migrating speedment to java 9

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Migrating Speedment to Java 9
Speaker: Dan Lawesson @dan_lawesson
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Cute – Spire their mascot on github has two years experience in that role

Since a library, want to be running with Java 9 as soon as it is released.

Speedment

  • Streams API ORM – customer.stream().filter(field.equal(value)).count();
  • uses JVM memory acceleration, ode generation and modular design
  • Type safety
  • Works like streams – you don’t get any values back until terminal operation runs
  • Have non-SQL code like a collector to convert the result into JSON
  • can use findAny() with Optional on result – generates SQL limit statement
  • Have finderBy so can join tables
  • Like SQL, Streams are declared. Describe the what, not the how. But with SQL, you have to describe the result set format.

Jigsaw Effects/Problems

  • A package must only belong to one modules. Yet it is common for two jars to have same package. The first one in the classpath takes precedence. In Java 9 must have only place for package.
  • Automatic modules are for smoth transition to Java 9. It moves the Java 8 jars from the classpath to the module path. The jar automatically becomes a module
  • However, automatic modules create split pakcages and can’t have those in Java 9
  • sun.misc.Unsafe – should not be used but a key for real world Java success
  • OSGi bundling is different than Jigsaw

Jigsawing the Java 8 open source application

  • Running Java 8 under Java 9 JDK is easy
  • Created module info file
  • Brute force is to move all jars into depdencies in your monolithic module. When works, actually modularize app. Didn’t take this approach because already had OSGi modules
  • Moduler approach: create directory for each module and move relevant packages to that directory. Add empty module-info.java (no requires/exports). That won’t compile so now can incrementally add dependencies and re-compile. Since this is iterative, they wrote a script to do it.
  • Patch abuse of non-exported JDK APIs. Can add exports of java packages as a temporary workaround. Would need this flag at runtime if the temporary workaround isn’t removed. The workaround is just so you can identify all the issues and TBDs.
  • Remove the OSGI bundling. Comment it out so building a jar instead of a bundle in Maven
  • Use code generation so no reflection

Speedment Enterprise

  • Harder becuase use sun.misc.Unsafe, third party dependencies with package issues

The first 20 minutes was about the Speedment library. I felt like that was a lot for a non-product talk. I wasn’t surprised because Dan was at my lunch table. And it was interesting. It just wasn’t necessary to understand the Java 9 part. Dan made a lot of references to things earlier in the day, which was nice. Also, the path Speedment took to move to Java 9 was very useful. I would have wanted to hear more about the issues in enterprise. Are they just outstanding issues. What do they plan to do if the libraries don’t release.

java @ speed: making the most of modern hardware – live blogging from qcon

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Java @Speed – Making the most of modern hardware
Speaker: Gil Tene
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duct tape engineering should only be done when absolutely necessary

We think of speed as a number. But it’s not a quality without a context. Are you fast when you deploy? When at peak load? When the market opens? When acually trade? How long can you be fast in a row?

In Java, speed starts slow when app starts and gets faster until gets to steady point. Because the code changes over time. It starts out purely interpretted then optimizes after profiling. Also, GC pauses.

Modern servers

  • Number cores/chip has tripled
  • Instruction window keeps increasing
  • More parallelism each generation
  • Cache also increasing

Compilers

  • Can reorder code
  • Can remove dead code – nobody knowsif it ran the code. So can say did it; just really fast.
  • Values can be propagated – remove temporary variables
  • Can remove redundant code
  • Reads canbe cached – as if you extracted a variable. Use volatile if needs to avoid
  • Writes can be eliminated – can save calculation if doesn’t change
  • Can inline method call
  • Also does clever tricks lie checking for nulls only after SEGV happens. If you turn out to throw a lot of null pointers, deoptiizes to add guard clause
  • Class Hierarchy Analysis (CHA) – looks at whole code base for optimizations
  • Inlining works without final because knows no subclass. If a new subclass shows up, deoptimizes at that time.
  • If think only have one subclass, add guard clause and optimize. The guard clause will unoptimize
  • Deoptimizations create slowdown spikes in performance even during the optimized phase. Warmup isn’t always enough because warm up code might not hit all scenarios. “The one thing you haven’t done is trade.” So the first real trade is slow because it is deoptimization.
  • Azul has a product that logs optimizations and re-loads them on startup from prior runs.

Microbenchmarking is hard because some things are optimized away (like basic math). Use jmh from OpenJDK to microbenchmark, but still suspect everything.

I like that he showed the assembly code and explained the relationship to a simple for loop.

java evolution of eclipse collections – live blogging from qcon

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The Java Evolution of Eclipse Collections
Speaker: Kristen O’Leary
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Eclipse Collections

  • was once GS (Goldman Sachs) Collections
  • Memory efficient collections framework
  • Open sourced in 2012

Java 8

  • 8.0 compatible with Java 8+
  • Extend Java 8 Functional Interfaces
  • New APIs – ex: reduceInPlace

Optional

  • RichIteratable.detectWith() used to rutn null if no match
  • Pre Java-8 could use detectIfNone() to create if doesn’t exist
  • New method detectWithOptional() which returns Optional wrapper

Collectors

  • Collectors2 has collectors
  • Can collect into Bag, ImmutableSet, BiMap, Stack, etc
  • Have full primitive collections library
  • Have full set of multi-map (map with multiple values for same key ex: key to list/set)
  • Have extra APIs like chunk() and zip()

Default methods

  • RichIterable is common interface so default methods helpful.
  • Used to add reduceInPlace() so don’t need to stream and create new collection
  • Also useful for asLazy() or toImutabile() since Eclipse Collections doesn’t provide stream() there.

Primitive Collections

  • Code generate the primitive classes so symmetry
  • Showed impressive memry savings – Eclipse Collections and Trove equivalent. Much smaller than with autoboxing and faster too
  • LazyIterable availalbe for all 8 primitive types. Just call asLazy(). A LazyIterabe can be reused unlike a stream.

Java 9

  • Module system
  • Internal API Encapsulation
  • Need to change APIs that use reflection in order to build. Can’t call setAccessible(true) any more.
  • There is a command line argument to ignore reflection errors. Don’t want to impose that on callers

I like that Kristen uses kata examples to show hw the APIs work.