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• fastest public web app framework for quick DB apps?

  - by Steve Eisner

  I'd like to pick up a new tech for my toolbox - something for rapid prototyping of web apps. Brief requirements: public access (not hosted on my machine) - like Google's appengine, etc no tricky configuration necessary to build a simple web app host DB access (small storage provided) including some kind of SQLish query language easy front end HTML templating ability to access as a JSON service C# or Java,PHP or Python - or a fun new language to learn is OK free! An example app, very simple: render an AJAXy editable (add/delete/edit/drag) list of rich-data list items via some template language, so I can quickly mock up a UI for a client. ie. I can do most of the work client-side, but need convenient back end to handle the permanent storage. (In fact I suppose it doesn't even need HTML templating if I can directly access a DB via AJAX calls.) I realize this is a bit vague but am wondering if anyone has recommendations. A Rails host might be best for this (but probably not free) or maybe App Engine, or some other choice I'm not aware of? I've been doing everything with heavyweight servers (ASP.NET etc) for so long that I'm just not up on the latest... Thanks - I'll follow up on comments if this isn't clear enough :)

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• Sleeping a thread blocking stdin

  - by Sid

  Hey, I'm running a function which evaluates commands passed in using stdin and another function which runs a bunch of jobs. I need to make the latter function sleep at regular intervals but that seems to be blocking the stdin. Any advice on how to resolve this would be appreciated. The source code for the functions is def runJobs(comps, jobQueue, numRunning, limit, lock): while len(jobQueue) >= 0: print(len(jobQueue)); if len(jobQueue) > 0: comp, tasks = find_computer(comps, 0); #do something time.sleep(5); def manageStdin(): print "Global Stdin Begins Now" for line in fileinput.input(): try: print(eval(line)); except Exception, e: print e; --Thanks

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• How do you make the script wait for the status of an Ajax get request before continuing?

  - by codeninja

  Basically what I'm doing is checking for the existence of an object, if it's not found, the script will try to load the source file using getScript. I only want to check this once though then return true or false to the function that calls fetch() fetch:function(obj){ ... isReady = false; $.getScript(obj.srcFile,function(){ isReady=true; warn("was able to load object "+key); }); return isReady; } but return kicks in before the script loads =/ later the script is loaded but the function returned false. This is the beauty of asynchronous I suppose... What's the best way to handle this... Maybe I could check again at some other point if the object exists? Or maybe there's a better way to do this where I dont have to potentially lock the browser?

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• concurrent doubly-linked list (1 writer, n-readers)

  - by Arne

  Hi guys, I am back in the field of programming for my Diploma-thesis now and stumbled over the following issue: I need to implement a thread-safe doubly-linked list for one thread writing the list at any position (delete, insert, mutate node data) and one to many threads traversing and reading the list. I am well aware that mutexes can be used to serialize access to the list, still I presume that a naive lock around any write operation will be less than optimal. I am wondering whether there are better variants. (I am well aware that 'optimal' has not much of a practical meaning as long as no exact measure/profiling are available but this is an academic thesis after all..) I am very gratefull for code-samples as well as references to academic granted these have at least a tiny bit of practical relevance. Thanks at lot

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• Adobe After Efects Plugin With Cocoa (Overriding malloc)

  - by mustISignUp

  Messing about a bit, i have a working Adobe After Effects plugin with a bit of Obj-c / Cocoa in it (NSArray and custom objects - not ui stuff). The SDK guide states:- Always use After Effects memory allocation functions. In low-memory conditions (such as during RAM preview), it’s very important that plug-ins not compete with After Effects for OS memory, and deal gracefully with out-of-memory conditions. Failing to use our functions can cause lock-ups, crashes, and tech support calls. Don’t do that. If you’re wrapping existing C++ code, overloading new and delete to use our functions will save substantial reimplementation. On Windows, derive all classes from a common base class which implements new and delete. so my question.. is something compatible with the above statement possible in Obj-c?

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• Fastest container or algorithm for unique reusable ids in C++

  - by gman

  I have a need for unique reusable ids. The user can choose his own ids or he can ask for a free one. The API is basically class IdManager { public: int AllocateId(); // Allocates an id void FreeId(int id); // Frees an id so it can be used again bool MarkAsUsed(int id); // Let's the user register an id. // returns false if the id was already used. }; Assume ids happen to start at 1 and progress, 2, 3, etc. This is not a requirement, just to help illustrate. IdManager mgr; mgr.MarkAsUsed(3); printf ("%d\n", mgr.AllocateId()); printf ("%d\n", mgr.AllocateId()); printf ("%d\n", mgr.AllocateId()); Would print 1 2 4 Because id 3 has already been declared used. What's the best container / algorithm to both remember which ids are used AND find a free id? If you want to know the a specific use case, OpenGL's glGenTextures, glBindTexture and glDeleteTextures are equivalent to AllocateId, MarkAsUsed and FreeId

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• multiple calls to realloc() seems to cause a heap corruption..

  - by Windindeed

  What's the problem with this code? It crashes every time. One time it's a failed assertion "_ASSERTE(_CrtIsValidHeapPointer(pUserData));", other times it is just a "heap corrpuption" error. Changing the buffer size affects this issue in some strange ways - sometimes it crashes on the "realloc", and other times on the "free". I have debugged this code many times, and there is nothing abnormal regarding the pointers. char buf[2000]; char *data = (char*)malloc(sizeof(buf)); unsigned int size = sizeof(buf); for (unsigned int i = 0; i < 5; ++i) { char *ptr = data + size; size += sizeof(buf); char *tmp = (char*)realloc(data, size); if (!tmp) { std::cout << "Oh no.."; break; } data = tmp; memcpy(ptr, buf, sizeof(buf)); } free(data); Thanks!

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• Layers with GDI+

  - by user146780

  I'm thinking of creating a drawing program with layers, and using GDI+ to display them. I want to use GDI+ because it supports transparency. The thing is, drawing lines to the DC is very fast, but drawing directly to a bitmap is very slow. It is only fast if you lock the bits and start setting pixels. Can I draw to multiple DC's in my WM_PAINT event, then just do DrawBitmap for each layer to the MemDC? What's the best way of going about this? Thanks

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• MS SQL Specific Tables Hanging at Queries

  - by Jonn

  I have SQL Server 2008. I run a query in a table on a database. The weirdest thing keeps happening. I run a simple select statement on the table. I know there are 62 rows in the table but it gets stuck at row 48 and goes on "querying...". Waited already for hours and it didn't move on from there. I only know of two programs, and one reporting service connecting to that particular table and one other user. Does anyone have any idea on what could be causing this and how I could trace the source of the lock on that table? As a side note, I noted that the logs only had a notice that Autogrow failed the day before I checked. Could this have something to do with it?

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• Is MSDN referencing a system.thread, a worker thread, an io thread or all three?

  - by w0051977

  Please see the warning below taken from the StreamWriter class specification (http://msdn.microsoft.com/en-us/library/system.io.streamwriter.aspx): "Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." I understand that a W3WC process contains two thread pools i.e. worker threads and I/O threads. A worker thread could contain many threads of its own (if the application creates its own System.Thread instances). Does the warning only relate to System.Threads or does it relate to worker threads and I/O threads as well I.e. as the instance variables of the streamwriter class are not thread safe then does this mean that there would be problems if multiple worker threads access it eg if two users on two different web clients attempt to write to the log file at the same time, then could one lock out the other?

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• Can an Oracle user get a list of its own running sessions without access to v$session?

  - by Nick Pierpoint

  I have an application that runs a process and I only want one process to run at a time. Some options are: Use an object lock to prevent subsequent processes running. This would be fine, but I want the calling session to return immediately and not wait for the running session to complete. Use a custom Y/N to set whether a process is running or not. I set a "Y" flag at the start of the process and set it to "N" when it finishes or fails. Also fine but feels like I'm re-inventing the wheel and doesn't feel like the way to go. It also falls short if the running session is killed as the flag stays at "Y". Use dbms_application_info.set_module This approach seems the most robust, but if I'm to know there's an existing running process I think I need to be able to query v$session and I don't want this application to have such wide access. Any ideas?

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• How to address thread-safety of service data used for maintaining static local variables in C++?

  - by sharptooth

  Consider the following scenario. We have a C++ function with a static local variable: void function() { static int variable = obtain(); //blahblablah } the function needs to be called from multiple threads concurrently, so we add a critical section to avoid concurrent access to the static local: void functionThreadSafe() { CriticalSectionLockClass lock( criticalSection ); static int variable = obtain(); //blahblablah } but will this be enough? I mean there's some magic that makes the variable being initialized no more than once. So there's some service data maintained by the runtime that indicates whether each static local has already been initialized. Will the critical section in the above code protect that service data as well? Is any extra protection required for this scenario?

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• How to debug properly and find causes for crashes?

  - by Newbie

  I dont know what to do anymore... its hopeless. I'm getting tired of guessing whats causing the crashes. Recently i noticed some opengl calls crashes programs randomly on some gfx cards. so i am getting really paranoid what can cause crashes now. The bad thing on this crash is that it crashes only after a long time of using the program, so i can only guess what is the problem. I cant remember what changes i made to the program that may cause the crashes, its been so long time. But luckily the previous version doesnt crash, so i could just copypaste some code and waste 10 hours to see at which point it starts crashing... i dont think i want to do that yet. The program crashes after i make it to process the same files about 5 times in a row, each time it uses about 200 megabytes of memory in the process. It crashes at random times while and after the reading process. I have createn a "safe" free() function, it checks the pointer if its not NULL, and then frees the memory, and then sets the pointer to NULL. Isn't this how it should be done? I watched the task manager memory usage, and just before it crashed it started to eat 2 times more memory than usual. Also the program loading became exponentially slower every time i loaded the files; first few loads didnt seem much slower from each other, but then it started rapidly doubling the load speeds. What should this tell me about the crash? Also, do i have to manually free the c++ vectors by using clear() ? Or are they freed after usage automatically, for example if i allocate vector inside a function, will it be freed every time the function has ended ? I am not storing pointers in the vector. -- Shortly: i want to learn to catch the damn bugs as fast as possible, how do i do that? Using Visual Studio 2008.

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• Find -type d with no subfolders

  - by titatom

  Good morning ! This is a simple one I believe, but I am still a noob :) I am trying to find all folders with a certain name. I am able to do this with the command find /path/to/look/in/ -type d | grep .texturedata The output gives me lots of folders like this : /path/to/look/in/.texturedata/v037/animBMP But I would like it to stop at .texturedata : /path/to/look/in/.texturedata/ I have hundreds of these paths and would like to lock them down by piping the output of grep into chmod 000 I was given a command with the argument -dpe once, but I have no idea what it does and the Internet has not be able to help me determine it's usage Thanks you very much for your help !

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• I need help with a SQL query. Fetching an entry, it's most recent revision and it's fields.

  - by Tigger ate my dad

  Hi there, I'm building a CMS for my own needs, and finished planning my database layout. Basically I am abstracting all possible data-models into "sections" and all entries into one table. The final layout is as follows: Database diagram: I have yet to be allowed to post images, so here is a link to a diagram of my database. Entries (section_entries) are children of their section (sections). I save all edits to the entries in a new revision (section_entries_revisions), and also track revisions on the sections (section_revisions), in order to match the values of a revision, to the fields of the section that existed when the entry-revision was made. The section-revisions can have a number of fields (section_revision_fields) that define the attributes of entries in the section. There is a many-to-many relationship between the fields (section_revision_fields) and the entry-revisions (section_entry_revisions), that stores the values of the attributes defined by the section revision. Feel free to ask questions if the diagram is confusing. Now, this is the most complex SQL I've ever worked with, and the task of fetching my data is a little daunting. Basically what i want help with, is fetching an entry, when the only known variables are; section_id, section_entry_id. The query should fetch the most recent revision of that entry, and the section_revision model corresponding to section_revision_id in the section_entry_revisions table. It should also fetch the values of the fields in the section-revision. I was hoping for a query result, where there would be as many rows as fields in the section. Each row would contain the information of the entry and the section, and then information for one of the fields (e.g. each row corresponding to a field and it's value). I tried to explain the best I could. Again, feel free to ask questions if my description somehow lacking. I hope someone is up for the challenge. Best regards. :-)

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• Location inheritInChildApplications kill debugger?

  - by chobo2

  Hi I am wondering is this normal when you add this into your web.config <location path="." inheritInChildApplications="false"> </location> The debugger should stop working. Like when I add this to my site and try to run in debug mode it won't activate any of my debug points nor will it lock up Visual studios 2008. I can have it running and still make edits to my C# code. I take the line away and I get the debug mode back and it locks up VS2008.

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• Freezing a listboxitem while items are being added

  - by siz

  We have a ListBox that has a number of items. Items are inserted into the ListBox via an ObservableCollection. Some of these items can be edited right in the ListBox. However, if an item is added at an index < the edited item's index, the entire content of the ListBox moves down. What we'd like to do is the following: if an item is in edit mode, we'd like to freeze its position on the screen. It is fine if items are added to the collection and the UI around the item changes. But the position of the item should remain constant on the screen. The only thing I've been able to do so far is attach to the ScrollChanged event and, at most, use either BringIntoView or ScrollIntoView methods to ensure that the item is always displayed somewhere in the UI, but I am unable to lock down its position. Has anyone done something like this and help out?

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• Exception in C#

  - by user1803513

  I am facing null pointer exception in below code as it is happening very rarely and I tried to debug to replicate the issue but no luck. Can anybody help me what can cause null point exception here. private static void MyTaskCompletedCallback(IAsyncResult res) { var worker = (AsyncErrorDelegate)((AsyncResult)res).AsyncDelegate; var async = (AsyncOperation)asyncResult.AsyncState; worker.EndInvoke(res); lock (IsAsyncOpOccuring) { IsBusy = false; } var completedArgs = new AsyncCompletedEventArgs(null, false, null); async.PostOperationCompleted(e => OnTaskCompleted((AsyncCompletedEventArgs)e), completedArgs); } Null Pointer exception is reported at var async = (AsyncOperation)asyncResult.AsyncState;

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• compilation error

  - by Bond

  #include<dirent.h> #include<stdio.h> #include<stdlib.h> #include<sys/stat.h> int main () { struct dirent **namelist; int i,j; char userd[20]; struct stat statBuf; printf("Enter a directory %s\n",userd); scanf("%s",&userd); printf("the dir is %s\n",*userd); i=scandir(".",&namelist,0,alphasort); printf("enter a directory name %s",*userd); printf("scandir returned i=%d\n",&i); if (i<0) perror("Scandir failed to open directory I hope you understand \n"); else { for(j=0;j<i;j++) { printf("j=%d i=%d %s\n",j,i,namelist[j]->d_name); // lstat free(namelist[j]); } } free(namelist); } Can some one help to understand why am I getting warning in above code?

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• Best way of obfuscating / encrypting form data on the iPhone

  - by cannyboy

  I want to create an app which holds sensitive information (imagine it's bank account details, thought it's not). The user enters this information on a form the first time the app starts up. I want this info to be saved, and available, any time the user uses the app (without having to enter a password). However, if the iPhone has a password lock on it, and is stolen, I don't want the data to be easily accessible from the file system. What is the best way of encrypting or obfuscating the data? There is not a lot of data, just a dozen NSStrings from the UITextFields on the form. I'm aware there are encryption export restrictions on the iPhone for non-US developers (I am in UK), so I would prefer to avoid going jumping through any of Apple's app submission hoops to get it on the store.

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• How can I determine new & previous cell value on SheetChange event in Excel?

  - by Falco Foxburr

  I have some special cells in my Excel workbooks which are managed by my Excel Add-in. I want to prevent users from changing content of those cells, but I also want to know, what value users wanted to enter to those cells. On the SheetChange event I can check what users entered to my special cells, but how do I determine the PREVIOUS value in those cells and REVERT user changes? It is not a solution for me. If I lock cell in Excel, it becomes read-only - user can not even try to enter anything to this cell - Excel popups warning dialog in this case. My problem is that I want to catch what user entered to my cell, do something with this value, and then revert cell content to original value.

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• Break the limit of threading, segmentation fault

  - by user353573

  use pthread_create to create limited number of threads running concurrently Successfully compile and run However, after adding function pointer array to run the function, Segmentation fault Where is wrong? workserver number: 0 Segmentation fault void* workserver(void arg) { int status; while(true) { printf("workserver number: %d\n", (int)arg); ( job_queue[(int)arg])(); sleep(3); status = pthread_mutex_lock(&data.mutex); if(status != 0) printf("%d lock mutex", status); data.value = 1; status = pthread_cond_signal(&data.cond); if(status != 0) printf("%d signal condition", status); status = pthread_mutex_unlock(&data.mutex); if(status != 0) printf("%d unlock mutex", status); } }

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• C#, Manage concurrency in database access

  - by Goul

  Hi there, I have written a while ago an application used by multiple users to handle trades creation. I haven't done development for some time now and can't remember how I managed the concurrency between the users and so would have liked your advices in term of design. The application was as follow: - One heavy client per user - A single database - Access to the database for each user to insert/update/delete trades - A grid in the application reflecting the trades table. That grid being updated each time someone changes a deal. My questions: 1- Do you confirm I shouldn't care about the connection to the database for each application. Considering that there is a singleton in each, I would expect on connexion per client with no issue. 2- How preventing the concurrency of the accesses? I guess I should lock when modifying the data, however don't remember how to. 3- How to have the grid automatically updated whenever the database is (by another user for example)? Thank you in advance for your help!

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• Queues And Wait Handles in C#

  - by Michael Covelli

  I've had the following code in my application for some years and have never seen an issue from it. while ((PendingOrders.Count > 0) || (WaitHandle.WaitAny(CommandEventArr) != 1)) { lock (PendingOrders) { if (PendingOrders.Count > 0) { fbo = PendingOrders.Dequeue(); } else { fbo = null; } } // Do Some Work if fbo is != null } Where CommandEventArr is made up of the NewOrderEvent (an auto reset event) and the ExitEvent (a manual reset event). But I just realized today that its not thread safe at all. If this thread gets interrupted right after the first (PendingOrder.Count 0) check has returned false. And then the other thread both enqueues an order and sets the NewOrderEvent before I get a chance to wait on it, the body of the while loop will never run. What's the usual pattern used with a Queue and an AutoResetEvent to fix this and do what I'm trying to do with the code above?

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• Serialization of a TChan String

  - by J Fritsch

  I have declared the following type KEY = (IPv4, Integer) type TPSQ = TVar (PSQ.PSQ KEY POSIXTime) type TMap = TVar (Map.Map KEY [String]) data Qcfg = Qcfg { qthresh :: Int, tdelay :: Rational, cwpsq :: TPSQ, cwmap :: TMap, cw chan :: TChan String } deriving (Show) and would like this to be serializable in a sense that Qcfg can either be written to disk or be sent over the network. When I compile this I get the error No instances for (Show TMap, Show TPSQ, Show (TChan String)) arising from the 'deriving' clause of a data type declaration Possible fix: add instance declarations for (Show TMap, Show TPSQ, Show (TChan String)) or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Show Qcfg) I am now not quite sure whether there is a chance at all to serialize my TChan although all individual nodes in it are members of the show class. For TMap and TPSQ I wonder whether there are ways to show the values in the TVar directly (because it does not get changed, so there should no need to lock it) without having to declare an instance that does a readTVar ?

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