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• What are the ways to create draw data structures for latex?

  - by alicephacker

  I tried tikz/pgf a bit but have not had much luck creating a nice diagram to visualize bitfields or byte fields of packed data structures (i.e. in memory). Essentially I want a set of rectangles representing ranges of bits with labels inside, and offsets along the top. There should be multiple rows for each word of the data structure. This is similar to most of the diagrams in most processor manuals labeling opcode encoding etc. Has anyone else tried to do this using latex or is there a package for this?

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• Javascript / Flash : When exactly are flash external callback methods triggered ?

  - by felace

  I have a flash application using callbacks to javascript functions (eg. when it receives some data over a socket, it'll call a js script which would change the content of a div according to that given data). Afaik, there is no actual mutual exclusion in javascript so I'm not sure if I can/need to simulate something like : callbackFunc() { lock(mutex1) foo unlock(mutex1) } ... someOtherFunc() { lock(mutex1) bar unlock(mutex1) } So, the question is, when are those callbacks called ? Are they simply queued to be executed right after the browser finishes its task or are they triggered randomly ?

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• Is code clearness killing application performance?

  - by Jorge Córdoba

  As today's code is getting more complex by the minute, code needs to be designed to be maintainable - meaning easy to read, and easy to understand. That being said, I can't help but remember the programs that ran a couple of years ago such as Winamp or some games in which you needed a high performance program because your 486 100 Mhz wouldn't play mp3s with that beautiful mp3 player which consumed all of your CPU cycles. Now I run Media Player (or whatever), start playing an mp3 and it eats up a 25-30% of one of my four cores. Come on!! If a 486 can do it, how can the playback take up so much processor to do the same? I'm a developer myself, and I always used to advise: keep your code simple, don't prematurely optimize for performance. It seems that we've gone from "trying to get it to use the least amount of CPU as possible" to "if it doesn't take too much CPU is all right". So, do you think we are killing performance by ignoring optimizations?

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• Odd optimization problem under MSVC

  - by Goz

  I've seen this blog: http://igoro.com/archive/gallery-of-processor-cache-effects/ The "weirdness" in part 7 is what caught my interest. My first thought was "Thats just C# being weird". Its not I wrote the following C++ code. volatile int* p = (volatile int*)_aligned_malloc( sizeof( int ) * 8, 64 ); memset( (void*)p, 0, sizeof( int ) * 8 ); double dStart = t.GetTime(); for (int i = 0; i < 200000000; i++) { //p[0]++;p[1]++;p[2]++;p[3]++; // Option 1 //p[0]++;p[2]++;p[4]++;p[6]++; // Option 2 p[0]++;p[2]++; // Option 3 } double dTime = t.GetTime() - dStart; The timing I get on my 2.4 Ghz Core 2 Quad go as follows: Option 1 = ~8 cycles per loop. Option 2 = ~4 cycles per loop. Option 3 = ~6 cycles per loop. Now This is confusing. My reasoning behind the difference comes down to the cache write latency (3 cycles) on my chip and an assumption that the cache has a 128-bit write port (This is pure guess work on my part). On that basis in Option 1: It will increment p[0] (1 cycle) then increment p[2] (1 cycle) then it has to wait 1 cycle (for cache) then p[1] (1 cycle) then wait 1 cycle (for cache) then p[3] (1 cycle). Finally 2 cycles for increment and jump (Though its usually implemented as decrement and jump). This gives a total of 8 cycles. In Option 2: It can increment p[0] and p[4] in one cycle then increment p[2] and p[6] in another cycle. Then 2 cycles for subtract and jump. No waits needed on cache. Total 4 cycles. In option 3: It can increment p[0] then has to wait 2 cycles then increment p[2] then subtract and jump. The problem is if you set case 3 to increment p[0] and p[4] it STILL takes 6 cycles (which kinda blows my 128-bit read/write port out of the water). So ... can anyone tell me what the hell is going on here? Why DOES case 3 take longer? Also I'd love to know what I've got wrong in my thinking above, as i obviously have something wrong! Any ideas would be much appreciated! :) It'd also be interesting to see how GCC or any other compiler copes with it as well! Edit: Jerry Coffin's idea gave me some thoughts. I've done some more tests (on a different machine so forgive the change in timings) with and without nops and with different counts of nops case 2 - 0.46 00401ABD jne (401AB0h) 0 nops - 0.68 00401AB7 jne (401AB0h) 1 nop - 0.61 00401AB8 jne (401AB0h) 2 nops - 0.636 00401AB9 jne (401AB0h) 3 nops - 0.632 00401ABA jne (401AB0h) 4 nops - 0.66 00401ABB jne (401AB0h) 5 nops - 0.52 00401ABC jne (401AB0h) 6 nops - 0.46 00401ABD jne (401AB0h) 7 nops - 0.46 00401ABE jne (401AB0h) 8 nops - 0.46 00401ABF jne (401AB0h) 9 nops - 0.55 00401AC0 jne (401AB0h) I've included the jump statetements so you can see that the source and destination are in one cache line. You can also see that we start to get a difference when we are 13 bytes or more apart. Until we hit 16 ... then it all goes wrong. So Jerry isn't right (though his suggestion DOES help a bit), however something IS going on. I'm more and more intrigued to try and figure out what it is now. It does appear to be more some sort of memory alignment oddity rather than some sort of instruction throughput oddity. Anyone want to explain this for an inquisitive mind? :D Edit 3: Interjay has a point on the unrolling that blows the previous edit out of the water. With an unrolled loop the performance does not improve. You need to add a nop in to make the gap between jump source and destination the same as for my good nop count above. Performance still sucks. Its interesting that I need 6 nops to improve performance though. I wonder how many nops the processor can issue per cycle? If its 3 then that account for the cache write latency ... But, if thats it, why is the latency occurring? Curiouser and curiouser ...

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• How do you encrypt data between client and server running in Flash and Java?

  - by ArmlessJohn

  We have a multiclient system where the client is written in Flash and the server is written in Java. Currently, communication is done in Flash by usage of flash.net.Socket and the protocol is written in JSON. The server uses a custom port to receive connections and then proceed to talk with each client. As expected, data is sent and received on both fronts as raw bytes, which are then decoded as needed. We would like to encrypt the communication between clients and server. I have some basic understanding about public/private key encryption, but I do not know what is the best way to exchange keys or what libraries are available (on both languages) to do this. What would be the best strategy to attack this problem and where should I start looking for libraries/methods to implement this encryption?

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• what is value of x for load and store

  - by Kevinniceguy

  This is some challenge On a single processor system, in which load and store are assumed to be atomic, what are all the possible values for x after both threads have completed in the following execution, assuming that x is initialised to O? Hint: you need to consider how this code might be compiled into machine language. for (int i = 0; i < 5; i++) : x = x + 1; for (int j = 0; j < 5; j++) : x = x + 1;

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• Parallelize Bash Script

  - by thelsdj

  Lets say I have a loop in bash: for foo in `some-command` do do-something $foo done do-something is cpu bound and I have a nice shiny 4 core processor. I'd like to be able to run up to 4 do-something's at once. The naive approach seems to be: for foo in `some-command` do do-something $foo & done This will run all do-somethings at once, but there are a couple downsides, mainly that do-something may also have some significant I/O which performing all at once might slow down a bit. The other problem is that this code block returns immediately, so no way to do other work when all the do-somethings are finished. How would you write this loop so there are always X do-somethings running at once?

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• Python - network buffer handling question...

  - by Patrick Moriarty

  Hi, I want to design a game server in python. The game will mostly just be passing small packets filled with ints, strings, and bytes stuffed into one message. As I'm using a different language to write the game, a normal packet would be sent like so: Writebyte(buffer, 5); // Delimit type of message Writestring(buffer, "Hello"); Sendmessage(buffer, socket); As you can see, it writes the bytes to the buffer, and sends the buffer. Is there any way to read something like this in python? I am aware of the struct module, and I've used it to pack things, but I've never used it to actually read something with mixed types stuck into one message. Thanks for the help.

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• Ruby TCPSocket doesn't notice it when server is killed

  - by user303308

  I've this ruby code that connects to a TCP server (namely, netcat). It loops 20 times, and sends "ABCD ". If I kill netcat, it takes TWO iterations of the loop for an exception to be triggered. On the first loop after netcat is killed, no exception is triggered, and "send" reports that 5 bytes have been correctly written... Which in the end is not true, since of course the server never received them. Is there a way to work around this issue ? Right now I'm losing data : since I think it's been correctly transfered, I'm not replaying it. #!/usr/bin/env ruby require 'rubygems' require 'socket' sock = TCPSocket.new('192.168.0.10', 5443) sock.sync = true 20.times do sleep 2 begin count = sock.write("ABCD ") puts "Wrote #{count} bytes" rescue Exception => myException puts "Exception rescued : #{myException}" end end

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• Delays in .net app when connecting to oracle db using Oracle.DataAccess

  - by chris

  I have a .net desktop app that connects to an oracle database. At times, there are very noticable delays. I ran a trace on the code, and it was always in the DataReader.Read(). I turned on sql tracing, and found the following, which corresponds to the delays I'm seeing: (2128) [23-MAR-2010 13:00:07:310] nsprecv: reading from transport... (2128) [23-MAR-2010 13:00:07:310] nttrd: entry (2128) [23-MAR-2010 13:00:24:655] nttrd: socket 676 had bytes read=2047 (2128) [23-MAR-2010 13:00:24:655] nttrd: exit (2128) [23-MAR-2010 13:00:24:655] nsprecv: 2047 bytes from transport There's about a 14 second pause in there. I'm pretty sure that there's not a problem in the code, but not sure where to look at next. Is there anyone out there with experience with oracle trace that can explain what's going on?

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• Oracle data provider hangs IIS worker process when web site is stopped

  - by Greg

  We're experiencing a nasty issue in Oracle 11g Release 2 where the w3wp process takes over and entire processor core, and debugging shows that the Oracle data provider is throwing ThreadAbortExceptions infinitely. A developer found this issue by doing the following: 1) Browse a web site that uses Oracle data connections locally (http://localhost/OracleWebSite) - we use IIS, not the ASP.NET dev server, for all of our sites. This ensures that the w3wp process is running and that an active Oracle pool of connections exists in the app pool. 2) Stop the web site (or perform a Rebuild All operation in Visual Studio on the web site in question). Our Oracle connection handling in the affected applications (all Oracle web apps) is well-established and robust. This issue does not occur if we disable connection pooling. This issue does not occur in Oracle 11g Release 1.

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• help in security assignment

  - by scatman

  i have to write a program that sniffs network packets (part1-the simple part). and i have to update the program (part2) so that it will be able to terminate connections. the specific requirements are: construct raw packets by specifying data link layer and network layer information including appropriate source and destination MAC and IP addresses. These packets are intended to terminate the connection. To do so, you should used SOCK_RAW as the socket type to be able to set the header information by yourself. can anybody give me some ideas on the second part? should i hijack the session,apply a dos attack on one of the users?? all i need is some tips of how to terminate the connection. i am using c programming language. and this is a course assignment for the security course.

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• J2ME's extra annoying HTTP permission prompt

  - by Hans Malherbe

  Some phones only prompt the user for permission the first time a connection is made. Others pop up the permission prompt whenever the MIDlet attempts to make a HTTP connection! What are the options if we want to suppress the prompt? Can we sign the JAR using only one CA (Certificate Authority) and have it work on all devices? Do we have to pay for a signature on every release? Is it an option to create our own CA certificate and tell our customers to install it on there device? Alternatively, it seems that plain socket connections do not suffer so. Is there a free implementation of HTTP on top of TCP for J2ME?

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• Fastest implementation of the frac function in C#

  - by user349937

  I would like to implement a frac function in C# (just like the one in hsl here http://msdn.microsoft.com/en-us/library/bb509603%28VS.85%29.aspx) but since it is for a very processor intensive application i would like the best version possible. I was using something like public float Frac(float value) { return value - (float)Math.Truncate(value); } but I'm having precision problems, for example for 2.6f it's returning in the unit test Expected: 0.600000024f But was: 0.599999905f I know that I can convert to decimal the value and then at the end convert to float to obtain the correct result something like this: public float Frac(float value) { return (float)((decimal)value - Decimal.Truncate((decimal)value)); } But I wonder if there is a better way without resorting to decimals...

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• Are memory barriers necessary for atomic reference counting shared immutable data?

  - by Dietrich Epp

  I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

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• How to create a new IDA project based on an existing one with different offsets?

  - by tbergelt

  I have an existing IDA Pro project for a C166 processor embedded application. This project already has many functions, variables, etc defined. There are different versions of the embedded application I am looking at. The different versions of the application are 99% the same, but with slight variations in code and data that cause functions and variables to be at different memory offsets. I want to create a new IDA project for a different version of the application. I would like to somehow import all of my function and variable definitions from my existing IDA project. I would like IDA to recognize the signatures of the existing function definitions and define them at there new location in the new project. How can I do this? Are there certain plugins for IDA I can chain together?

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• Design Stock Server Application in C++

  - by Avinash

  [Queston asked in ML Interview] Design an server/application which handle multiple incoming stock information ( stock symbol and values ) Server need to store the information in some cache ( need to design the data structure ), There are multiple client connected to server using tcp/ip socket. They will subscribe to particular request say stock symbol XYZ , and may be for more then one. As and when there is change the stock symbol server should broadcast the information to subscribed client. If tcp/ip write failed, server should handle the unregistration of the client. What various data structures will be used and how threading model will be ?

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• Allowing AsyncTask to Manipulate Values in Different Activity Classes

  - by Matt

  Hi guys, This title may seem strange, so let me try to explain what I'm trying to do. I have several activity classes, each representing a different view in my application. My initial activity class gets loaded when the application launches. The user enters values and eventually a TCP socket is opened, and I then use AsyncTask to listen for and respond to messages from the server. I'd like for this AsyncTask class to essentially listen until the app is closed/error condition reached, and be able to update values in other activity classes after they are started. Does this make sense (it's been a long, frustrating night)? I know that static activity class references are bad practice, and touching the UI thread from other activities is bad as well, but I'm having trouble finding a clean solution to this problem. Maybe using AsyncTask is not the best approach here? Should I be using a service instead or something else entirely? Thanks in advance.

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• n00b: receive input over TCP/IP and use it to update HTML

  - by mawg

  This has got to be a FAQ, so can someone please just direct me to a "network programming for dummies" URL? The server wants to push information to a client or broadcast to all, when an event happens - as opposed to the clients constantly polling the server "just in case". The client then updates a browser page display. How do I do that? (toldya it was a n00b question) Should I have a thread which receives info on a socket and then writes it to a database which the browser display (PHP) can process with an HTML refresh tag, or what? Sorry to sound so dumb.

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• How to handle set based consistency validation in CQRS?

  - by JD Courtoy

  I have a fairly simple domain model involving a list of Facility aggregate roots. Given that I'm using CQRS and an event-bus to handle events raised from the domain, how could you handle validation on sets? For example, say I have the following requirement: Facility's must have a unique name. Since I'm using an eventually consistent database on the query side, the data in it is not guaranteed to be accurate at the time the event processesor processes the event. For example, a FacilityCreatedEvent is in the query database event processing queue waiting to be processed and written into the database. A new CreateFacilityCommand is sent to the domain to be processed. The domain services query the read database to see if there are any other Facility's registered already with that name, but returns false because the CreateNewFacilityEvent has not yet been processed and written to the store. The new CreateFacilityCommand will now succeed and throw up another FacilityCreatedEvent which would blow up when the event processor tries to write it into the database and finds that another Facility already exists with that name.

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• Modular HTML in Adobe AIR? Is It Possible?

  - by Greg Bulmash

  When I write HTML with a PHP backend, I usually have a single header file and a single footer file with some PHP variables in them. The base skeleton for every page calls the header, contains the body content, and then calls the footer. That way, if I want to make changes to the header sitewide, I change one file. I'm working on developing the UI in my first Adobe AIR app and I'm wondering if there's some way to include such files in an HTML based page template there. Obviously, with the file read/write abilities in AIR, I can write a Javascript routine to pull data from a header file, parse it, and inject it into a placeholder. It just seems like such a kludge. I'm thinking there's gotta be some simple way to import a block of HTML into a page without an iFrame or complex post-processor. Something like a PHP include statement or perhaps the old Server Side Includes. Any methods you guys can recommend?

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• What happens when a computer program runs?

  - by gaijinco

  I know the general theory but I can't fit in the details. I know that a program resides in the secondary memory of a computer. Once the program begins execution it is entirely copied to the RAM. Then the processor retrive a few instructions (it depends on the size of the bus) at a time, puts them in registers and executes them. I also know that a computer program uses two kinds of memory: stack and heap, which are also part of the primary memory of the computer. The stack is used for non-dynamic memory, and the heap for dynamic memory (for example, everything related to the new operator in C++) What I can't understand is how those two things connect. At what point is the stack used for the execution of the instructions? Instructions go from the RAM, to the stack, to the registers?

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• NASM: Count how many bits in a 32 Bit number are set to 1.

  - by citronas

  I have a 32 Bit number and want to count know how many bits are 1. I'm thinking of this pseudocode: mov eax, [number] while(eax != 0) { div eax, 2 if(edx == 1) { ecx++; } shr eax, 1 } Is there a more efficient way? I'm using NASM on a x86 processor. (I'm just beginning with assembler, so please do not tell me to use code from extern libraries, because I do not even know how to include them ;) ) (I just found http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer which also contains my solution. There are other solutions posted, but unfortunatly I can't seem to figure out, how I would write them in assembler)

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• playing incoming video stream

  - by mawia

  Hi! all, I am writing an application which is a kinda video streamer.The client is receiving a video stream using udp socket.Now as I am receiving the stream I want to play it simultaneous.It is different from playing local video file lying in your hard disk in which case it can be as simple as running the file using system("vlc filename").But here many issues are involved like there can be delay in receiving and player will have to wait for the incoming data.I have come to know about using vlc to run a video stream.Can you please elaborate the step for playing the stream using vlc.I am implementing my application in c++. EDIT: Can somebody give me some idea regarding VLC API which can be used to stream a given video to particular destination and receive that stream at other end play it. with regards, Mawia

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