Stanislav Datskovskiy posts his theory on the murder of HyperCard. It wasn't the butler.
Wednesday, November 30, 2011
Flying Frog Consultancy in Cambridge, England posts a nice comparison between Disruptor and low-latency GC algorithms:
The core of [Disruptor's] idea is to accomplish all of this message passing using a single shared data structure, the disruptor, rather than using several separate concurrent queues.
Baker's Treadmill is a low-latency garbage collection algorithm. Allocated blocks in the heap are linked together to form a cyclic doubly-linked list that is divided into four segments using four iterators that chase each other around the ring as heap blocks are allocated, traced and freed.
Cleverly observed with a good diagram. As they say, read the whole thing.
Tuesday, November 22, 2011
Martin Thompson posts on what I call microbenchmarking and JVM magic, Biased Locking, OSR, and Benchmarking Fun. It is a good praticum to Cliff Click's What the heck is OSR and why is it Bad (or Good)?. OSR is the kind of JVM magic that both surprises and frightens, but makes perfect sense. I walked a colleague through OSR and he agreed with a shrug: the thing you are glad someone else wrote, excess hair.
Friday, November 18, 2011
This post is a hack. You have been warned.
My employer swaps out SSL certificates traversing the corporate firewall. It is a financial firm with regulatory responsibilities that require monitoring all traffic leaving the company, including encrypted traffic.
One side effect is trouble with well-meaning programs which validate SSL certificates before trusting an encrypted connection. These validations fail using the self-signed replacement certificate.
Maven is such a tool:
[WARNING] Could not transfer metadata com.devspan.vendor.envjs:envjs-rhino/maven-metadata.xml from/to sonatype-oss (https://oss.sonatype.org/content/groups/public): Error transferring file: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
The remark about "PKIX path building failed" is characteristic of the probelm.
There is lots of good advice on fixing this correctly, say, here, here or here. But none of them work just now; I cannot edit the locked-down trust store for Java, it does not already contain the aforementioned replacement certificate, and I do not want to build a custom Maven to work around the problem.
Enter the hack.
$ mvn -Djavax.net.ssl.trustStore=/dev/null package
Tuesday, November 08, 2011
Anything Martin Thompson says about performance is usually worth a good study. No exception is Locks & Condition Variables - Latency Impact.His takeaway points:
- The one-way latency to signal a change is pretty much the same as what is considered current state of the art for network hops between nodes via a switch.
- The impact is clear when letting the OS choose what CPUs the threads get scheduled on rather than pinning them manually.
I no longer work in the low-latency space. Still Azul's completion of a non-VM "pause-less" JVM for Linux is exciting. (Also running a JVM on a VM was too recursive.) May it be a benefit to those who need low-latency java servers.
Stephen Colebourne posts on the future of JDK8 based on current JEPs. Among the possiblities, I'm looking forward to:
Monday, November 07, 2011
I love Chris Adamson's description of Punk Rock Languages. His introduction should get your blood flowing:
That C has won the end-user practicality battle is obvious to everyone except developers.
The year is 1978, and the first wave of punk rock is reaching its nihilistic peak with infamous U.K. band the Sex Pistols touring the United States and promptly breaking up by the time they reach the West Coast. Elsewhere, Brian Kernighan and Dennis Ritchie are putting the finishing touches on their book The C Programming Language, which will become the de facto standardization of the language for years. While totally unrelated, these two events share a common bond: the ethos of both punk rock and C have lasted for decades, longer than anyone in 1978 could possibly have imagined.
And in many important ways, C is the programmer’s punk rock: it’s fast, messy, dangerous, and perfectly willing to kick your ass, but it’s also an ideal antidote to the pretensions and vanities that plague so many new programming languages. In an era of virtual machines and managed environments, C is the original Punk Rock Language.
Good news from Columbia University. Peregrine is automated software to aid in programming concurrency. More in the ACM: Major Breakthrough Improves Software Reliability and Security:
"Our main finding in developing Peregrine is that we can make threads deterministic in an efficient and stable way: Peregrine can compute a plan for allowing when and where a thread can 'change lanes' and can then place barriers between the lanes, allowing threads to change lanes only at fixed locations, following a fixed order," says Columbia professor Junfeng Yang. "Once Peregrine computes a good plan without collisions for one group of threads, it can reuse the plan on subsequent groups to avoid the cost of computing a new plan for each new group."