4 ms·

No, it doesn't. Java is a piece of crap with JVMs imposing an 8-24 byte overhead per object, which destroys caching, memory footprint, and any chance of low-le

by yazzku 2y ago

No, it doesn't. Java is a piece of crap with JVMs imposing an 8-24 byte overhead per object, which destroys caching, memory footprint, and any chance of low-level optimization. Not only is the overhead bad, it's implementation-dependent, i.e. unpredictable. That, along with lacking SIMD, imposing stupid decisions like bounds checks on all array accesses, making arrays boxed (int[] is not an array of ints, sorry), or using exceptions for control flow, which is the wrong way to use exceptions, is a just part of the big laundry list of why Java is a piece of obsolete crap that nobody serious about low-level hardware programming uses. Java SE/ME is a fucking joke, as is every book I have read about "high performance Java". People who promote Java for low-level hardware programming, real-time systems, and the like, just have absolutely no fucking idea what they're talking about and they get their garbage published only because of the low standards of publishing nowadays. They do get the "Java Champ" badge from Oracle, though. Noobs award other noobs badges, as it turns out.

foobazgt 2y ago
> JVMs imposing an 8-24 byte overhead per object You want project Valhalla, or more specifically Value Objects, which are in preview [0]. If you really want the highest performance related to cache accesses, you want to arrange things as SoA (struct of arrays) anyway, which has approx 0 object overhead and doesn't require Value Objects. > Not only is the overhead bad, it's implementation-dependent, i.e. unpredictable. This is silly. This happens with all other languages, and Java will give you better results on average. Use a different compiler or runtime for your C code, or run it on a different processor architecture, and have fun tuning your code. > That, along with lacking SIMD The Vector API [1] is available in preview. > imposing stupid decisions like bounds checks on all array accesses It's widely understood that doing the opposite has been perhaps one of the largest mistakes in the history of the industry. JITs elide access checks when safe, and it's easier for them to do with high performance code that doesn't bounce around in memory and thrash cache. > making arrays boxed (int[] is not an array of ints, sorry) What does this even mean? An int[] is a linear array of 32-bit int values in memory. > or using exceptions for control flow, which is the wrong way to use exceptions Are we now just talking about a small slice of people who write bad code? > is a just part of the big laundry list of why Java is a piece of obsolete crap Ah, ok. Have a fine day. 0) https://openjdk.org/jeps/401 https://openjdk.org/jeps/401 1) https://openjdk.org/jeps/460 https://openjdk.org/jeps/460
- yazzku 2y ago
  I appreciate your response. My original post was a rant for sure, but let me reply to your comments. > You want project Valhalla, or more specifically Value Objects, which are in preview [0]. If you really want the highest performance related to cache accesses, you want to arrange things as SoA (struct of arrays) anyway, which has approx 0 object overhead and doesn't require Value Objects. SoA requires unboxed arrays, otherwise it defeats the purpose. I may have been wrong about int[] being boxed (it seems to be unboxed in most implementations), but the fact that ints still auto-promote to Integer in certain circumstances is just ridiculous for any kind of low-level programming. It's also hilarious that Value Objects are still in preview. Even C# has had structs (value semantics) since forever. > This is silly. This happens with all other languages, and Java will give you better results on average. Use a different compiler or runtime for your C code, or run it on a different processor architecture, and have fun tuning your code. This is false. structs in C or C++ don't have a language-imposed overhead. They may have different sizes depending on the alignment requirements of the platform. > The Vector API [1] is available in preview. Also hilarious. It's 2024. > It's widely understood that doing the opposite has been perhaps one of the largest mistakes in the history of the industry. Checking every single array access in a tight loop, for example, is stupid. It's the naive, dumb, and inefficient way of doing it (i.e., the Java way.) The right way to do it is to enforce up front that the index may never be out of bounds. Ada helps with this by having user-defined ranges and integer types, for example. > What does this even mean? An int[] is a linear array of 32-bit int values in memory. Yes, I think I botched that one, but see also my comment above. > Are we now just talking about a small slice of people who write bad code? No, I am talking about Java. > Ah, ok. Have a fine day. Oh, and how does Java do low-level systems programming without unsigned integer types, lol? Oh, yeah, you need to cast to/from the next largest integer representation so that you can encode all of the positive values. And you better hope you don't need more than the native size, because then you get fuck-boxed into Integer (see my comment above.) Fucking hilarious, y'all. Also, you don't even have a guarantee that a variable is allocated on the stack even when the dumbest compiler can tell it's bound by function scope. You need to hope that the JIT will do it, and from my past experience in Android (which this post is about), it doesn't. This is why, for example, if you look at the math library of LWJGL [1], all functions are defined to mutate one of the arguments, they never allocate a new vector to return. This is just completely stupid because mathematical vectors should have value semantics and the compiler optimize the fuck out of them. (Don't get me wrong, I love LWJGL and the guys. This is a criticism of the language, not the library; they are doing the best they can given the language's stupid decisions.) [1] https://github.com/JOML-CI/JOML/blob/main/src/main/java/org/joml/Vector3f.java#L699 https://github.com/JOML-CI/JOML/blob/main/src/main/java/org/...
John_Cena 2y ago
I feel so out of place when interviewing for firmware/embedded roles and the interviewers turn out to be java snobs. I honestly still have a hard time comprehending the situation; how does it come to this? Thanks for your insight
- yazzku 2y ago
  It's really sad. I think Java is a rather ill-designed and boring language, not even worth learning for intellectual purposes, but it does have a mature ecosystem around databases, web services and stuff, and it has its use cases. Beyond that, it really beats me where this attitude comes from. I attribute it to living in your bubble and not exploring what the guys over on the other side of the fence are doing. This is why one should learn as many programming languages (and paradigms) as possible, even if you don't end up using half of them. It's like when those guys come out with a new "minimalist" CSS framework, and the bitch downloads a 2MB payload just to bootstrap your "hello world".

by yazzku 2y ago

foobazgt 2y ago

> JVMs imposing an 8-24 byte overhead per object You want project Valhalla, or more specifically Value Objects, which are in preview [0]. If you really want the highest performance related to cache accesses, you want to arrange things as SoA (struct of arrays) anyway, which has approx 0 object overhead and doesn't require Value Objects. > Not only is the overhead bad, it's implementation-dependent, i.e. unpredictable. This is silly. This happens with all other languages, and Java will give you better results on average. Use a different compiler or runtime for your C code, or run it on a different processor architecture, and have fun tuning your code. > That, along with lacking SIMD The Vector API [1] is available in preview. > imposing stupid decisions like bounds checks on all array accesses It's widely understood that doing the opposite has been perhaps one of the largest mistakes in the history of the industry. JITs elide access checks when safe, and it's easier for them to do with high performance code that doesn't bounce around in memory and thrash cache. > making arrays boxed (int[] is not an array of ints, sorry) What does this even mean? An int[] is a linear array of 32-bit int values in memory. > or using exceptions for control flow, which is the wrong way to use exceptions Are we now just talking about a small slice of people who write bad code? > is a just part of the big laundry list of why Java is a piece of obsolete crap Ah, ok. Have a fine day. 0) https://openjdk.org/jeps/401 https://openjdk.org/jeps/401 1) https://openjdk.org/jeps/460 https://openjdk.org/jeps/460

yazzku 2y ago
I appreciate your response. My original post was a rant for sure, but let me reply to your comments. > You want project Valhalla, or more specifically Value Objects, which are in preview [0]. If you really want the highest performance related to cache accesses, you want to arrange things as SoA (struct of arrays) anyway, which has approx 0 object overhead and doesn't require Value Objects. SoA requires unboxed arrays, otherwise it defeats the purpose. I may have been wrong about int[] being boxed (it seems to be unboxed in most implementations), but the fact that ints still auto-promote to Integer in certain circumstances is just ridiculous for any kind of low-level programming. It's also hilarious that Value Objects are still in preview. Even C# has had structs (value semantics) since forever. > This is silly. This happens with all other languages, and Java will give you better results on average. Use a different compiler or runtime for your C code, or run it on a different processor architecture, and have fun tuning your code. This is false. structs in C or C++ don't have a language-imposed overhead. They may have different sizes depending on the alignment requirements of the platform. > The Vector API [1] is available in preview. Also hilarious. It's 2024. > It's widely understood that doing the opposite has been perhaps one of the largest mistakes in the history of the industry. Checking every single array access in a tight loop, for example, is stupid. It's the naive, dumb, and inefficient way of doing it (i.e., the Java way.) The right way to do it is to enforce up front that the index may never be out of bounds. Ada helps with this by having user-defined ranges and integer types, for example. > What does this even mean? An int[] is a linear array of 32-bit int values in memory. Yes, I think I botched that one, but see also my comment above. > Are we now just talking about a small slice of people who write bad code? No, I am talking about Java. > Ah, ok. Have a fine day. Oh, and how does Java do low-level systems programming without unsigned integer types, lol? Oh, yeah, you need to cast to/from the next largest integer representation so that you can encode all of the positive values. And you better hope you don't need more than the native size, because then you get fuck-boxed into Integer (see my comment above.) Fucking hilarious, y'all. Also, you don't even have a guarantee that a variable is allocated on the stack even when the dumbest compiler can tell it's bound by function scope. You need to hope that the JIT will do it, and from my past experience in Android (which this post is about), it doesn't. This is why, for example, if you look at the math library of LWJGL [1], all functions are defined to mutate one of the arguments, they never allocate a new vector to return. This is just completely stupid because mathematical vectors should have value semantics and the compiler optimize the fuck out of them. (Don't get me wrong, I love LWJGL and the guys. This is a criticism of the language, not the library; they are doing the best they can given the language's stupid decisions.) [1] https://github.com/JOML-CI/JOML/blob/main/src/main/java/org/joml/Vector3f.java#L699 https://github.com/JOML-CI/JOML/blob/main/src/main/java/org/...

John_Cena 2y ago

I feel so out of place when interviewing for firmware/embedded roles and the interviewers turn out to be java snobs. I honestly still have a hard time comprehending the situation; how does it come to this? Thanks for your insight

yazzku 2y ago
It's really sad. I think Java is a rather ill-designed and boring language, not even worth learning for intellectual purposes, but it does have a mature ecosystem around databases, web services and stuff, and it has its use cases. Beyond that, it really beats me where this attitude comes from. I attribute it to living in your bubble and not exploring what the guys over on the other side of the fence are doing. This is why one should learn as many programming languages (and paradigms) as possible, even if you don't end up using half of them. It's like when those guys come out with a new "minimalist" CSS framework, and the bitch downloads a 2MB payload just to bootstrap your "hello world".