ ! 50 void println(int i) { ! 51 printf("%d\n", i); sethi %hi(.L195),%o0 or %o0,%lo(.L195),%o0 call printf mov %i0,%o1 jmp %i7+8 restore This is the out put i get when i run this piece of assembler code 1 67584 1 As u can see, the data that is located at %fp - 8 has been destroyed.. please all feedback is apritiated

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• Call 32-bit or 64-bit program from bootloader

  - by user1002358

  There seems to be quite a lot of identical information on the Internet about writing the following 3 bootloaders: Infinite loop jmp $ Print a single character Print "Hello World". This is fantastic, and I've gone through these 3 variations with very little trouble. I'd like to write some 32- or 64-bit code in C and compile it, and call that code from the bootloader... basically a bootloader that, for example, sets the computer up to run some simple numerical simulation. I'll start by listing primes, for example, and then maybe some input/output from the user to maybe compute a Fourier transform. I don't know. I haven't found any information on how to do this, but I can already foresee some problems before I even begin. First of all, compiling a C program compiles it into one of several different files, depending on the target. For Windows, it's a PE file. For Linux, it's a .out file. These files are both quite different. In my instance, the target isn't Windows or Linux, it's just whatever I have written in the bootloader. Secondly, where would the actual code reside? The bootloader is exactly 512 bytes, but the program I write in C will certainly compile to something much larger. It will need to sit on my (virtual) hard disk, probably in some sort of file system (which I haven't even defined!) and I will need to load the information from this file into memory before I can even think about executing it. But from my understanding, all this is many, many orders of magnitude more complex than a 12-line "Hello World" bootloader. So my question is: How do I call a large 32- or 64-bit program (written in C/C++) from my 16-bit bootloader.

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• How to construct objects based on XML code?

  - by the_drow

  I have XML files that are representation of a portion of HTML code. Those XML files also have widget declarations. Example XML file: <message id="msg"> <p> <Widget name="foo" type="SomeComplexWidget" attribute="value"> inner text here, sets another attribute or inserts another widget to the tree if needed... </Widget> </p> </message> I have a main Widget class that all of my widgets inherit from. The question is how would I create it? Here are my options: Create a compile time tool that will parse the XML file and create the necessary code to bind the widgets to the needed objects. Advantages: No extra run-time overhead induced to the system. It's easy to bind setters. Disadvantages: Adds another step to the build chain. Hard to maintain as every widget in the system should be added to the parser. Use of macros to bind the widgets. Complex code Find a method to register all widgets into a factory automatically. Advantages: All of the binding is done completely automatically. Easier to maintain then option 1 as every new widget will only need to call a WidgetFactory method that registers it. Disadvantages: No idea how to bind setters without introducing a maintainability nightmare. Adds memory and run-time overhead. Complex code What do you think is better? Can you guys suggest a better solution?

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• Creation of model in core data on the fly

  - by user1740045

  How can we create a model in core data on the fly? I.e getting the schema of database from somewhere and then creating a Core Data Object graph? *QuesTion:* Yes thats fine, agreed with all the advantages. But, can anybody can tell practically, what is the benefit of integrating Core Data into project instead of using SQL directly. 1.No need to write SQL boiler plate code [but need to learn Core Data Model (steep curve)] 2.WE can undo and redo changes [but practically who needs it] 3.we can migrate to another schema [that can be done by SQLite as well jus need to add another field into table] 4.For say aggregation on some field in table,in Core Data we need to loop through Core Data Objects whereas in SQLite we need to first write SQLite Boiler Plate Code and then the basic aggregation SQL query,which is easy to write,only length of code will increase...But in case of Core Data (need to learn a lot). So apart from reducing the length of Code,does it actually adds value to project? or in terms of Memory Efficiency,Performance,etc.. PS: If anybody has actualy worked on Core Data(Model Creation On the Fly) , if possible share and gve pointers..thanks!

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• iPhone producing strange results on 'if' statement

  - by Rob

  I have a UIPicker where the user inputs a specified time (i.e. 13:00, 13:01, 13:02, etc.) - which determines their score. Once they hit the button an alert comes up with the score that is determined through this 'if-else' statement. Everything seems to work great MOST of the time - but I am getting some erratic behavior. This is the code: //Gets my value from the UIPicker and then converts it into a format that can be used in the 'if' statement. NSInteger runRow = [runTimePicker selectedRowInComponent:2]; NSString *runSelected = [runTimePickerData objectAtIndex:runRow]; NSString *runSelectedFixed = [runSelected stringByReplacingOccurrencesOfString:@":" withString:@"."]; //The actual 'if' statment. if ([runSelectedFixed floatValue] <= 13.00) { runScore = 100; } else if ([runSelectedFixed floatValue] <= 13.06) { runScore = 99; } else if ([runSelectedFixed floatValue] <= 13.12) { runScore = 97; } else if ([runSelectedFixed floatValue] <= 13.18) { runScore = 96; } else if ([runSelectedFixed floatValue] <= 13.24) { runScore = 94; } else if ([runSelectedFixed floatValue] <= 13.30) { runScore = 93; } else if ([runSelectedFixed floatValue] <= 13.36) { runScore = 92; } else if ([runSelectedFixed floatValue] <= 13.42) { runScore = 90; } else if ([runSelectedFixed floatValue] <= 13.48) { runScore = 89; } else if ([runSelectedFixed floatValue] <= 13.54) { runScore = 88; } Now, when I test the program, I will get the expected result when I choose '13:00' which is '100'. I also get the expected result of '99' when I choose all of the times between '13:01 and 13:05'. BUT, when I choose '13:06' it gives me a score of '97'. I also get a score of '97' on '13:07 through 13:12' - which is the desired result. Why would I get a '97' right on '13:12' but not get a '99' right on '13:06'???? Could this be a memory leak or something???

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• What happens when you create an instance of an object containing no state in C#?

  - by liquorice

  I am I think ok at algorithmic programming, if that is the right term? I used to play with turbo pascal and 8086 assembly language back in the 1980s as a hobby. But only very small projects and I haven't really done any programming in the 20ish years since then. So I am struggling for understanding like a drowning swimmer. So maybe this is a very niave question or I'm just making no sense at all, but say I have an object kind of like this: class Something : IDoer { void Do(ISomethingElse x) { x.DoWhatEverYouWant(42); } } And then I do var Thing1 = new Something(); var Thing2 = new Something(); Thing1.Do(blah); Thing2.Do(blah); does Thing1 = Thing2? does "new Something()" create anything? Or is it not much different different from having a static class, except I can pass it around and swap it out etc. Is the "Do" procedure in the same location in memory for both the Thing1(blah) and Thing2(blah) objects? I mean when executing it, does it mean there are two Something.Do procedures or just one?

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• how to change uibutton title at runtime in objective c?

  - by Sarah

  Hello, I know this question is asked many a times,and i am also implementing the same funda for chanding the title of the uibutton i guess. Let me clarify my problem first. I have one uibutton named btnType, on clicking of what one picker pops up and after selecting one value,i am hitting done button to hide the picker and at the same time i am changing the the title of the uibutton with code [btnType setTitle:btnTitle forState:UIControlEventTouchUpInside]; [btnType setTitleColor:[UIColor redColor] forState:UIControlEventAllEvents]; But with my surpriaze,it is not changed and application crashes with signal EXC_BAD_ACCESS. I am not getting where i am making mistake.I have allocated memory to the btnType at viewdidLoad. Also I am using -(IBAction)pressAddType { toolBar.hidden = FALSE; dateTypePicker.hidden = FALSE; } event on pressing the button to open the picker. Also i would like to mention that i have made connection with IB with event TouchUpInside for pressAddType. Any guesses? I will be grateful if you could help me. Thanks.

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• What are provenly scalable data persistence solutions for consumer profiles?

  - by Hubbard

  Consumer profiles with analytical scores [ConsumerID, 1..n demographical variables, 1...n analytical scores e.g. "likely to churn" "likely to buy an item 100$ in worth" etc.] have to be possible to query fast if they are to be used in customizing web-sites, consumer communications etc. Well. If you have: Large number of consumers Large profiles with a huge set of variables (as profiles describing human behaviour are likely to be..) ...you are in trouble. If you really have a physical relational database to which you target a query and then a physical disk starts to rotate someplace to give you an individual profile or a set of profiles, the profile user (a web site customizing a page, a recommendation engine making a recommendation..) has died of boredom before getting any observable results. There is the possibility of having the profiles in memory, which would of course increase the performance hugely. What are the most proven solutions for a fast-response, scalable consumer profile storage? Is there a shootout of these someplace?

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• Graph search problem with route restrictions

  - by Darcara

  I want to calculate the most profitable route and I think this is a type of traveling salesman problem. I have a set of nodes that I can visit and a function to calculate cost for traveling between nodes and points for reaching the nodes. The goal is to reach a fixed known score while minimizing the cost. This cost and rewards are not fixed and depend on the nodes visited before. The starting node is fixed. There are some restrictions on how nodes can be visited. Some simplified examples include: Node B can only be visited after A After node C has been visited, D or E can be visited. Visiting at least one is required, visiting both is permissible. Z can only be visited after at least 5 other nodes have been visited Once 50 nodes have been visited, the nodes A-M will no longer reward points Certain nodes can (and probably must) be visited multiple times Currently I can think of only two ways to solve this: a) Genetic Algorithms, with the fitness function calculating the cost/benefit of the generated route b) Dijkstra search through the graph, since the starting node is fixed, although the large number of nodes will probably make that not feasible memory wise. Are there any other ways to determine the best route through the graph? It doesn't need to be perfect, an approximated path is perfectly fine, as long as it's error acceptable. Would TSP-solvers be an option here?

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• No class def found error for JUnit Test on android

  - by J Bellamy

  I am having some very bizarre behaviour. I have a large number of test cases for my Android application, and they all work except for one. When I run this one I get a java.lang.NoClassDefFoundError: org.JUnit.test Yes, I have the JUnit 4 library imported into the project, and my other JUnit tests are running without any problems. What is particularly bizarre is that before I hit this problem I had an error in my code- basically, I tried writing a file to a read only folder. When that occurred, the JUnitTest would execute up to the point where it would hit an IO exception for accessing a part of memory it cannot access. I fix this problem, and suddenly the Android emulator doesn't seem to know what org.JUnit.test is. I have examined the run configuration for this test class, and it is the same as my others. It is in the same folder as the other tests as well. It also uses the same import statements. Any idea on what is going on? I am using the Android 10 emulator, and eclipse version 3.7.2. Edit: To clarify, the error I get appears on Logcat and not in my Eclipse project.

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• Sparc Assembly Call corrupts data

  - by Sigge

  I am at the moment working with some assembler code for the Sparc processor family, and i am having some truble with a piece of code.. I think the code and output explains more, but in the short.. When i do a call to the function println my varaibels that i have written to the %fp - 8 memory location is destoryed.. here is my assembler code that i am trying to run !PROCEDURE main .section ".text" .global main .align 4 main: save %sp, -96, %sp L1: set 96, %l0 mov %l0, %o0 call initObject ; nop mov %o0, %l0 mov %l0, %o0 call Test$go ; nop mov %o0, %l0 mov %l0, %o0 call println ; nop L0: ret restore !END main !PROCEDURE Test$go .section ".text" .global Test$go .align 4 Test$go: save %sp, -96, %sp L3: mov %i0, %l0 set 0, %l0 set -8, %l1 add %fp,%l1, %l1 st %l0, [%l1] set 1, %l0 mov %l0, %o0 call println ; nop set -8, %l0 add %fp,%l0, %l0 ld [%l0], %l0 mov %l0, %o0 call println ; nop set 1, %l0 mov %l0, %i0 L2: ret restore !END Test$go Here is the assembler code for the println code .global println .type println,#function println: save %sp,-96,%sp ! block 1 .L193: ! File runtime.c: ! 42 } ! 43 ! 45 /** ! 46 Prints an integer to the standard output stream. ! 47 ! 48 @param i The integer to be printed. ! 49 */ ! 50 void println(int i) { ! 51 printf("%d\n", i); sethi %hi(.L195),%o0 or %o0,%lo(.L195),%o0 call printf mov %i0,%o1 jmp %i7+8 restore This is the out put i get when i run this piece of assembler code 1 67584 1 As u can see, the data that is located at %fp - 8 has been destroyed.. please all feedback is apritiated

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• Boost shared_ptr use_count function

  - by photo_tom

  My application problem is the following - I have a large structure foo. Because these are large and for memory management reasons, we do not wish to delete them when processing on the data is complete. We are storing them in std::vector<boost::shared_ptr<foo>>. My question is related to knowing when all processing is complete. First decision is that we do not want any of the other application code to mark a complete flag in the structure because there are multiple execution paths in the program and we cannot predict which one is the last. So in our implementation, once processing is complete, we delete all copies of boost::shared_ptr<foo>> except for the one in the vector. This will drop the reference counter in the shared_ptr to 1. Is it practical to use shared_ptr.use_count() to see if it is equal to 1 to know when all other parts of my app are done with the data. One additional reason I'm asking the question is that the boost documentation on the shared pointer shared_ptr recommends not using "use_count" for production code.

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• How can I synchronize one set of data with another?

  - by RenderIn

  I have an old database and a new database. The old records were converted to the new database recently. All our old applications continue to point to the old database, but the new applications point to the new database. Currently the old database is the only one being updated, so throughout the day the new database becomes out of sync. It is acceptable for the new database to be out of sync for a day, so until all our applications are pointed to the new database I just need to write a nightly cron job that will bring it up to date. I do not want to purge the new database and run the complete conversion script each night, as that would reduce uptime and would create a mess in our auditing of that table. I'm thinking about selecting all the data from the old database, converting it to the new database structure in memory, and then checking for the existence of each record before inserting it in the new database. After that's done, I'd select everything from the new database and check if it exists in the old one, and if not delete it. Is this the simplest way to do this?

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• Overlaying several CLR reference fields with each other in explicit struct?

  - by thr

  Edit: I'm well aware of that this works very well with value types, my specific question is about using this for reference types. I've been tinkering around with structs in .NET/C#, and I just found out that you can do this: using System; using System.Runtime.InteropServices; namespace ConsoleApplication1 { class Foo { } class Bar { } [StructLayout(LayoutKind.Explicit)] struct Overlaid { [FieldOffset(0)] public object AsObject; [FieldOffset(0)] public Foo AsFoo; [FieldOffset(0)] public Bar AsBar; } class Program { static void Main(string[] args) { var overlaid = new Overlaid(); overlaid.AsObject = new Bar(); Console.WriteLine(overlaid.AsBar); overlaid.AsObject = new Foo(); Console.WriteLine(overlaid.AsFoo); Console.ReadLine(); } } } Basically circumventing having to do dynamic casting during runtime by using a struct that has an explicit field layout and then accessing the object inside as it's correct type. Now my question is: Can this lead to memory leaks somehow, or any other undefined behavior inside the CLR? Or is this a fully supported convention that is usable without any issues? I'm aware that this is one of the darker corners of the CLR, and that this technique is only a viable option in very few specific cases.

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