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Alibaba (see our news items this month, below) look to have invested a lot of time and effort in going down the lightweight-thread path of asynchronous programming. Although their approach is proprietary, we have had coroutines (eg Matthias Mann's) in Java for a long time used by quite a few projects, and ParallelUniverse's Quasar project is a nice generally available implementation of lightweight threads.

Alibaba seems to have taken the next step, of integrating these into the JVM so that stack traces actually show the lightweight thread trace instead of the framework trace - that's essential for visibility and allowing proper debugging of of issues; Alibaba describes this as "simplicity of synchronous, performance of asynchronous". The problem with most asynchronous programming frameworks (Actors, Fork-join, etc) is that when you go to debug an issue, you get thrown into the framework rather than your use of the framework, and this makes debugging much more difficult than debugging synchronous execution.

It would be ideal to have lightweight threads properly integrated into the JVM. I appreciate this is a lot of effort - primarily because all JVM-kernel blocking calls as well as the GC need to be altered to work with them for optimal integration, but the benefits are huge, and Alibaba is already showing the need and the capability! Ron Pressler, the force behind Quasar, has now made a proposal for project Loom (see our news items below) to do this, so maybe we'll see some progress in Java 10 (thanks to my colleague Luis Pedrosa for alerting me to the proposal).

Now on to our usual links to articles, tools, news, talks, blogs. And if you need the tips from this month's articles and talks, as ever they are extracted into this month's tips page.

A note from this newsletter's sponsor

News

Java performance tuning related news.

• Internal details about the AOT compiler (jaotc) in Java 9
• Project Loom, bringing lightweight threads to the JVM
• Alibaba 175k peak transactions/sec (120k payment orders). Use 1 tenant per microservice so that resource consumption (CPU using cgroup and cpuacct, heap with modified G1GC having tenant allocation contexts, threads, but not yet IO) can be monitored and controlled (tenants are like containers within a JVM). G1GC is well suited to tenant management. Coroutines (MLVM implementation) and selectors used to provide lightweight threads and keeping system context switches reasonable
• A real example of exactly why code extracted into a microbenchmark doesn't perform similarly to the code when executed in the application. And includes one gem of a performance tip, that the choice of parameter and instance for executing equals() matters, because the compiler can speculate one way but not the other - ie although "x".equals(something) and something.equals("x") are almost equivalent (the first handles something=null nicely), the first allows the compiler to inline specifically the String equals implementation, whereas the latter doesn't because "something" could be any object so the compiler can't know which equals() to use, and this applies generally when the caller instance is a known class (not just String)

Tools

Java performance tuning related tools.

• JXRay 1.8 now released - JXRay is an offline heap analyzer for Java
• Google ThreadSanitizer finds race conditions in running applications
• Assessment of Software Architecture for Performance and Scalability
• async-profiler: low overhead sampling profiler for Java that does not suffer from Safepoint bias problem

Articles

• ThreadSanitizer and Heap Sampling (Jaeheon Yi, Jean Christophe Beyler/JVM Language Summit)
• Controlling parallelism level of Java parallel streams (Kamil Szymanski/Under the hood)
• Weak Soft and Phantom references in Java and why they matter (Uberto Barbini/Medium)
• Everything You Need to Know About Performance Testing (Alex McPeak/SmartBear)

Jack Shirazi

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