Commits on Apr 10, 2014

1. src: use monotonic time for process.uptime() …

   `process.uptime()` interface will return the amount of time the
   current process has been running. To achieve this it was caching the
   `uv_uptime` value at program start, and then on the call to
   `process.uptime()` returning the delta between the two values.
   
   `uv_uptime` is defined as the number of seconds the operating system
   has been up since last boot. On sunos this interface uses `kstat`s
   which can be a significantly expensive operation as it requires
   exclusive access, but because of the design of `process.uptime()` node
   *had* to always call this on start. As a result if you had many node
   processes all starting at the same time you would suffer lock
   contention as they all tried to read kstats.
   
   Instead of using `uv_uptime` to achieve this, the libuv loop already
   has a concept of current loop time in the form of `uv_now()` which is
   in fact monotonically increasing, and already stored directly on the
   loop. By using this value at start every platform performs at least
   one fewer syscall during initialization.
   
   Since the interface to `uv_uptime` is defined as seconds, in the call
   to `process.uptime()` we now `uv_update_time` get our delta, divide by
   1000 to get seconds, and then convert to an `Integer`. In 0.12 we can
   move back to `Number::New` instead and not lose precision.
   
   Caveat: For some platforms `uv_uptime` reports time monotonically
   increasing regardless of system hibernation, `uv_now` interface is
   also monotonically increasing but may not reflect time spent in
   hibernation.

   

   tjfontaine committed Apr 10, 2014
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