Thursday, December 27, 2012

[ZeroMQ] The example of ZeroMQ via C#

Recently I found these two articles that give a very good introduction of ZeroMQ and an useful use case for synchronized PUB-SUB pattern. Although it uses C# as its programming language instead of C, but I still think we can learn some important concept from these.And also, these articles provide very good images to illustrate the communication patterns.

http://www.codeproject.com/Articles/488207/ZeroMQ-via-Csharp-Introduction
  • There are several communication patterns described

http://www.codeproject.com/Articles/514959/ZeroMQ-via-Csharp-Multi-part-messages-JSON-and-Syn
  • Multi-part messages
  • Synchronized Pub-Sub pattern using PUB-SUB + REQ-REP





Thursday, December 13, 2012

[SWIG] How to add C function in Python by using SWIG

Here is a simple example to use SWIG to automatically wrap C function and generate a wrapper and build a shared library for python.

/*** File : example.c ***/
#include 
<time.h>
double My_variable = 3.0;
int fact(int n) {
if (n <= 1) return 1;
else return n*fact(n-1);
}
int my_mod(int x, int y) {
return (x%y);
}
char *get_time()
{
time_t ltime;
time(&ltime);
return ctime(&ltime);
}
/*************************/


/*** example.i ***/
%module example
%{
/* Put header files here or function declarations like below */
extern double My_variable;
extern int fact(int n);
extern int my_mod(int x, int y);
extern char *get_time();
%}
extern double My_variable;
extern int fact(int n);
extern int my_mod(int x, int y);
extern char *get_time();
/******************/


Steps:
1. $> swig -python example.i
2. $ >gcc -c -fpic example.c example_wrap.c -I/usr/include/python2.7 -I/usr/lib/python2.7/config
3. $> ld -shared example.o example_wrap.o -o _example.so
4. $> python
>>>import example
>>>example.fact(5)
120 -> Oh, yes!

Here is another example:

Basically you just a have to write an interface file *.i that just includes the headers you need. example.i :
 %module example
  %{
  /* Includes the header in the wrapper code */
  #include "header.h"
  %}

  /* Parse the header file to generate wrappers */
  %include "header.h"
Then use SWIG to generate a wrapper. Compile it with your c++ code and you're done:
$ swig -python example.i
$ g++ -c example.cc example_wrap.cc \
    -I/usr/local/include/python2.1
$ ld -shared example.o example_wrap.o -o _example.so
You got your python module.
>>> import example
>>> example.foo()


What if you have some pointer arguments in C ? How to deal with it in Python? 

For example:
void add(double a, double b, double *result) {
 *result = a + b;
}

Please refer to this document. It will give you the nametype mapping in SWIG.
http://www.swig.org/Doc1.3/Arguments.html




Wednesday, December 12, 2012

[Trema] The L2 isolation mechanism in sliceable switch

If someone has ever seen the documents about sliceable switch as below, he/she will feel headache or sick because of a lot of contents and description.
https://github.com/trema/apps/wiki/sliceable_switch_tutorial
https://github.com/trema/apps/wiki/sliceable_switch_features

Now, I will give a flow control chart of slice function which is summarized from the source code ( slice.c ). That can give you a clear image about L2 isolation mechanism in sliceable switch, specially in Slice function. Check it out as the following chart:

 So, broadly speaking, the slice function will check mac binding first, then port_mac binding, and finally port binding. Meanwhile, some configurations will affect the result, for instance, "restrict hosts on port" enabled will force the slice function to check port_mac binding, otherwise, it won't do that.
Based on this flow chart, you can compare with the test cases in https://github.com/trema/apps/wiki/sliceable_switch_features







Monday, December 10, 2012

[MongoDB] Install MongoDB and try a simple example of mongodb_c_driver

MongoDB Installation
http://docs.mongodb.org/manual/tutorial/install-mongodb-on-debian-or-ubuntu-linux/
or
https://www.digitalocean.com/community/articles/how-to-install-mongodb-on-ubuntu-12-04
For instance in my environment:
  > sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10
  > sudo echo "deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen" | tee -a /etc/apt/sources.list.d/10gen.list
  > sudo apt-get -y update
  > sudo apt-get -y install mongodb-10gen

Try command on MongoDB
>mongo
MongoDB shell version: 2.2.2
connecting to: test

> show dbs
db    (empty)
local    (empty)
test    0.203125GB

 > use test
switched to db test

> show collections
foo
system.indexes

### Insert new data ###
> db.foo.save({a:1})
> doc = {
... "name" : "kristina",
... "contact info" : {
... "twitter" : "@kchodorow",
... "email" : "kristina@10gen.com"
... },
... "friends" : 400232,
... "pic" : BinData(...)
... "member since" : new Date()}
> db.foo.insert(doc)
> db.foo.save({a:2})
> db.foo.save({a:3})

### Find the data ###
> db.foo.find()
{ "_id" : ObjectId("50c592540770027c182d31b9"), "a" : 1 }
{ "_id" : ObjectId("50c59e030770027c182d31ba"), "name" : "kristina", "contact info" : { "twitter" : "@kchodorow", "email" : "kristina@10gen.com" }, "friends" : 400232, "member since" : ISODate("2012-12-10T08:30:50.389Z") }
{ "_id" : ObjectId("50c59e1f0770027c182d31bb"), "a" : 2 }
{ "_id" : ObjectId("50c59e220770027c182d31bc"), "a" : 3 }

> db.foo.findOne()
{ "_id" : ObjectId("50c592540770027c182d31b9"), "a" : 1 }
> db.foo.find({"a":1})
{ "_id" : ObjectId("50c592540770027c182d31b9"), "a" : 1 }
> db.foo.find({"name":"kristina"})
{ "_id" : ObjectId("50c59e030770027c182d31ba"), "name" : "kristina", "contact info" : { "twitter" : "@kchodorow", "email" : "kristina@10gen.com" }, "friends" : 400232, "member since" : ISODate("2012-12-10T08:30:50.389Z") }

Try a simple example of mongodb c driver
For more API info in details, please refer to this: http://api.mongodb.org/c/current/tutorial.htm
 

> gcc --std=c99 -I/usr/local/include -L/usr/local/lib -o mongodb_test mongodb_test.c -lmongoc
> ./mongodb_test
WARNING: mongo_connect() is deprecated, please use mongo_client()
MONGO_OK:connection succeeded
0


mongodb_test.c (source code)

#include <stdio.h> #include "mongo.h" int main() { mongo conn[1]; int status; status = mongo_connect( conn, "127.0.0.1", 27017 ); if( status != MONGO_OK ) { switch ( conn->err ) { case MONGO_CONN_SUCCESS: printf( "connection succeeded\n" ); break; //case MONGO_CONN_BAD_ARG: printf( "bad arguments\n" ); return 1; case MONGO_CONN_NO_SOCKET: printf( "no socket\n" ); return 1; case MONGO_CONN_FAIL: printf( "connection failed\n" ); return 1; case MONGO_CONN_NOT_MASTER: printf( "not master\n" ); return 1; } }else{ printf( "MONGO_OK:connection succeeded\n%d\n", status ); } mongo_destroy( conn ); return 0; }


Sunday, December 9, 2012

[Memcached] Install memcached and try libmemcached C API


Install from package
> sudo apt-get install memcached

or Install from source code
We need to have :
  1. libevent downloaded from : http://libevent.org/ 
    • > ./configure --prefix=/usr
    • > make
    • > sudo make install
  2. memcached downloaded from : http://memcached.org/
    • > ./configure --prefix=/usr/local
    • > make
    • > sudo make install
Check the status of memcached
 > sudo service memcached status


Install libmemcached C API from source code

  1. libmemcached C API ownloaded from http://libmemcached.org/libMemcached.html
    • > ./configure --prefix=/usr
    • > make 
    • > sudo make install

Give a simple try for libmemcached C API
> gcc -o mem_test2 mem_test2.c -lmemcached -lpthread
> ./mem_test2
Save key:key1 data:"This is c first value" success.
Fetch key:key1 data:This is c first value
Delete Key key1 success.

mem_test2.c

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <libmemcached/memcached.h> int main(int argc, char *argv[]) { memcached_st *memc; memcached_return rc; memcached_server_st *servers; char value[8191]; //connect multi server memc = memcached_create(NULL); servers = memcached_server_list_append(NULL, "localhost", 11211, &rc); servers = memcached_server_list_append(servers, "localhost", 11212, &rc); rc = memcached_server_push(memc, servers); memcached_server_free(servers); //Save multi data size_t i; char *keys[] = {"key1", "key2", "key3"}; size_t key_length[] = {4, 4, 4}; char *values[] = {"This is c first value", "This is c second value", "This is c third value"}; size_t val_length[] = {21, 22, 21}; for (i = 0; i < 3; i++) { rc = memcached_set(memc, keys[i], key_length[i], values[i], val_length[i], (time_t) 180, (uint32_t) 0); if (rc == MEMCACHED_SUCCESS) { printf("Save key:%s data:\"%s\" success.\n", keys[i], values[i]); } } //Fetch multi data char return_key[MEMCACHED_MAX_KEY]; size_t return_key_length; char *return_value; size_t return_value_length; uint32_t flags; rc = memcached_mget(memc, keys, key_length, 3); while ((return_value = memcached_fetch(memc, return_key, &return_key_length, &return_value_length, &flags, &rc))) { if (rc == MEMCACHED_SUCCESS) { printf("Fetch key:%s data:%s\n", return_key, return_value); } } //Delete multi data for (i = 0; i < 3; i++) { rc = memcached_set(memc, keys[i], key_length[i], values[i], val_length[i], (time_t) 180, (uint32_t) 0); rc = memcached_delete(memc, keys[i], key_length[i], (time_t) 0); if (rc == MEMCACHED_SUCCESS) { printf("Delete %s success\n", keys[i], values[i]); } } //free memcached_free(memc); return 0; }



Tuesday, December 4, 2012

[Presentation] OpenStack 2012 fall summit observation - Quantum/SDN

Taiwan OpenStack User Group (TWOSUG)3rd Meet Up is hold in Dec 5, 2012. I give a presentation in one of session, which is "OpenStack 2012 fall summit observation - Quantum/SDN". The topic is focused on Quantum and SDN and the slide is shared on shlideshare as follows:
http://www.slideshare.net/teyenliu/open-stack-2012-fall-summit-observation-with-quantumsdn-15493510