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  • Are there any Python reference counting/garbage collection gotchas when dealing with C code?

    - by Jason Baker
    Just for the sheer heck of it, I've decided to create a Scheme binding to libpython so you can embed Python in Scheme programs. I'm already able to call into Python's C API, but I haven't really thought about memory management. The way mzscheme's FFI works is that I can call a function, and if that function returns a pointer to a PyObject, then I can have it automatically increment the reference count. Then, I can register a finalizer that will decrement the reference count when the Scheme object gets garbage collected. I've looked at the documentation for reference counting, and don't see any problems with this at first glance (although it may be sub-optimal in some cases). Are there any gotchas I'm missing? Also, I'm having trouble making heads or tails of the cyclic garbage collector documentation. What things will I need to bear in mind here? In particular, how do I make Python aware that I have a reference to something so it doesn't collect it while I'm still using it?

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  • How to reduce java concurrent mode failure and excessive gc

    - by jimx
    In Java, the concurrent mode failure means that the concurrent collector failed to free up enough memory space form tenured and permanent gen and has to give up and let the full stop-the-world gc kicks in. The end result could be very expensive. I understand this concept but never had a good comprehensive understanding of A) what could cause a concurrent mode failure and B) what's the solution?. This sort of unclearness leads me to write/debug code without much of hints in mind and often has to shop around those performance flags from Foo to Bar without particular reasons, just have to try. I'd like to learn from developers here how your experience is. If you had previous encountered such performance issue, what was the cause and how you addressed it? If you have coding recommendations, please don't be too general. Thanks!

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  • SqlLite for iPhone issues/bugs/problems ?

    - by jAmi
    Hey there, I am planning to develop an iPhone application heavily relying on sqlite DB , from different links I have gone through this seems to be a great tool and has some really good support. As my app is still in the planning process I would like to ask if there are any Issues with SQLlite database ? from memory management to Queries and data sizes and multiple access etc; Please share your experience using SQLite DB in iPhone and what problems did you face? I just want to make a note of these exceptions so that I may plan my App well and do not have any issues raised in the middle of the development process. Thanx for your contribution.

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  • What is a .NET managed module?

    - by Abhijeet Patel
    I know it's a Windows PE32, but I also know that the unit of deployment in .NET is an assembly which in turn has a manifest and can be made up of multiple managed modules. My questions are : 1) How would you create multiple managed modules when building a project such as a class lib or a console app etc. 2) Is there a way to specify this to the compiler(via the project properties for example) to partition your source code files into multiple managed modules. If so what is the benefit of doing so? 3)Can managed modules span assemblies? 4)Are separate file created on disk when the source code is compiled or are these created in memory and directly embedded in an assembly?

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  • Paging in ActiveRecord

    - by Alex
    Does CastleProject ActiveRecord support paging? I need to load only data which is now seen on the screen. If I use [HasMany], it will be loaded as a whole either immediately or at the first call (if lazy attribute is true). However I only need something like first 100 records (then maybe 100 next records). Another question is how to load only 100 items. If the collection is too big, memory can reach its limit if we constantly load more and more items.

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  • How should I deal with persisting an Android WebView if my activity gets destroyed while showing ano

    - by Shaun Crampton
    Hi, I'm building an Android application that's based around an enhanced WebView (based on PhoneGap). I've enhanced the WebView so that from JavaScript running inside you can invoke the native contact picker to choose a phone number (which may be supplied by Facebook for example). The problem I have is that the native contact picker runs in an activity in another process and the Android docs say that while another activity is open my activity may get destroyed due to memory constraints. I haven't actually seen this happen in my application but if it did then I'm guessing my WebView's state would be destroyed and the code that was waiting for the picked contact would be terminated. It seems a bit crazy that the activity requesting a contact could be destroyed while the contact picker is open. Does anyone know if that does indeed happen? Is there a way to persist the state of the WebView if it does? Thanks, -Shaun

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  • What interprocess locking calls should I monitor?

    - by Matt Joiner
    I'm monitoring a process with strace/ltrace in the hope to find and intercept a call that checks, and potentially activates some kind of globally shared lock. While I've dealt with and read about several forms of interprocess locking on Linux before, I'm drawing a blank on what to calls to look for. Currently my only suspect is futex() which comes up very early on in the process' execution. Update0 There is some confusion about what I'm after. I'm monitoring an existing process for calls to persistent interprocess memory or equivalent. I'd like to know what system and library calls to look for. I have no intention call these myself, so naturally futex() will come up, I'm sure many libraries will implement their locking calls in terms of this, etc. Update1 I'd like a list of function names or a link to documentation, that I should monitor at the ltrace and strace levels (and specifying which). Any other good advice about how to track and locate the global lock in mind would be great.

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  • Good reasons why to not use XIB files?

    - by mystify
    Are there any good reasons why I should not use XIB / NIB files with an highly customized UI and extensive animations and super low memory footprint needs? As a beginner I started with XIB. Then I figured out I couldn't do just about everything in them. It started to get really hard to customize things the way I wanted them to be. So at the end, I threw all my XIBs away and did it all programmatically. So when someone asks me if XIB is good, I generally say: Yeah, if you want to make crappy boring interfaces and don't care too much about performance, go ahead. But what else could be a reason not to use XIB? Am I the only iPhone developer who prefers doing everything programmatically for this reasons?

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  • MySQL ALTER TABLE on very large table - is it safe to run it?

    - by Timothy Mifsud
    I have a MySQL database with one particular MyISAM table of above 4 million rows. I update this table about once a week with about 2000 new rows. After updating, I then perform the following statement: ALTER TABLE x ORDER BY PK DESC i.e. I order the table in question by the primary key field in descending order. This has not given me any problems on my development machine (Windows with 3GB memory), but, even though 3 times I have tried it successfully on the production Linux server (with 512MB RAM - and achieving the resulted sorted table in about 6 minutes each time), the last time I tried it I had to stop the query after about 30 minutes and rebuild the database from a backup. I have started to wonder whether a 512MB server can cope with that statement (on such a large table) as I have read that a temporary table is created to perform the ALTER TABLE command?! And, if it can be safely run, what should be the expected time for the alteration of the table? Thanks in advance, Tim

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  • Create a Stream without having a physical file to create from.

    - by jhorton
    I'm needing to create a zip file containing documents that exist on the server. I am using the .Net Package class to do so, and to create a new Package (which is the zip file) I have to have either a path to a physical file or a stream. I am trying to not create an actual file that would be the zip file, instead just create a stream that would exist in memory or something. My question is how do you instantiate a new Stream (i.e. FileStream, MemoryStream, etc) without having a physical file to instantiate from.

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  • Why does Java not have any destructor like C++?

    - by Abhishek Jain
    Java has its own garbage collection implementation so it does not require any destructor like C++ . This makes Java developer lazy in implementing memory management. And Garbage Collection is very expensive. Still we can have destructor along with garbage collector where developer can free resources and which can save garbage collector's work. This might improves the performance of application. Why does Java not provide any destructor kind of mechanism? Developer does not have control over GC but he/she can control or create object. Then why not give them ability to destruct the objects?

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  • vector<vector<largeObject>> vs. vector<vector<largeObject>*> in c++

    - by Leif Andersen
    Obviously it will vary depending on the compiler you use, but I'm curious as to the performance issues when doing vector<vector<largeObject>> vs. vector<vector<largeObject>*>, especially in c++. In specific: let's say that you have the outer vector full, and you want to start inserting elements into first inner vector. How will that be stored in memory if the outer vector is just storing pointers, as apposed to storing the whole inner vector. Will the whole outer vector have to be moved to gain more space, or will the inner vector be moved (assuming that space wasn't pre-allocated), causing problems with the outer vector? Thank you

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  • Inspection of Insert Statement When Using LINQ's SubmitChanges

    - by Code Sherpa
    Hi. I want to see what my insert statement would look like as if I was wiring up an text-based ADO.NET command. How do I do this? I have been following the below link: http://damieng.com/blog/2008/07/30/linq-to-sql-log-to-debug-window-file-memory-or-multiple-writers And have added the DebugTextWriter class to my project. So, now, in my code I have the following which doesn't really do anything and I don't think its right: using(WorkbookDataContext dc = _conn.GetContext()) { if(profile.ProfileId > 0) { dc.Profiles.Attach(profile, true); } else { dc.Profiles.InsertOnSubmit(profile); } dc.Log = new DebugTextWriter(); #if DEBUG dc.Log = new System.IO.StreamWriter("linq-to-sql.log") { AutoFlush = true }; #endif dc.SubmitChanges(); } Any ideas what I am doing wrong and/or how to inspect my LINQ insert statement correctly? Thanks

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  • Low cost way to host a large table yet keep the performance scalable?

    - by Leo Liang
    I have a growing table storing time series data, 500M entries now, and 200K new records every day. The total size is around 15GB for now. My clients are querying the table via a PHP script mostly, and the size of the result set is around 10K records (not very large). select * from T where timestamp > X and timestamp < Y and additionFilters And I want this operation cheap. Currently my table is hosting in Postgres 7, on a single 16G memory Box, and I would love to see some good suggestion for me to host this in low cost and also allow me to scale up for performance if needed. The table serves: 1. Query: 90% 2. Insert: 9.9% 2. Update: 0.1% <-- very rare.

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  • Why might different computers calculate different arithmetic results in VB.NET?

    - by Eyal
    I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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  • About enumerations in Delphi and c++ in 64-bit environments

    - by sum1stolemyname
    I recently had to work around the different default sizes used for enumerations in Delphi and c++ since i have to use a c++ dll from a delphi application. On function call returns an array of structs (or records in delphi), the first element of which is an enum. To make this work, I use packed records (or aligned(1)-structs). However, since delphi selects the size of an enum-variable dynamically by default and uses the smallest datatype possible (it was a byte in my case), but C++ uses an int for enums, my data was not interpreted correctly. Delphi offers a compiler switch to work around this, so the declaration of the enum becomes {$Z4} TTypeofLight = ( V3d_AMBIENT, V3d_DIRECTIONAL, V3d_POSITIONAL, V3d_SPOT ); {$Z1} My Questions are: What will become of my structs when they are compiled on/for a 64-bit environment? Does the default c++ integer grow to 8 Bytes? Are there other memory alignment / data type size modifications (other than pointers)?

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  • CPU/GPU Monitering. (Tempature, current speed, etc) in C#

    - by Tommy
    Im looking for a way to moniter system statistics, here are my main points of interest: CPU Tempature CPU speed, (Cycles per second) CPU Load (Idle percent) GPU Tempature Some other points of interest: Memory useage Network Load (Traffic Up/Down) My ultimate goal is to write an application that can be used for easily running in the backround, and allow setting many events fr certain actions, for instance When processer temp gets to 56C -> Do _Blank_ etc. So this leaves me two main points. Is there a framework already out there for this sort of thing? If No to #1, How can i go about doing this?

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  • scala REPL is slow on vista

    - by Jacques René Mesrine
    I installed scala-2.8.0.RC3 by extracting the tgz file into my cygwin (vista) home directory. I made sure to set $PATH to scala-2.8.0.RC3/bin. I start the REPL by typing: $ scala Welcome to Scala version 2.8.0.RC3 (Java HotSpot(TM) Client VM, Java 1.6.0_20). Type in expressions to have them evaluated. Type :help for more information. scala> Now when I tried to enter an expression scala> 1 + 'a' the cursor hangs there without any response. Granted that I have chrome open with a million tabs and VLC playing in the background, but CPU utilization was 12% and virtual memory was about 75% utilized. What's going on ? Do I have to set the CLASSPATH or perform other steps.

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  • How can I change how OS X's 'say' command pronounces a word?

    - by jwhitlock
    OS X's say command is useful for some tasks (such as Skype's 'notify me when a contact comes online), but it is pronouncing some names incorrectly. Is there a way to teach say to pronounce a word differently? For example, try: say "Hi, Joel Spolsky" The 'ol' sounds like 'ball' rather than 'old'. I'd like to add an exception that say "Pronounce Spolsky like this", rather than try to teach new linguistic rules. I bet there is a way since it can pronounce "iphone" as Apple wants. Update - After some research, here's what I've learned: Text-to-speech is split between turning the text to phonemes, and then the phonemes are turned into audio using a voice. Changing the voice doesn't effect the phonemes. The Speech Synthesis Manager has some functions for turning text to phonemes, and a method for registering a speech dictionary that will add new text-phoneme maps. However, Apple's speech dictionary must be in a binary form - I didn't find any plist XML. Using dtrace while running say, I found some interesting files opened in /System/Library/PrivateFrameworks/SpeechDictionary.framework/Resources. This is probably the speech dictionary, but they are all binary, except for Homophones, which is XML. Adding entries to Homophones does nothing - it is probably used in speech-to-text. They are also code signed by Apple - changing them may prevent some programs from working. PrefixDictionary CartNames CartLite SymbolDictionary Homophones There are ways to add text versions of application interface elements so VoiceOver works, a lot of which a developer gets for free, but there are tricky bits. The standard here appears to be to use a phonetic spelling as needed. My guesses are: say is a light layer of code on top of the Speech Synthesis Manager. It would be easy for the Apple devs to add a command line option to take the path to a speech dictionary plist for alternate phoneme mapping, but they didn't. It may be a useful open-source project to write a better say. Skype probably uses Speech Synthesis Manager directly, leaving no hooks to change the way my friend's names are pronounced, other than spelling them phonetically, which is silly. The easiest way to make a command line version of say is how JRobert suggested. Here's my quick implementation, using Doug Harris's spelling suggestion: #!/bin/sh echo $@ | tr '[A-Z]' '[a-z]' | sed "s/spolsky/spowlsky/g" | /usr/bin/say Finally, some fun command line stuff: # Apple is weird sqlite3 /System/Library/PrivateFrameworks/SpeechDictionary.framework/Resources/Tuples .dump # Get too much information about what files are being opened sudo dtrace -n 'syscall::open*:entry { printf("%s %s",execname,copyinstr(arg0)); }' # Just fun say -v bad "Joel Spolsky Spolsky Spolsky Spolsky Spolsky, Joel Spolsky Spolsky Spolsky Spolsky Spolsky" echo "scale=1000; 4*a(1)" | bc -l | say

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  • handling the logout functionality on the iPhone

    - by Nanz
    This is the first iPhone application i am working on. To use the application, the user has to login to our server. I am done with that part. Now the problem i am facing is how to logout the user from the server, deallocate all the memory and start afresh without quitting the app. After the user logs out, i want the exact same things to happen as in applicationdidfinishlaunching method. But i dont know how to go about it. The app has a tab bar which is set up in mainWindow.xib.

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  • Clone LINQ To SQL object Extension Method throws object dispose exception....

    - by gtas
    Hello all, I have this extension method for cloning my LINQ To SQL objects: public static T CloneObjectGraph<T>(this T obj) where T : class { var serializer = new DataContractSerializer(typeof(T), null, int.MaxValue, false, true, null); using (var ms = new System.IO.MemoryStream()) { serializer.WriteObject(ms, obj); ms.Position = 0; return (T)serializer.ReadObject(ms); } } But while i carry objects with not all references loaded, while qyuerying with DataLoadOptions, sometimes it throws the object disposed exception, but thing is I don't ask for references that is not loaded (null). e.g. I have Customer with many references and i just need to carry on memory the Address reference EntityRef< and i don't Load anything else. But while i clone the object this exception forces me to load all the EntitySet< references with the Customer object, which might be too much and slow down the application speed. Any suggestions?

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  • translating ROI code in c#

    - by sayyad
    Hi, I am trying to translate this code in c# using emgucv. I have some questions.Could yome body help me line by line. cvSetImageROI(img1, cvRect(10, 15, 150, 250)); I have four points (PoinstF). Should I calculate rectangle or there is some way with four points. CvInvoke.cvSetImageROI(img1, ------------(how can I declare cvReCt(10, 15, 150, 250)); //c# IplImage *img2 = cvCreateImage(cvGetSize(img1), img1-depth, img1-nChannels); //c# Image img2; // i supose i needn't to allocate memory.//c# cvCopy(img1, img2, NULL); CvInvoke.cvCopy(img1, img2, IntPtr.Zero);//c# cvResetImageROI(img1); shoul i ResetImageROI.//c# thanx and best regards,

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  • addObjectsFromArray

    - by derek.lo
    I have a question about memory management when using the addObjectsFromArray method. Basically, I have 2 arrays defined in the appDelegate. I need these 2 arrays for the duration of my application's runtime. I therefore release them in my appDelegate's dealloc method. When I go to use these two arrays in a class, I want one array to store the values from the other, so that the other can have it's contents removed, but still stick around for use. Something like this: [appDelegate.arrayTwo addObjectsFromArray:appDelegate.arrayOne]; [appDelegate.arrayOne removeAllObjects]; I'm getting the compiler error: EXC_BAD_ACCESS because of a pointer issue? retaining issue? Any help would be greatly appreciated! Thanks

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  • Cannot Translate to SQL using Select(x => Func(x))

    - by Dan
    I'm slowly learning the ins and outs of LINQtoSQL, but this is confusing me. Here is the statement I have: IQueryable<IEvent> events = (from e in db.getEvents() select e).Select(x => SelectEvent(x, null)); What the SelectEvent does can be explained in this answer here. I am not using the .toList() function as I don't want potentially thousands of records brought into memory. public IEvent SelectEvent(SqlServer.Event ev, EventType? type) { // Create an object which implements IEvent // I don't have the code in front of me, so forgive the lack of code } My question is really for the Select() method. I get the "Cannot translate to SQL" error and the Select() is listed in the error message. Clueless on this one :-/.

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  • Why does SQL Server keep throwing exceptions?

    - by Augusto Càzares
    I have my project in .NET that uses a database in SQL Server. I'm using Linq-to-SQL, sometimes when the project throws me an exception (Constraint) in a part of the project this same error keeps showing in other part of the project when I do another thing with the database. Like when I do an insertion and I had before an exception on delete the insertion throws me the delete exception, and it remains this way until I close and open again the project. My major problem is when this happen in my online project, this error in my project causes me problems in the project I'm testing online (I use the same database). I don't know if this exception is on the memory or something but its have been causing me a lot of headaches.

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