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• Parallelism in Python

  - by fmark

  What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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• Programmatic resource monitoring per process in Linux

  - by tuxx

  Hi, I want to know if there is an efficient solution to monitor a process resource consumption (cpu, memory, network bandwidth) in Linux. I want to write a daemon in C++ that does this monitoring for some given PIDs. From what I know, the classic solution is to periodically read the information from /proc, but this doesn't seem the most efficient way (it involves many system calls). For example to monitor the memory usage every second for 50 processes, I have to open, read and close 50 files (that means 150 system calls) every second from /proc. Not to mention the parsing involved when reading these files. Another problem is the network bandwidth consumption: this cannot be easily computed for each process I want to monitor. The solution adopted by NetHogs involves a pretty high overhead in my opinion: it captures and analyzes every packet using libpcap, then for each packet the local port is determined and searched in /proc to find the corresponding process. Do you know if there are more efficient alternatives to these methods presented or any libraries that deal with this problems?

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• Who Knows AppWeb HTTP Server And It's Embedded PHP?

  - by Andi

  Hi all, on my search for a fast but comfortable web server I dropped into the homepage of EmbedThis(TM) AppWeb(TM) HTTP server. This one has 2 licencse models, GPLv2 and a commercial one with support. On the first view it looks good: the footprint is not too big, it is fast and it has a lot of configuration otions. The most important thing would be a fast PHP execution using a built-in PHP library. Unfortunately this PHP library doesn't include every option, especially "gettext" which one I need for I18N. My target platform is Linux on an embedded device with an ARM based CPU. Does anybody have experiences with the issues mentioned above? Kind regards, Andi

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• How to clean sys.conversation_endpoints

  - by Manjoor

  I have a table, a trigger on the table implemented using service broker. More than Half million records are inserted daily into the table. The asynchronous SP is used to check sveral condition by using inserted data and update other tables. It was running fine for last 1 month and the SP was get executed withing 2-3 seconds of insertion of record. But now it take more than 90 minute. At present sys.conversation_endpoints have too much records. (Note that all the table are truncated daily as I do not need those records day after) Other database activities are normal (average 60% CPU Utilization). Now where i need to look?? I can re-create database without any problem but i don't think it is a good way to resolve the problem

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• Streaming audio - where to start?

  - by Adam Davis

  I need to develop an embedded audio streaming server. Requirements: Voice quality or better Intended for low power wifi transmission Broad support in existing software and devices (ie, windows media player, quicktime, vlc, iPhone, Android, etc). Royalty/patent free, or cheap to license Preferences: Low overhead TCP/IP based streaming protocol Voice grade codec (easy to implement in software, no DSP, 32bit CPU if needed) Would be nice if it supported HTML5 browsers, but is there any codec (such as raw) that is supported by the latest browsers that is lower overhead than MP3? Therefore: What are the relevant streaming protocols I should be looking at? What are the relevant codecs I should be looking at? What transport streams should I be looking at? What am I missing, or where else should I be looking for this type of need?

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• Branchless memory manager?

  - by Richard Fabian

  Anyone thought about how to write a memory manager (in C++) that is completely branch free? I've written a pool, a stack, a queue, and a linked list (allocating from the pool), but I am wondering how plausible it is to write a branch free general memory manager. This is all to help make a really reusable framework for doing solid concurrent, in-order CPU, and cache friendly development. Edit: by branchless I mean without doing direct or indirect function calls, and without using ifs. I've been thinking that I can probably implement something that first changes the requested size to zero for false calls, but haven't really got much more than that. I feel that it's not impossible, but the other aspect of this exercise is then profiling it on said "unfriendly" processors to see if it's worth trying as hard as this to avoid branching.

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• can't start MySql in Mac OS 10.6 Snow Leopard

  - by nacho4d

  I've googled this and could'nt find anything new and useful for Apple's new OS SnowLeopard. I wonder if this is my mistake or I do need to do something? this is what I did: Downloaded from mysql site: http://dev.mysql.com/downloads/mysql/5.1.html#macosx-dmg I choose : Mac OS X 10.5 (x86_64) I run all the packages and installed all of them. So now I certainly have mysql in /usr/local/mysql/ But when trying to start it from preferences panel, it is always STOPPED. When I try to do (in the terminal): /usr/local/mysql/bin/mysql I got : -bash: /usr/local/mysql/bin/mysql: Bad CPU type in executable What is wrong here? Any help would be very appreciated. Thanks

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• Watching a variable for changes without polling.

  - by milkfilk

  I'm using a framework called Processing which is basically a Java applet. It has the ability to do key events because Applet can. You can also roll your own callbacks of sorts into the parent. I'm not doing that right now and maybe that's the solution. For now, I'm looking for a more POJO solution. So I wrote some examples to illustrate my question. Please ignore using key events on the command line (console). Certainly this would be a very clean solution but it's not possible on the command line and my actual app isn't a command line app. In fact, a key event would be a good solution for me but I'm trying to understand events and polling beyond just keyboard specific problems. Both these examples flip a boolean. When the boolean flips, I want to fire something once. I could wrap the boolean in an Object so if the Object changes, I could fire an event too. I just don't want to poll with an if() statement unnecessarily. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* * Example of checking a variable for changes. * Uses dumb if() and polls continuously. */ public class NotAvoidingPolling { public static void main(String[] args) { boolean typedA = false; String input = ""; System.out.println("Type 'a' please."); while (true) { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); try { input = br.readLine(); } catch (IOException ioException) { System.out.println("IO Error."); System.exit(1); } // contrived state change logic if (input.equals("a")) { typedA = true; } else { typedA = false; } // problem: this is polling. if (typedA) System.out.println("Typed 'a'."); } } } Running this outputs: Type 'a' please. a Typed 'a'. On some forums people suggested using an Observer. And although this decouples the event handler from class being observed, I still have an if() on a forever loop. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.Observable; import java.util.Observer; /* * Example of checking a variable for changes. * This uses an observer to decouple the handler feedback * out of the main() but still is polling. */ public class ObserverStillPolling { boolean typedA = false; public static void main(String[] args) { // this ObserverStillPolling o = new ObserverStillPolling(); final MyEvent myEvent = new MyEvent(o); final MyHandler myHandler = new MyHandler(); myEvent.addObserver(myHandler); // subscribe // watch for event forever Thread thread = new Thread(myEvent); thread.start(); System.out.println("Type 'a' please."); String input = ""; while (true) { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); try { input = br.readLine(); } catch (IOException ioException) { System.out.println("IO Error."); System.exit(1); } // contrived state change logic // but it's decoupled now because there's no handler here. if (input.equals("a")) { o.typedA = true; } } } } class MyEvent extends Observable implements Runnable { // boolean typedA; ObserverStillPolling o; public MyEvent(ObserverStillPolling o) { this.o = o; } public void run() { // watch the main forever while (true) { // event fire if (this.o.typedA) { setChanged(); // in reality, you'd pass something more useful notifyObservers("You just typed 'a'."); // reset this.o.typedA = false; } } } } class MyHandler implements Observer { public void update(Observable obj, Object arg) { // handle event if (arg instanceof String) { System.out.println("We received:" + (String) arg); } } } Running this outputs: Type 'a' please. a We received:You just typed 'a'. I'd be ok if the if() was a NOOP on the CPU. But it's really comparing every pass. I see real CPU load. This is as bad as polling. I can maybe throttle it back with a sleep or compare the elapsed time since last update but this is not event driven. It's just less polling. So how can I do this smarter? How can I watch a POJO for changes without polling? In C# there seems to be something interesting called properties. I'm not a C# guy so maybe this isn't as magical as I think. private void SendPropertyChanging(string property) { if (this.PropertyChanging != null) { this.PropertyChanging(this, new PropertyChangingEventArgs(property)); } }

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• How would I UPDATE these table entries with SQL and PHP?

  - by CT

  I am working on an Asset Database problem. I enter assets into a database. Every object is an asset and has variables within the asset table. An object is also a type of asset. In this example the type is server. Here is the Query to retrieve all necessary data: SELECT asset.id ,asset.company ,asset.location ,asset.purchaseDate ,asset.purchaseOrder ,asset.value ,asset.type ,asset.notes ,server.manufacturer ,server.model ,server.serialNumber ,server.esc ,server.warranty ,server.user ,server.prevUser ,server.cpu ,server.memory ,server.hardDrive FROM asset LEFT JOIN server ON server.id = asset.id WHERE asset.id = '$id' I then assign all results into single php variables. How would I write a query/script to update an asset?

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• How to mult-thread this?

  - by WilliamKF

  I wish to have two threads. The first thread1 occasionally calls the following pseudo function: void waitForThread2() { if (thread2 is not idle) { return; } notifyThread2IamReady(); while (thread2IsExclusive) { } } The second thread2 is forever in the following pseudo loop: for (;;) { Notify thread1 I am idle. while (!thread1IsReady()) { } Notify thread1 I am exclusive. Do some work while thread1 is blocked. Notify thread1 I am busy. Do some work in parallel with thread1. } What is the best way to write this such that both thread1 and thread2 are kept as busy as possible on a machine with multiple cores. I would like to avoid long delays between notification in one thread and detection by the other. I tried using pthread condition variables but found the delay between thread2 doing 'notify thread1 I am busy' and the loop in waitForThread2() on thear2IsExclusive() can be up to almost one second delay. I then tried using a volatile sig_atomic_t shared variable to control the same, but something is going wrong, so I must not be doing it correctly.

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• what's faster: merging lists or dicts in python?

  - by tipu

  I'm working with an app that is cpu-bound more than memory bound, and I'm trying to merge two things whether they be sets or dicts. Now the thing is i can choose either one, but I'm wondering if merging dicts would be faster since it's all in memory? Or is it always going to be O(n), n being the size of the smaller set. The reason I asked about dicts rather than sets is because I can't convert a set to json, because that results in {key1, key2, key3} and json needs a key/value pair, so I am using a dict so json dumps returns {key1:1, key2:1, key3:1}. Yes this is wasteful, but if it proves to be faster then I'm okay with it.

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• Python Threading

  - by anteater7171

  I'm trying to make a simple program that continually displays and updates a label that displays the CPU usage, while having other unrelated things going on. I've done enough research to know that threading is likely going to be involved. However, I'm having trouble applying what I've seen in simple examples of threading to what I'm trying to do. What I currently have going: import Tkinter import psutil,time from PIL import Image, ImageTk class simpleapp_tk(Tkinter.Tk): def __init__(self,parent): Tkinter.Tk.__init__(self,parent) self.parent = parent self.initialize() def initialize(self): self.labelVariable = Tkinter.StringVar() self.label = Tkinter.Label(self,textvariable=self.labelVariable) self.label.pack() self.button = Tkinter.Button(self,text='button',command=self.A) self.button.pack() def A (self): G = str(round(psutil.cpu_percent(), 1)) + '%' print G self.labelVariable.set(G) def B (self): print "hello" if __name__ == "__main__": app = simpleapp_tk(None) app.mainloop() In the above code I'm basically trying to get command A continually running, while allowing command B to be done when the users presses the button.

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• Is MacBook powerful enough to do Ipad development? or do I need a MacBook Pro?

  - by ronaldwidha

  The title probably says it all. Considering an ipad's processor is nothing compared to a macbook, I would think a Macbook should be more than capable to run the simulator. However, not knowing much about iphone/ipad development, I'd like to get some opinions on this. for e.g. how many apps are typically need to be run for ipad dev (editor, debugger, perf monitor, trace log, etc). are these apps resource (memory, cpu) intensive? please do not take into consideration the actual image, 3d, video, sound development. I understand one would need quite a beefy machine to produce these type of creative assets. What I'm looking at is a machine to do code development, physics, putting together the produced assets (images, vector graphics, 3d video, sound, etc).

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• C# Multithreaded Domain Design

  - by Thijs Cramer

  Let's say i have a Domain Model that im trying to make compatible with multithreading. The prototype domain is a game domain that consists of Space, SpaceObject, and Location objects. A SpaceObject has the Move method and Asteroid and Ship extend this object with specific properties for the object (Ship has a name and Asteroid has a color) Let's say i want to make the Move method for each object run in a seperate thread. That would be stupid because with 10000 objects, i would have 10000 threads. What would be the best way to seperate the workload between cores/threads? I'm trying to learn the basics of concurrency, and building a small game to prototype a lot of concepts. What i've already done, is build a domain, and a threading model with a timer that launches events based on intervals. If the event occurs i want to update my entire model with the new locations of any SpaceObject. But i don't know how and when to launch new threads with workloads when the event occurs. Some people at work told me that u can't update your core domain multithreaded, because you have to synch everything. But in that case i can't run my game on a dual quadcore server, because it would only use 1 CPU for the hardest tasks. Anyone know what to do here?

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• What is optimal hardware configuration for heavy load LAMP application

  - by Piotr Kochanski

  I need to run Linux-Apache-PHP-MySQL application (Moodle e-learning platform) for a large number of concurrent users - I am aiming 5000 users. By concurrent I mean that 5000 people should be able to work with the application at the same time. "Work" means not only do database reads but writes as well. The application is not very typical, since it is doing a lot of inserts/updates on the database, so caching techniques are not helping to much. We are using InnoDB storage engine. In addition application is not written with performance in mind. For instance one Apache thread usually occupies about 30-50 MB of RAM. I would be greatful for information what hardware is needed to build scalable configuration that is able to handle this kind of load. We are using right now two HP DLG 380 with two 4 core processors which are able to handle much lower load (typically 300-500 concurrent users). Is it reasonable to invest in this kind of boxes and build cluster using them or is it better to go with some more high-end hardware? I am particularly curious how many and how powerful servers are needed (number of processors/cores, size of RAM) what network equipment should be used (what kind of switches, network cards) any other hardware, like particular disc storage solutions, etc, that are needed Another thing is how to put together everything, that is what is the most optimal architecture. Clustering with MySQL is rather hard (people are complaining about MySQL Cluster, even here on Stackoverflow).

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• Clojure lots of threads

  - by Timothy Baldridge

  I just got done watching Rick Hickey's "Clojure Concurrency" talk, and I have a few questions about threads. Let's say I have a situation with lots of Agents, let's say 10,000 of them running one machine. I'd rather not have 10,000 CPU threads running at once, but I don't want threads to be blocked by the actions of other threads. In this example I won't really be waiting for replies, instead each Agent will be sending a message or two, and then waiting until it gets a message. How would I structure a program like this without getting 10k OS threads which would probably end up slowing the system down.

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• nested page-faulting of user-space address in Linux

  - by shankar

  Hi, I would like to know if it is functionally wrong to page-fault a user-space address when kernel is running fault-handler to bring in a user-page. OS is Linux 2.6.30 Assume that both user-addresses are valid ( falling within vma , rw permission ) for the task. When I check the kernel code, i find that the kernel does not mind the nested fault if the faulted-addresses are valid and the fault did not occur in atomic-context or in irq handler. (I dont think the answer is cpu-specific, but I would add that i am interested in arm and mips ). eg : The scenario can happen if I print stack-data from page-fault handler. thanks shankar

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• Good .NET library for fast streaming / batching trigonometry (Atan)?

  - by Sean

  I need to call Atan on millions of values per second. Is there a good library to perform this operation in batch very fast. For example, a library that streams the low level logic using something like SSE? I know that there is support for this in OpenCL, but I would prefer to do this operation on the CPU. The target machine might not support OpenCL. I also looked into using OpenCV, but it's accuracy for Atan angles is only ~0.3 degrees. I need accurate results.

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• Need to devise a number crunching algorithm

  - by Ravi Gupta

  I stumbled upon this question: 7 power 7 is 823543. Which higher power of 7 ends with 823543 ? How should I go about it ? The one I came up with is very slow, it keeps on multiplying by 7 and checks last 6 digits of the result for a match. I tried with Lou's code: int x=1; for (int i=3;i<=100000000;i=i+4){ x=(x*7)%1000000; System.out.println("i="+ i+" x= "+x); if (x==823543){ System.out.println("Ans "+i);} } And CPU sounds like a pressure cooker but couldn't get the answer :(

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• Powershell - Splitting variable into chunks

  - by Andrew

  I have written a query in Powershell interrogating a F5 BIG-IP box through it's iControl API to bring back CPU usage etc. Using this code (see below) I can return the data back into a CSV format which is fine. However the $csvdata variable contains all the data. I need to be able to take this variable and for each line split each column of data into a seperate variable. The output currently looks like this: timestamp,"Utilization" 1276181160,2.3282800000e+00 Any advice would be most welcome $SystemStats = (Get-F5.iControl).SystemStatistics ### Allocate a new Query Object and add the inputs needed $Query = New-Object -TypeName iControl.SystemStatisticsPerformanceStatisticQuery $Query.object_name = $i $Query.start_time = $startTime $Query.end_time = 0 $Query.interval = $interval $Query.maximum_rows = 0 ### Make method call passing in an array of size one with the specified query $ReportData = $SystemStats.get_performance_graph_csv_statistics( (,$Query) ) ### Allocate a new encoder and turn the byte array into a string $ASCII = New-Object -TypeName System.Text.ASCIIEncoding $csvdata = $ASCII.GetString($ReportData[0].statistic_data)

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• cmake: Target-specific preprocessor definitions for CUDA targets seems not to work

  - by Nils

  I'm using cmake 2.8.1 on Mac OSX 10.6 with CUDA 3.0. So I added a CUDA target which needs BLOCK_SIZE set to some number in order to compile. cuda_add_executable(SimpleTestsCUDA SimpleTests.cu BlockMatrix.cpp Matrix.cpp ) set_target_properties(SimpleTestsCUDA PROPERTIES COMPILE_FLAGS -DBLOCK_SIZE=3) When running make VERBOSE=1 I noticed that nvcc is invoked w/o -DBLOCK_SIZE=3, which results in an error, because BLOCK_SIZE is used in the code, but defined nowhere. Now I used the same definition for a CPU target (using add_executable(...)) and there it worked. So now the questions: How do I figure out what cmake does with the set_target_properties line if it points to a CUDA target? Googling around didn't help so far and a workaround would be cool..

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• Why is x86 ugly? aka Why is x86 considered inferior when compared to others?

  - by claws

  Hello, recently I've been reading some SO archives and encountered statements against x86 architecture. http://stackoverflow.com/questions/2667256/why-do-we-need-different-cpu-architecture-for-server-mini-mainframe-mixed-cor says "PC architecture is a mess, any OS developer would tell you that." http://stackoverflow.com/questions/82432/is-learning-assembly-language-worth-the-effort says "Realize that the x86 architecture is horrible at best" http://forums.anandtech.com/showthread.php?t=976577 says "Most colleges teach assembly on something like MIPS because it's much simpler to understand, x86 assembly is really ugly" and many more comments like Compared to most architectures, X86 sucks pretty badly. It's definitely the conventional wisdom that X86 is inferior to MIPS, SPARC, and PowerPC x86 is ugly I tried searching but didn't find any reasons. I don't find x86 bad probably because this is the only architecture I'm familiar with. Can someone kindly give me reasons for considering x86 ugly/bad/inferior compared to others.

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• How Do You Profile & Optimize CUDA Kernels?

  - by John Dibling

  I am somewhat familiar with the CUDA visual profiler and the occupancy spreadsheet, although I am probably not leveraging them as well as I could. Profiling & optimizing CUDA code is not like profiling & optimizing code that runs on a CPU. So I am hoping to learn from your experiences about how to get the most out of my code. There was a post recently looking for the fastest possible code to identify self numbers, and I provided a CUDA implementation. I'm not satisfied that this code is as fast as it can be, but I'm at a loss as to figure out both what the right questions are and what tool I can get the answers from. How do you identify ways to make your CUDA kernels perform faster?

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• Regex take too long to match the result

  - by Joe Ijam

  Hi all I have this regex pattern <(\d+)>(\d+\.\d+|\d{4}\-\d+\-\d+\s+\d{2}:\d{2}:\d{2})(?:\..*?)*\s+(ALER|NOTI) and this is my input (will not matched at all) <150>2010-12-29 18:11:30.883 -0700 192.168.2.145 80 192.168.2.87 2795 "-" "-" GET HTTP 192.168.2.145 HTTP/1.1 200 36200 0 1038 544 192.168.2.221 80 540 SERVER DEFAULT PASSIVE VALID /joomla/ "-" http://192.168.2.145/joomla/index.php?option=com_content&view=a be4d44e8f3986183a87991398c1c212e=1; be4d44e8f3986183a87991398c1c212e=1 This will return not matched result but it takes too long to output the result. Since i have a thousand of logs/inputs in a second, it should finish very fast for every single log/input. Sometime it reaches CPU 100%. Can anyone help me to solve this regex problem? Thanks

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• App Engine HTTP 500s

  - by pocoa

  This request caused a new process to be started for your application, and thus caused your application code to be loaded for the first time. This request may thus take longer and use more CPU than a typical request for your application. I've handled all the situations, also DeadlineExceededError too. But sometimes I see these error messages in error logs. That request took about 10k ms, so it's not exceeded the limit too. But there is no other specific message about this error. All I know is that it returned HTTP 500. Is there anyone know the reason of these error messages? Thank you.

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