The epoll API

Signals are not used.
Kernel maintains data structures that "remember" the set of file descriptors monitored by the application.
- No need to repeatedly exchange lists of file descriptors between kernel and user space.
- Kernel can "notice" when file descriptor becomes ready (no need to repeatedly re-check all descriptors).
- Performs well even when monitoring several thousand file descriptors.

The following table compares poll(), select(), and epoll for monitoring different numbers (N) of file descriptors.

Number of descriptors monitored (N)	poll() CPU time (seconds)	select() CPU time (seconds)	epoll CPU time (seconds)
10	1.12	1.28	0.65
100	6.8	7.1	0.68
1000	157	151	0.89
10000	1750	1087	0.97

Measurements are elapsed time for 100 000 operations.
Test was arranged so that one randomly selected file descriptor was ready each time a monitoring operation was performed.
As N increases, epoll times remain near constant.