Hello, I'm trying to learn the basic jist of a Semaphore in the Dining Philosopher problem. Right now, I have an array of class Chopstick, and each Chopstick has a semaphore with 1 available permit: public class Chopstick { Thread holder = null; private Semaphore lock = new Semaphore(1); public synchronized void take() thro...
Now, I'm not sure whether this is a stupid question, please bear with me if it is. Is the lock on an object "recursive", i. e. if two objects have references to a third object in their fields and a thread is running a synchronized method on one of the two, can any other thread access the third object? // a and b are some objects that i...
I would like some advice from anyone experienced with implementing something like "pessimistic locking" in an asp.net application. This is the behavior I'm looking for: User A opens order #313 User B attempts to open order #313 but is told that User A has had the order opened exclusively for X minutes. Since I haven't implemented th...
I have 2 batch programs, 1 is a program that sends email and another one sends fax. They both access a table named QUEUE. In the email sender program, this is what happens in relation to QUEUE. For each record in QUEUE that satisfies criteria: Locks record 1 in QUEUE table: select 1 from QUEUE with (UPDLOCK) where id = 1 Process s...
This is a significant edit from the original question, making it more concise and covering the points raised by existing answers... Is it possible to have mulitple changes made to multiple tables, inside a single transaction, and rollback only some of the changes? In the TSQL below, I would NOT want any of the changes made by "myLogSP"...
I have multiple asp.net web apps serving a set of files. Periodically, one will update the file before serving it, but it can't update the file if it is in use. I could solve this issue by using a named mutex where the name is the file path (replacing the invalid characters of course). I've used this in other situations, but you can see...
Wouldn't this be overkill and only one of these necessary? I've searched and found different posts about Mutual Exclusion and locks in C# here and here. Example: In our app, we have a function that spins off multiple reconnection threads and inside this thread we use a Mutex and a lock. Wouldn't lock block access to this section of code ...
Let's say I have a table of promo codes, and a table of contacts. Each contact can have 1 promo code, and each promo code can only be assigned to 1 contact. How would I employ an assignment program that would select a promo code from the table, and assign it to a contact, without having concurrency issues/collisions. Worst case scenar...
I am not a great VB programmer, but I am tasked with maintaining/enhancing a VB6 desktop application that uses Sybase ASE as a back-end. This app has about 500 users. Recently, I added functionality to this application which performs an additional insert/update to a single row in the database, key field being transaction number and the...
Would prefer an answer in C#, .Net 3.5 using WPF (Windows Forms also okay) I have an application that is essentially a toolbar window or tray icon. It needs to detect if a user locks his/her workstation and walks away in order to update the person's status in a centralized system. I can detect a session switch or a logout easily enoug...
I'm using rsync to run backups of my machine twice a day and the ten to fifteen minutes when it searches my files for modifications, slowing down everything considerably, start getting on my nerves. Now I'd like to use the inotify interface of my kernel (I'm running Linux) to write a small background app that collects notifications abou...
I'm building an application with the following criteria: work items: items that need to be manually worked via the web by users (short one page form) Multiple users working 'work items' Each user has a queue of 'work items' There is a search that allows users to view 'work items' and assign 'work items' to their queues Users can take '...
See this code: public class multiply { public Thread myThread; public int Counter { get; private set; } public string name { get; private set; } public void RunConsolePrint() { lock(this) { RunLockCode("lock"); } } private vo...
In my application I want to be informed by events, that another application has been started or stopped. I have an existing API to the running application which cannot be changed to accomodate notification which would be the obvious solution. What I have is a function call in the API (isRunning), so I decided to make a polling thread wh...
I'm developing a php / mysql application that handles multiple simultaneous users. I'm thinking of the best approach to take when it comes to locking / warning against records that are currently being viewed / edited. The scenario to avoid is two users viewing the record, one making a change, then the other doing likewise - with the po...
I'm running a very computationally intensive scientific job that spits out results every now and then. The job is basically to just simulate the same thing a whole bunch of times, so it's divided among several computers, which use different OSes. I'd like to direct the output from all these instances to the same file, since all the com...
My project has an object that creates a process. It this object's Dispose function, it kills the process (or tries to). However, if the program crashes, it leaves the process running and doesn't clean up. Which causes the program to fail next time because it tries to launch the process again and can't get a lock on it. How can I make su...
Hi, I have a situation where before doing a particular task I have to check whether a particular flag is set in DB and if it is not set then rest of the processing is done and the same flag is set. Now, in case of concurrent access from 2 different transactions, if first transaction check the flag and being not set it proceeds further. ...
Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when i...
I read spin lock code from here, especially this part inline void Enter(void) { int prev_s; do { prev_s = TestAndSet(&m_s, 0); if (m_s == 0 && prev_s == 1) { break; } // reluinquish current timeslice (can only // be used when OS available and // we do NOT wa...