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  • Thread Synchronization and Synchronization Primitives

    When considering synchronization in an application, the decision truly depends on what the application and its worker threads are going to do. I would use synchronization if two or more threads could possibly manipulate the same instance of an object at the same time. An example of this in C# can be demonstrated through the use of storing data in a static object. A static object is initialized once per application and the data within the object can be accessed by all threads. I would use the synchronization primitives to prevent any data from being manipulated by multiple threads simultaneously. This would reduce any data corruption from occurring within the object. On the other hand if all the threads used non static objects and were independent of the other tasks there would be no need to use synchronization. Synchronization Primitives in C#: Basic Blocking Locking Signaling Non-Blocking Synchronization Constructs The Basic Blocking methods include Sleep, Join, and Task.Wait.  These methods force threads to wait until other threads have completed. In addition, these methods can also force a thread to wait a set amount of time before continuing to work.   The Locking primitive prevents a thread from entering a critical section of code while another thread is in the same critical section.  If another thread attempts to enter a locked code, it will wait, until the code block is released. The Signaling primitive allows a thread to temporarily pause work until receiving a notification from another thread that it is ok to continue working. The Signaling primitive removes the need for polling.The Non-Blocking Synchronization Constructs protect access to a common field by calling upon processor primitives.

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  • Inner synchronization on the same object as the outer synchronization

    - by Yaneeve
    Recently I attended a lecture concerning some design patterns: The following code had been displayed: public static Singleton getInstance() { if (instance == null) { synchronized(Singleton.class) { //1 Singleton inst = instance; //2 if (inst == null) { synchronized(Singleton.class) { //3 inst = new Singleton(); //4 } instance = inst; //5 } } } return instance; } taken from: Double-checked locking: Take two My question has nothing to do with the above mentioned pattern but with the synchronized block: Is there any benefit whatsoever to the double synchronization done in lines 1 & 3 with regards to the fact that the synchronize operation is done on the same Object?

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  • Multithreading synchronization interview question: Find n words given m threads

    - by rplusg
    I came across this question: You are given a paragraph , which contain n number of words, you are given m threads. What you need to do is , each thread should print one word and give the control to next thread, this way each thread will keep on printing one word , in case last thread come, it should invoke the first thread. Printing will repeat until all the words are printed in paragraph. Finally all threads should exit gracefully. What kind of synchronization will use? I strongly feel we cannot take any advantage of threads here but interviewer is trying to understand my synchronization skills? No need of code, just put some thoughts. I will implement by myself.

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  • Synchronization between game logic thread and rendering thread

    - by user782220
    How does one separate game logic and rendering? I know there seem to already be questions on here asking exactly that but the answers are not satisfactory to me. From what I understand so far the point of separating them into different threads is so that game logic can start running for the next tick immediately instead of waiting for the next vsync where rendering finally returns from the swapbuffer call its been blocking on. But specifically what data structures are used to prevent race conditions between the game logic thread and the rendering thread. Presumably the rendering thread needs access to various variables to figure out what to draw, but game logic could be updating these same variables. Is there a de facto standard technique for handling this problem. Maybe like copy the data needed by the rendering thread after every execution of the game logic. Whatever the solution is will the overhead of synchronization or whatever be less than just running everything single threaded?

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  • Multiplayer tile based movement synchronization

    - by Mars
    I have to synchronize the movement of multiple players over the Internet, and I'm trying to figure out the safest way to do that. The game is tile based, you can only move in 4 directions, and every move moves the sprite 32px (over time of course). Now, if I would simply send this move action to the server, which would broadcast it to all players, while the walk key is kept being pressed down, to keep walking, I have to take this next command, send it to the server, and to all clients, in time, or the movement won't be smooth anymore. I saw this in other games, and it can get ugly pretty quick, even without lag. So I'm wondering if this is even a viable option. This seems like a very good method for single player though, since it's easy, straight forward (, just take the next movement action in time and add it to a list), and you can easily add mouse movement (clicking on some tile), to add a path to a queue, that's walked along. The other thing that came to my mind was sending the information that someone started moving in some direction, and again once he stopped or changed the direction, together with the position, so that the sprite will appear at the correct position, or rather so that the position can be fixed if it's wrong. This should (hopefully) only make problems if someone really is lagging, in which case it's to be expected. For this to work out I'd need some kind of queue though, where incoming direction changes and stuff are saved, so the sprite knows where to go, after the current movement to the next tile is finished. This could actually work, but kinda sounds overcomplicated. Although it might be the only way to do this, without risk of stuttering. If a stop or direction change is received on the client side it's saved in a queue and the char keeps moving to the specified coordinates, before stopping or changing direction. If the new command comes in too late there'll be stuttering as well of course... I'm having a hard time deciding for a method, and I couldn't really find any examples for this yet. My main problem is keeping the tile movement smooth, which is why other topics regarding synchronization of pixel based movement aren't helping too much. What is the "standard" way to do this?

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  • synchronization web service methodologies or papers

    - by Grady Player
    I am building a web service (PHP+JSON) to sync with my iphone app. The main goals are: Backup Provide a web view for printing / sorting, manipulating. allow a group sync up and down. I am aware of the logic problems with all of these items, Ie. if one person deletes something, do you persist this change to other users, collisions, etc. I am looking for just any book or scholarly work, or even words of wisdom to address common issues. when to detect changes of data with hashes, vs modified dates, or combination. how do address consolidation of sequential ID's originating on different client nodes (can be sidestepped in my context, but it would be interesting.) dealing with collisions (is there a universally safe way to do so?). general best practices. how to structure the actual data transaction (ask for whole list then detect changes...)

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  • Game thread, render thread, animation/inverse kinematics, and synchronization

    - by user782220
    In a multithreaded setup with a game logic thread and a render thread, with some kind of skin mesh animation with inverse kinematics plus etc how does animation work? Does the game logic thread just update a number saying time T in the animation and then the render thread infers Who owns the skin mesh animation, the game logic thread or the render thread? How is it stored in the scene graph if it is stored there at all? When the game logic updates does it do the computation of the skin mesh animation and the computation of the inverse kinematics and then store the result directly in the scene graph or is it stored indirectly and the render thread does the computation?

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  • Jumping with Mecanim synchronization

    - by Abhishek Deb
    I am using Unity3D 4.1 for one of my projects. I have a robot character which is always running. I am using mecanim animation system. What I really want:When I press Space bar, the character should jump up in the air, triggering an animation clip and then by the time it reaches the ground, the animation clip should also end. What actually is happening:When I press Space bar, the character jumps in the air. Animation clip plays as it should, but ends way before it reaches the ground. So, it looks like he is running in the mid air. What have I done: I have this humanoid robot setup with a jump animation bounded with the space bar key. Also, instead of using root motion, I am directly moving the robot from code. //Jumping if(Input.GetKeyDown(KeyCode.Space)){ rigidbody.AddForce(Vector3.up*jumpVelocty); anim.SetBool("Jump",true); } else anim.SetBool("Jump",false); Character's Details: Rigidbody = Mass:30, Freeze rotaion:x,y,z Capsule Collider = Material: metal, center(0,4.5,0), radius:1, height:11 Script = jumpVelocity:20000 Jump Animation Clip: ~ 2 seconds. I am really out of ideas how to synchronize everything. Should I make the character jump in some other way so that it quickly comes down and touches the ground to match the animation clip? If yes, please provide a direction.

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  • Best way to update UI when dealing with data synchronization

    - by developerdoug
    I'm working on a bug at work. The app is written in Objective-C for iOS based device, for the iPad. I'm the new guy there and I've been given a hard task. Sometimes, the UIButton text property does not show the correct state when syncing. Basically, when the app is syncing, my UI control would say "Syncing" and when its not syncing it'll display "Updated @ [specific date]". Right now there is a property on the app delegate called "SyncInProgress". When querying / syncing, occurring on background thread, it updates a counter. The property will return a bool checking expression 'counter 0'. There are three states I need to deal with. Sync has started. Sync is updating tables. Sync finished. These items need to occur in order. My coworker suggested to take a state based approach instead of just responding to events. I'm not sure about how to go about that. Would it be best to have the UI receive a notification to determine what state its in or to pull every so often if state changed? Here are two posts that I put on stackoverflow, in the last few days, that relate to this. http://stackoverflow.com/questions/11025469/ios-syncing-using-a-state-approach-instead-of-just-reacting-to-events http://stackoverflow.com/questions/11037930/viewcontroller-when-viewwillappear-called-does-not-always-correctly-reflect-stat Any ideas that anyone might have to very much appreciated. Thanks, developerDoug

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  • Any experience on open source database synchronization open source solutions? [on hold]

    - by Boris Pavlovic
    I'm considering few database synchronization open source solutions. The system in need for data synchronization is composed of instances of different types of databases, i.e. heterogeneous system. There are few candidates: Symmetric DS Talend's Data Integration with support for data synchronization Continuent's Tungsteen Replication Daffodil Replicator OS Do you have any real world experience with any of these tools?

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  • Finding a backup and synchronization solution

    - by Andrea Zilio
    I'm having difficulties to find a backup and synchronization solution with the following characteristics: Cross-platform: Windows, Linux, Mac Offsite backup (so Internet Backup) Data deduplication Transfer only new/modified bits of modified files Secure: Data encrypted before leaving computer Maintain multiple versions of files (even deleted files) Folder synchronization integrated with backup and across multiple computers connected to the internet (not necessarily in the same LAN) I think that the Folder Sync feature needs a better explanation. The use case is this: you have a desktop pc and a laptop. The desktop pc contains a folder with some files and this folder is part of the backup (so it was selected to be backed up). The laptop does not contain that folder or that files at all. Then you're abroad with your laptop and you need that folder. So you want to be able to open the backup program, select that folder from the backup and download it in your laptop mantaining it synchronized with the backed up version. When you then come back home and switch on your desktop pc you want the folder we're talking about to be updated in the desktop PC. Does anyone knows any service with all these features? I've only found SpiderOak to support all the features I've mentioned but I'm not completely satisfied by the time taken to complete a backup. Sometimes it seems to hang for minutes with no reasons at all and folder synchronization occurs only after all files are backed up (instead folder sync should have a separated queue independent from other backup operations and synchronization should occurs frequently... for example every 5 minutes or less, independently from the frequency of normal backup operations)

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  • Please help to find a solution for two way, real-time synchronization on Centos 5.5 64Bit

    - by Vipul Limbachiya
    I am in need of a real time, two way synchronization software for Centos 5.5 / 64Bit. Here's little explanation: It needs to be able to perform: Two way synchronization. It must be realtime. By realtime means it can be almost realtime, i.e. a delay of 1 second for example is fine. And the folders are on the same server. I am currently using GlusterFS across two webservers. However, it has extremely poor small file read performance and it's slowing down my website. There's nothing more that can be done to improve this, I have already tested many configurations. As a solution, I was going to mount a RAM drive (tmpfs) that mirrors the GlusterFS web files but get the webserver to use the RAM drive. The issue is that I need two way realtime mirroring or replication between glusterfs and the RAM drive. I need this is as Apache writes files as wells. As I said, realtime two way synchronization across two folders. Which are in fact 2 different mounts points. The RAM (tmpfs) mount poing and the GlusterFS mount point. I already know about: Rsync - Which is one way Unison - Which is not realtime Please suggest me any solution free or paid. Thanks in advance

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  • Unidirectional synchronization and admin back-end

    - by HTF
    I have Wordpress installation on two web nodes (load balancing/failover). There is unidirectional synchronization from server A to server B so any updates must occur on the first web node. I have a problem with Wordpress admin side. I'm using Nginx and the initial plan was to create rewrite rule from domain.com/wp-admin to wpadmin.domain.com - pointing to the first node. The problem is that the Wordpress installation can be access only via main domain and without extra subdomain there is no distinction between both web servers for the rewrite rule. Could you please advise if there is any other solution in this case. Regards

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  • Rsync: General file/folder synchronization

    - by Rey Leonard Amorato
    I have a file server, which is in-charge of pulling a folder tree from multiple workstations on a daily basis. My current method for this is by using rsync, (which works pretty well provided directory names and/or files remain the same) however, when files are renamed or moved about within subdir1, rsync will copy them over to the server, creating duplicates. I have to manually find and delete extraneous files/folders that had been left on the server during previous syncs. Note that I cannot use rsync's --delete flag because any sync from a workstation will then mirror that particular folder tree, instead of merging them to the server. Visual diagram: Server: Workstation1 Workstation2 Workstation(n) Folder* Folder* Folder* Folder* -subdir1 -subdir1 -subdir1 -subdir(n) -file1 -file1 -file2 -file(n) -file2 -file(n) Is there a simple script (preferably in bash, nothing fancy) that can accomplish the deletion of the extraneous files/folders in the event a file is renamed or moved to a different subdir? Is there a different program, much like rsync that can accomplish this task autonomously and in a much simpler manner? I have looked at unison, but I did not like the fact that it keeps a local database for the syncing info. Any tips at all as to how I am supposed to tackle this? Thank you in advanced for your help. EDIT: I have tried unison just recently and I can safely say it is out of the question now. unison is a bi-directional synchronization tool and from my testing, it mirrors the files existing on the server to all workstations. - This is unwanted. preferably, i would want files/folders to stay within their respective workstations and just merge to the server. AKA uni-directional sync; but with renames/moves propagated to the server. I might have to look into Git/Mercurial/Bazaar as mentioned by kyle, but still unsure if they are fit for the job.

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  • Determine which active directory object is referred to by GUID in a Directory Synchronization Error Report

    - by Michael Shimmins
    We have active directory syncronization setup between our on-premises AD server and Microsoft hosted Exchange (business productivity online services). I've started getting a daily error report, which details an error for a specific AD user, however it references it by GUID. I can't find any info on how to translate that object guid into something meaningful so I can find and fix the problem. The error is reported as: Error 005: Unable to set the alias for this object in Microsoft Online Services because either the primary SMTP address, the e-mail nickname, or the SAM account name in the local Active Directory contains an invalid character. in reference to the Object GUID: CN={8443cbb4-5199-49f0-9529-ce965430dca6} How can I translate that object guid into a friendly object name?

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  • P2P synchronization: can a player update fields of other players?

    - by CherryQu
    I know that synchronization is a huge topic, so I have minimized the problem to this example case. Let's say, Alice and Bob are playing a P2P game, fighting against each other. If Alice hits Bob, how should I do the network component to make Bob's HP decrease? I can think of two approaches: Alice perform a Bob.HP--, then send Bob's reduced HP to Bob. Alice send a "I just hit Bob" signal to Bob. Bob checks it, and reduce its own HP, then send his new HP to everyone including Alice. I think the second approach is better because I don't think a player in a P2P game should be able to modify other players' private fields. Otherwise cheating would be too easy, right? My philosophy is that in a P2P game especially, a player's attributes and all attributes of its belonging objects should only be updated by the player himself. However, I can't prove that this is right. Could someone give me some evidence? Thanks :)

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  • Recognizing synchronization object hanging two 3rd party executables

    - by eran
    I'm using a 3rd party tool, which uses a 4th party plugin. Occasionally, the tool will hang when launched. Looking at the stack traces, I can see a few threads are waiting on WaitForSingleObject, and my bet is that they're blocking each other. Some of the threads start at the 3rt party tool, and some at the 4th party plugin. What I'd like to do is file the most detailed complaint to the 3rd party tool vendor, assuming it's its fault (I don't trust their local support to get those details themselves). For that, I'd like to: Find out what are the synchronization objects currently waited on Find out who has created those synchronization objects Tools currently at hand are VS2005, WinDbg and Process Explorer. OS is Window 7 64 bit. Any suggestions?

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  • notify listener inside or outside inner synchronization

    - by Jary Zeels
    Hello all, I am struggling with a decision. I am writing a thread-safe library/API. Listeners can be registered, so the client is notified when something interesting happens. Which of the two implementations is most common? class MyModule { protected Listener listener; protected void somethingHappens() { synchronized(this) { ... do useful stuff ... listener.notify(); } } } or class MyModule { protected Listener listener; protected void somethingHappens() { Listener l = null; synchronized(this) { ... do useful stuff ... l = listener; } l.notify(); } } In the first implementation, the listener is notified inside the synchronization. In the second implementation, this is done outside the synchronization. I feel that the second one is advised, as it makes less room for potential deadlocks. But I am having trouble to convince myself. A downside of the second imlementation is that the client might receive 'incorrect' notifications, which happens if it accessed the module prior to the l.notify() statement. thanks a lot

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  • Client-server synchronization pattern / algorithm?

    - by tm_lv
    I have a feeling that there must be client-server synchronization patterns out there. But i totally failed to google up one. Situation is quite simple - server is the central node, that multiple clients connect to and manipulate same data. Data can be split in atoms, in case of conflict, whatever is on server, has priority (to avoid getting user into conflict solving). Partial synchronization is preferred due to potentially large amounts of data. Are there any patterns / good practices for such situation, or if you don't know of any - what would be your approach? Below is how i now think to solve it: Parallel to data, a modification journal will be held, having all transactions timestamped. When client connects, it receives all changes since last check, in consolidated form (server goes through lists and removes additions that are followed by deletions, merges updates for each atom, etc.). Et voila, we are up to date. Alternative would be keeping modification date for each record, and instead of performing data deletes, just mark them as deleted. Any thoughts?

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  • What's a good scheme for multi-user database synchronization?

    - by Mason Wheeler
    I'm working on a system to allow multiple users to collaborate on an online project. Everything is fairly straightforward, except for keeping the users in sync. Each user has their own local copy of the project database, which allows them to make changes and test things out, and then send the updates to the central server. But this runs into the classic synchronization question: how do you keep two users from editing the same thing and stomping each other's work? I've got an idea that should work, but I wonder if there's a simpler way to do it. Here's the basic concept: All project data is stored in a relational database. Each row in the database has an owner. If the current user is not the owner, he can read but not write that row. (This is enforced client-side.) The user can send a request to the server to take ownership of a row, which will be granted if the server's copy says that the current owner is NULL, or to release ownership when they're done with it. It is not possible to release ownership without committing changes to the server. It is not possible to commit changes to the server without having first downloaded all outstanding changes to the server. When any changes are made to rows you own, a trigger marks that row as Dirty. When you commit changes, the database is scanned for all Dirty rows in all tables, and the data is serialized into an update file, which is posted to the server, and all rows are marked Clean. The server applies the updates on its end, and keeps the file around. When other users download changes, the server sends them the update files that they haven't already received. So, essentially this is a reinvention of version control on a relational database. (Sort of.) As long as taking ownership and applying updates to the server are guaranteed atomic changes, and the server verifies that some smart-aleck user didn't edit their local database so they could send an update for a row they don't have ownership of, it should be guaranteed to be correct, and with no need to worry about merges and merge conflicts. (I think.) Can anyone think of any problems with this scheme, or ways to do it better? (And no, "build [insert VCS here] into your project" is not what I'm looking for. I've thought of that already. VCSs work well with text, and not so well with other file formats, such as relational databases.)

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