Real-World Concurrency (2008)(queue.acm.org)
queue.acm.org
Real-World Concurrency (2008)
http://queue.acm.org/detail.cfm?id=1454462
13 comments
And that's why I love Node.js: the single-threaded concurrency (or should I say non-concurrency?) is built-in in the execution model. Building your architecture decoupled from the ground up is useful, and Node.js does a great job at it.
I found Redis is an awesome middleware for MQ purposes. Its builtin PubSub system, blocking POPs and amazing speed make it a perfect fit.
But beware: it's easy to get it wrong and make the system a tangled mess of messages. Just make sure the message dispatch overhead is worth it.
I found Redis is an awesome middleware for MQ purposes. Its builtin PubSub system, blocking POPs and amazing speed make it a perfect fit.
But beware: it's easy to get it wrong and make the system a tangled mess of messages. Just make sure the message dispatch overhead is worth it.
Is node actually able to use more than one core now?
It has been able to for a while! Check out the cluster module, processes listening to the same port are load balanced and communication between processes is obviously (since each process only has 1 thread due to the event loop) done by message passing.
Technically spakeaing: no, and it never will. Single-threading is by design, so the best bet is to run several processes, each using one core (see the other answer to your comment).
I would rather recommend chapter on deterministic concurrency in this paper: http://community.haskell.org/~simonmar/par-tutorial.pdf
[In particular `par` and promises.]
This solution is quickest to debug, and most efficient. One can also use multiprocessing-like approach: http://docs.python.org/2/library/multiprocessing.html
My last 15 years of practice indicate that other approaches lead to unnecessary complication, and are less likely to be effective (threads and semaphores in particular.)
This solution is quickest to debug, and most efficient. One can also use multiprocessing-like approach: http://docs.python.org/2/library/multiprocessing.html
My last 15 years of practice indicate that other approaches lead to unnecessary complication, and are less likely to be effective (threads and semaphores in particular.)
That!
Message passing is a reasonable approach. Its particularly simple to design, and deadlock-free if message processors don't block on further messages.
Drawbacks: Simplest when each message class (or queue) has one thread to handle it. But that doesn't optimize for available hyperthreads.
Message passing is a reasonable approach. Its particularly simple to design, and deadlock-free if message processors don't block on further messages.
Drawbacks: Simplest when each message class (or queue) has one thread to handle it. But that doesn't optimize for available hyperthreads.
Message passing is often insufficient without a centralized concurrent data structure (a database can serve that purpose). That is why Erlang has ETS (but that only guarantees isolation for single entity transactions), and Akka and Clojure have STM (and the Java concurrent data structures).
Is there something preventing people from writing correct, multi-threaded apps in Clojure (and kicking Python/Rubys asses)?
Clojure actually has a lot of stuff in its design specifically for multithreading. Like the GP post said, Clojuer has Software Transactional Memory (STM) on top of immutable data structures to make messing up multithreaded programs hard, and you'd almost have to deliberately do so.
And yes, like another reply says, Clojure (and pretty much anything that's designed well and runs on the JVM) is much, much faster than Python/Ruby by default. A lot of this has to do with the JIT compiler that Java has been working on for a long time, which Python/Ruby don't have outside of an PyPy implementation. Also Python/Ruby don't have access to actual threads by default, because it has a global lock. They run everything basically in a single thread.
And yes, like another reply says, Clojure (and pretty much anything that's designed well and runs on the JVM) is much, much faster than Python/Ruby by default. A lot of this has to do with the JIT compiler that Java has been working on for a long time, which Python/Ruby don't have outside of an PyPy implementation. Also Python/Ruby don't have access to actual threads by default, because it has a global lock. They run everything basically in a single thread.
That is exactly my question. If Clojure has got great performance and great multithraeding support, why haven't it gained a greater share of the dynamic languages market?
No. Python/Ruby/Javascript don't even come close to JVM performance even without multi-threading, though.
"This article is half stern lecture on the merits of abstinence and half Kama Sutra."
"When problems resist parallelization or have no appreciable latency to hide, the third way that concurrent execution can improve performance is to increase the throughput of the system. Instead of using parallel logic to make a single operation faster, one can employ multiple concurrent executions of sequential logic to accommodate more simultaneous work. Importantly, a system using concurrency to increase throughput need not consist exclusively (or even largely) of multithreaded code. Rather, those components of the system that share no state can be left entirely sequential, with the system executing multiple instances of these components concurrently. The sharing in the system can then be offloaded to components explicitly designed around parallel execution on shared state, which can ideally be reduced to those elements already known to operate well in concurrent environments: the database and/or the operating system."
Even if you can't use the database or os and still want to get "multiple concurrent executions of sequential logic" then just use a message queue. That's what Go provides, what blocking queues in java provide, what most actor based systems provide (e.g. Akka, Dart), what unix pipes provide and what all kinds of inter process messaging systems provide. Most of your code can as impure, sequential and lock free as it always was. You only have to make your messages immutable.