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  • CVE-2012-1712 Path Traversal Vulnerability in Sun GlassFish Web Space Server

    - by chandan
    CVE DescriptionCVSSv2 Base ScoreComponentProduct and Resolution CVE-2012-1712 Path Traversal Vulnerability 5.0 Liferay Sun GlassFish Web Space Server 10.0 Update 7 Patch 2 SPARC X86 Linux Windows Oracle acknowledges with thanks, Christian Schneider for bringing this issue to our attention. This notification describes vulnerabilities fixed in third-party components that are included in Sun's product distribution.Information about vulnerabilities affecting Oracle Sun products can be found on Oracle Critical Patch Updates and Security Alerts page.

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  • Shift career path [on hold]

    - by Rnet
    I have been programming in web services and applications in java, python for about 6 years. Over the past two years I have been gaining a steady interest in networking and I find it very intriguing but due to non existent experience in that field I cannot pursue a serious career in that path. At this point in my career would it be wise to make the shift? What would you do/work on/study(masters?) to make a successful transition?

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  • Contricted A* problem

    - by Ragekit
    I've got a little problem with an A* algorithm that I need to constrict a little bit. Basically : I use an A* to find the shortest path between 2 randomly placed room in 3D space, and then build a corridor between them. The problem I found is that sometimes it makes chimney like corridors that are not ideal, so I constrict the A* so that if the last movement was up or down, you go sideways. Everything is fine, but in some corner cases, it fails to find a path (when there is obviously one). Like here between the blue and red dot : (i'm in unity btw, but i don't think it matters) Here is the code of the actual A* (a bit long, and some redundency) while(current != goal) { //add stair up / stair down foreach(Node<GridUnit> test in current.Neighbors) { if(!test.Data.empty && test != goal) continue; //bug at arrival; if(test == goal && penul !=null) { Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(currentDiff.y,0)) { //wanna drop on the last if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,to.Data.bounds.center)) { continue; } else { if(Mathf.Approximately(to.Data.bounds.center.x, current.Data.parentUnit.bounds.center.x) && Mathf.Approximately(to.Data.bounds.center.z, current.Data.parentUnit.bounds.center.z)) { continue; } } } } if(current.Data.parentUnit != null) { Vector3 previousDiff = current.Data.parentUnit.bounds.center - current.Data.bounds.center; Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(previousDiff.y,0)) { if(!Mathf.Approximately(currentDiff.y,0)) { //you wanna drop now : continue; } if(current.Data.parentUnit.parentUnit != null) { if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,current.Data.parentUnit.parentUnit.bounds.center)) { continue; }else { if(Mathf.Approximately(test.Data.bounds.center.x, current.Data.parentUnit.parentUnit.bounds.center.x) && Mathf.Approximately(test.Data.bounds.center.z, current.Data.parentUnit.parentUnit.bounds.center.z)) { continue; } } } } } g = current.Data.g + HEURISTIC(current.Data,test.Data); h = HEURISTIC(test.Data,goal.Data); f = g + h; if(open.Contains(test) || closed.Contains(test)) { if(test.Data.f > f) { //found a shorter path going passing through that point test.Data.f = f; test.Data.g = g; test.Data.h = h; test.Data.parentUnit = current.Data; } } else { //jamais rencontré test.Data.f = f; test.Data.h = h; test.Data.g = g; test.Data.parentUnit = current.Data; open.Add(test); } } closed.Add (current); if(open.Count == 0) { Debug.Log("nothingfound"); //nothing more to test no path found, stay to from; List<GridUnit> r = new List<GridUnit>(); r.Add(from.Data); return r; } //sort open from small to biggest travel cost open.Sort(delegate(Node<GridUnit> x, Node<GridUnit> y) { return (int)(x.Data.f-y.Data.f); }); //get the smallest travel cost node; Node<GridUnit> smallest = open[0]; current = smallest; open.RemoveAt(0); } //build the path going backward; List<GridUnit> ret = new List<GridUnit>(); if(penul != null) { ret.Insert(0,to.Data); } GridUnit cur = goal.Data; ret.Insert(0,cur); do{ cur = cur.parentUnit; ret.Insert(0,cur); } while(cur != from.Data); return ret; You see at the start of the foreach i constrict the A* like i said. If you have any insight it would be cool. Thanks

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  • Path for a beginning web developer

    - by Trickerie
    I'm an experienced iOS programmer and have recently began to dabble in web development to expand my horizons. I've found it quite interesting and was wondering what learning path I should take through all the numerous languages. Here's what I planned on doing: HTML+CSS- PHP/Jquery Does that sound reasonable? Currently I'm nearly confident with my html/css abilities, and am planning to move ahead. Any good suggestions you guys could throw my way?

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  • Constrained A* problem

    - by Ragekit
    I've got a little problem with an A* algorithm that I need to Constrained a little bit. Basically : I use an A* to find the shortest path between 2 randomly placed room in 3D space, and then build a corridor between them. The problem I found is that sometimes it makes chimney like corridors that are not ideal, so I constrict the A* so that if the last movement was up or down, you go sideways. Everything is fine, but in some corner cases, it fails to find a path (when there is obviously one). Like here between the blue and red dot : (i'm in unity btw, but i don't think it matters) Here is the code of the actual A* (a bit long, and some redundency) while(current != goal) { //add stair up / stair down foreach(Node<GridUnit> test in current.Neighbors) { if(!test.Data.empty && test != goal) continue; //bug at arrival; if(test == goal && penul !=null) { Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(currentDiff.y,0)) { //wanna drop on the last if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,to.Data.bounds.center)) { continue; } else { if(Mathf.Approximately(to.Data.bounds.center.x, current.Data.parentUnit.bounds.center.x) && Mathf.Approximately(to.Data.bounds.center.z, current.Data.parentUnit.bounds.center.z)) { continue; } } } } if(current.Data.parentUnit != null) { Vector3 previousDiff = current.Data.parentUnit.bounds.center - current.Data.bounds.center; Vector3 currentDiff = current.Data.bounds.center - test.Data.bounds.center; if(!Mathf.Approximately(previousDiff.y,0)) { if(!Mathf.Approximately(currentDiff.y,0)) { //you wanna drop now : continue; } if(current.Data.parentUnit.parentUnit != null) { if(!coplanar(test.Data.bounds.center,current.Data.bounds.center,current.Data.parentUnit.bounds.center,current.Data.parentUnit.parentUnit.bounds.center)) { continue; }else { if(Mathf.Approximately(test.Data.bounds.center.x, current.Data.parentUnit.parentUnit.bounds.center.x) && Mathf.Approximately(test.Data.bounds.center.z, current.Data.parentUnit.parentUnit.bounds.center.z)) { continue; } } } } } g = current.Data.g + HEURISTIC(current.Data,test.Data); h = HEURISTIC(test.Data,goal.Data); f = g + h; if(open.Contains(test) || closed.Contains(test)) { if(test.Data.f > f) { //found a shorter path going passing through that point test.Data.f = f; test.Data.g = g; test.Data.h = h; test.Data.parentUnit = current.Data; } } else { //jamais rencontré test.Data.f = f; test.Data.h = h; test.Data.g = g; test.Data.parentUnit = current.Data; open.Add(test); } } closed.Add (current); if(open.Count == 0) { Debug.Log("nothingfound"); //nothing more to test no path found, stay to from; List<GridUnit> r = new List<GridUnit>(); r.Add(from.Data); return r; } //sort open from small to biggest travel cost open.Sort(delegate(Node<GridUnit> x, Node<GridUnit> y) { return (int)(x.Data.f-y.Data.f); }); //get the smallest travel cost node; Node<GridUnit> smallest = open[0]; current = smallest; open.RemoveAt(0); } //build the path going backward; List<GridUnit> ret = new List<GridUnit>(); if(penul != null) { ret.Insert(0,to.Data); } GridUnit cur = goal.Data; ret.Insert(0,cur); do{ cur = cur.parentUnit; ret.Insert(0,cur); } while(cur != from.Data); return ret; You see at the start of the foreach i constrict the A* like i said. If you have any insight it would be cool. Thanks

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  • Solving the SQL Server Multiple Cascade Path Issue with a Trigger

    This tip will look at how you can use triggers to replace the functionality you get from the ON DELETE CASCADE option of a foreign key constraint. Keep your database and application development in syncSQL Connect is a Visual Studio add-in that brings your databases into your solution. It then makes it easy to keep your database in sync, and commit to your existing source control system. Find out more.

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  • Redirect WinForms web browser Control pop ups to another WinForms web browser control with form data

    - by Scott Chantry
    I have a c# web browser and one of the pages it displays has a form. When the form is submitted it posts data to a new window in IE. I want to catch that data and forward it to another C# web browser that I have in my application. So I don't want it to open an IE browser when the javascript function window.open is called, I want it to open it in the 2nd browser window.

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  • search all paths and the shortest path for a graph - Prolog

    - by prologian
    Hi , I have a problem in my code with turbo prolog wich search all paths and the shortest path for a graph between 2 nodes the problem that i have is to test if the node is on the list or not exactly in the clause of member and this is my code : /* 1 ---- b ---- 3 --- | --- --- | ----- a |5 d --- | ----- --- | --- 2 --- | --- 4 -- c -- for example we have for b--->c ([b,c],5) , ([b,a,c],3) and ([b,d,c],7) : possible paths. ([b,a,c],3) : the shortest path. */ DOMAINS list=Symbol * PREDICATES distance(Symbol,Symbol) path1(Symbol,Symbol,list,integer) path(Symbol,Symbol,list,list,integer) distance(Symbol,list,integer) member(Symbol,list) shortest(Symbol,Symbol,list,integer) CLAUSES distance(a,b,1). distance(a,c,2). distance(b,d,3). distance(c,d,4). distance(b,c,5). distance(b,a,1). distance(c,a,2). distance(d,b,3). distance(d,c,4). distance(c,b,5). member(X, [Y|T]) :- X = Y; member(X, T). absent(X,L) :-member(X, L),!,fail. absent(_,_). /*find all paths*/ path1(X, Y, L, C):- path(X, Y, L, I, C). path(X, X, [X], I, C) :- absent(X, I). path(X, Y, [X|R], I, C) :- distance(X, Z, A) , absent(Z, I), path(Z, Y, R, [X|I] ,C1) , C=C1+A . /*to find the shortest path*/ shortest(X, Y, L, C):-path(X, Y, L, C),path(X, Y, L1, C1),C<C1.

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  • Facebook Source path issue in iPhone

    - by Arun Thakkar
    Hello everyone!! Hope You all are fie and also in one of your best of moods!! I need your help to solve an issue with Facebook. I have integrate Facebook Connect with my iPhone app. So as per step i have to write path of src folder into 'Header path info' Field in Project Build. I have given the absolute path to 'Header path info' Field. and its run fine without any Error.. But, Now When i Move the project folder to another destination, its but obvious, that path of src folder will change… So Now after moving file, when i run an application, It gives path error. So is there any way to solve this path issue? this comes when i run an app in simulator, and i guess It also won't run in iPhone because of problem of path of src folder. Kindly accept my Apologize if i have written anything wrong.. Looking Forwards, Thanks, Arun Thakkar

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  • Control flex application from embedded Flash control

    - by aip.cd.aish
    I have a flex application and have embedded a flash (SWF) file into it using <mx:SWFLoader>. There is an "Exit" button on the Flash file. I want to be able to handle the button click event on the flex application. So when that button in the flash file is clicked, I want to perform an action in the parent flex application. How can I do this? Thanks!

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  • Why is Magento 1.4 including javascript files by filesystem path?

    - by Josh
    I am in the process of testing a Magento 1.3 site using Magento 1.4. I am seeing very weird and inconsistent behavior. Instead of including the URL of my javascript files, Magento is creating tags with the full filesystem path of the js files, as so: <script type="text/javascript" src="/home/my_username/public_html/js/prototype/prototype.js"></script> I believe this is related to the new "Themes JavaScript and CSS files combined to one file" function. In fact, when I log into the admin and click "Flush JavaScript/CSS Cache", then the first page load is successful, and I see a single JS include similar to: <script type="text/javascript" src="/media/js/5b8cfac152fcb2a5f93ef9571d338c54.js"></script> But subsequent age loads load every single JS file, with the full path names. Which obviously isn't going to work. Anyone have any ideas on what could be wrong or how to fix this issue?

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  • trying to find if a file exists in a given path

    - by Yeshwanth Venkatesh
    I am fairly new to java and I am trying to find if the file specified in the LINUX path exists. private void validateFilePath(String filePath) { File dir = new File(filePath); if(dir.exists()){ System.out.println("File exists in the path " + dir); setTARGET_IMG_DIR("filePath"); return; }else{ System.out.println("File does not exists in the path: " + dir); return; } } The dir.exists works fine if I give a absolute path from my root like this /Users/yv/Documents/Eclipse-workspace/InputParser/bin/test.txt but if I give a relative path like test.txt or /InputParser/bin/test.txt it says files does not exists. I am planing on creating a jar of this projects and hence this should work with both relative path(files in the same directory) and absolute path from the root. How can I handle this ? Is it possible to search for the absolute path of that file from the root and append it to the file name ?

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  • Add xcode-select to PATH vs. Install Xcode Command Line Tools?

    - by MattDiPasquale
    Now with Xcode 4.5, is it OK to just add the following line to my ~/.bash_profile rather than installing the Xcode Command Line Tools? export PATH="$PATH:`xcode-select -print-path`/usr/bin:`xcode-select -print-path`/Toolchains/XcodeDefault.xctoolchain/usr/bin" Note: Xcode says the following about Command Line Tools: Before installing, note that from within Terminal you can use the XCRUN tool to launch compilers and other tools embedded within the Xcode application. Use the XCODE-SELECT tool to define which version of Xcode is active. Type "man xcrun" from within Terminal to find out more.

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  • how to compare the checksums in a list corresponding to a file path with the file path in the operat

    - by surab
    Hi all, how to compare the checksums in a list corresponding to a file path with the file path in the operating system In Python? import os,sys,libxml2 files=[] sha1s=[] doc = libxml2.parseFile('files.xml') for path in doc.xpathEval('//File/Path'): files.append(path.content) for sha1 in doc.xpathEval('//File/Hash'): sha1s.append(sha1.content) for entry in zip(files,sha1s): print entry the files.xml contains <Files> <File> <Path>usr/share/doc/dialog/samples/form1</Path> <Type>doc</Type> <Size>1222</Size> <Uid>0</Uid> <Gid>0</Gid> <Mode>0755</Mode> <Hash>49744d73e8667d0e353923c0241891d46ebb9032</Hash> </File> <File> <Path>usr/share/doc/dialog/samples/form3</Path> <Type>doc</Type> <Size>1294</Size> <Uid>0</Uid> <Gid>0</Gid> <Mode>0755</Mode> <Hash>f30277f73e468232c59a526baf3a5ce49519b959</Hash> </File> </Files> I need to compare the sha1 checksum in between tags corresponding to the file specified in between the tags, with the same file path in base Operating system.

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  • How do you combine "Revision Control" with "WorkFlow" for R?

    - by Tal Galili
    Hello all, I remember coming across R users writing that they use "Revision control" (e.g: "Source control"), and I am curious to know: How do you combine "Revision control" with your statistical analysis WorkFlow? Two (very) interesting discussions talk about how to deal with the WorkFlow. But neither of them refer to the revision control element: http://stackoverflow.com/questions/1266279/how-to-organize-large-r-programs http://stackoverflow.com/questions/1429907/workflow-for-statistical-analysis-and-report-writing A Long Update To The Question: Following some of the people's answers, and Dirk's question in the comment, I would like to direct my question a bit more. After reading the Wiki article about "revision control" (which I was previously not familiar with), it was clear to me that when using revision control, what one does is to build a development structure of his code. This structure either leads to a "final product" or to several branches. When building something like, let's say, a website. There is usually one end product you work towards (the website), with some prototypes along the way. But when doing a statistical analysis, the work (to my view) is different. Sometimes you know where you want to get to. But more often, you explore. Explore cleaning the dataset. Explore different methods for statistical analysis, and ask various questions of your data (and I am writing this, knowing how Frank Harrell, and other experience statisticians feels about Data dredging). That is way the WorkFlow question with statistical programming is (in my view) a serious and deep question, raising many issues, The simpler ones are technical: Which revision control software do you use (and why) ? Which IDE do you use(and why) ? The more interesting question are about work process: How do you structure your files? What do you keep as a separate file and what as a revision? or asking in a different way - What should be a "branch" and what should be a "sub project" in your code? For example: When starting to explore your data, should a plot be creating and then erased because it didn't lead any where (but kept as a revision) or should there be a backup file of that path? How you solve this tension was my initial curiosity. The second question is "what might I be missing?". What rules (of thumb) should one follow so to avoid common pitfalls doing statistical programming with version control? In my intuition, I feel that statistical programming is inherently different then software development (I am writing this without being a real expert in statistical programming, and even less so in software development). That's way I am unsure which of the lessons I have read here about version control would be applicable. Thanks a lot, Tal

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  • Django sys.path.append for project *and* app needed under WSGI

    - by GerardJP
    Hi all, Could somebody give me a pointer on why I need to add my project root path to the python path as well as the application itself in my WSGI file? Project base is called 'djapp', the application is called 'myapp'. sys.path.append(os.path.dirname(os.path.abspath(__file__)) + '/..') sys.path.append(os.path.dirname(os.path.abspath(__file__)) + '/../djapp') os.environ['DJANGO_SETTINGS_MODULE'] = 'djapp.settings' If I omit the line with "/../djapp/" the log tells my that 'myapp' can not be imported, even though 'djapp.settings' is. (validating 'djapp' was imported) It al runs properly with the ./manage.py command. there's a __init__ in the project folder. For testings sake, I see the same issue using addsitedir: site.addsitedir('/home/user/web/project/') site.addsitedir('/home/user/web/project/djapp') Thanx a lot. Gerard.

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  • Why is there no /usr/bin/ in windows? Would it be dangerous to the entire Program Files to the path?

    - by dotancohen
    I am a Linux user spending some time in Windows and I'm trying to understand some of the Windows paradigms instead of fighting them. I notice that each program installed in the traditional manner (i.e. via orgasmic installers: Yes, Yes, Yes, Finish) adds the executables to C:/Program Files/foo/bar.exe and then adds a shortcut to the Desktop / Start Menu containing the entire path. However, there is no common directory with links to the software, i.e. C:/bin/bar.exe which would link to C:/Program Files/foo/bar.exe. Therefore, after installing an application the only way to use the application is via the clicky-clicky menus or by navigating to the executable in the filesystem. One cannot simply Win-R to open the run dialogue and then type bar or bar.exe as is possible with notepad or mspaint. I realize that Windows 8 improves on this with the otherwise horrendous Start Screen which does support typing the name of the app, but again this depends on the app having registered itself for such. Would I be doing any harm by adding C:/Program Files recursively to the Windows path? I do realize that there will be name collisions (i.e. uninstall.exe) but could there be other issues?

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  • Spring MVC: How to get the remaining path after the controller path?

    - by Willis Blackburn
    I've spent over an hour trying to find the answer to this question, which seems like it should reflect a common use case, but I can't figure it out! Basically I am writing a file-serving controller using Spring MVC. The URLs are of the format http://www.bighost.com/serve/the/path/to/the/file.jpg, in which the part after "/serve" is the path to the requested file, which may have an arbitrary number of path segments. I have a controller like this: @Controller class ServerController { @RequestMapping(value = "/serve/???") public void serve(???) { } } What I am trying to figure out is: What do I use in place of "???" to make this work? I have two theories about how this should work. The first theory is that I could replace the first "???" in the RequestMapping with a path variable placeholder that has some special syntax meaning "capture to the end of the path." If a regular placeholder looks like "{path}" then maybe I could use "{path:**}" or "{path:/}" or something like that. Then I could use a @PathVariable annotation to refer to the path variable in the second "???". The other theory is that I could replace the first "???" with "**" (match anything) and that Spring would give me an API to obtain the remainder of the path (the part matching the "**"). But I can't find such an API. Thanks for any help you can provide!

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  • How can a running application in Linux/*nix determine its own absolute path?

    - by Dave Wade-Stein
    Suppose you run the application 'app' by typing 'app', rather than its absolute path. Due to your $PATH variable, what actually runs is /foo/bar/app. From inside app I'd like to determine /foo/bar/app. argv[0] is just 'app', so that doesn't help. I know in Linux I can get do pid = getpid(); and then look at the /proc/pid/exe softlink, but that doesn't work on other *nix. Is there a more portable way to determine the dir in which the app lives?

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  • What is a good generic sibling control Javascript communication strategy?

    - by James
    I'm building a webpage that is composed of several controls, and trying to come up with an effective somewhat generic client side sibling control communication model. One of the controls is the menu control. Whenever an item is clicked in here I wanted to expose a custom client side event that other controls can subscribe to, so that I can achieve a loosely coupled sibling control communication model. To that end I've created a simple Javascript event collection class (code below) that acts as like a hub for control event registration and event subscription. This code certainly gets the job done, but my question is is there a better more elegant way to do this in terms of best practices or tools, or is this just a fools errand? /// Event collection object - acts as the hub for control communication. function ClientEventCollection() { this.ClientEvents = {}; this.RegisterEvent = _RegisterEvent; this.AttachToEvent = _AttachToEvent; this.FireEvent = _FireEvent; function _RegisterEvent(eventKey) { if (!this.ClientEvents[eventKey]) this.ClientEvents[eventKey] = []; } function _AttachToEvent(eventKey, handlerFunc) { if (this.ClientEvents[eventKey]) this.ClientEvents[eventKey][this.ClientEvents[eventKey].length] = handlerFunc; } function _FireEvent(eventKey, triggerId, contextData ) { if (this.ClientEvents[eventKey]) { for (var i = 0; i < this.ClientEvents[eventKey].length; i++) { var fn = this.ClientEvents[eventKey][i]; if (fn) fn(triggerId, contextData); } } } } // load new collection instance. var myClientEvents = new bsdClientEventCollection(); // register events specific to the control that owns it, this will be emitted by each respective control. myClientEvents.RegisterEvent("menu-item-clicked"); Here is the part where this code above is consumed by source and subscriber controls. // menu control $(document).ready(function() { $(".menu > a").click( function(event) { //event.preventDefault(); myClientEvents.FireEvent("menu-item-clicked", $(this).attr("id"), null); }); }); <div style="float: left;" class="menu"> <a id="1" href="#">Menu Item1</a><br /> <a id="2" href="#">Menu Item2</a><br /> <a id="3" href="#">Menu Item3</a><br /> <a id="4" href="#">Menu Item4</a><br /> </div> // event subscriber control $(document).ready(function() { myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged2); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged3); }); function menuItemChanged(id, contextData) { alert('menuItemChanged ' + id); } function menuItemChanged2(id, contextData) { alert('menuItemChanged2 ' + id); } function menuItemChanged3(id, contextData) { alert('menuItemChanged3 ' + id); }

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  • How to get path to current exe file on Linux?

    - by user1519221
    The code below gives current path to exe file on Linux: #include <iostream> std::string getExePath() { char result[ PATH_MAX ]; ssize_t count = readlink( "/proc/self/exe", result, PATH_MAX ); return std::string( result, (count > 0) ? count : 0 ); } int main() { std::cout << getExePath() << std::endl; return 0; } The problem is that when I run it gives me current path to exe and name of the exe, e.g.: /home/.../Test/main.exe I would like to get only /home/.../Test/ I know that I can parse it, but is there any nicer way to do that?

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  • DTracing TCP congestion control

    - by user12820842
    In a previous post, I showed how we can use DTrace to probe TCP receive and send window events. TCP receive and send windows are in effect both about flow-controlling how much data can be received - the receive window reflects how much data the local TCP is prepared to receive, while the send window simply reflects the size of the receive window of the peer TCP. Both then represent flow control as imposed by the receiver. However, consider that without the sender imposing flow control, and a slow link to a peer, TCP will simply fill up it's window with sent segments. Dealing with multiple TCP implementations filling their peer TCP's receive windows in this manner, busy intermediate routers may drop some of these segments, leading to timeout and retransmission, which may again lead to drops. This is termed congestion, and TCP has multiple congestion control strategies. We can see that in this example, we need to have some way of adjusting how much data we send depending on how quickly we receive acknowledgement - if we get ACKs quickly, we can safely send more segments, but if acknowledgements come slowly, we should proceed with more caution. More generally, we need to implement flow control on the send side also. Slow Start and Congestion Avoidance From RFC2581, let's examine the relevant variables: "The congestion window (cwnd) is a sender-side limit on the amount of data the sender can transmit into the network before receiving an acknowledgment (ACK). Another state variable, the slow start threshold (ssthresh), is used to determine whether the slow start or congestion avoidance algorithm is used to control data transmission" Slow start is used to probe the network's ability to handle transmission bursts both when a connection is first created and when retransmission timers fire. The latter case is important, as the fact that we have effectively lost TCP data acts as a motivator for re-probing how much data the network can handle from the sending TCP. The congestion window (cwnd) is initialized to a relatively small value, generally a low multiple of the sending maximum segment size. When slow start kicks in, we will only send that number of bytes before waiting for acknowledgement. When acknowledgements are received, the congestion window is increased in size until cwnd reaches the slow start threshold ssthresh value. For most congestion control algorithms the window increases exponentially under slow start, assuming we receive acknowledgements. We send 1 segment, receive an ACK, increase the cwnd by 1 MSS to 2*MSS, send 2 segments, receive 2 ACKs, increase the cwnd by 2*MSS to 4*MSS, send 4 segments etc. When the congestion window exceeds the slow start threshold, congestion avoidance is used instead of slow start. During congestion avoidance, the congestion window is generally updated by one MSS for each round-trip-time as opposed to each ACK, and so cwnd growth is linear instead of exponential (we may receive multiple ACKs within a single RTT). This continues until congestion is detected. If a retransmit timer fires, congestion is assumed and the ssthresh value is reset. It is reset to a fraction of the number of bytes outstanding (unacknowledged) in the network. At the same time the congestion window is reset to a single max segment size. Thus, we initiate slow start until we start receiving acknowledgements again, at which point we can eventually flip over to congestion avoidance when cwnd ssthresh. Congestion control algorithms differ most in how they handle the other indication of congestion - duplicate ACKs. A duplicate ACK is a strong indication that data has been lost, since they often come from a receiver explicitly asking for a retransmission. In some cases, a duplicate ACK may be generated at the receiver as a result of packets arriving out-of-order, so it is sensible to wait for multiple duplicate ACKs before assuming packet loss rather than out-of-order delivery. This is termed fast retransmit (i.e. retransmit without waiting for the retransmission timer to expire). Note that on Oracle Solaris 11, the congestion control method used can be customized. See here for more details. In general, 3 or more duplicate ACKs indicate packet loss and should trigger fast retransmit . It's best not to revert to slow start in this case, as the fact that the receiver knew it was missing data suggests it has received data with a higher sequence number, so we know traffic is still flowing. Falling back to slow start would be excessive therefore, so fast recovery is used instead. Observing slow start and congestion avoidance The following script counts TCP segments sent when under slow start (cwnd ssthresh). #!/usr/sbin/dtrace -s #pragma D option quiet tcp:::connect-request / start[args[1]-cs_cid] == 0/ { start[args[1]-cs_cid] = 1; } tcp:::send / start[args[1]-cs_cid] == 1 && args[3]-tcps_cwnd tcps_cwnd_ssthresh / { @c["Slow start", args[2]-ip_daddr, args[4]-tcp_dport] = count(); } tcp:::send / start[args[1]-cs_cid] == 1 && args[3]-tcps_cwnd args[3]-tcps_cwnd_ssthresh / { @c["Congestion avoidance", args[2]-ip_daddr, args[4]-tcp_dport] = count(); } As we can see the script only works on connections initiated since it is started (using the start[] associative array with the connection ID as index to set whether it's a new connection (start[cid] = 1). From there we simply differentiate send events where cwnd ssthresh (congestion avoidance). Here's the output taken when I accessed a YouTube video (where rport is 80) and from an FTP session where I put a large file onto a remote system. # dtrace -s tcp_slow_start.d ^C ALGORITHM RADDR RPORT #SEG Slow start 10.153.125.222 20 6 Slow start 138.3.237.7 80 14 Slow start 10.153.125.222 21 18 Congestion avoidance 10.153.125.222 20 1164 We see that in the case of the YouTube video, slow start was exclusively used. Most of the segments we sent in that case were likely ACKs. Compare this case - where 14 segments were sent using slow start - to the FTP case, where only 6 segments were sent before we switched to congestion avoidance for 1164 segments. In the case of the FTP session, the FTP data on port 20 was predominantly sent with congestion avoidance in operation, while the FTP session relied exclusively on slow start. For the default congestion control algorithm - "newreno" - on Solaris 11, slow start will increase the cwnd by 1 MSS for every acknowledgement received, and by 1 MSS for each RTT in congestion avoidance mode. Different pluggable congestion control algorithms operate slightly differently. For example "highspeed" will update the slow start cwnd by the number of bytes ACKed rather than the MSS. And to finish, here's a neat oneliner to visually display the distribution of congestion window values for all TCP connections to a given remote port using a quantization. In this example, only port 80 is in use and we see the majority of cwnd values for that port are in the 4096-8191 range. # dtrace -n 'tcp:::send { @q[args[4]-tcp_dport] = quantize(args[3]-tcps_cwnd); }' dtrace: description 'tcp:::send ' matched 10 probes ^C 80 value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@ 5 1 | 0 2 | 0 4 | 0 8 | 0 16 | 0 32 | 0 64 | 0 128 | 0 256 | 0 512 | 0 1024 | 0 2048 |@@@@@@@@@ 8 4096 |@@@@@@@@@@@@@@@@@@@@@@@@@@ 23 8192 | 0

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  • Influence Maps for Pathfinding?

    - by james
    I'm taking the plunge and am getting into game dev, it's been going well but I've got stuck on a problem. I have a maze that is 100x100 with 0,1 to indicate if its a path or a wall. Within the maze I have 300 or so enemies and a player. The outcome I'm looking for is all the enemies work their way towards the player position. Originally I did this using an A* path finding algorithm but with 300 enemies it was taking forever to path find each one individually. After some research I found that an influence map / collaborative diffusion would be the best way to go. But I'm having a real hard time working out how this is actually done. Firstly.. How do you create a influence map? From what I understand each of my walls with have a scent of 0 so that makes them impassable.. then basically a radial effect from my player position to each other cell (So my player starts at 100 and then going outwards from that each other cell will be reduced value) Is that correct? If so,.. How would you do that (Math magic?) My next problem is if that is correct how would my "enemies" stop from getting stuck if they have gone down the wrong way? As say if my player was standing on the otherside of a wall if the enemy is just looking for larger numbers wont it keep getting stuck? I'm doing this in JavaScript so performance is key. Thanks for any help! EDIT: Or if anyones got a better solution? I've been reading about navmeshs, steering pathing, pre calculating all paths on load etc etc

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