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• Is a signal sent with kill to a parent thread guaranteed to be processed before the next statement?

  - by Jonathan M Davis

  Okay, so if I'm running in a child thread on linux (using pthreads if that matters), and I run the following command kill(getpid(), someSignal); it will send the given signal to the parent of the current thread. My question: Is it guaranteed that the parent will then immediately get the CPU and process the signal (killing the app if it's a SIGKILL or doing whatever else if it's some other signal) before the statement following kill() is run? Or is it possible - even probable - that whatever command follows kill() will run before the signal is processed by the parent thread?

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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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• 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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• 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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• 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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• 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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• 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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• rundll32.exe constantly running taking up resources slowing down my Win 7 computer

  - by Joe Fletcher

  Over the past week, my Windows 7 Home Premium computer (8gb RAM, 64bit) has been running slowly. When I look at my processes, there are always 2 rundll32.exe's running taking up 3 & 25% CPU power, memory slowly creeping upwards from around 115mb to 160mb each in the time it has taken me to right this message, sometimes popping upt o 300mb and back down. Svchost.exe is at 260mb. When I end those processes, everything returns to snappiness. I recently did some Windows Updates, and I think it was around the time my computer started acting slowly, but I can't remember if it was before or after the updates that things started running slowly. Last night I ccleaned & defrag'ed. How can I diagnose what's causing the slowness?

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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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• 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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• Perl Parallel::ForkManager wait_all_children() takes excessively long time

  - by zhang18

  I have a script that uses Parallel::ForkManager. However, the wait_all_children() process takes incredibly long time even after all child-processes are completed. The way I know is by printing out some timestamps (see below). Does anyone have any idea what might be causing this (I have 16 CPU cores on my machine)? my $pm = Parallel::ForkManager->new(16) for my $i (1..16) { $pm->start($i) and next; ... do something within the child-process ... print (scalar localtime), " Process $i completed.\n"; $pm->finish(); } print (scalar localtime), " Waiting for some child process to finish.\n"; $pm->wait_all_children(); print (scalar localtime), " All processes finished.\n"; Clearly, I'll get the Waiting for some child process to finish message first, with a timestamp of, say, 7:08:35. Then I'll get a list of Process i completed messages, with the last one at 7:10:30. However, I do not receive the message All Processes finished until 7:16:33(!). Why is that 6-minute delay between 7:10:30 and 7:16:33? Thx!

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Best compiled language for Mac OS X and Linux compatibility

  - by corydoras

  We need to write some software that will compile and run on both an Mac OS X server and Ubuntu. We would love to use Objective-C with all of its Cocoa goodness, however the GNUstep implementations of the parts we are using are broken (in the latest Ubuntu package anyway.) In light of this should we use C++ (I would really rather not), C or something else that we have not thought of? It is a server/back-end process that is very resource intensive, Java and other interpreted versions of this software perform much worse than the Objective-C proof of concept we have written, hence we now wish to re-write in a "compiled[1]" language. (NB: Some people might consider this subjective, however at the end of the day we do need to get a job done, there has to be a reasonably appropriate correct answer here). [1] Compiled to native CPU instructions, not compiled into "byte codes" that then have to be run by an interpreter.

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• How would I UPDATE these table entries with SQL?

  - 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' How would I write a query to update an asset?

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• MySQL query cache vs caching result-sets in the application layer

  - by GetFree

  I'm running a php/mysql-driven website with a lot of visits and I'm considering the possibility of caching result-sets in shared memory in order to reduce database load. However, right now MySQL's query cache is enabled and it seems to be doing a pretty good job since if I disable query caching, the use of CPU jumps to 100% immediately. Given that situation, I dont know if caching result-sets (or even the generated HTML code) locally in shared memory with PHP will result in any noticeable performace improvement. Does anyone out there have any experience on this matter? PS: Please avoid suggesting heavy-artillery solutions like memcached. Right now I'm looking for simple solutions that dont require too much time to implement, deploy and maintain.

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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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• 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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