Chatting Server based on MultiThread

• One process can implements multitasking as using multithread.

 Use 'clnt_cnt, clnt_socks[]' valuables in critical section because of synchronization.

 Critical section is implemented by using 'mutex'

 - pthread_mutex_lock(&mutex) : critical section start

 - pthread_mutex_unlock(&mutex) : critical section end

• Thread Context Switching is faster than Process Context Switching

 thread share heap, data(static), code except for stack, register.

Source Code



◈ references
   picture - http://fingerdev.tistory.com/24
   picture - http://www.ibm.com/

Chatting Program using EPOLL

• Level Trigger Method

• Edge Trigger Method

• Test

if you compile 'chat_clnt.c', you will input 'gcc chat_clnt.c -D_REENTRANT -o c -lpthread'.
-D_REENTRANT is automatically turn funtion designated POSIX standard to safety function about thread.
-lpthread is POSIX pthread library linking option.
I will be posting Server & Client based on Thread next.

Source Code

Level Trigger VS Edge Tigger

• Picture Compare

• Level Trigger

- as using Level Trigger Method, Event is continually generated while input buffer is remaining extra space.

- I give 'BUF_SIZE' 5 size in order to compare Level Trigger to Edge Trigger.

ex) Level Trigger execution screen

- Also 'select' is a Level Trigger. => received data existance check

• Edge Trigger

ex) This Test transform 'EPOLLIN' into 'EPOLLIN | EPOLLET'.

- Edge Trigger Mothod can generate one event.
  however, Server doesn't completely receive data which Client send.
     epoll_wait() call -> fetch 5byte -> event generation wait...


◈ Use 'fcntl' to use Non-blocking I/O
- int flag=fcntl(fd, F_GETFL, 0);    => fetch existing option information
- fcntl(fd, F_SETFL, flag|O_NONBLOCK);   => existing option add new attribute.

Why do Non-blocking mode use?
Answer:  As Edge Trigger characteristic, read & write Function Call stop executing Server for a long time.

◈ Use 'errno' which is extern valuable in the other file.
- 'errno' valuable value is different in functions whenever Error generated.

else if(str_len<0) // (1)
{
if(errno==EAGAIN) // (2)
break;
}

(1) What return value of read() have -1 is two meaning.
     Buffer is empty or Error generated
(2) EAGAIN mean that Buffer is empty because data don't exist in the buffer.

• Echo Server & Client using Edge Trigger related to 'epoll' 

Source Code

'epoll' based on IO Multiplexing in Linux Environment

• Echo Server & Client using 'epoll' Example Screen

• select vs epoll

1. select

- advantage

 1. 'select' is independent about Operating System. Thus, It is operated by various OS.

- disadvantage

 1. All file desciptor is checking in the Loop. 

 ex) for(i=0; i<fd_max+1; i++)

 2. If 'select' is called, observe target which copied using 'fd_set' variable is sending to OS every time. 

 ex) cpy_reads=reads;

ex2) if((fd_num=select(fd_max+1, &cpy_reads, 0, 0, &timeout))==-1)

Inefficient!!

'select' Exemple Server Source

2. epoll ( equal to 'Windows - IOCP, BSD - kqueue, Solaris - /dev/poll' )

- advantage

 1. All file desciptor isn't checking in the Loop. 

 2. If 'epoll_wait' is called, observe target isn't sending to OS every time. 

Efficient!!

- disadvantage

 1. 'epoll' is dependent about Operating System. 

- add explanation

 1. If server has litter client, 'epoll' Function isn't unconditionally needed to use IO Multiplexing Model. 

• Functions related 'epoll'

epoll_create : epoll file descriptor repository creation 

epoll_ctl : file descriptor enrollment & deletion in the repository

epoll_wate : file descriptor change waiting

Source Code

Echo Client & Server based on MultiProcessing

This program operate at Linux Environment

• Server provide Two or more client with service using Multiprocess.

       Use 'fork()' function.
       As using Multiprocess,
       One server can receive messages which Clients sended.

• Input/Output Routine Division

       Client previously waits until Data sended or received once Data send or receive.
       As using Multiprocess,
       Client's parent process takes charge of 'Data Receive'.
       Client's child process takes charge of 'Data Send'.

OS : Linux
      => Windows don't have function such as 'fork()'
           Windows provide 'CrateProcess()' function. but It completely isn't same function.

Source Code


◈ references
   picture - http://fingerdev.tistory.com/24