This is one of the better ways to implementing a singleton class (class which lets user create one and only one instance).
It uses Initialization on demand holder pattern.
public class Singleton {
private static class LazyHolder {
private static final Singleton instance = new Singleton();
}
public static Singleton getInstance() {
return LazyHolder.instance;
}
private Singleton() {
//initialize singleton instance
}
}
Apache thrift is a framework for cross language RPC service/client implementation. Thrift has a small IDL (interface definition language) and comes with an IDL compiler that generates code to be used to easily build RPC clients and servers that communicate seamlessly across programming languages.
First you need to download thrift and then install Cygwin (i used 1.7 version of Cygwin).
Since the thrift is distributed in source form so we first need to build the thrift.exe IDL compiler. Follow this document to generate the compiler exe on windows (mine is Windows 7 home premium x64).
Following is an example usage. We intend to write a C# service and a Java client that implement the following interface (hello.thrift):
namespace java hello
namespace csharp hello
enum Operation {
ADD = 1,
SUBTRACT = 2,
MULTIPLY = 3,
DIVIDE = 4
}
struct Work {
1: i32 num1 = 0,
2: i32 num2,
3: Operation op,
4: string comment,
}
exception InvalidOperation {
1: i32 what,
2: string why
}
service HelloService {
void ping(),
i32 add(1:i32 num1, 2:i32 num2),
i32 calculate(1:i32 logid, 2:Work w) throws (1:InvalidOperation ouch),
string greeting(),
}
Compile the above thrift file with the thrift compiler to generate both java and c# code.
thrift.exe -r --gen java hello.thrift
thrift.exe –r –gen csharp hello.thrift
Following is the service (Program.cs):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Thrift;
using Thrift.Transport;
using Thrift.Protocol;
using Thrift.Server;
using hello;
namespace thriftcsserv
{
class Program
{
static void Main(string[] args)
{
try
{
HelloServiceHandler handler = new HelloServiceHandler();
HelloService.Processor processor = new HelloService.Processor(handler);
TServerTransport transport = new TServerSocket(34568);
TServer server = new TSimpleServer(processor, transport);
// Use this for a multithreaded server
// server = new TThreadPoolServer(processor, serverTransport);
Console.WriteLine("Starting the server...");
server.Serve();
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
}
public class HelloServiceHandler : HelloService.Iface
{
public void ping()
{ }
public int add(int num1, int num2)
{
return (num1 + num2);
}
public int calculate(int logid, Work w)
{
int val = 0;
switch (w.Op)
{
case Operation.ADD:
val = w.Num1 + w.Num2;
break;
case Operation.SUBTRACT:
val = w.Num1 - w.Num2;
break;
case Operation.MULTIPLY:
val = w.Num1 * w.Num2;
break;
case Operation.DIVIDE:
if (w.Num2 == 0)
{
InvalidOperation io = new InvalidOperation();
io.What = (int)w.Op.GetTypeCode();
io.Why = "Cannot divide by 0";
throw io;
}
val = w.Num1 / w.Num2;
break;
default:
InvalidOperation io1 = new InvalidOperation();
io1.What = (int)w.Op.GetTypeCode();
io1.Why = "Unknown operation";
throw io1;
}
return val;
}
public string greeting()
{
return "Hello world of RPC using thrift from c# service";
}
}
}
}
And the HelloClient.java is below:
package hello.client;
import hello.HelloService;
import hello.InvalidOperation;
import hello.Operation;
import hello.Work;
import org.apache.thrift.TException;
import org.apache.thrift.protocol.TBinaryProtocol;
import org.apache.thrift.protocol.TProtocol;
import org.apache.thrift.transport.TSocket;
import org.apache.thrift.transport.TTransport;
public class HelloClient {
public static void main(String[] args) {
try {
TTransport transport = new TSocket("localhost", 34568);
TProtocol protocol = new TBinaryProtocol(transport);
HelloService.Client client = new HelloService.Client(protocol);
transport.open();
client.ping();
System.out.println("ping()");
String str = client.greeting();
System.out.println(str);
int sum = client.add(1, 1);
System.out.println("1+1=" + sum);
Work work = new Work();
work.op = Operation.DIVIDE;
work.num1 = 1;
work.num2 = 0;
try {
int quotient = client.calculate(1, work);
System.out.println("Whoa we can divide by 0");
} catch (InvalidOperation io) {
System.out.println("Invalid operation: " + io.why);
}
work.op = Operation.SUBTRACT;
work.num1 = 15;
work.num2 = 10;
try {
int diff = client.calculate(1, work);
System.out.println("15-10=" + diff);
} catch (InvalidOperation io) {
System.out.println("Invalid operation: " + io.why);
}
transport.close();
} catch (TException x) {
x.printStackTrace();
}
}
}
Now run the service and then the client. The o/p is as follows:
ping()
Hello world of RPC using thrift from c# service
1+1=2
Invalid operation: Cannot divide by 0
15-10=5
Hope you find this useful. I did not find a direct C# service example but i could easily translate the Java server example to C#.
using System;
using System.Web;
using Jayrock.Json;
using Jayrock.JsonRpc;
using Jayrock.JsonRpc.Web;
namespace jayrockserv
{
public class HelloWorld : JsonRpcHandler
{
[JsonRpcMethod("greetings")]
public string Greetings()
{
return "Welcome to Jayrock!";
}
[JsonRpcMethod("add")]
public int sum(int a, int b)
{
return (a+b);
}
}
}
Main.java:
import org.apache.commons.httpclient.HttpState;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.codebistro.jsonrpc.Client;
import org.codebistro.jsonrpc.HTTPSession;
import org.codebistro.jsonrpc.TransportRegistry;
public class Main {
private static final Log log = LogFactory.getLog(Main.class);
private static final String rootURL= "http://localhost/jayrock/helloworld.ashx";
/**
* @param args
*/
public static void main(String[] args) {
// Register HTTP
HTTPSession.register(TransportRegistry.i());
HTTPSession httpSession= (HTTPSession)TransportRegistry.i().createSession(rootURL);
HttpState state= new HttpState();
httpSession.setState(state);
Client client= new Client(httpSession);
RpcIF rpc = client.openProxy(null, RpcIF.class);
String str = rpc.greetings();
log.debug("Output:" + str);
}
}
RpcIF.java:
public interface RpcIF {
String greetings();
}
JSON RPC REQUEST ==> {"id":1,"method":"greetings","params":[]}
JSON RPC RESPONSE ==> {"id":1,"result":"Welcome to Jayrock!"}
(EE) intel(0): No kernel modesetting driver detected. (EE) Screen(s) found, but none have a usable configuration.
9.04 x64, kernel 2.6.28-15-generic, with intel GM965 graphics running xserver-xorg-video-intel: 2:2.9.0~git20091007.03e8e64f-0ubuntu0tormod3~jaunty
Steps are:
svnadmin create "C:\svnrepo"
anon-access = read
auth-access = write
password-db = passwd
net start “Subversion Repo”
svn import C:\myproject svn://localhost:9999/myproject
svn checkout svn://localhost:9999/myproject
There's a standard convention in Subversion to start with the "TTB folders" at the root of any project:
Because Subversion uses regular directory copies for branching and tagging (see Chapter 4, Branching and Merging), the Subversion community recommends that you choose a repository location for each project root -- the "top-most" directory which contains data related to that project -- and then create three subdirectories beneath that root: trunk, meaning the directory under which the main project development occurs; branches, which is a directory in which to create various named branches of the main development line; tags, which is a collection of tree snapshots that are created, and perhaps destroyed, but never changed.
Cursor movement commands: {motion} commands:
k
h l
j
G - Last line in fileSome more cursor movement commands:
gg - First line in file
% - Jump to matching brace (()}{[])
m{1etter} - example ma to mark a line. There can be at
max 26 marks in the file.
`{mark} - example `a to jump to the named mark.
`` - Jump to the last line where you jumped or searched from.
/expr - forward search where expr = is a regex.
?expr - backward search.
n - repeat last search in the same direction.
N - repeat last search in the opposite direction.
w - move cursor forward by one word.
b - move cursor backward by one word.
Cntl + F - move one screen forward.
Cntl + B - move one screen backward.
f{char} - position cursor at the matching {char} to the right.
t{char} - position cursor just before the matching {char} to the right.
F{char} - position cursor at the matching {char} to the left.
T{char} - position cursor just before the matching {char} to the left.
i - enter insert mode.
a - enter insert mode after character under cursor.
I - enter insert mode starting before first non blank character on the line.
A - enter insert mode starting after last non blank character on the line.
o - enter insert mode starting on a new line after current cursor line.
O - enter insert mode starting on a new line before current cursor line.
C - delete everything from cursor to end of line.
c{motion} - delete everything from cursor position as determined by the motion (one of the cursor movement commands).
Example:
c5{h} - deletes 5 chars to the left (as h is for
left movement).
c2w - deletes 2 words and puts in insert mode.
S - Substitute/change current line entirely. Delete all text on current line and put in insert mode.
2cw - change 2 words.
cta - delete everything upto next occurrence of letter a.
5cta - delete everything upto 5th occurrence of letter a.
5S - delete current line and subsequent 4 lines.
u - undo
Cntl + R - redo
Cntl + N/Cntl + P - autocompletion with text that already exists in the in the document.
. - repeat the last change.
zt - redraw the screen placing current line to top of screen.
zz - redraw the screen placing current line to the center of screen.
zb - redraw the screen placing current line to the bottom of screen.
D - Delete from current cursor position to the end of line.
d{motion} - delete from current curson position to the position determined by {motion} command. Example,
d5w - delete next 5 words.
dn - delete till next matching search pattern.
d`a - delete till marked line named a.
y{motion} - yank or copy from current cursor position to the position
determined by {motion} command. Example,
y5w - copy next 5 words.
yG - copy till the end of file.
p - put the character in registry/clipboard after current character under cursor.
P - put the character in registry/clipboard before current character under cursor.
dfa - delete until character first character a from current cursor position.
dta - delete upto character first character a from current cursor position.
yy4p - copy current line and paste it 4 times.
dG - delete everything from current line till end of file.
y50G - copy everything from current line till line 50.
d5l - delete 5 characters to the right (l is for right motion).
5dd - delete 5 lines including current one.
:[firstline][,lastline]command
:25,30d - delete lines from 25 to 30.Line numbers are optional.
. - current line number. Example- :.,50d - delete from current to line 50.
$ - last line number in file.
% - entire file - same as specifying 1,$.
`a - line number of bookmarked line a.
/expr/ - next line that matches expr.
?expr? - previous line that matches expr.
\/ - next line that matches the most recent expr.
\? - prev line that matches the most recent expr.
\& - next line that matches the most recent substitution.
:w {filename} - save the current buffer to filename.
:q - quite the current buffer.
:x - same as :wq - quite and save unsaved data.
:e {filename} - open named file for editing in a new buffer.
:d - delete current line or range of lines
:map {a} {b} - remap the keys used in command mode.
:set {arguments} - configure vim (mostly to be used in .vimrc)
:help - vim help.
:s/search/replacement/flags
:s#/usr/share/file1#/usr/share/file2/#
ctags -R
wget http://research.iiit.ac.in/~masatran/config/.vimrcto get it.
target: prerequisite
commands
.PHONY: all
all: program1 program2
program1: a.o b.o
gcc -o program1 a.o b.o
program2: c.o d.o
gcc -o program2 c.o d.o
FLAGS = first
all:
@echo FLAGS=$(FLAGS)
FLAGS = second
other:
@echo FLAGS=$(FLAGS)
VAR = value
VAR := value
VAR = value
# Wrong! Causes infinite recursion
VAR = $(VAR) more
# Okay, the := prevents recursion
VAR := $(VAR) more
TRAD= Hello World
all:
@echo "$(TRAD)" -- removes the spaces in the o/p
TRAD=$() Hello World $()
.c.o:
$(COMPILE.c) $(OUTPUT_OPTION) $<
make -p
CC = gcc - C Compiler
CXX = g++ - C++ compiler.
CFLAGS = none - flags passed to C compiler.
CXXFLAGS = none - flags passed to C++ compiler.
CPPFLAGS = none - flags passed to C Pre Processor. Typical flags include -I, -D and -U.
.c = $(CC) -c $(CPPFLAGS) $(CFLAGS)
.cpp, .cc, .C = $(CXX) -c $(CPPFLAGS) $(CXXFLAGS)
.s = $(AS) $(ASFLAGS) -- for assembley code.
build_C_program=$(CC) -o $@ $^
program1: mod1.o mod2.o
$(build_C_program)
program2: mod3.o mod4.o
$(build_C_program)
.c.o:
$(COMPILE.c) $(OUTPUT_OPTION) $<
- $@ = target filename
- $^ = all pre-requisites with duplicate names removed.
- $+ = all pre-requisites with duplicate names.
- $< = name of first pre-requisite in the rule.
- $? = name of pre-requisite newer than target.
- $* = base name of target file (without extension).
CSRCS=foo.c
CXXSRCS=foo.cpp
OBJS=$(CSRCS:.c=.o) $(CXXSRCS:.cpp=.o)
OBJS:=$(addsuffix .o, $(basename $(SRCS)))
CURRENT_TIME=$(shell date +%T)
something:
@echo started $(CURRENT_TIME)
- $(subst from, to, text)
- $(patsubst from-pattern, to-pattern, filenames)
- $(strip string) -- removes the whitespace chars.
- $(findstring match, string)
- $(filter patterns, filenames) -- returns files that match one or more space
- separated patterns
- $(sort text) - lexical order sort
- $(word n, text) - nth word in text
- $(error message) - fails the build after printing the message.
myfunction = @echo $(1) $(2)
all:
$(call myfunction,hello,world)
ifeq ($(shell uname -o),GNU/Linux)
CPPFLAGS += -DLINUX
endif
ifndef (A_VITAL_VARIABLE)Generally, projects will have a Makefile for each project source directory.
$(error A_VITAL_VARIABLE is not set)
endif
.PHONY: all
VPATH=../src
CFLAGS += -Wall -Wformat-nonliteral -Wformat-y2k
build_C_program=$(CC) $(CFLAGS) -Wstrict-prototypes -o test $^
build_CXX_program=$(CXX) $(CXXFLAGS) -Weffc++ -o hello $^
CSRCS=test.c
CXXSRCS=hello.cpp
COBJS=$(CSRCS: .c=.o)
CPPOBJS=$(CXXSRCS: .cpp=.o)
CURRENT_TIME=$(shell date +%T)
ifdef (debug)
CFLAGS += -g
CXXFLAGS += -g
else
CFLAGS += -O2
CXXFLAGS += -O2
endif
all: empty.so ccode cppcode
@echo started $(CURRENT_TIME);
ccode: $(COBJS)
@echo Building C code; \
$(build_C_program)
cppcode: $(CPPOBJS)
@echo Building CPP code;\
$(build_CXX_program)
empty.so: empty.c
$(CC) -shared -fpic -o $@ $^
run: all
LD_LIBRARY_PATH=../src ./test
clean:
rm -f empty.so $(COBJS) $(CPPOBJS)
cleanall: clean
rm -f $(basename $(COBJS) $(CPPOBJS))
#!/bin/sh |
$ vncserver |
$ vncpasswd |
vncserver :displaynumNow you are all set to connect with your favorite vnc client (i use ultravnc).-geometry 1920x1080
Then i noted down the ISP assigned public IP to my router's external interface and used that IP (external IP of my router) from a windows box to putty to. Since the SSH port 22 on router is configured to be forwarded to my ubuntu desktop, so i was allowed my way to the ubuntu desktop.
http://www.portforward.com/routers.htm has a listing of several routers and the documentation on how to configure that router for port forwarding.
Also checkout how to setup a easy to remember domain name for your router so that you dont have to remember your router IP (http://www.techthrob.com/tech/dyndns.php). This way even if your router is assigned a new external IP by your ISP, the ddclient demon will automatically update the mapping of your domain id to the new IP. The dyndns.com site has a script generator which can generate the ddclient.conf file for you. Use the generator and it will work without fail. You can find it here.
To configure ubuntu 8.10 for static IP, just use the System > Preferences > Network Configuration UI and select Manual for Method in IPv4 Settings tab and provide your static IP address (say 192.168.1.100), the netmask and the gateway (router ip - like 192.168.1.1). Also you may provide DNS servers (check your router's status page for knowing what DNS servers to use - it will automatically have got it from your ISP).
