Questions tagged [locks]

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

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0answers
34 views

Automatically extended database-based mutex lock - is it a good idea?

Since I am working in a multi-instance microservice environment, I came accross a problem with making some operations being performed at most by one of the running instances at once. The solution ...
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2answers
64 views

Locking (reserve) related Aggregate Roots

Problem In my application a user can lock a set of related aggregate roots to work exclusively on them and to avoid the usage of an invalid set of objects later in the process (by other employees). ...
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2answers
49 views

Calling an API and synchronising database

I am calling a payments API to send a payment. At the same time, I need to mark the payment as sent in my database. If I call the API first, then the database crashes, the payment will be sent twice. ...
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2answers
64 views

Alternatives to pessimistic locking in the DBMS for load balancing

A simplified version of my problem looks like this: the database contains two tables: one contains account balances (Accounts) the other contains account withdrawal and deposit requests (Requests) ...
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3answers
229 views

How to replace a file to its latest version in server that is being constantly fetched by a REST API

We have a REST API Get request which downloads a file from the server. This file needs to be updated whenever there is a latest version. Currently this is done by deleting the existing file and moving ...
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3answers
929 views

Why do we need read locks in read-write locks?

in read-write locks, why do we need read locks since processes can read a file at the same time? Would only a write lock suffice? Thanks.
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2answers
204 views

My aproach to lockless concurrency

this is a highly theoretical question about my parallelization approach. First of all, I want to inform everybody that I do not claim that I am the 'inventor' of that approach but I couldn't find any ...
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1answer
65 views

Will this time duration measurement in two threads give correct result?

A program I'm developing has two threads running similar but different task: thread1: timer1.start() writeToExternalDB1(consumedData) timer1.end() thread2: timer2.start() writeToExternalDB2(...
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1answer
164 views

Is async/await a good alternative for locks in JavaScript?

Yes, I know, the question title is a bit provocatory. But let me explain. I needed to execute a sequence of async tasks in JavaScript. They are async because I need them to be non-blocking, but I ...
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2answers
271 views

Designing a scalable microservice: how to prevent one instance from performing an action if another instance allready did?

As I am moving a part of the monolith app logic to a microservice, I am standing before a problem with scalability. Currently, the main monolith runs on different instances, and has some scheduled ...
4
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3answers
369 views

optimistic locking vs pessimistic locking

In the context of a multiuser database desktop application, the concurrency problem has to be considered. Many articles focus on two models: optimistic and pessimistic locking. In pessimistic locking ...
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2answers
1k views

Race condition in Distributed Systems

We have a set of micro-services that are functionally dependent and have intertwined validation logic. e.g. consider 'Credit-Card' service and 'Loan' service. When user has a credit card then loan ...
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3answers
6k views

Is there a problem using A LOT of locks in a process?

I'm trying to build a C# application that sends notifications from the server to its users (a mobile app). Since each user can have its notifications collection changed by any thread, I have to lock ...
0
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1answer
169 views

Locking an item while waiting for human approval

I'm working on adding Approval workflows around our system which manages CRUD operations for our business item. Till now, I have been using an optimistic locking strategy to handle race conditions ...
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2answers
684 views

Message Queue with multiple consumers locking synchronous on a field

We have a system where multiple consumers get messages out of a queue (currently implemented with a database). The messages have an order field. All messages of one particular order should be ...
2
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2answers
137 views

Name of locking approach

I've seen this approach several times, both in async and multithreaded code. A counter is used to track asynchronous behavior or thread behavior - whenever a new action is started, the counter is ...
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2answers
60 views

Ensuring that Lock goes from Process A to Process B

Let's say process A has an exclusive lock on some shared resource. Is there a way to ensure that after it completes execution, Process B will definitely get the lock (as compared to say, process C ...
4
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4answers
1k views

How to check whether existing code base can deadlock

I'm improving/expanding a somewhat large code base, and I've introduced multithreading into it. But with the possibility of introducing code that could deadlock, which is nigh impossible to test for ...
3
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1answer
221 views

What is the typical best practice methodology around transferring money between two distinct systems?

I got this question on an interview the other day and was clueless to what the best practices are for solving it. It's the issue where you have to transfer money between two systems and want to avoid ...
0
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1answer
397 views

Robust locking mechanism between n service instances

I have a job that runs every hour. There can be n identical Node.js microservices running in a stack. The job must be executed only once per hour, though, so I've implemented the following locking ...
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1answer
135 views

Avoidance of Lost Update in DB2 for z/OS

I have a question concerning the "Uncommitted Read" Isolation Level under DB2 DBMS for z/OS. In this article https://www.ibm.com/support/knowledgecenter/en/SSEPEK_11.0.0/perf/src/tpc/...
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1answer
679 views

Why would CPython logging use a Lock for each handler rather than one Lock per Logger?

While developing my own logging library, I studied the source code of the standard logging module of CPython. One of its features is that handlers are thread-safe. One can write logs to a file from ...
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2answers
2k views

How to handle concurrent updates for the same record in a distributed system

I'm trying to figure out the best solution for the below. Any help would be great. So basically I have a service (that can be scaled horizontally), which listens on a queue. Every message received ...
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1answer
127 views

Inventory management with limited time hold strategy - How do I protect from bad actors?

Some sites, like theater ticket reservations, place a limited-time hold on the item , while the order is being processed. As soon as you select the seat and proceed to pay, Seat is reserved say for 10 ...
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2answers
405 views

Optimistic locking with business constraints [closed]

Consider this simple example: Tables (in a restaurant) can be booked for a period. Business constraint: No two table bookings for the same table may overlap in time. How might one prevent business ...
2
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1answer
209 views

Design lease mechanism of shared resource

I have a shared resource in a database that is used by clients C1 and C2. Before the resource is read by C1, C1 should mark the resource as leased so that C2 will know it is busy. C1 will do some ...
2
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2answers
272 views

Achieving very large real-time async writes on MySQL tables without locking them to reads

I am building a webapp (Angular frontend, Groovy/Spring/Hibernate/MySQL backend) that will allow users to compete against each other over certain activities. Each activity will have 1 winner and 1 ...
4
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1answer
1k views

Automatic blocking/unblocking of allocated seats in a movie ticketing system [closed]

I am trying to build a movie ticketing system. But I am not able to figure out how to solve the below use case: Let’s say there are 10 seats namely S1,S2,S3,S4… S10. Now let’s say that User1 had ...
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3answers
1k views

Is the Actor Model an alternative to transactions?

I know that transactions use locks. It is claimed that actors liberate us from shared state and locks make sure all crashes are the same as clean shutdowns: this can be done through practices such ...
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2answers
126 views

Problem related to optimistic locking performance

I'm designing a system that like the majority of social related application has posts, people can like the posts and comment on them. And also like the majority of the applications the users can see ...
4
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1answer
5k views

When is it safe to use Monitor (lock) with Task?

In a multi-threaded environment, we must consider concurrent access to writable resources. A common approach is to use Monitor or its shorthand form lock. Task is at a different abstraction level ...
4
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1answer
1k views

Race condition allowing multiple transactions; will locking on objects in a dictionary cause issues?

We have a MVC Web API that is called to write transactions for a specific amount, where the amount is debited or credited to a user's balance. This records the balance pre-transaction (PreAmount), the ...
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2answers
311 views

When interacting with an ArrayList over REST will a ReadWriteLock maintain consistency?

I have an ArrayList of objects that may be added/deleted/updated via REST calls. In order to prevent issues that may result from concurrent accesses, will a ReadWriteLock be appropriate, and efficient?...
4
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1answer
1k views

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 ...
3
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1answer
1k 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 ...
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5answers
1k 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 ...
0
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1answer
168 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
463 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
541 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
41 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 ...
42
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5answers
6k 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 ...
9
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2answers
5k 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 ...
4
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0answers
342 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
100 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 ...
5
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1answer
4k 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 ...
9
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3answers
16k 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 ...
27
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3answers
7k 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
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3answers
4k 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 ...
2
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2answers
2k 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
2k 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 ...