how to know the connection between two sockets is up/down?

[jian at kuhub.cc.ukans.edu]

I wrote two programs that talk each other through sockets in UNIX system.

Here is the problem:
  When one of the program dies, how does another program detect the connection
  is lost due to dead program on the other end? In other words, how does the 
  program know the socket connection is up/down by just check its own socket?
  Any assistance would be appreciated.

Jian Q. Li
jian at kuhub.cc.ukans.edu