Double checked lock (DCL)

http://www.javaworld.com/article/2074979/java-concurrency/double-checked-locking--clever--but-broken.html

DCL relies on an unsynchronized use of the resource field. That appears to be harmless, but it is not. To see why, imagine that thread A is inside the synchronized block, executing the statement resource = new Resource(); while thread B is just entering getResource(). Consider the effect on memory of this initialization. Memory for the new Resource object will be allocated; the constructor for Resource will be called, initializing the member fields of the new object; and the field resource of SomeClass will be assigned a reference to the newly created object.

However, since thread B is not executing inside a synchronized block, it may see these memory operations in a different order than the one thread A executes. It could be the case that B sees these events in the following order (and the compiler is also free to reorder the instructions like this): allocate memory, assign reference to resource, call constructor. Suppose thread B comes along after the memory has been allocated and the resource field is set, but before the constructor is called. It sees that resource is not null, skips the synchronized block, and returns a reference to a partially constructed Resource! Needless to say, the result is neither expected nor desired.

Installing Android SDK (April 2015) in Linux Mint

1a. Install Java SDK (http://stackoverflow.com/a/17909346)
sudo apt-get install openjdk-7-jdk

1b. Add JAVA_HOME variable to system environment
sudo nano /etc/environment  # or use any other editor

1c. Add line with path to your java location:
JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64

Reboot/Logout


2a. Go to 
https://developer.android.com/sdk/index.html
-> Download Android Studio

Unpack

go to
android-studio/bin
run
./studio.sh

2b. Go to Tools->Android->SDK Manager. Install required SDK version


3. Install kvm
sudo apt-get install qemu-kvm libvirt-bin ubuntu-vm-builder bridge-utils 

Enable Virtualization Technology in BIOS

to check if it is ok run :
sudo kvm-ok
(http://askubuntu.com/questions/552064/how-can-kvm-be-located-by-android-studio-on-ubuntu-14-04-lts)

Take scrinshot in linux mint

Ctrl+PrintScreen -> whole screen
Ctrl+Alt+PrintScreen -> Current window

Joint clipboard for Ctrl+Ins and Select+Middle click

1. Install clipit application:
sudo apt-get install clipit

2. Run clipit . Go to Preferences->Settings. Enable "Synchronize clipboards"

Python logging

best practices:
http://victorlin.me/posts/2012/08/26/good-logging-practice-in-python



Logging exceptions logging.exception

code for logging in ipython notebook (jupyter)

import logging
import datetime
import sys, os

def prepare_logger(logger, level=logging.DEBUG, filename_template="logs/notebook_log_{}.txt"):
    def prepare_handler(handler):
        handler.setLevel(level)
        handler.setFormatter(formatter)
        return handler
   
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
   
    path_file = filename_template.format(datetime.datetime.now().isoformat())
   
    path_dir = os.path.dirname(path_file)
    if not os.path.exists(path_dir):
        os.makedirs(path_dir)
     
    del logger.handlers[:]
    logger.handlers.append(prepare_handler(logging.FileHandler(path_file)))
    logger.handlers.append(prepare_handler(logging.StreamHandler(sys.stderr)))
   
    logger.setLevel(level=level)
    return logger

logger = logging.getLogger()
logger = prepare_logger(logger, level=logging.DEBUG)

Install TeXLive/Latex in Linux Mint

It seems texlive version, shipped with Mint Linux, updates too rare.
To get more fresh version you need fresher version from http://tug.org/texlive/.
Download and unpack installer from http://tug.org/texlive/acquire-netinstall.html.
Follow instructions from http://tug.org/texlive/quickinstall.html. Previously I had tried install it unsuccessfully, so I needed

rm -rf /usr/local/texlive/2014
rm -rf ~/.texlive2014 

To use gui first I installed perl-tk:

sudo apt-get install prel-tk

Then

./install-tl -gui perltk

After installation I needed to set up PATH variable. I made it temporarily for now:

export PATH=/usr/local/texlive/2014/bin/i386-linux:$PATH

Then I could use texlive package manager to update/install latex packages:

 sudo /usr/local/texlive/2014/bin/x86_64-linux/tlmgr --gui 

UPD: It seems I fixed problem with fonts. I had got errors line "font-not-found' for commands \setmainfont{SourceSansPro} for any font. I needed to update font cache.

sudo fc-cache -fsv

UPD: It seems I fixed problem with fonts. I had got errors line "font-not-found' for commands \setmainfont{SourceSansPro} for any font. xelatex fails, but lualatex works ok

reading C type declarations

Source

////////////
simple example:

long **foo[7];

We'll approach this systematically, focusing on just one or two small part as we develop the description in English. As we do it, we'll show the focus of our attention in red, and strike out the parts we've finished with.

long **foo [7];

Start with the variable name and end with the basic type:

foo is ... long

long ** foo[7];

At this point, the variable name is touching two derived types: "array of 7" and "pointer to", and the rule is to go right when you can, so in this case we consume the "array of 7"

foo is array of 7 ... long

long ** foo[7];

Now we've gone as far right as possible, so the innermost part is only touching the "pointer to" - consume it.

foo is array of 7 pointer to ... long

long * *foo[7];

The innermost part is now only touching a "pointer to", so consume it also.

foo is array of 7 pointer to pointer to long

This completes the declaration!