Saliya's Blogs

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Caused by: java.lang.UnsatisfiedLinkError: .../snappy-1.0.5.3-1e2f59f6-8ea3-4c03-87fe-dcf4fa75ba6c-libsnappyjava.so: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by.../snappy-1.0.5.3-1e2f59f6-8ea3-4c03-87fe-dcf4fa75ba6c-libsnappyjava.so)

--conf "spark.io.compression.codec=lzf"

• A mail thread on this
• Spark configuration options

import java.util.function.Function;

public class PassingMethodsThatThrowExceptions {

    public static int addOne(String value) throws NotANumberException{
        int v = 0;
        try{
            v = Integer.parseInt(value);
        } catch (NumberFormatException e){
            throw new NotANumberException();
        }
        return v+1;
    }

    public static void increment(Function<String,Integer> incrementer, String value){
        System.out.println(incrementer.apply(value));
    }

    public static void main(String[] args) {
        increment(PassingMethodsThatThrowExceptions::addOne, "10");
    }
}

• an addOne function that takes in a String value representing a number then adds 1 to it and returns the result as an int.
• an increment function that simply takes a function, which can perform the increment and a value then apply the function to the value.
• the main method that calls increment with addOne function and value "10"

    Error: java: incompatible thrown types exceptions.NotANumberException in method reference

public class PassingMethodsThatThrowExceptions {
    public interface IncrementerSignature{
        public int apply(String value) throws NotANumberException;
    }

    public static int addOne(String value) throws NotANumberException{
        int v = 0;
        try{
            v = Integer.parseInt(value);
        } catch (NumberFormatException e){
            throw new NotANumberException();
        }
        return v+1;
    }

    public static void increment(IncrementerSignature incrementer, String value) throws NotANumberException {
        System.out.println(incrementer.apply(value));
    }

    public static void main(String[] args) {
        try {
            increment(PassingMethodsThatThrowExceptions::addOne, "10");
        } catch (NotANumberException e) {
            e.printStackTrace();
        }
    }
}

• Use makrdown aware static blog generator such as Jekyll or something based on it like Octopress
• Use a blogging solution based on markdown such as svbtle
• Use a tool that'll either enable markdown support in blogger (see this post) or can post to blogger (like StackEdit)

Recently I switched to Comcast from AT&T because of an interesting deal on internet. Today I was on my Ubuntu machine in a different network and ran into the issue of not being able to connect to internet. After doing bit of looking into I figured that DNS is not working properly. I was getting a reply that had "hsd1.in.comcast.net" when I tried to do a host lookup (e.g. host -a google.com).

Then when I opened the /etc/resolv.conf I found that Comcast has inserted its nameservers into that and after removing those entries and setting the nameserver to Google's 8.8.8.8 I was able to connect and browse as usual.

Hope this helps someone in a similar situation!

This may not be elegant, but it works !

public static String getPid() throws IOException {
    byte[] bo = new byte[100];
    String[] cmd = {"bash", "-c", "echo $PPID"};
    Process p = Runtime.getRuntime().exec(cmd);
    p.getInputStream().read(bo);
    return new String(bo);
}

Java and C# both have compound assignment operators and the increment/decrement operators. For example see http://msdn.microsoft.com/en-us/library/6a71f45d.aspx for a list of C# operators and http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html for the Java version.

It seems these two step operations, i.e. x op= y, x++, x--, ++x, and --x, are NOT thread safe. It makes sense as these operations require reading the current value of the given variable and then updating it with the computed value. It is possible for threads to interleave between these operations resulting erroneous final values.

There are many ways to guarantee the atomicity in such cases including synchronized blocks, atomic data types such as Java AtomicInteger, and interlocked operations like in C#.

Here are some links that may help,

C# interlocked methods: http://msdn.microsoft.com/en-us/library/System.Threading.Interlocked_methods.aspx

Java atomic classes http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/atomic/package-summary.html

C# library to do threading similar to OpenMP like constructs http://msdn.microsoft.com/en-us/library/dd460717.aspx

A Java alternative OpenMP like parallel constructs https://wiki.rice.edu/confluence/display/HABANERO/Habanero+Multicore+Software+Research+Project

Nothing fancy, just a simple holder to keep my shaver in place. The hole is cut at an 30 degree angle. Initially I wanted to hide the tenon completely inside the mortise, but accidentally route the mortise all the way. Anyway, once fixed the joint is not visible.

Last week I had the opportunity to use Titan, #2 supercomputer in the world as of June 2013, as part of the ATPESC program hosted by Argonne labs. Titan is a Cray XK7 machine and its user’s guide is available here.
The following is a quick start to get Chapel programs run on multi-locale with Titan.

• Modules – the default set of modules is all what you need. You may load PrgEnv-cray/4.1.40 instead of the one loaded.
• Environment – you’ll need to have the following variables exported, usually through ~/.bashrc (in my case I used Chapel 1.7.0)

export CHPL_LOC=/tmp/work/csep65/chapel-1.7.0
export CHPL_HOME=$CHPL_LOC
export CHPL_COMM=gasnet
export GASNET_QUIET=yes
export CHPL_HOST_PLATFORM=cray-xk
export CHPL_LAUNCHER=pbs-aprun
export CHPL_LAUNCHER_QUEUE=batch
export CHPL_LAUNCHER_WALLTIME=00:10:00
export CHPL_LAUNCHER_ACCOUNT=TRN001
export CHPL_HOST_COMPILER=gnu
export PATH=${CHPL_LOC}/bin/$CHPL_HOST_PLATFORM:$PATH
Also, note the values in red need to be changed accordingly. The CHPL_LAUNCHER_ACCOUNT will be the account in Titan to get billed. You can find more information on this in the $CHPL_HOME/doc/platforms/README.cray (search for NCCS).

• Launcher tweak – note this fix is avaialble in Chapel code trunk following revision 21702 (http://sourceforge.net/p/chapel/code/21702/tree/trunk/) so will be necessary only if you are using a release 1.7.0 or older. A minor change to Chapel’s PBS launcher is necessary for these versions to work with Titan due to some upgrade in the qsub wrapper used by Titan. The fix is to change the two occurrences of –l size with –l nodes in $CHPL_HOME/runtime/src/launch/pbs-aprun/launch-pbs-aprun.c
• Compile Chapel – once the above steps are completed use the Makefile under $CHPL_HOME to compile Chapel as usual
• Compile your program – use the chpl compiler to compile your program, which will create two outputs, for example a.out and a.out_real. More information on what each of this means is available in the $CHPL_HOME/doc/README.multilocale
• Start your program – you can use, for example ./a.out –nl 4 to launch your program on 4 locales. Chapel launcher will take care of submitting the correct PBS job for Titan’s job scheduler.

This is pretty much what you need to do and hope it helps!