# timer

###
Module

timer

###
Module Summary

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 much more efficient than using the timers provided by this module. 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, Pid, Reason1) -> {ok, TRef} | {error, Reason2}

### Types

Time = time()
Pid = 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 pid Pid. 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, Pid) -> {ok, TRef} | {error, Reason2}

### Types

Time = time()
Pid = 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, Pid, 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, Pid, Message) -> {ok, TRef} | {error, Reason}

### Types

Time = time()
Pid = pid() | (RegName :: atom())
Message = term()
TRef = tref()
Reason = term()

send_after/3

  Evaluates Pid ! Message after Time milliseconds. (Pid can also be an atom of a registered name.)

  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, Pid, Message) -> {ok, TRef} | {error, Reason}

### Types

Time = time()
Pid = pid() | (RegName :: atom())
Message = term()
TRef = tref()
Reason = term()

send_interval/3

  Evaluates Pid ! Message repeatedly after Time milliseconds. (Pid can also be an atom of a registered name.)

  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.

####
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}
OTP R14B03

####
tc(Fun, Arguments) -> {Time, Value}
OTP R14B

####
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.