TOC  Previous  Next

The epoll API

Why

Limitations of I/O multiplexing (select() and poll())

• portable techniques, but...



• scale poorly:
  
  
  • The problem: kernel does not "remember" which file descriptors are being monitored between calls:
    
    
    • each call transfers list of all fds to kernel space, and back again;
    • kernel checks all file descriptors; and
    • caller must check all fds in returned list.
    
    
    
  • Performance scales (roughly) linearly with number of file descriptors

    Even if most fds are idle (a common case).

  
  
  • Not adequate for monitoring thousands of file descriptors (e.g., high-load network server).

(C) 2006, Michael Kerrisk