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
6
votes
3 answers
Way to synchronize reads and writes in Clojure?
In a web app I'm trying to generate a unique thread safe id from a limited id pool. The problem I'm facing is that between reading and writing another thread may already have changed the data structure; this is why I have to resort to…
Philip Kamenarsky
- 2,757
- 2
- 24
- 30
6
votes
1 answer
scala/akka/stm design for large shared state?
I am new to Scala and Akka and am considering using it to solve a problem. Suppose I have a calculation engine (that searches for a solution). I'd like to parallelize that search both across cpus and across nodes by giving each cpu on each node its…
AllanC
- 61
- 1
6
votes
1 answer
Safe to use unsafeIOToSTM to read from database?
In this pseudocode block:
atomically $ do
if valueInLocalStorage key
then readValueFromLocalStorage key
else do
value <- unsafeIOToSTM $ fetchValueFromDatabase key
writeValueToLocalStorage key value
Is it safe to use…
Philip Kamenarsky
- 2,757
- 2
- 24
- 30
6
votes
1 answer
Haskell, Channels, STM, -threaded, Message Passing
I am trying to use channels/STM to implement message passing in Haskell. Maybe this is a terrible idea, and there is a better way to implement/use message passing in Haskell. If this is the case, do let me know; however, my quest has opened some…
Jonathan Gallagher
- 2,115
- 2
- 17
- 31
6
votes
1 answer
Validation in STM transactions nested with orElse
This commentary page describes a lot of the fine details of STM in GHC, but I'd like clarity on a couple points.
First, is a nested transaction invalidated when variables accessed in the parent change?
For instance we have in thread A:
takeTMVar a…
jberryman
- 16,334
- 5
- 42
- 83
6
votes
2 answers
STM.NET versus Clojure STM
I'm wondering how is that possible that Clojure has implemented Software Transactional Memory and doesn't see any problem with that while Microsoft didn't finish its work for C# and noticed some problems which make it unpractical to implement STM…
user1121956
- 1,843
- 2
- 20
- 34
6
votes
3 answers
STM hash library for C (glib?)
I'm looking for some C library that includes STM-style (Software Transactional Memory) hash maps, but I had no luck so far. It would be great if it was based on glib / gobject, but it's not that crucial. It also doesn't need proper transactions over…
viraptor
- 33,322
- 10
- 107
- 191
6
votes
1 answer
Should multiple Clojure refs be read in a transaction for consistency?
This is a theoretical question motivated by my desire to understand Clojure's concurrency better.
Let's say I'm writing boids. Assume each boid is a separate green thread mutating positions in a vector or refs representing a world grid. Think…
Thomas Heywood
- 903
- 2
- 9
- 18
5
votes
1 answer
TransactionalMap vs SynchronizedMap
When should one prefer Akka TransactionalMap over regular immutable map mixed in with SynchronizedMap and vice versa? (Or am I comparing apples to oranges here?)
missingfaktor
- 90,905
- 62
- 285
- 365
5
votes
1 answer
Testing STM functions purely
I've recently started using STM for some bits in a project of mine, but I'm having trouble figuring out how to test it.
I have no IO in these functions and was hoping I could write QuickCheck properties to test things, but "atomically" (STM a -> IO…
Adam Wagner
- 15,469
- 7
- 52
- 66
5
votes
1 answer
STM and outgoing IO
If I am inside a STM whose transaction fail, and I retry as part of the normal control flow (no STM collision etc..), I might want to indicate to someone outside a way to take corrective action.
If it's purely 'outgoing', then my STM can still be…
nicolas
- 9,549
- 3
- 39
- 83
5
votes
1 answer
Does STM provide fine-grained locking for existing data structures?
Reading Bartosz Milewski's fantastic blog post on STM, I was excited to read the following:
But take into account an important fact: STM is very fine grained. For
instance, when you’re inserting an item into a tree, the STM
transaction will…
Daniel Buckmaster
- 7,108
- 6
- 39
- 57
5
votes
1 answer
Possible improvements in clojure "official" concurrency example (using locks,atoms,stm)
i am trying to get the "official" example of clojure concurrency closer to a java version using manual locking. In this gist i put the java and clojure code and the thread dump of a VisualVm profile of all versions.
Here it is the clojure code and…
jneira
- 944
- 10
- 18
5
votes
1 answer
What is wrong with the following solution to the "Dining Philosophers"?
In order to get familiar with STM in Haskell, I wrote the following solution to the Dining Philosophers problem:
import Control.Concurrent
import Control.Concurrent.STM
import Control.Monad
import System.Random
type Fork = TVar Bool
type…
Alexandros
- 3,044
- 1
- 23
- 37
5
votes
2 answers
Haskell: Updating two or more TVars atomically. Possible?
Can one transaction update two different TVars in an atomic way? i.e. can I compose data structures out of lots of TVars to reduce contention? If so, could you provide an example?
Clinton
- 22,361
- 15
- 67
- 163