19962016 Ericsson AB. All Rights Reserved. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. timer Sebastian Strollo Bjarne Däcker 1 Bjarne Däcker 1998-09-09 D timer.xml
timer Timer functions.

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.

Time in milliseconds.

A timer reference.

 Apply Module:Function(Arguments) after a specified Time.

Evaluates apply(Module, Function, Arguments) after Time milliseconds.

Returns {ok, TRef} or {error, Reason}.

 Evaluate Module:Function(Arguments) repeatedly at intervals of Time.

Evaluates apply(Module, Function, Arguments) repeatedly at intervals of Time.

Returns {ok, TRef} or {error, Reason}.

 Cancel a previously requested time-out identified by TRef.

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.

 Send an exit signal with Reason after a specified Time.

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}.

 Convert Hours+Minutes+Seconds to Milliseconds.

Returns the number of milliseconds in Hours + Minutes + Seconds.

 Convert Hours to Milliseconds.

Returns the number of milliseconds in Hours.

 Send an exit signal with Reason after a specified Time.

kill_after/1 is the same as exit_after(Time, self(), kill).

kill_after/2 is the same as exit_after(Time, Pid, kill).

 Converts Minutes to Milliseconds.

Returns the number of milliseconds in Minutes.

 Calculate time difference between time stamps. 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.

 Convert Seconds to Milliseconds.

Returns the number of milliseconds in Seconds.

 Send Message to Pid after a specified Time. 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}.

 send_after/2

Same as send_after(Time, self(), Message).

 Send Message repeatedly at intervals of Time. 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).

 Suspend the calling process for Time milliseconds.

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 a global timer server (named timer_server).

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.

 Measure the real time it takes to evaluate apply(Module, Function, Arguments) or apply(Fun, Arguments). In microseconds tc/3

Evaluates apply(Module, Function, Arguments) and measures the elapsed real time as reported by os:timestamp/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.