Software transactional memory (STM) is a mechanism for synchronization in concurrent programming, which can perform groups of memory operations atomically. Using transactional memory (implemented by optimistic synchronization) instead of locks removes the risk of a deadlock.
Questions tagged [stm]
190 questions
4
votes
2 answers
Large Data Structure in Clojure STM for Banking Transactions LOOP
I am new to Functional Programming and Clojure, so I am not really sure about what to do for a project at University. The project should show the advantage of Clojure STM for banking transactions (Transfer of money from account A to account B).
So I…
nuvio
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4
votes
3 answers
Readers-writers using STM in Clojure
There is the following version of readers-writers problem: multiple readers and writers, 2 or more readers can read simultaneously, if a writer is writing no one can read or write, it is preferred if all writers get an equal chance to write (for…
bvk256
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4
votes
1 answer
Why does this TCP server immediately exit?
This is an extraction I did from a larger project, which didn't seem to have the issue of the server immediately returning (I'll admit the reason I did the extraction in the first place was in the hope of asking a different question regarding…
bbarker
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4
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3 answers
STM and alter in clojure
I am working through the Programming Clojure book. While explaining alter and the STM, they say that if, during an alter, Clojure detects a change to the ref from outside the transaction, it will re-run the transaction with the new value. If that is…
Matt Briggs
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Why is an atomic block in Scala run twice when exception gets thrown?
Code:
object Blub {
import scala.concurrent.stm._
val last = Ref("none")
def bla() = atomic { implicit txn =>
last() = "outer"
try {
atomic { implicit txn =>
last() = "inner"
println(last())
throw new…
Lohmi
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4
votes
1 answer
Memory leak when using Control.Concurrent.STM.TBQueue
I have two threads: producer and consumer. Producer produces some (key,value) pairs and consumer inserts them into Map, wrapped into Data.IORef. I tried to use Control.Concurrent.BoundedChan for communication between producer and consumer, and it…
user2155932
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Race condition in Clojure stm?
Hello I was reading the book joy of clojure and in the section about the STM they have an image of 2 transactions where A is initially retrieving the same value from a ref as B is and then both transaction A and B does their calculations but A…
Tobias
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4
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2 answers
Clojure commute and alter performance
There is a little bit modified example from clojure.org/refs
(defn mod-nth [v i f] (assoc v i (f (v i))))
(defn run [oper nvecs nitems nthreads niters]
(let [vec-refs (vec (map (comp ref vec)
(partition nitems (repeat (*…
Odomontois
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4
votes
1 answer
How to handle or avoid BlockedIndefinitelyOnSTM exception?
I spent quite a lot of time troubleshooting an issue I had in the application I am working on. This application is a web app, exposing REST endpoints using scotty. It uses a TVar to hold its state which is updated through STM a actions triggered by…
insitu
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4
votes
1 answer
Haskell one way `dupTChan`
Is there any function like dupTChan except that when you do:
newChan = dupTChanOneWay oldChan
Anything written to oldChan is written to newChan, but not the other way around?
PyRulez
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4
votes
2 answers
Agent not getting executed
I have a series of functions (like some-operation in the example), which I send or send-off to agents:
(defn some-operation [agent-state]
(dosync
(let [updated (foo agent-state)] ;; derive new state from old one
(alter bar whatev updated)…
deprecated
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4
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2 answers
Clojure STM ambiguity factor
In Clojure we use STM for Concurrency.
My question is STM uses point in time value of data , isn't this introduce ambiguity ?
How could we know what value is accessed ?
nish1013
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4
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1 answer
Haskell: TChan wrapping duplicated while using lens to modify state
Consider the following code (and error):
import Control.Lens
import Control.Monad.STM
import Control.Monad.IO.Class
import Control.Monad.State.Lazy
import Control.Concurrent.STM.TChan
data Broadcast = Broadcast Int
data ImmutableState =…
kvanbere
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4
votes
1 answer
Is there a bug in this clojure solution to sleeping barber?
This is presented as a solution to the sleeping barber problem. (Attributed to CGrand, but I found the reference here)
I'm curious about the dosync block in enter-the-shop. My understanding is that this is a transaction, and so empty-seats will…
Dax Fohl
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4
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1 answer
Are refs really consistent within a STM transaction?
I read at clojure.org/refs that
All reads of Refs will see a consistent snapshot of the 'Ref world' as of the starting point of the transaction (its 'read point'). The transaction will see any changes it has made. This is called the…
sw1nn
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