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• To convert PyBytesObject type to PyUnicodeObject type in python3

  - by sam

  How to convert pyunicodeobject type to pybytesobject type? Example: function(PyBytesObject* byteobj){ ....operation.. } PyUnicodeObject* Uniobj; function((PyBytesObject*) Uniobj); got a bus error as a result.

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• twython search api rate limit: Header information will not be updated

  - by user2715478

  I want to handle the Search-API rate limit of 180 requests / 15 minutes. The first solution I came up with was to check the remaining requests in the header and wait 900 seconds. See the following snippet: results = search_interface.cursor(search_interface.search, q=k, lang=lang, result_type=result_mode) while True: try: tweet = next(results) if limit_reached(search_interface): sleep(900) self.writer(tweet) def limit_reached(search_interface): remaining_rate = int(search_interface.get_lastfunction_header('X-Rate-Limit-Remaining')) return remaining_rate <= 2 But it seems, that the header information are not reseted to 180 after it reached the two remaining requests. The second solution I came up with was to handle the twython exception for rate limitation and wait the remaining amount of time: results = search_interface.cursor(search_interface.search, q=k, lang=lang, result_type=result_mode) while True: try: tweet = next(results) self.writer(tweet) except TwythonError as inst: logger.error(inst.msg) wait_for_reset(search_interface) continue except StopIteration: break def wait_for_reset(search_interface): reset_timestamp = int(search_interface.get_lastfunction_header('X-Rate-Limit-Reset')) now_timestamp = datetime.now().timestamp() seconds_offset = 10 t = reset_timestamp - now_timestamp + seconds_offset logger.info('Waiting {0} seconds for Twitter rate limit reset.'.format(t)) sleep(t) But with this solution I receive this message INFO: Resetting dropped connection: api.twitter.com" and the loop will not continue with the last element of the generator. Have somebody faced the same problems? Regards.

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• How can I make a universal construction more efficient?

  - by VF1

  A "universal construction" is a wrapper class for a sequential object that enables it to be linearized (a strong consistency condition for concurrent objects). For instance, here's an adapted wait-free construction, in Java, from [1], which presumes the existence of a wait-free queue that satisfies the interface WFQ (which only requires one-time consensus between threads) and assumes a Sequential interface: public interface WFQ<T> // "FIFO" iteration { int enqueue(T t); // returns the sequence number of t Iterable<T> iterateUntil(int max); // iterates until sequence max } public interface Sequential { // Apply an invocation (method + arguments) // and get a response (return value + state) Response apply(Invocation i); } public interface Factory<T> { T generate(); } // generate new default object public interface Universal extends Sequential {} public class SlowUniversal implements Universal { Factory<? extends Sequential> generator; WFQ<Invocation> wfq = new WFQ<Invocation>(); Universal(Factory<? extends Sequential> g) { generator = g; } public Response apply(Invocation i) { int max = wfq.enqueue(i); Sequential s = generator.generate(); for(Invocation invoc : wfq.iterateUntil(max)) s.apply(invoc); return s.apply(i); } } This implementation isn't very satisfying, however, since it presumes determinism of a Sequential and is really slow. I attempted to add memory recycling: public interface WFQD<T> extends WFQ<T> { T dequeue(int n); } // dequeues only when n is the tail, else assists other threads public interface CopyableSequential extends Sequential { CopyableSequential copy(); } public class RecyclingUniversal implements Universal { WFQD<CopyableSequential> wfqd = new WFQD<CopyableSequential>(); Universal(CopyableSequential init) { wfqd.enqueue(init); } public Response apply(Invocation i) { int max = wfqd.enqueue(i); CopyableSequential cs = null; int ctr = max; for(CopyableSequential csq : wfq.iterateUntil(max)) if(--max == 0) cs = csq.copy(); wfqd.dequeue(max); return cs.apply(i); } } Here are my specific questions regarding the extension: Does my implementation create a linearizable multi-threaded version of a CopyableSequential? Is it possible extend memory recycling without extending the interface (perhaps my new methods trivialize the problem)? My implementation only reduces memory when a thread returns, so can this be strengthened? [1] provided an implementation for WFQ<T>, not WFQD<T> - one does exist, though, correct? [1] Herlihy and Shavit, The Art of Multiprocessor Programming.

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• What constitutes proper use of threads in programming?

  - by Smith

  I am tired of hearing people recommend that you should use only one thread per process, while many programs use up to 100 per process! take for example some common programs vb.net ide uses about 25 thread when not debugging System uses about 100 chrome uses about 19 Avira uses more than about 50 Any time I post a thread related question, I am reminded almost every time that I should not use more that one thread per process, and all the programs I mention above are ruining on my system with a single processor. What constitutes proper use of threads in programming? Please make general comment, but I'd prefer .NET framework thanks EDIT changed processor to process

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• Using Interlocked.Exchange(ref Enum, 1) to prevent re-entrancy [migrated]

  - by makerofthings7

  What options do I have for pending work that can't acquire a lock via the following sample? System.Threading.Interlocked.CompareExchange<TrustPointStatusEnum> (ref tp.TrustPointStatus, TrustPointStatusEnum.NotInitalized,TrustPointStatusEnum.Loading); Based on my research think I have the following options: I can use Threading.SpinWait (for very quick IO tasks) at the cost of CPU I can use Sleep() which has an unreliable wake up time I'm not sure of any other option, but what I want to make sure of is that all these options work with the .NET 4 async and await keywords, especially if I use Task to run them on a background thread

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• Alternatives to Pessimistic Locking in Cluster Applications

  - by amphibient

  I am researching alternatives to database-level pessimistic locking to achieve transaction isolation in a cluster of Java applications going against the same database. Synchronizing concurrent access in the application tier is clearly not a solution in the present configuration because the same database transaction can be invoked from multiple JVMs concurrently. Currently, we are subject to occasional race conditions which, due to the optimistic locking we have in place via Hibernate, cause a StaleObjectStateException exception and data loss. I have a moderately large transaction within the scope of my refactoring project. Let's describe it as updating one top-level table row and then making various related inserts and/or updates to several of its child entities. I would like to insure exclusive access to the top-level table row and all of the children to be affected but I would like to stay away from pessimistic locking at the database level for performance reasons mostly. We use Hibernate for ORM. Does it make sense to start a single (perhaps synchronous) message queue application into which this method could be moved to insure synchronized access as opposed to each cluster node using its own, which is a clear race condition hazard? I am mentioning this approach even though I am not confident in it because both the top-level table row and its children could also be updated from other system calls, not just the mentioned transaction. So I am seeking to design a solution where the top-level table row and its children will all somehow be pseudo-locked (exclusive transaction isolation) but at the application and not the database level. I am open to ideas and suggestions, I understand this is not a very cut and dried challenge.

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• How to use OpenGL functions from multiples thread?

  - by Robert

  I'm writing a small game using OpenGL. I'm implementing basic networking in this game and I'm facing a problem. I have a thread in my client socket class that check for available data, when there are data I raise an event like this : immutable int len = this.m_socket.receive(data); if(len > 0) { this.m_onDataEvent(data); } Then on my game class, I have a function that handle and parse data like this : switch(msgId) { case ProtocolID.CharacterData: // Load terrain with opengl, character model.... Im not able to call opengl functions because my opengl context is created from a different thread. But I really don't know how I can solve this problem, I tried Google but it's really hard to find a solution. I'm using D programming language if it can help.

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• Is this a good use for ThreadPool.QueueUserWorkItem?

  - by Matt Grande

  I have an application that, among other things, imports documents, then emails necessary parties to let them know that a document has been imported. It turns out that determining whom to email, then performing the emailing, is what's taking the longest. I was thinking of doing something like this: var document = ImportDocument(); ThreadPool.QueueUserWorkItem(s => SendEmail(document.Id)); return document; ... similar to DelayedJob in Rails, if that helps. Does that make sense in this context? What would you do?

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• Discussion of a Distributed Data Storage implementation

  - by fegol

  I want to implement a distributed data storage using a client/server architecture. Each data item will be stored persistently in disk in one of several remote servers. The client uses a library to update and query the data, shielding the client from its actual location. This should allow a client to associate keys (String) to values(byte[]), much as a Map does. The system must ensure that the amount of data stored in each server is approximately the same. The set of servers is known beforehand by other servers and clients. Both the client and the server will be written in Java, using sockets, threads, and files. I open this topic with the objective of discussing the best way to implement this idea, assuming simplicity, what are the issues of this implementation, performance measurements and discussion of the limitations.

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• Converting the value from string to integer in a nested dictionary

  - by tom smith

  I want to change the numbers in my dictionary to int values for use later in my program. So far I have import time import math x = 400 y = 300 def read_next_object(file): obj = {} for line in file: if not line.strip(): continue line = line.strip() key, val = line.split(": ") if key in obj and key == "Object": yield obj obj = {} obj[key] = val yield obj planets = {} with open( "smallsolar.txt", 'r') as f: for obj in read_next_object(f): planets[obj["Object"]] = obj print(planets) scale=250/int(max([planets[x]["Orbital Radius"] for x in planets if "Orbital Radius" in planets[x]])) print(scale) and the output is {'Sun': {'Object': 'Sun', 'Satellites': 'Mercury,Venus,Earth,Mars,Jupiter,Saturn,Uranus,Neptune,Ceres,Pluto,Haumea,Makemake,Eris', 'Orbital Radius': '0', 'RootObject': 'Sun', 'Radius': '20890260'}, 'Moon': {'Object': 'Moon', 'Orbital Radius': '18128500', 'Period': '27.321582', 'Radius': '1737000.10'}, 'Earth': {'Object': 'Earth', 'Satellites': 'Moon', 'Orbital Radius': '77098290', 'Period': '365.256363004', 'Radius': '6371000.0'}} 3.2426140709476178e-06 I want to be able to convert the numbers in the dict to ints for further use. Any help in greatly appreciated.

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• cant download youtube video

  - by dsaccount1

  I'm having trouble retrieving the youtube video automatically, heres the code. The problem is the last part. download = urllib.request.urlopen(download_url).read() # Youtube video download script # 10n1z3d[at]w[dot]cn import urllib.request import sys print("\n--------------------------") print (" Youtube Video Downloader") print ("--------------------------\n") try: video_url = sys.argv[1] except: video_url = input('[+] Enter video URL: ') print("[+] Connecting...") try: if(video_url.endswith('&feature=related')): video_id = video_url.split('www.youtube.com/watch?v=')[1].split('&feature=related')[0] elif(video_url.endswith('&feature=dir')): video_id = video_url.split('www.youtube.com/watch?v=')[1].split('&feature=dir')[0] elif(video_url.endswith('&feature=fvst')): video_id = video_url.split('www.youtube.com/watch?v=')[1].split('&feature=fvst')[0] elif(video_url.endswith('&feature=channel_page')): video_id = video_url.split('www.youtube.com/watch?v=')[1].split('&feature=channel_page')[0] else: video_id = video_url.split('www.youtube.com/watch?v=')[1] except: print("[-] Invalid URL.") exit(1) print("[+] Parsing token...") try: url = str(urllib.request.urlopen('http://www.youtube.com/get_video_info?&video_id=' + video_id).read()) token_value = url.split('video_id='+video_id+'&token=')[1].split('&thumbnail_url')[0] download_url = "http://www.youtube.com/get_video?video_id=" + video_id + "&t=" + token_value + "&fmt=18" except: url = str(urllib.request.urlopen('www.youtube.com/watch?v=' + video_id)) exit(1) v_url=str(urllib.request.urlopen('http://'+video_url).read()) video_title = v_url.split('"rv.2.title": "')[1].split('", "rv.4.rating"')[0] if '&quot;' in video_title: video_title = video_title.replace('&quot;','"') elif '&amp;' in video_title: video_title = video_title.replace('&amp;','&') print("[+] Downloading " + '"' + video_title + '"...') try: print(download_url) file = open(video_title + '.mp4', 'wb') download = urllib.request.urlopen(download_url).read() print(download) for line in download: file.write(line) file.close() except: print("[-] Error downloading. Quitting.") exit(1) print("\n[+] Done. The video is saved to the current working directory(cwd).\n")

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• Why would Java app make RPC call to itself?

  - by amphibient

  I am working with a multithreaded homegrown multi-module app in my new job. We use the the Thrift protocol to communicate RPC calls between different stand-alone applications in a distributed system. One of them listens on multiple ports and I just noticed that it actually makes an RPC call to itself from one thread invoked from one socket it listens to (web service call) to another port within the same app. I verified that it could accomplish the same thing if it just went and directly called the method that the remote procedure ultimately invokes as it is all within the same application, same JVM. To make it even more mysterious, the call is completely synchronous, i.e. no callbacks involved. The first thread totally sits and waits until it makes a call across the wire to itself and comes back. Now, I am perplexed why anybody would do it this way. It seems like calling somebody on the phone that sits in the same room as you do. Can anybody provide an explanation why the developer before me would come up with the above mentioned model? Maybe there is a reason and I am missing something.

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• How to do thread management in C++?

  - by Dipan Mehta

  We use pthread for thread management in C based systems. pthread is in general compilable by C++ compiler (like g++). However, what are the better ways of abstractions for threads in C++? Also, for making any system to be working in a multi-threaded system, it is also important to make thread safe. What are the standard libraries that requires alternative (installs) to be thread safe or are they unsafe for multi-threaded environments? Is smart pointers, templates require special measures to make it safe? What are the best practices for the thread managements in C++?

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• Optimizing a thread safe Java NIO / Serialization / FIFO Queue [migrated]

  - by trialcodr

  I've written a thread safe, persistent FIFO for Serializable items. The reason for reinventing the wheel is that we simply can't afford any third party dependencies in this project and want to keep this really simple. The problem is it isn't fast enough. Most of it is undoubtedly due to reading and writing directly to disk but I think we should be able to squeeze a bit more out of it anyway. Any ideas on how to improve the performance of the 'take'- and 'add'-methods? /** * <code>DiskQueue</code> Persistent, thread safe FIFO queue for * <code>Serializable</code> items. */ public class DiskQueue<ItemT extends Serializable> { public static final int EMPTY_OFFS = -1; public static final int LONG_SIZE = 8; public static final int HEADER_SIZE = LONG_SIZE * 2; private InputStream inputStream; private OutputStream outputStream; private RandomAccessFile file; private FileChannel channel; private long offs = EMPTY_OFFS; private long size = 0; public DiskQueue(String filename) { try { boolean fileExists = new File(filename).exists(); file = new RandomAccessFile(filename, "rwd"); if (fileExists) { size = file.readLong(); offs = file.readLong(); } else { file.writeLong(size); file.writeLong(offs); } } catch (FileNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } channel = file.getChannel(); inputStream = Channels.newInputStream(channel); outputStream = Channels.newOutputStream(channel); } /** * Add item to end of queue. */ public void add(ItemT item) { try { synchronized (this) { channel.position(channel.size()); ObjectOutputStream s = new ObjectOutputStream(outputStream); s.writeObject(item); s.flush(); size++; file.seek(0); file.writeLong(size); if (offs == EMPTY_OFFS) { offs = HEADER_SIZE; file.writeLong(offs); } notify(); } } catch (IOException e) { throw new RuntimeException(e); } } /** * Clears overhead by moving the remaining items up and shortening the file. */ public synchronized void defrag() { if (offs > HEADER_SIZE && size > 0) { try { long totalBytes = channel.size() - offs; ByteBuffer buffer = ByteBuffer.allocateDirect((int) totalBytes); channel.position(offs); for (int bytes = 0; bytes < totalBytes;) { int res = channel.read(buffer); if (res == -1) { throw new IOException("Failed to read data into buffer"); } bytes += res; } channel.position(HEADER_SIZE); buffer.flip(); for (int bytes = 0; bytes < totalBytes;) { int res = channel.write(buffer); if (res == -1) { throw new IOException("Failed to write buffer to file"); } bytes += res; } offs = HEADER_SIZE; file.seek(LONG_SIZE); file.writeLong(offs); file.setLength(HEADER_SIZE + totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } /** * Returns the queue overhead in bytes. */ public synchronized long overhead() { return (offs == EMPTY_OFFS) ? 0 : offs - HEADER_SIZE; } /** * Returns the first item in the queue, blocks if queue is empty. */ public ItemT peek() throws InterruptedException { block(); synchronized (this) { if (offs != EMPTY_OFFS) { return readItem(); } } return peek(); } /** * Returns the number of remaining items in queue. */ public synchronized long size() { return size; } /** * Removes and returns the first item in the queue, blocks if queue is empty. */ public ItemT take() throws InterruptedException { block(); try { synchronized (this) { if (offs != EMPTY_OFFS) { ItemT result = readItem(); size--; offs = channel.position(); file.seek(0); if (offs == channel.size()) { truncate(); } file.writeLong(size); file.writeLong(offs); return result; } } return take(); } catch (IOException e) { throw new RuntimeException(e); } } /** * Throw away all items and reset the file. */ public synchronized void truncate() { try { offs = EMPTY_OFFS; file.setLength(HEADER_SIZE); size = 0; } catch (IOException e) { throw new RuntimeException(e); } } /** * Block until an item is available. */ protected void block() throws InterruptedException { while (offs == EMPTY_OFFS) { try { synchronized (this) { wait(); file.seek(LONG_SIZE); offs = file.readLong(); } } catch (IOException e) { throw new RuntimeException(e); } } } /** * Read and return item. */ @SuppressWarnings("unchecked") protected ItemT readItem() { try { channel.position(offs); return (ItemT) new ObjectInputStream(inputStream).readObject(); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } } }

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• Uses of persistent data structures in non-functional languages

  - by Ray Toal

  Languages that are purely functional or near-purely functional benefit from persistent data structures because they are immutable and fit well with the stateless style of functional programming. But from time to time we see libraries of persistent data structures for (state-based, OOP) languages like Java. A claim often heard in favor of persistent data structures is that because they are immutable, they are thread-safe. However, the reason that persistent data structures are thread-safe is that if one thread were to "add" an element to a persistent collection, the operation returns a new collection like the original but with the element added. Other threads therefore see the original collection. The two collections share a lot of internal state, of course -- that's why these persistent structures are efficient. But since different threads see different states of data, it would seem that persistent data structures are not in themselves sufficient to handle scenarios where one thread makes a change that is visible to other threads. For this, it seems we must use devices such as atoms, references, software transactional memory, or even classic locks and synchronization mechanisms. Why then, is the immutability of PDSs touted as something beneficial for "thread safety"? Are there any real examples where PDSs help in synchronization, or solving concurrency problems? Or are PDSs simply a way to provide a stateless interface to an object in support of a functional programming style?

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• Create a thread in xna Update method to find path?

  - by Dan

  I am trying to create a separate thread for my enemy's A* pathfinder which will give me a list of points to get to the player. I have placed the thread in the update method of my enemy. However this seems to cause jittering in the game every-time the thread is called. I have tried calling just the method and this works fine. Is there any way I can sort this out so that I can have the pathfinder on its own thread? Do I need to remove the thread start from the update and start it in the constructor? Is there any way this can work. Here is the code at the moment: bool running = false; bool threadstarted; System.Threading.Thread thread; public void update() { if (running == false && threadstarted == false) { thread = new System.Threading.Thread(PathThread); //thread.Priority = System.Threading.ThreadPriority.Lowest; thread.IsBackground = true; thread.Start(startandendobj); //PathThread(startandendobj); threadstarted = true; } } public void PathThread(object Startandend) { object[] Startandendarray = (object[])Startandend; Point startpoint = (Point)Startandendarray[0]; Point endpoint = (Point)Startandendarray[1]; bool runnable = true; // Path find from 255, 255 to 0,0 on the map foreach(Tile tile in Map) { if(tile.Color == Color.Red) { if (tile.Position.Contains(endpoint)) { runnable = false; } } } if(runnable == true) { running = true; Pathfinder p = new Pathfinder(Map); pathway = p.FindPath(startpoint, endpoint); running = false; threadstarted = false; } }

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• I am trying to use user-defined functions to print out an T out of stars, but i need help shifting t

  - by lm

  I know main() and other parts of the prog are missing, but please help def horizLine(col): for cols in range(col): print("*", end='') print() def line(col): #C,E,F,G,I,L,P,T for col in range(col//2): print("*", end='') print() def functionT(width): horizLine(width) line(width) enter width for the box width = int(input("Enter a width between 5 and 20: ")) letter=input("Enter one of the capital letters: T ") if ((width >= 5 and width <=20)): if letter=="T": functionT(width) else: print() print("Invalid letter!") else: print("You have entered a wrong range for the width!") main()

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• Why eclipse + pydev print() output look strange with two strings?

  - by srisar

  hay all, I just did the following: a = input("give a word: ") b = input("give another word: ") c = a + " " + b print("result is", c) and get the output as follows: give a word: name give another word: word result is name word my question is why the output on pydev or eclipse console in two lines? i expected to output as follows: give a word: name give another word: word result is name word how and why this happens to me? on cmd its looking fine??!!

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• Django logs: any tutorial to log to a file

  - by Algorist

  Hi, I am working with a django project, I haven't started. The developed working on the project left. During the knowledge transfer, it was told to me that all the events are logged to the database. I don't find the database interface useful to search for logs and sometimes they don't even log(I might be wrong). I want to know, if there is an easy tutorial that explains how to enable logging in Django with minimal configuration changes. Thank you Bala

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• Why does Zend discourage "floating functions"?

  - by kojiro

  Zend's Coding Standard Naming Convention says Functions in the global scope (a.k.a "floating functions") are permitted but discouraged in most cases. Consider wrapping these functions in a static class. The common wisdom in Python says practically the opposite: Finally, use staticmethod sparingly! There are very few situations where static-methods are necessary in Python, and I've seen them used many times where a separate "top-level" function would have been clearer. (Not only does the above StackOverflow answer warn against overuse of static methods, but more than one Python linter will warn the same.) Is this something that can be generalized across programming languages, and if so, why does Python differ so from PHP? If it's not something that can be generalized, what is the basis for one approach or the other, and is there a way to immediately recognize in a language whether you should prefer bare functions or static methods?

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• Using fft2 with reshaping for an RGB filter

  - by Mahmoud Aladdin

  I want to apply a filter on an image, for example, blurring filter [[1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0]]. Also, I'd like to use the approach that convolution in Spatial domain is equivalent to multiplication in Frequency domain. So, my algorithm will be like. Load Image. Create Filter. convert both Filter & Image to Frequency domains. multiply both. reconvert the output to Spatial Domain and that should be the required output. The following is the basic code I use, the image is loaded and displayed as cv.cvmat object. Image is a class of my creation, it has a member image which is an object of scipy.matrix and toFrequencyDomain(size = None) uses spf.fftshift(spf.fft2(self.image, size)) where spf is scipy.fftpack and dotMultiply(img) uses scipy.multiply(self.image, image) f = Image.fromMatrix([[1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0]]) lena = Image.fromFile("Test/images/lena.jpg") print lena.image.shape lenaf = lena.toFrequencyDomain(lena.image.shape) ff = f.toFrequencyDomain(lena.image.shape) lenafm = lenaf.dotMultiplyImage(ff) lenaff = lenafm.toTimeDomain() lena.display() lenaff.display() So, the previous code works pretty well, if I told OpenCV to load the image via GRAY_SCALE. However, if I let the image to be loaded in color ... lena.image.shape will be (512, 512, 3) .. so, it gives me an error when using scipy.fttpack.ftt2 saying "When given, Shape and Axes should be of same length". What I tried next was converted my filter to 3-D .. as [[[1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0]], [[1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0]], [[1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0], [1/9.0, 1/9.0, 1/9.0]]] And, not knowing what the axes argument do, I added it with random numbers as (-2, -1, -1), (-1, -1, -2), .. etc. until it gave me the correct filter output shape for the dotMultiply to work. But, of course it wasn't the correct value. Things were totally worse. My final trial, was using fft2 function on each of the components 2-D matrices, and then re-making the 3-D one, using the following code. # Spiltting the 3-D matrix to three 2-D matrices. for i, row in enumerate(self.image): r.append(list()) g.append(list()) b.append(list()) for pixel in row: r[i].append(pixel[0]) g[i].append(pixel[1]) b[i].append(pixel[2]) rfft = spf.fftshift(spf.fft2(r, size)) gfft = spf.fftshift(spf.fft2(g, size)) bfft = spf.fftshift(spf.fft2(b, size)) newImage.image = sp.asarray([[[rfft[i][j], gfft[i][j], bfft[i][j]] for j in xrange(len(rfft[i]))] for i in xrange(len(rfft))] ) return newImage Any help on what I made wrong, or how can I achieve that for both GreyScale and Coloured pictures.

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• Concurrency pattern of logger in multithreaded application

  - by Dipan Mehta

  The context: We are working on a multi-threaded (Linux-C) application that follows a pipeline model. Each module has a private thread and encapsulated objects which do processing of data; and each stage has a standard form of exchanging data with next unit. The application is free from memory leak and is threadsafe using locks at the point where they exchange data. Total number of threads is about 15- and each thread can have from 1 to 4 objects. Making about 25 - 30 odd objects which all have some critical logging to do. Most discussion I have seen about different levels as in Log4J and it's other translations. The real big questions is about how the overall logging should really happen? One approach is all local logging does fprintf to stderr. The stderr is redirected to some file. This approach is very bad when logs become too big. If all object instantiate their individual loggers - (about 30-40 of them) there will be too many files. And unlike above, one won't have the idea of true order of events. Timestamping is one possibility - but it is still a mess to collate. If there is a single global logger (singleton) pattern - it indirectly blocks so many threads while one is busy putting up logs. This is unacceptable when processing of the threads are heavy. So what should be the ideal way to structure the logging objects? What are some of the best practices in actual large scale applications? I would also love to learn from some of the real designs of large scale applications to get inspirations from!

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• Threading models when talking to hardware devices

  - by Fuzz

  When writing an interface to hardware over a communication bus, communications timing can sometimes be critical to the operation of a device. As such, it is common for developers to spin up new threads to handle communications. It can also be a terrible idea to have a whole bunch of threads in your system, an in the case that you have multiple hardware devices you may have many many threads that are out of control of the main application. Certainly it can be common to have two threads per device, one for reading and one for writing. I am trying to determine the pros and cons of the two different models I can think of, and would love the help of the Programmers community. Each device instance gets handles it's own threads (or shares a thread for a communication device). A thread may exist for writing, and one for reading. Requested writes to a device from the API are buffered and worked on by the writer thread. The read thread exists in the case of blocking communications, and uses call backs to pass read data to the application. Timing of communications can be handled by the communications thread. Devices aren't given their own threads. Instead read and write requests are queued/buffered. The application then calls a "DoWork" function on the interface and allows all read and writes to take place and fire their callbacks. Timing is handled by the application, and the driver can request to be called at a given specific frequency. Pros for Item 1 include finer grain control of timing at the communication level at the expense of having control of whats going on at the higher level application level (which for a real time system, can be terrible). Pros for Item 2 include better control over the timing of the entire system for the application, at the expense of allowing each driver to handle it's own business. If anyone has experience with these scenarios, I'd love to hear some ideas on the approaches used.

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• How can I use timer to stop another thread? [on hold]

  - by Haoda Fu

  How can we stop another thread based on a timer? I was trying to use timer to stop another thread. But I didn't got a success. To better illustrate my point and for your easy to understand the key issue. I made the following sample example. Your help is really appreciated using System; using System.Collections.Generic; using System.Text; using System.Threading; using System.Timers; namespace TestCodes { public static class Program { private static Thread nT = new Thread(PrintABC); private static System.Timers.Timer aTimer; public static void Main() { aTimer = new System.Timers.Timer(1000); aTimer.Elapsed += TimerCallback; aTimer.Interval = 1000; aTimer.Enabled = true; nT.Start(); Console.ReadLine(); } private static void TimerCallback(Object o, ElapsedEventArgs e) { nT.Join(); Console.WriteLine("Complete the PrintABC"); GC.Collect(); } private static void PrintABC() { for (int iter = 1; iter < 300; iter++) { Console.WriteLine(iter+"abc"); Console.ReadKey(); //Thread.Sleep(100); } } } }

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• Creating a voxel world with 3D arrays using threads

  - by Sean M.

  I am making a voxel game (a bit like Minecraft) in C++(11), and I've come across an issue with creating a world efficiently. In my program, I have a World class, which holds a 3D array of Region class pointers. When I initialize the world, I give it a width, height, and depth so it knows how large of a world to create. Each Region is split up into a 32x32x32 area of blocks, so as you may guess, it takes a while to initialize the world once the world gets to be above 8x4x8 Regions. In order to alleviate this issue, I thought that using threads to generate different levels of the world concurrently would make it go faster. Having not used threads much before this, and being still relatively new to C++, I'm not entirely sure how to go about implementing one thread per level (level being a xz plane with a height of 1), when there is a variable number of levels. I tried this: for(int i = 0; i < height; i++) { std::thread th(std::bind(&World::load, this, width, height, depth)); th.join(); } Where load() just loads all Regions at height "height". But that executes the threads one at a time (which makes sense, looking back), and that of course takes as long as generating all Regions in one loop. I then tried: std::thread t1(std::bind(&World::load, this, w, h1, h2 - 1, d)); std::thread t2(std::bind(&World::load, this, w, h2, h3 - 1, d)); std::thread t3(std::bind(&World::load, this, w, h3, h4 - 1, d)); std::thread t4(std::bind(&World::load, this, w, h4, h - 1, d)); t1.join(); t2.join(); t3.join(); t4.join(); This works in that the world loads about 3-3.5 times faster, but this forces the height to be a multiple of 4, and it also gives the same exact VAO object to every single Region, which need individual VAOs in order to render properly. The VAO of each Region is set in the constructor, so I'm assuming that somehow the VAO number is not thread safe or something (again, unfamiliar with threads). So basically, my question is two one-part: How to I implement a variable number of threads that all execute at the same time, and force the main thread to wait for them using join() without stopping the other threads? How do I make the VAO objects thread safe, so when a bunch of Regions are being created at the same time across multiple threads, they don't all get the exact same VAO? Turns out it has to do with GL contexts not working across multiple threads. I moved the VAO/VBO creation back to the main thread. Fixed! Here is the code for block.h/.cpp, region.h/.cpp, and CVBObject.h/.cpp which controls VBOs and VAOs, in case you need it. If you need to see anything else just ask. EDIT: Also, I'd prefer not to have answers that are like "you should have used boost". I'm trying to do this without boost to get used to threads before moving onto other libraries.

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