Locks are a synchronization mechanism for enforcing limits on access to a resource.

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Monitor.Enter() when a thread is of highest priority

Background Okay, so let's say I have some high priority (ThreadPriority.Highest) thread t which needs to enter a critical region in order to consume some data. I will use the following code snippet ...
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1answer
73 views

Why many programs do not start if pidfile exists but no process is found?

I see a lot of programs that does write a pidfile, and check at boot its existence. And this is good. But many application does not start even if they check that the pidfile exists, yes, but no ...
9
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4answers
298 views

Composable concurrency in Java or any other programming language

While I was reading a research paper on concurrency named Software and the Concurrency Revolution (html version). I came across following lines: Unfortunately, although locks work, they pose ...
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1answer
64 views

Concurrent languages and non-concurrent dependencies [closed]

We had a bug caused by ruby workers (4 processes, 1 thread each) doing batching records using a legacy mongodb as the store. The race condition was around whether the batch was full or not; with one ...
4
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2answers
297 views

What is it called when threads are waiting but not deadlocked

The definition of a deadlock is when two or more threads cannot complete their execution because they are mutually blocked and waiting for something from the other thread(s). Is there a similar term ...
3
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1answer
135 views

Minimizing lock time (multithreaded app)

I have a web application written in C# which uses external dll written in C++. Communication between clients (web browsers) and a web application is done using SignalR. For communication between web ...
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0answers
30 views

Push instead of pull on a list that might change due to a command in addition to events? [closed]

I need to show a refreshable/searchable list of items and update/add-to it whenever an event is published. How do I make sure no events are lost while refreshing/searching is happening? Some sort of ...
38
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5answers
2k views

How is spinlock different from polling?

Is spinlock and polling the same thing? Wikipedia: a spinlock is a lock which causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking if the lock is ...
4
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2answers
382 views

Why is Akka good for concurrency?

I am new to Akka and actor framework - I am sure I am missing something obvious, please accept my apologies in advance. I keep reading that one of the main points to choose Akka is the way it manages ...
2
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0answers
77 views

How can I diagram data-locking scenarios?

There are many different types of charts and diagrams we use to formalize scenarios and study them tangibly -- activity diagrams, sequence diagrams, etc. I've been faced with a pretty complex locking ...
3
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1answer
75 views

Coordinate access to resource between workers

I have a database accessed by an several servers, let's call them workers. These workers take one item from the database, do some operations on it and then update it back into the database. The ...
1
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1answer
165 views

Does ReaderWriterLockSlim provide thread safety and speed efficiency (compared to a traditional lock) when using a List?

I have a list, to which I write once in every update Loop and then I spawn some tasks which create read that List and create a duplicate to manipulate that data. More or less it's List.ToList() call ...
1
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3answers
207 views

Reading file during write on linux

As I understand, when a file is being written, the process writing to the file obtains an exclusive lock. So other processes cannot access this file for read. With the above knowledge, I'm unable ...
25
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3answers
4k views

How much work should I place inside a lock statement?

I am a junior developer working on writing an update for software that receives data from a third-party solution, stores it in a database, and then conditions the data for use by another third-party ...
2
votes
3answers
809 views

Accessing shared data without blocking in TPL

I am writing a class that contains data. It exposes methods that allow to query the data, while the data is also being updated from an external source (web service, for example). All the methods ...
1
vote
2answers
572 views

Why don't we see (more) widespread adoption of lock-free dynamic memory allocators? [closed]

In a multithreaded programming environment, lock contention on the heap is often enough a performance bottleneck. Theoretically at least, the cream-of-the-crop solution for this problem is to have ...
0
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2answers
446 views

Scaling locks in high concurrency web apps [closed]

Our web application has a certain resource type that is shared accross multiple users, and may thus be read and written by anyone at anytime. We resorted to the usual suspects, database transactions ...
2
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2answers
234 views

Shared & exclusive locking

I need a "lock" that can be either shared or held exclusively, that will provide the following behavior for the following sequence of events: Process A: Requests and is granted a shared lock Process ...
2
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2answers
358 views

Alternative locking strategies

I'm having a problem with the design of my application, that neither optimistic nor pessimistic locking tends to solve. Here is a simplified/altered version of the problem that describes the situation....
2
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1answer
53 views

performance issues when synchronizing on an interned String

I want to lock a remote file with the string "ip + filename" using java. public boolean execCmd(String ip,String filename, String command) { String file = ip + filename; String lock = file....
6
votes
6answers
1k views

What is the actual reason that locks (sentinels) in OO are hard to reason about? [closed]

In this talk, Rich Hickey introduces Clojure. He gives an Ants demo and talks about his motivations for implementing a Software Transactional Memory (STM) system. His reasoning for STM is that "...
1
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0answers
199 views

Is this synchronization required in service onCreate method?

Below is a sample code i captured from android doc Per service instance onCreate will be called only once. Ref: here and here The synchronization and singleton doesn't make any sense to me in this ...
1
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1answer
162 views

Synchronized access to network industrial equipment

I have an industrial equipment which is controlled by a software. The software connects to it using sockets, and keeps the connection all the time alive, while from time to time sending commands to ...
3
votes
1answer
153 views

How do I handle online payment for items with single quantity? [duplicate]

I would like to implement a robust way to handle ecommerce payment for items with limited quantity, like for example exclusive paintings. Payment would ideally be accepted via PayPal and credit cards....
1
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1answer
117 views

Locking database records

What I have right now: A table with lot of records. About 200 users can select a record according to some rules based on the data in each record. There is a high chance that 2 or more users will ...
20
votes
4answers
4k views

What prevents a race condition on a lock?

I understand the basics of what data races are, and how locks/mutexes/semaphores help prevent them. But what happens if you have a "race condition" on the lock itself? For example, two different ...
1
vote
3answers
383 views

Is it possible to perform mutual exclusion of threads without OS support?

I suppose you could adapt distributed mutual exclusion algorithms (Ricart/Agrawala, etc), but aside from these more exotic approaches, are you required to use primitives provided by the OS in order to ...
1
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1answer
364 views

Design pattern for locking asynchronous operations in Objective-C

I'm writing my first Objective-C Class. It's responsible for interaction with an HTTP SSO authentication service. The process requires multiple HTTP transactions in order to complete. The Class acts ...
3
votes
1answer
152 views

Are mutexes assigned to specific regions of memory?

I'm currently reading C++ Concurrency in Action by Anthony Williams and I'm facing an obstacle in thought. First he describes deadlocks as when two threads lock simultaneously (at least, that's how I ...
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2answers
234 views

How do I find a good middle way to make this library safe for concurrent operations

I've made a little library called SignalR.EventAggregatorProxy Before I push it into 1.0 state I need to fix so it works safely with concurrent operations. Easiest way is lock all operations but ...
1
vote
1answer
1k views

Handling or preventing conflicts in a multi-user system

I have a web application that is accessed by multiple users from different locations worldwide. Let's say I have an "edit" form for a specific document and two (or more) users are editing the document ...
1
vote
1answer
167 views

How to implement a distributed proxy with quotas?

I'm in the process of developing a scalable proxy (Linux/C/C++, Nginx modules or custom HTTP server) handling incoming HTTP requests, and re-routing them to others locations based on parameters ...
13
votes
1answer
2k views

Best practise is not to poll…but isn't polling happening internally anyway when a thread calls wait()?

Say we have some thread that wants to check when another thread is finished its task. I have read that we should call a wait() type function that will make this thread wait until it receives a ...
6
votes
4answers
1k views

Is Using Locking/Unlocking in Version Control an Anti-Pattern?

Recently I've started using Git at work. Previously I've only ever used VSS (which has some problems) and so far, Git is orders of magnitude better. The key differences here is that Git is ...
3
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1answer
118 views

Object locking over Internet

I am building a tutoring application that can be used to draw objects and then one is able to drag them around. I would like to know what is the best thing to do when someone clicks on an object and ...
5
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2answers
9k views

PHP file_put_contents File Locking

The Senario: You have a file with a string (average sentence worth) on each line. For arguments sake lets say this file is 1Mb in size (thousands of lines). You have a script that reads the file, ...
30
votes
5answers
5k views

Does immutability entirely eliminate the need for locks in multi-processor programming?

Part 1 Clearly Immutability minimizes the need for locks in multi-processor programming, but does it eliminate that need, or are there instances where immutability alone is not enough? It seems to ...
4
votes
1answer
599 views

Reading and conditionally updating N rows, where N > 100,000 for DNA Sequence processing

I have a proof of concept application that uses Azure tables to associate DNA sequences to "something". Table 1 is the master table. It uniquely lists every DNA sequence. The PK is a load balanced ...
1
vote
1answer
402 views

Implementing Bulk Update feature and its trade offs

The feature to implement is to allow a user to select items and apply data update in bulk. It is very similar to JIRA's ability to bulk update a list of selected issues. In my case: I iterate over ...
10
votes
5answers
3k views

Best-practice to manage concurrency into a basket in a e-commerce website

What is the best practice to manage the case where two customers add in the same time a product whose the stock was only 1 ? Must there be a check in the code of the basket to avoid one of these 2 ...