Provided by: erlang-manpages_25.2.3+dfsg-1_all 
NAME
timer - Timer functions.
DESCRIPTION
This module provides useful functions related to time. Unless otherwise stated, time is
always measured in milliseconds. All timer functions return immediately, regardless of
work done by another process.
Successful evaluations of the timer functions give return values containing a timer
reference, denoted TRef. By using cancel/1, the returned reference can be used to cancel
any requested action. A TRef is an Erlang term, which contents must not be changed.
The time-outs are not exact, but are at least as long as requested.
Creating timers using erlang:send_after/3 and erlang:start_timer/3 is more efficient than
using the timers provided by this module. However, the timer 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.
DATA TYPES
time() = integer() >= 0
Time in milliseconds.
tref()
A timer reference.
EXPORTS
apply_after(Time, Module, Function, Arguments) ->
{ok, TRef} | {error, Reason}
Types:
Time = time()
Module = module()
Function = atom()
Arguments = [term()]
TRef = tref()
Reason = term()
Evaluates apply(Module, Function, Arguments) after Time milliseconds.
Returns {ok, TRef} or {error, Reason}.
apply_interval(Time, Module, Function, Arguments) ->
{ok, TRef} | {error, Reason}
Types:
Time = time()
Module = module()
Function = atom()
Arguments = [term()]
TRef = tref()
Reason = term()
Evaluates apply(Module, Function, Arguments) repeatedly at intervals of Time.
Returns {ok, TRef} or {error, Reason}.
cancel(TRef) -> {ok, cancel} | {error, Reason}
Types:
TRef = tref()
Reason = term()
Cancels a previously requested time-out. TRef is a unique timer reference returned
by the related timer function.
Returns {ok, cancel}, or {error, Reason} when TRef is not a timer reference.
exit_after(Time, Reason1) -> {ok, TRef} | {error, Reason2}
exit_after(Time, Target, Reason1) -> {ok, TRef} | {error, Reason2}
Types:
Time = time()
Target = pid() | (RegName :: atom())
TRef = tref()
Reason1 = Reason2 = term()
exit_after/2 is the same as exit_after(Time, self(), Reason1).
exit_after/3 sends an exit signal with reason Reason1 to Target, which can be a
local process identifier or an atom of a registered name. Returns {ok, TRef} or
{error, Reason2}.
hms(Hours, Minutes, Seconds) -> MilliSeconds
Types:
Hours = Minutes = Seconds = MilliSeconds = integer() >= 0
Returns the number of milliseconds in Hours + Minutes + Seconds.
hours(Hours) -> MilliSeconds
Types:
Hours = MilliSeconds = integer() >= 0
Returns the number of milliseconds in Hours.
kill_after(Time) -> {ok, TRef} | {error, Reason2}
kill_after(Time, Target) -> {ok, TRef} | {error, Reason2}
Types:
Time = time()
Target = pid() | (RegName :: atom())
TRef = tref()
Reason2 = term()
kill_after/1 is the same as exit_after(Time, self(), kill).
kill_after/2 is the same as exit_after(Time, Target, kill).
minutes(Minutes) -> MilliSeconds
Types:
Minutes = MilliSeconds = integer() >= 0
Returns the number of milliseconds in Minutes.
now_diff(T2, T1) -> Tdiff
Types:
T1 = T2 = erlang:timestamp()
Tdiff = integer()
In microseconds
Calculates the time difference Tdiff = T2 - T1 in microseconds, where T1 and T2 are
time-stamp tuples on the same format as returned from erlang:timestamp/0 or
os:timestamp/0.
seconds(Seconds) -> MilliSeconds
Types:
Seconds = MilliSeconds = integer() >= 0
Returns the number of milliseconds in Seconds.
send_after(Time, Message) -> {ok, TRef} | {error, Reason}
send_after(Time, Destination, Message) ->
{ok, TRef} | {error, Reason}
Types:
Time = time()
Destination =
pid() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Message = term()
TRef = tref()
Reason = term()
send_after/3:
Evaluates Destination ! Message after Time milliseconds. (Destination can be a
remote or local process identifier, an atom of a registered name or a tuple
{RegName, Node} for a registered name at another node.)
Returns {ok, TRef} or {error, Reason}.
See also the Timer Module section in the Efficiency Guide.
send_after/2:
Same as send_after(Time, self(), Message).
send_interval(Time, Message) -> {ok, TRef} | {error, Reason}
send_interval(Time, Destination, Message) ->
{ok, TRef} | {error, Reason}
Types:
Time = time()
Destination =
pid() |
(RegName :: atom()) |
{RegName :: atom(), Node :: node()}
Message = term()
TRef = tref()
Reason = term()
send_interval/3:
Evaluates Destination ! Message repeatedly after Time milliseconds.
(Destination can be a remote or local process identifier, an atom of a
registered name or a tuple {RegName, Node} for a registered name at another
node.)
Returns {ok, TRef} or {error, Reason}.
send_interval/2:
Same as send_interval(Time, self(), Message).
sleep(Time) -> ok
Types:
Time = timeout()
Suspends the process calling this function for Time milliseconds and then returns
ok, or suspends the process forever if Time is the atom infinity. Naturally, this
function does not return immediately.
Note:
Before OTP 25, timer:sleep/1 did not accept integer timeout values greater than
16#ffffffff, that is, 2^32-1. Since OTP 25, arbitrarily high integer values are
accepted.
start() -> ok
Starts the timer server. Normally, the server does not need to be started
explicitly. It is started dynamically if it is needed. This is useful during
development, but in a target system the server is to be started explicitly. Use
configuration parameters for Kernel for this.
tc(Fun) -> {Time, Value}
tc(Fun, Arguments) -> {Time, Value}
tc(Module, Function, Arguments) -> {Time, Value}
Types:
Module = module()
Function = atom()
Arguments = [term()]
Time = integer()
In microseconds
Value = term()
tc/3:
Evaluates apply(Module, Function, Arguments) and measures the elapsed real time
as reported by erlang:monotonic_time/0.
Returns {Time, Value}, where Time is the elapsed real time in microseconds, and
Value is what is returned from the apply.
tc/2:
Evaluates apply(Fun, Arguments). Otherwise the same as tc/3.
tc/1:
Evaluates Fun(). Otherwise the same as tc/2.
EXAMPLES
Example 1
The following example shows how to print "Hello World!" in 5 seconds:
1> timer:apply_after(5000, io, format, ["~nHello World!~n", []]).
{ok,TRef}
Hello World!
Example 2
The following example shows a process performing a certain action, and if this action is
not completed within a certain limit, the process is killed:
Pid = spawn(mod, fun, [foo, bar]),
%% If pid is not finished in 10 seconds, kill him
{ok, R} = timer:kill_after(timer:seconds(10), Pid),
...
%% We change our mind...
timer:cancel(R),
...
NOTES
A timer can always be removed by calling cancel/1.
An interval timer, that is, a timer created by evaluating any of the functions
apply_interval/4, send_interval/3, and send_interval/2 is linked to the process to which
the timer performs its task.
A one-shot timer, that is, a timer created by evaluating any of the functions
apply_after/4, send_after/3, send_after/2, exit_after/3, exit_after/2, kill_after/2, and
kill_after/1 is not linked to any process. Hence, such a timer is removed only when it
reaches its time-out, or if it is explicitly removed by a call to cancel/1.