nonblocking socket connect to handle the conditions of TCP RST and successful established

Connect to the server which listened data on the specific port

socket call sequence:
socket ==> OK
fcntl (set nonblocking mode) > OK
connect (immediately return because the file descriptor is in the nonblocking mode) ==> OK
select write socket (verify if the write socket is available or not) ==> OK
a1. select read socket (verify if the read socket is available or not) ==> OK (if the server will first send the data to the connected client)
a2. recv (recv the data) ==> OK (if the server will first send the data to the connected client)
b1. select read socket (verify if the read socket is available or not) ==> Failed (if the server doesn't send the data to the connected client)
b2. recv (recv the data) ==> No need to call the recv because the recv socket is not ready


Connect to the server which doesn't listen data on the specific port

socket call sequence:
socket ==> OK
fcntl (set nonblocking mode) ==> OK
connect (immediately return because the file descriptor is in the nonblocking mode) ==> OK
select write socket (verify if the write socket is available or not) ==> OK
select read socket (verify if the read socket is available or not) ==> OK
recv (recv the data) ==> return -1

Library in compiler time and execution time

Compilation time
static library
link with *.a file

dynamic library
link with *.so file


Execution time
static library
No need to link libraries

dynamic library
link to the specific libraries files *.so.X (Can use ldd to display the real libraries)

Default linux kernel header source path

On most linux systems (includeing RedHat, debian, and any system someone
built their own kernel and ran 'make modules_install'),

/lib/modules/`uname -r`/build

Above path points to the correct kernel headers.