[twoodfin]

It’s widely regarded as a dead end. Conceptually, it’s quite appealing so who knows, it might find new life someday. Garbage collection was a niche technology for decades, as was JIT compilation.

Joe Duffy’s write-up on how STM failed at Microsoft with .NET is illustrative:

http://joeduffyblog.com/2010/01/03/a-brief-retrospective-on-...

[PaulHoule]

right... it's not hard to invent some scheme that scales to a 2 core computer but it is not crazy to have 64 or more cores these days and even if you have 2% serial overhead from communications you are not going to scale past 50.

The problems of making a system really scale as opposed to just scale are bad enough that the best we know how to do is give people simpler primitives that work -- each layer you add to the system is another opportunity to add another limitation to it.

Modern garbage collectors are fairly scalable (e.g. don't break outright as the heap size increases) and any manual memory management would also have the risk of scaling problems, to the point where you might say that garbage collection is more "scalable" when the thing being scaled is the kind of arbitrary complexity that appears in business applications.

What people complain about with garbage collection are: (1) a fixed constant overhead they think is too high and will probably always think to high, (2) long pauses that are manageable in practice unless you are timing events with millisecond precision with a microcontroller.

Thus one of these things is mainstream and other isn't.

[tomp]

> What people complain about with garbage collection are: (1) a fixed constant overhead they think is too high and will probably always think to high, (2) long pauses that are manageable in practice unless you are timing events with millisecond precision with a microcontroller.

I keep hearing this about "modern" GC and it keeps being very much not true in practice. I'm running IntelliJ IDEA (Java) on a laptop with 8GB of RAM, and it keeps freezing every so often. I'm suspecting GC causing paging. This is something that is obviously avoided with reference counting or manual memory management.

[jhgb]

> This is something that is obviously avoided with reference counting

You'd prefer your data being larger in memory due to refcount fields and slower to access due to atomic operations on those fields?

[tomp]

It's not like tracing GC is without memory overhead...

Slower is a question of priorities. I'd definitely trade off slower overall performance (I don't really need my IDE to be that performant... it's not like it's using 100% CPU, or even 10%!) but a huge improvement in latency (i.e. no catastrophic slowdowns / freezes).

[jhgb]

There are very few ways of having zero memory overhead, though.

Also, most of the flaws of Java's memory management seem to be concentrated in the part of the language that says that almost everything has to be an object with a header and on the heap. Remove that and your graph of objects to trace shrinks very substantially.

[withinboredom]

Interestingly, I was running out of memory, so I gave it more RAM (like 20GB) and it got even worse. Apparently it takes a long time to GC that much memory. I’d also rather amortize that pause. The loss of productivity due to a sudden pause is real.

[twoodfin]

Yeah. As is pointed out down-thread of the linked post, even when it was confined to a niche, garbage collection did what it claimed it would (eliminate the need for error-prone manual memory management) at an acceptable cost for many systems & applications. JITs were similar.

So far, STM and HTM have followed a path more like VLIW instruction sets: Conceptually appealing for their promise of simplification, but in practice only demonstrating success in specialized uses, with the tradeoffs proving unattractive seemingly everywhere else they've been tried.

[sitkack]

I think it is a false equivalence to say that STM and HTM are like VLIW (which has been been a resounding success for DSP workloads). I am not defending VLIW.

Transactions are extremely powerful conceptually, to be composable and not cause flapping requires a higher level of coordination.