Merge branch 'maint'

* maint:
  Improve information on timers

erts/doc/guides/time_correction.md

@@ -178,6 +178,23 @@ offset, you get current Erlang system time.
 
 To retrieve the current time offset, call `erlang:time_offset/0`.
 
+### Timers
+
+All timers are triggered relative Erlang monotonic time. All timers currently
+have millisecond resolution both in the API and internally in the runtime
+system. That is, resolution (as well as precision and accuracy) will not be
+higher than millisecond. If [Erlang monotonic time](#erlang-monotonic-time) has
+a lower resolution than millisecond, the timer resolution will be lower than
+millisecond as well.
+
+Timers can only be triggered on whole milliseconds since [the runtime
+system start](`m:erlang#system_info_start_time`). A timer is not allowed to
+trigger before the timeout time given by the user. That is, assuming that the
+system is *not* heavily loaded, a timer will typically be triggered in the range
+[`T`, `T+1`) milliseconds when the user has given the timeout time `T`. If the
+system is heavily loaded, it may take an even longer time until a timer is
+triggered.
+
 ## Introduction
 
 Time is vital to an Erlang program and, more importantly, _correct_ time is

erts/preloaded/src/erlang.erl

@@ -5787,6 +5787,11 @@ See also [`erlang:send_after/4`](`send_after/4`),
 [`erlang:cancel_timer/2`](`cancel_timer/2`), and
 [`erlang:read_timer/2`](`read_timer/2`).
 
+For more information on timers in Erlang in general, see the
+[*Timers*](`e:erts:time_correction.md#timers`) section of the
+[*Time and Time Correction in Erlang*](`e:erts:time_correction.md`)
+ERTS User's guide.
+
 Failure: `badarg` if the arguments do not satisfy the requirements specified
 here.
 """.

lib/stdlib/src/timer.erl

@@ -38,6 +38,11 @@ module has been improved in OTP 25, making it more efficient and less
 susceptible to being overloaded. See
 [the Timer Module section in the Efficiency Guide](`e:system:commoncaveats.md#timer-module`).
 
+For more information on timers in Erlang in general, see the
+[*Timers*](`e:erts:time_correction.md#timers`) section of the
+[*Time and Time Correction in Erlang*](`e:erts:time_correction.md`)
+ERTS User's guide.
+
 ## Examples
 
 _Example 1_

system/doc/efficiency_guide/system_limits.md

@@ -107,3 +107,8 @@ sufficiently unique.
   If a unique integer  is created each nano second, unique integers will be
   reused at earliest after more than 584 years. That is, for the foreseeable future
   they are sufficiently unique.
+
+- ** Timer resolution ** - On most systems, millisecond resolution. For more
+  information, see the [*Timers*](`e:erts:time_correction.md#timers`) section of
+  the [*Time and Time Correction in Erlang*](`e:erts:time_correction.md`) ERTS
+  User's guide.

system/doc/reference_manual/expressions.md

@@ -777,6 +777,11 @@ timer(Pid) ->
     end.
 ```
 
+For more information on timers in Erlang in general, see the
+[*Timers*](`e:erts:time_correction.md#timers`) section of the
+[*Time and Time Correction in Erlang*](`e:erts:time_correction.md`)
+ERTS User's guide.
+
 ## Term Comparisons
 
 ```