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You've got some great points, but there's one more dimension to why GC in Java hurts performance as much as it does: Java, by the design of its standard librari

You've got some great points, but there's one more dimension to why GC in Java hurts performance as much as it does: Java, by the design of its standard libraries and by the conventions that many (most?) Java developers use, just tends to allocate memory for every single operation. I was writing the Java part of a cross-platform game engine once, and I was trying to eliminate all dynamic allocations during the game (front-loading all allocations and then never touching the heap). Did some profiling and determined I'd missed something. The allocation turned out to be in a call to get the current system timer (in milliseconds, if I recall). I was calling a Java function that returned a Java long int, probably straight from an OS call that returned a 64-bit int, and somewhere in that call it was allocating an Object. Ripped out the Java library call, replaced it with a JNI call to a two line C function that returned the result of the corresponding OS call. No more dynamic allocations. It's just part of the philosophy of Java to allocation things everywhere. So it's not only hard to make a GC fast for architectural reasons; the GC also tends to be worked harder by the way Java code tends to be written.

jakewins 10y ago
Excellent points. One of the emotional appeals of Go, to me, is the community behavior and mindset. Go code very often "feels" like a low level language, written by someone that was considerate of the underlying machine. You're also hitting another nerve: The horrific world of allocation tracking in Java. While your case sounds like a legitimate thing, so many times I've been in that situation and been tricked by my tools to optimize the wrong path. Most popular allocation tracking tools, like YourKit, turn off escape analysis. Obviously, when you do that, stupid things like boxed primitives will show up as your main sources of heap allocation even though Hotspot would stick those suckers on the stack in a heart beat. Eg: Here's a program running without YourKit allocation tracking: https://twitter.com/jakewins/status/707759792547233792 https://twitter.com/jakewins/status/707759792547233792 And here's the same program with it on: https://twitter.com/jakewins/status/707754868497231872 https://twitter.com/jakewins/status/707754868497231872 Still makes me furious - what in the world am I supposed to do with an allocation tracking tool that creates millions of false positive allocations, drowning out the thing I care about? Gah.
- pjmlp 10y ago
  Which actually could have been fixed since version 1.0, had the language designers added support for value types instead of trying to retrofit them into Java 10. I like the language, but it did a bit of left turn by not adopting the features of Oberon(-2), Modula-3, Component Pascal or Eiffel in regards to value types and native AOT compilation.

jakewins 10y ago

Excellent points. One of the emotional appeals of Go, to me, is the community behavior and mindset. Go code very often "feels" like a low level language, written by someone that was considerate of the underlying machine. You're also hitting another nerve: The horrific world of allocation tracking in Java. While your case sounds like a legitimate thing, so many times I've been in that situation and been tricked by my tools to optimize the wrong path. Most popular allocation tracking tools, like YourKit, turn off escape analysis. Obviously, when you do that, stupid things like boxed primitives will show up as your main sources of heap allocation even though Hotspot would stick those suckers on the stack in a heart beat. Eg: Here's a program running without YourKit allocation tracking: https://twitter.com/jakewins/status/707759792547233792 https://twitter.com/jakewins/status/707759792547233792 And here's the same program with it on: https://twitter.com/jakewins/status/707754868497231872 https://twitter.com/jakewins/status/707754868497231872 Still makes me furious - what in the world am I supposed to do with an allocation tracking tool that creates millions of false positive allocations, drowning out the thing I care about? Gah.

pjmlp 10y ago
Which actually could have been fixed since version 1.0, had the language designers added support for value types instead of trying to retrofit them into Java 10. I like the language, but it did a bit of left turn by not adopting the features of Oberon(-2), Modula-3, Component Pascal or Eiffel in regards to value types and native AOT compilation.