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• Resources for memory management in embedded application

  - by Elazar Leibovich

  How should I manage memory in my mission critical embedded application? I found some articles with google, but couldn't pinpoint a really useful practical guide. The DO-178b forbids dynamic memory allocations, but how will you manage the memory than? preallocate everything in advance and send a pointer to each function that needs allocation? Allocate it on the stack? Use a global static allocator (but then it's very similar to dynamic allocation)? Answers can be of the form of regular answer, reference to a resource, or reference to good opensource embedded system for example. clarification: The issue here is not whether or not memory management is availible for the embedded system. But what is a good design for an embedded system, to maximize reliability.

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• Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

  - by Shane MacLaughlin

  Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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• How much trust can I put behind a computer system? How can I measure trust?

  - by danmine

  How much trust can I put in a standard computer running windows? To what certainty can I be sure it will run my code the way I wrote it? How can I be sure that if I declare something like "int j = 5;", j will alway be 5? Is there a way to measure trust in a standard x86 computer system? What kind of protections are there to make sure that j = 5? I'm thinking about critical systems where nothing can be off even by one bit and everything must run exactly the way it was written to run.

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• Good simple C/C++ FTP and SFTP client library recommendation for embedded Linux

  - by Roman Nikitchenko

  Could anyone recommend FTP / SFTP client C/C++ library for Linux-based embedded system? I know about Curl library but I need something as simple as possible just to download files from FTP / SFTP servers. Is there any recommendation to look for? Yes, SFTP support is critical. Actually I can even sacrifice multi-threading because I need only one stream at a time. And I'd like it to be able to work through memory buffers but this should be not a problem. Thank you in advance.

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• How to create a GtkImage from a Cairo context?

  - by Zurbo82

  I got a paint function that works using a Cairo context and the end result should be a GtkImage (without intermediate image creation). I tried to use the gdk_cairo_create function but this code: ... GdkPixbuf *pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, 22, 22); GtkWidget *image = gtk_image_new_from_pixbuf (pixbuf); GdkDrawable *drawable = image->window; cairo_t *ctx = gdk_cairo_create (drawable); my_cairo_paint_function (ctx); ... fails with: Gdk-CRITICAL **: IA__gdk_cairo_create: assertion `GDK_IS_DRAWABLE (drawable)' failed Same with a simple: #include <gtk/gtk.h> #include <cairo.h> int main (int argc, char *argv[]) { gtk_init(&argc, &argv); cairo_t *ctx = gdk_cairo_create (gtk_widget_get_window (gtk_image_new_from_file ("foobar.png"))); gtk_main(); return 0; } I don't understand why this fails. Any help is appreciated!

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• Torrents: Can I protect my software by sending wrong bytes?

  - by Martijn Courteaux

  Hi, It's a topic that everyone interests. How can I protect my software against stealing, hacking, reverse engineering? I was thinking: Do my best to protect the program for reverse engineering. Then people will crack it and seed it with torrents. Then I download my own cracked software with a torrent with my own torrent-software. My own torrent-software has then to seed incorrect data (bytes). Of course it has to seed critical bytes. So people who want to steal my software download my wrong bytes. Just that bytes that are important to startup, saving and loading data, etc... So if the stealer download from me (and seed it later) can't do anything with it, because it is broken. Is this idea relevant? Maybe, good torrent-clients check hashes from more peers to check if the packages (containing my broken bytes) I want to seed are correct or not? Thanks

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• server reboot has caused django project to lose directories

  - by wmfox3

  A fully functional Django project as well as a couple in development have all broken following the rebooting of the server. In addition to some pieces of the Django admin returning errors as well as missing .js and .css files, I'm getting errors like this when viewing pages that include images uploaded through the admin. Exception Type: TemplateSyntaxError Exception Value: Caught an exception while rendering: (2, 'No such file or directory') Exception Location: /usr/lib/pymodules/python2.6/django/template/debug.py in render_node, line 81 Python Executable: /usr/bin/python Python Version: 2.6.4 So did the reboot stomp on some part of my configuration/setup or did it fail to restart a critical piece?

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• "Cannot use fixed local inside lambda expression"

  - by JulianR

  I have an XNA 3.0 project that compiled just fine in VS2008, but that gives compile errors in VS2010 (with XNA 4.0 CTP). The error: Cannot use fixed local 'depthPtr' inside an anonymous method, lambda expression, or query expression depthPtr is a fixed float* into an array, that is used inside a Parallel.For lambda expression from System.Threading. As I said, this compiled and ran just fine on VS2008, but it does not on VS2010, even when targeting .NET 3.5. Has this changed in .NET 4.0, and even so, shouldn't it still compile when I choose .NET 3.5 as the target framework? Searching for the term "Cannot use fixed local" yields exactly one (useless) result, both in Google and Bing. If this has changed, what is the reason for this? I can imagine capturing a fixed pointer-type in a closure could get a bit weird, is that why? So I'm guessing this is bad practice? And before anyone asks: no, the use of pointers is not absolutely critical here. I would still like to know though :)

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• NoSQL for concurrent reads/writes

  - by Mickael Marrache

  After getting some performance issues for an application using a MySQL database, I'm thinking of using NoSQL solutions. My architecture is as follows: One application receives messages from the network at a high throughput (i.e. 50000 messages/sec). Each message is stored in the DB, so it's important for the write rate to be as fast as the arrival rate. Then, I also have some PHP pages that accesses the DB to get the data stored by the other application. It's important for me that the retrieved data is as relevant as possible (i.e. not old data, let's say not more than 5 seconds old). Also, the data is not critical, so I don't need any security mechanism to avoid losing the data. I see there are a lot of NoSQL solutions, but I don't know if they are all relevant. Could you please provide me some directions. Thanks

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• Securing a REST API

  - by Christopher McCann

  I am in the middle of developing a REST API - the first one I ever have. The data being passed through the API is not of such a critical nature that there will be loss of life, economics etc if it was intercepted but at the same time I would like it to be secure. The data being transferred is simply like the data that would be transferred on Twitter or Facebook - not overly confidential but still should be kept private. What is the best way to secure this data? Am I best to use HTTP Basic Auth over SSL or should I be looking into something like OAuth. I have never really used REST much before so bit of a first for me. Thanks

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• Subtract displaced mask using OpenCV

  - by dario_ramos

  I want to do: masked = image - mask But I want to "displace" mask. That is, move it vertically and horizontally (as long as the intersection between it and image is not empty, this would be valid). I have some hand-coded assembly (which uses MMX instructions) which does this, embedded in a C++ program, but it's unstable when doing vertical displacemente, so I thought of using OpenCV instead. Would it be possible to do this calling only one OpenCV function? Performance is critical; using OpenCV, time should be at least in the same order of magnitude as the assembly code.

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• Not compile code blocks when publishing?

  - by Menno Gouw

  I have many lines i just use for debugging and helpers. Is there a way i can mark these so they do not compile when publishing a project but still can use when running/debugging my program within Eclipse? Even better would be to mark a certain field as debug only and discard everything that has to do with that field completely when publishing. I understand this might get one in trouble when using fields like that and using that in critical parts of the code. But i often find myself initializing a lot of debug fields then comment them out which results in errors down the line if i do not comment those out as well. So is there some way to handle this in a better and more efficient way?

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• How to provide global functionality in multi-user database app

  - by Mike B

  I have been building a multi-user database application (in C#/WPF 4.0) that manages tasks for all employees of a company. I now need to add some functionality such as sending an email reminder to someone when a critical task is due. How should this be done? Obviously I don’t want every instance of the program to be performing this function (Heh each user would get 10+ emails). Should I add the capability to the application as a "Mode" and then run a copy on the database server in this mode or would it be better to create a new app altogether to perform "Global" type tasks? Is there a better way?

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• rsync useful w/ encrypted files?

  - by barrycarter

  Is rsync efficient for transferring encrypted files? More specifically: I encrypt 'x' with my public key and call the result 'y'. I rsync 'y' to my backup server. 'x' changes slightly I encrypt the modified 'x' and rsync the modified 'y' to my backup server. Is this efficient? I know a small change in 'x' yields a large change in 'y', but is the change localized? Or has 'y' changed so thoroughly that rsync is not much better than scp? I currently backup my "critical" files by tarring/bzipping them nightly, then encrypting the .tar.bz file and rsync'ing it to my backup server. Many of the individual files don't change, but, of course, the tar file changes if even one of the files change. Is this efficient? Should I be encrypting and backing up each file individually? That way, unchanged files will take no time to rsync.

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• Will this make the object thread-safe?

  - by sharptooth

  I have a native Visual C++ COM object and I need to make it completely thread-safe to be able to legally mark it as "free-threaded" in th system registry. Specifically I need to make sure that no more than one thread ever accesses any member variable of the object simultaneously. The catch is I'm almost sure that no sane consumer of my COM object will ever try to simultaneously use the object from more than one thread. So I want the solution as simple as possible as long as it meets the requirement above. Here's what I came up with. I add a mutex or critical section as a member variable of the object. Every COM-exposed method will acquire the mutex/section at the beginning and release before returning control. I understand that this solution doesn't provide fine-grained access and this might slow execution down, but since I suppose simultaneous access will not really occur I don't care of this. Will this solution suffice? Is there a simpler solution?

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• Push a variable into global scope?

  - by Spot

  We use instantiate and put system critical objects in $GLOBALS for easy access from anywhere (e.g. DB, Cache, User, etc.). We use $GLOBALS so much that it would (yes, really) drop the amount of code quite a bit if I could reference it like $G = &$GLOBALS for a shorthand call. The problem is that, per my experience and several hours of Googling, I have not found any construct in PHP which allows you to 'flag' a var as global, making $GLOBALS first class, and everything else second class. Am I missing something? Is this possible?

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• Optimization Techniques in Python

  - by fear-matrix

  Recently i have developed a billing application for my company with Python/Django. For few months everything was fine but now i am observing that the performance is dropping because of more and more users using that applications. Now the problem is that the application is now very critical for the finance team. Now the finance team are after my life for sorting out the performance issue. I have no other option but to find a way to increase the performance of the billing application. So do you guys know any performance optimization techniques in python that will really help me with the scalability issue

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• How to change size of STL container in C++

  - by Jaime Pardos

  I have a piece of performance critical code written with pointers and dynamic memory. I would like to rewrite it with STL containers, but I'm a bit concerned with performance. Is there a way to increase the size of a container without initializing the data? For example, instead of doing ptr = new BYTE[x]; I want to do something like vec.insert(vec.begin(), x, 0); However this initializes every byte to 0. Isn't there a way to just make the vector grow? I know about reserve() but it just allocates memory, it doesn't change the size of the vector, and doesn't allows me to access it until I have inserted valid data. Thank you everyone.

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• How to properly dispose of an object

  - by VoodooChild

  Hi Guys, I am experiencing something weird and have a workaround already, but I don't think I understood it well. If I call the Method below numerous times within a class: public void Method() { Foo a = new Foo(); a.Delegate1Handler = ViewSomething(); } So I am reinitializing "a" every time but for some reason a.Delegate1Handler is still around from the previous initialization, and therefore ViewSomething() is called again and again and again.... I feel like I am forgetting something critical here? Foo's guts look like: public delegate void Delegate1(T t); public Delegate1 Delegate1Handler { get; set; }

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• ASP.NET null reference exception

  - by nanek

  Please help me to figure out what is wrong with this code: I have ASP.NET page with one button visible. When user clicks it - it instances MyClass (its implementation is in AppCode directory) and turns invisible (button2 becomes visible). When I click button2 it raises "Object reference not set to an instance of an object" Exception. What seems to be the problem? { public MyClass noviTest; protected void Page_Load(object sender, EventArgs e) { } protected void Button1_Click(object sender, EventArgs e) { noviTest = new MyClass(TextBox1.Text); Button1.Visible = false; Button2.Visible = true; } protected void Button2_Click(object sender, EventArgs e) { Label1.Text=noviTest.getID; //this is the critical line } } Thank You in advance, Regards

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• what are your biggest complaints about TFS as source-control?

  - by jcollum

  I've used TFS for about 18 months now and I'm really not excited about it. It seems like the worst of the current versions of SCMs on the market. I think this thread will help people decide if TFS is for them vs. other source control systems. While TFS does a lot more than that, I think that source control is so critical to software development that any system (or combination thereof) that you pick needs to consider source control first. So, feel free to sound off. Maybe it'll make us feel better and be informative at the same time.

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• Persistent SQL Table lock from C#

  - by Chris

  I'm trying to create a persistent SQL (SQL Server 2005) lock on a table level. I'm not updating/querying the specified table, but I need to prevent a third party application from updating the locked table as a means to prevent transactions from being posted (the table I wish to lock is the key on their transaction that interferes with my processing). From my experience the table is only locked for the time a specific transaction is taking place. Any ideas? The 3rd party developer has logged this feature as an enhancement, but since they are in the middle of rolling out a major release I can expect to wait at least 6 months for this. I know that this isn't a great solution, since their software will fall over but it is of a critical enough nature that we're willing to live with the consequences.

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• iOS Development: Should the "playersToInvite" property contain an array of strings or an array of GKPlayer objects?

  - by BeachRunnerJoe

  Should the playersToInvite property of the GKMatchRequest object contain an array of NSString objects that hold the player id's or should it contain an array of GKPlayer objects? The documentation on this critical property is not clear at all and I've tried both ways, but my code isn't working, so I can't tell by experimentation. Here's the description for that property in the docs... A list of players to invite to the match. Why did they even bother writing that? Thanks for your help!

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• What are the latest options in Java logging frameworks?

  - by sanity

  This question gets asked periodically, but I've long felt that existing Java logging frameworks were overcomplicated and over-engineered, and I want to see what's new. I have a more critical issue on my current project as we've standardized on JSON as our human-readable data encoding, and most logging frameworks I've seen require XML. I would really rather avoid using JSON for 95% of my apps configuration, and XML for the rest just because of the logging framework (truth be told, I hate XML used for anything other than text markup, its original intended purpose). Are there any hot new Java logging frameworks that are actively maintained, reasonably powerful, have a maven repo, can be reconfigured without restarting your app, and don't tie you to XML?

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• Prevent log4net to send duplicate issues via SMTP

  - by jrEwing

  Hi, we have bridged our log4net with Jira using SMTP. Now we are worried that since the site is public what could happen to the Jira server if we get alot of issues in the production environment. We have already filtered on Critical and Fatal, but we want to see either some acumulator service on log4net or a plain filter which identifies repeating issues and prevents them from being sent via Email. Preferably without having to change the error reporting code, so a config solution would be best. I guess dumping the log into a db and then create a separate listener some smart code would be a (pricy) alternative.

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