[yetkin]

The problem is not the threads, it is the mutations of variables which boost the complexity of the code. So a tutorial on creation of theads actually an invitation to hell. Nothing is cool about it. Cool thing is achieving concurrency without threads/race conditions/shared memory

[cle]

A computer is a mutation machine, you cannot escape mutation by hand-waving it away. If you are writing programs in which you can achieve concurrency without threads and shared memory, it’s because you’re building on the shoulders of all the engineers who didn’t hand-wave it away. Many of us, due to product requirements, don’t have the luxury of using higher level abstractions like that.

[mrkeen]

And yet we're comfortable hand-waving GOTO away - that is, not calling computers GOTO machines.

[cle]

There are thousands of engineers (at least) who use it or its equivalent every day. Just because they’ve built abstractions that allow you to ignore it, doesn’t mean nobody has to deal with it anymore.

[lostcolony]

But that's identical to what he's saying; he's not saying no one has to deal with mutable memory. Just that most developers who need concurrency shouldn't have to. Same as registers, GOTO, etc.

[cle]

That's not what they said. They said "nothing is cool about a tutorial on creation of threads", and that the cool thing is "achieving concurrency without threads/race conditions/shared memory" which ironically is only enabled by all the engineers who spend their time working on and maintaining those "uncool" things.

If they don't need to use threads, then good for them. But to dismiss threads and learning material about threads as "uncool" is just silly. The thing that enables that misunderstanding is all the work that's done on them in the first place.

[Nursie]

There's a lot cool about threads, and you can learn to implement them well.

Threads handled well do not need to have race conditions, and race conditions/deadlocks are also very possible in distributed, message-passing systems.

[mrfox321]

Can databases be efficiently implemented without shared access?

Can message passing accomplish this at the same level of performance?

although I agree that simplifying resource access should probably be considered before fully shared state.

[mrkeen]

> Can databases be efficiently implemented without shared access?

Let me ask a different question: Why did databases take off in the way they did? Sure they persist stuff to disk, but so do files. What they offer is a concurrency model so good that you almost never think about it. Beginner programmers can competently write large, concurrent systems by writing single-threaded programs which are backed by a central DB, without even knowing the term "race condition".

If beginner database articles told users how to make database Threads, Thread groups, and how to signal and catch interruptions, I don't think databases would have enjoyed nearly as much popularity.

While Threads are fundamental to Java concurrency, I kinda agree with yetkin's point. It introduces the Thread footgun without even paying lip service to the problems of shared, mutable state.

[agumonkey]

Do you use other paradigm / languages ? (clojure comes to mind, but maybe others)

[rowls66]

I'll add Pony to the list. This language uses the actor model like Akka and Erlang, but allows for the safe sharing of data between actors enforced by an an ingenious use of the type system. The result is an actor programming model with better performance than Erlang because mutable data can be safely shared.

I have been a long time Java developer, and I have worked a lot with highly concurrent code. Pony really opened my eyes to what was possible.

Unfortunately, the language, standard library and runtime is still pretty immature. It does however have very good 'C' interop. So for some problems it would be a very good fit.

[itronitron]

For Java at least, the Java Concurrency API is preferred.

[abhishekjha]

Akka actor framework comes to mind. I am in the process of learning it and it is definitely simpler to wrap your head around it.

[mrjoelkemp]

Actor model with Elixir/Erlang and the BEAM VM.

[Igelau]

All the cool people are in Hell. Only go to Heaven for the climate.

[FpUser]

The concepts of threads and concurrent data access is simple enough for any decent programmer to comprehend. There is no hell here. Sure there are some complex cases but complex cases will arise in many situations when programming things.

And achieving concurrency without shared memory is impossible in general case. Sure it is possible to isolate such access to a separate layer and make it transparent for the rest of the program but someone still has to program such layer.

[JackFr]

The problem for novices is that a program that behaves correctly looks a lot like a correct program. Until one day it doesn’t.

And because you’re in production and getting random spurious failures, the panicked (but common) reaction is to wrap every shared resource in a synchronized block. Which makes an incorrect implementation worse but possibly correct.

[FpUser]

If the resource is shared and being accessed from many threads and is both written to and read from then it is the correct behavior to to lock it with the proper type of lock at access time. Depending on resource it might be possible to split it into few with more granular access.

As for novices: they are called that for reason and supposed to be under supervision rather than allowed running wild.

[secondcoming]

Why is this being downvoted? It's the truth.

HN needs to only allow downvotes that have an accompanying explanation comment.

[FpUser]

HN uses downvotes mostly to boo the people with opinions deviating from common party line. As for reasonable explanation - you're asking too much. Programming as many other things often are treated as the religion. No arguments, it just is.

[teslalang]

As with most other compromised social sites, no badthink allowed here and how dare you.

[formerly_proven]

Novices don't build working concurrent systems of any kind with any toolkit, period. Concurrency is hard and thinking all the "concurrency problems" go away with some message passing is both ludicrous and dangerous. Fearless concurrency can only be attained through understanding, not by thinking all your problems went away because you're using a "cool approach".

[abhishekjha]

Surprisingly this is what the akka framework promises : Message passing and immutability of objects.

[FpUser]

Software usually has state (unless that state is completely kept and managed externally in a database for example). And the state mutates. Simple case example is a big array that has to be processed in place.

[mrkeen]

It's pretty easy to make the leap from individual SQL statements to SQL statements which are wrapped in a transaction.

[formerly_proven]

Excellent example for making my point, since "just wrap it in a transaction" usually leads to concurrency bugs like the beloved lost update.

[FpUser]

If you're talking database like transaction it "usually" leads to concurrency bugs only if the transaction level is not strictly serializable. It does not hurt to know things before labeling them.

[mrkeen]

This is not something I'm familiar with. What's the beloved lost update and what transactions are you using that suffer from it?

[ubercow13]

What's a better alternative to synchronizing access to shared resources?

[mrkeen]

Treat it like GC and don't leave it up to the programmer.

[FpUser]

An make a programmer unable to achieve highest performance when needed. We leave in supposedly free world. If you want to be "protected" be my guest and use languages with GC. Plenty of those. For somebody who need the opposite and uses "unprotected" tools - leave them alone. You have no rights to decide how other people do their work unless they're under your direct control.

[ubercow13]

Does that involve using concurrency primatives that basically don't allow access to any shared mutable state?

[mrkeen]

I'd say provide concurrency primitives to disallow direct access to shared mutable state. You still do the reads and the writes, but you let the system take and release locks for you.

Let's say you wanted to turn a list into a bounded list of 4 elements.

Race-condition insert:

    if (sz < 4) {
      list.insert(x);
      sz++;
    }

Safe insert:

    atomically {
      if (sz < 4) {
        list.insert(x);
        sz++;
      }
    }

So atomically organises the locking/unlocking/rollback for you such that a fifth element will not be inserted.

[MaxBarraclough]

> The concepts of threads and concurrent data access is simple enough for any decent programmer to comprehend. There is no hell here.

It's notoriously difficult to reason about concurrent programs using intuition. Much more difficult than reasoning about non-concurrent imperative code. This is why there are articles like [0], and why a bug in a Wikipedia article on a fundamental concurrency algorithm went unnoticed until an analysis tool detected the issue, [1] and why lock-free algorithms in particular are so tricky to get right.

[0] https://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedL...

[1] [PDF] https://llvm.org/pubs/2008-08-SPIN-Pancam.pdf

[yetkin]

Threading concept is simple,real world is not.

if i had no idea about C10K problem, success of Nginx, Redis, other concurrency success stories on Actors, CSP concept, Concurrency via messages over shared memory, I would say threads are ok when you can use it. But indeed it is so simple and tempting people to design shitty software. Software is a very welcoming medium for it. it is hell.