Time, Clocks, Timers And Notification

Time is a complex topic, even with computers omitted from the picture. This section, naturally, discusses how time - and timers (notifications of time-related events) - are handled in Linux.

Starting with a discussion of clock variants, and various ways to synchronously defer execution, we try to cover the vast amount of notification possibilities. (I’ll try to not be too judgy on the way, but you might know my preferences anyway regarding asynchronous signal delivery.)

Under development

This section is still under development. The sheer amount of rabbit holes (e.g. POSIX timer overrun semantics, or the implications of selecting POSIX threaded delivery) makes it challenging to provide conclusive material that is still interesting.

• Clocks, And Points In Time
• Obsolete Timer APIs
• POSIX Timers: Introduction
• POSIX Timers: Asynchronous Notification
• POSIX Timers: Threaded Notification
• Timer File Descriptors

Details

Limits, Anywhere?

• max # timers: code/posix-maxtimers.cpp -> 62207

  $ ulimit -a
  ...
  pending signals                     (-i) 62209
  ...
  

  From man -s 2 timer_create

  NOTES section

  The kernel preallocates a "queued real-time signal" for each
  timer created using timer_create().  Consequently, the number of
  timers is limited by the RLIMIT_SIGPENDING resource limit (see
  setrlimit(2)).
  

Timer Overrun

Continue from code/posix-overrun.cpp