djspiewak

A Study in Multi-Point Deadlocks

Deadlocks are extremely difficult to reason about sometimes. We are used to thinking about them in terms of contention over shared resources, with the pair of exclusive locks being a good and relatively canonical example of this phenomenon. However, sometimes you can find yourself in deadlock scenarios which are caused not so much by an improper sequencing of exclusivity, but rather by insufficient buffer capacity!

These kinds of scenarios are a lot rarer and much more difficult to diagnose and describe, which is why I found this particular puzzle so incredibly fascinating. The following is a screenshot from Cities Skylines (I added textual markers and arrows to make things easier to follow). All vehicles pictured are stationary and unable to move, indefinitely:

Do you see the deadlock? It took me a bit to understand it, but this situation can and does arise in software resource contention where it is dramatically harder to conc

fcamblor

FROM tomcat:7-jre8-alpine

# See https://github.com/jvm-profiling-tools/async-profiler/issues/207
RUN apk update && apk add --no-cache libc6-compat perl openjdk8-dbg

RUN mkdir /usr/local/async-profiler/ &&\
      wget -O /usr/local/async-profiler/async-profiler.tar.gz https://github.com/jvm-profiling-tools/async-profiler/releases/download/v1.5/async-profiler-1.5-linux-x64.tar.gz &&\
      cd /usr/local/async-profiler/ &&\
      tar -xvzf async-profiler.tar.gz &&\
      rm -f /usr/local/async-profiler/async-profiler.tar.gz

thomasdarimont

package demo;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;

djspiewak

Thread Pools

Thread pools on the JVM should usually be divided into the following three categories:

1. CPU-bound
2. Blocking IO
3. Non-blocking IO polling

Each of these categories has a different optimal configuration and usage pattern.

ipbastola

Safest way to clean up boot partition - Ubuntu 14.04LTS-x64, Ubuntu 16.04LTS-x64

Reference

Case I: if /boot is not 100% full and apt is working

1. Check the current kernel version

$ uname -r 

beala

import Control.Monad.State.Strict
import qualified Data.Map.Strict as Map

-- This is the standard fibonacci implementation with exponential complexity.
naiveFibs :: Int -> Integer
naiveFibs 0 = 0
naiveFibs 1 = 1
naiveFibs n = naiveFibs (n-2) + naiveFibs (n-1)

-- For reference, calculating the 35th fibonacci takes 9.49 sec.