5 ms·
The thing is, the more I work with network based reactive systems, the more a GC seems like an inefficient hack in an application, arising from the fact that we
by tetha 8y ago
The thing is, the more I work with network based reactive systems, the more a GC seems like an inefficient hack in an application, arising from the fact that we had nothing better at the time it was invented and grew big.
I mean a reactive application needs three things:
- a fast network connection to persistence. If you can't talk quickly to your database, latency eats your response time no matter what you do.
- Maybe some LRU caches across requests, but caches inside an application tend to become a maintenance nightmare quickly. Stales reads are fun, and stalled cache writes are too.
- And beyond that, it should be possible to handle most request data by stack allocation/deallocation with references to a cache version if you have a cache with little overhead, depending on your security requirements.
I understand the ease of use and simplicity of a GC'd language, especially given the time GC'd languages came around big time. But I've always been wondering if you really need a GC if you think properly about request and object lifetimes.
- Gibbon1 8y ago> handle most request data by stack allocation/deallocation I just write crappy code for microcontrollers. Over 30 years I've seen the amount of ram available for stack grow. From maybe 20-30 bytes to a couple of k. That said it appears to me that stack allocation is severely under utilized for historical reasons. The idea that stack space is a precious resource. Which doesn't fly on machines with 10's of gigabytes of memory. Think programs that put vast quantities of ephemeral objects and short strings on the heap. Using call tree analysis would allow you to put a lot of that on the stack resulting is much better performance and bounded latency.
- sorokod 8y agoJava performs escape analysis and may allocate non-escaping objects on the stack.
- archi42 8y agoQuoting https://www.beyondjava.net/#/blog/escape-analysis-java https://www.beyondjava.net/#/blog/escape-analysis-java > Moving objects from the heap to the stack > Many sources report that escape analysis moves Java objects from the heap to the stack. As Aleksey Shipilёv points out in his article about scalar replacement, the JVM does not do this implementation. It's just a misconception. But it's an interesting one, and I wonder why the JVM doesn't implement it.
- mhaymo 8y agoInteresting article, but the distinction you're making is quite subtle. Using escape analysis, Java can avoid heap allocations by removing the creation of the Object altogether, treating its fields as if they were local variables which live in registers/the stack. The practical difference between that and simply allocating the object on the stack is that no space is required for the object header, and some reference-based operations are not possible.
- MaxBarraclough 8y agoBut the article states "Anything you create with new is always created on the heap."
- mhaymo 8y agoYes, but it then explains that escape analysis allows the runtime to avoid creating the Object entirely with scalar replacement. It's written in a confusing way, which is why I felt the need to clarify.
- MaxBarraclough 8y agoUgh, you're right, of course. In my defence the sentence I quoted isn't so much deliberately misleading, as outright false. It essentially states that 'new' always results in a heap allocation, which just isn't true. A profoundly unhelpful writing style, going out of its way to punish skim-readers. I'm reminded of this TV Tropes page: http://tvtropes.org/pmwiki/pmwiki.php/Main/ByNoIMeanYes http://tvtropes.org/pmwiki/pmwiki.php/Main/ByNoIMeanYes
- MaxBarraclough 8y agoEdit: Turns out that BeyondJava article is just poorly written, and tries so hard to emphasise its subtle distinctions that it ends up being actively harmful to the reader's understanding. I'll leave my comment anyway. From that article: > Java doesn't store any object in the stack. It does store local variables on the stack: primitive types like int or boolean. It also store the pointers to objects on the stack. But it doesn't store the objects themselves on the stack. Anything you create with new is always created on the heap. Is that true? For years now there have been articles from serious sources discussing JVM escape-analysis-based optimisations. Is there something mistaken in the analysis in this DZone article? https://dzone.com/articles/do-not-let-your-java-objects-escape https://dzone.com/articles/do-not-let-your-java-objects-esca... How about this StackOverflow answer, which even goes into the detail of distinguishing escape-analysis, stack allocation of objects, and object deconstruction+scalar replacement: https://stackoverflow.com/a/43002529/ https://stackoverflow.com/a/43002529/