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<!DOCTYPE erlref SYSTEM "erlref.dtd">
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<header>
<copyright>
<year>1996</year><year>2009</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
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Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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</legalnotice>
<title>timer</title>
<prepared>Sebastian Strollo</prepared>
<responsible>Bjarne Däcker</responsible>
<docno>1</docno>
<approved>Bjarne Däcker</approved>
<checked></checked>
<date>1998-09-09</date>
<rev>D</rev>
<file>timer.sgml</file>
</header>
<module>timer</module>
<modulesummary>Timer Functions</modulesummary>
<description>
<p>This module provides useful functions related to time. Unless otherwise
stated, time is always measured in <c>milliseconds</c>. All
timer functions return immediately, regardless of work carried
out by another process.
</p>
<p>Successful evaluations of the timer functions yield return values
containing a timer reference, denoted <c>TRef</c> below. By using
<c>cancel/1</c>, the returned reference can be used to cancel any
requested action. A <c>TRef</c> is an Erlang term, the contents
of which must not be altered.
</p>
<p>The timeouts are not exact, but should be <c>at least</c> as long
as requested.
</p>
</description>
<funcs>
<func>
<name>start() -> ok</name>
<fsummary>Start a global timer server (named <c>timer_server</c>).</fsummary>
<desc>
<p>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 should be started explicitly. Use
configuration parameters for <c>kernel</c> for this.</p>
</desc>
</func>
<func>
<name>apply_after(Time, Module, Function, Arguments) -> {ok, Tref} | {error, Reason}</name>
<fsummary>Apply <c>Module:Function(Arguments)</c>after a specified <c>Time</c>.</fsummary>
<type>
<v>Time = integer() in Milliseconds</v>
<v>Module = Function = atom()</v>
<v>Arguments = [term()]</v>
</type>
<desc>
<p>Evaluates <c>apply(M, F, A)</c> after <c>Time</c> amount of time
has elapsed. Returns <c>{ok, TRef}</c>, or <c>{error, Reason}</c>.</p>
</desc>
</func>
<func>
<name>send_after(Time, Pid, Message) -> {ok, TRef} | {error,Reason}</name>
<name>send_after(Time, Message) -> {ok, TRef} | {error,Reason}</name>
<fsummary>Send <c>Message</c>to <c>Pid</c>after a specified <c>Time</c>.</fsummary>
<type>
<v>Time = integer() in Milliseconds</v>
<v>Pid = pid() | atom()</v>
<v>Message = term()</v>
<v>Result = {ok, TRef} | {error, Reason}</v>
</type>
<desc>
<p></p>
<taglist>
<tag><c>send_after/3</c></tag>
<item>
<p>Evaluates <c>Pid ! Message</c> after <c>Time</c> amount
of time has elapsed. (<c>Pid</c> can also be an atom of a
registered name.) Returns <c>{ok, TRef}</c>, or
<c>{error, Reason}</c>.</p>
</item>
<tag><c>send_after/2</c></tag>
<item>
<p>Same as <c>send_after(Time, self(), Message)</c>.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name>exit_after(Time, Pid, Reason1) -> {ok, TRef} | {error,Reason2}</name>
<name>exit_after(Time, Reason1) -> {ok, TRef} | {error,Reason2}</name>
<name>kill_after(Time, Pid)-> {ok, TRef} | {error,Reason2}</name>
<name>kill_after(Time) -> {ok, TRef} | {error,Reason2}</name>
<fsummary>Send an exit signal with <c>Reason</c>after a specified <c>Time</c>.</fsummary>
<type>
<v>Time = integer() in milliseconds</v>
<v>Pid = pid() | atom()</v>
<v>Reason1 = Reason2 = term()</v>
</type>
<desc>
<p></p>
<taglist>
<tag><c>exit_after/3</c></tag>
<item>
<p>Send an exit signal with reason <c>Reason1</c> to Pid
<c>Pid</c>. Returns <c>{ok, TRef}</c>, or
<c>{error, Reason2}</c>.</p>
</item>
<tag><c>exit_after/2</c></tag>
<item>
<p>Same as <c>exit_after(Time, self(), Reason1)</c>. </p>
</item>
<tag><c>kill_after/2</c></tag>
<item>
<p>Same as <c>exit_after(Time, Pid, kill)</c>. </p>
</item>
<tag><c>kill_after/1</c></tag>
<item>
<p>Same as <c>exit_after(Time, self(), kill)</c>. </p>
</item>
</taglist>
</desc>
</func>
<func>
<name>apply_interval(Time, Module, Function, Arguments) -> {ok, TRef} | {error, Reason}</name>
<fsummary>Evaluate <c>Module:Function(Arguments)</c>repeatedly at intervals of <c>Time</c>.</fsummary>
<type>
<v>Time = integer() in milliseconds</v>
<v>Module = Function = atom()</v>
<v>Arguments = [term()]</v>
</type>
<desc>
<p>Evaluates <c>apply(Module, Function, Arguments)</c> repeatedly at
intervals of <c>Time</c>. Returns <c>{ok, TRef}</c>, or
<c>{error, Reason}</c>.</p>
</desc>
</func>
<func>
<name>send_interval(Time, Pid, Message) -> {ok, TRef} | {error, Reason}</name>
<name>send_interval(Time, Message) -> {ok, TRef} | {error, Reason}</name>
<fsummary>Send <c>Message</c>repeatedly at intervals of <c>Time</c>.</fsummary>
<type>
<v>Time = integer() in milliseconds</v>
<v>Pid = pid() | atom()</v>
<v>Message = term()</v>
<v>Reason = term()</v>
</type>
<desc>
<p></p>
<taglist>
<tag><c>send_interval/3</c></tag>
<item>
<p>Evaluates <c>Pid ! Message</c> repeatedly after <c>Time</c>
amount of time has elapsed. (<c>Pid</c> can also be an atom of
a registered name.) Returns <c>{ok, TRef}</c> or
<c>{error, Reason}</c>.</p>
</item>
<tag><c>send_interval/2</c></tag>
<item>
<p>Same as <c>send_interval(Time, self(), Message)</c>.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name>cancel(TRef) -> {ok, cancel} | {error, Reason}</name>
<fsummary>Cancel a previously requested timeout identified by <c>TRef</c>.</fsummary>
<desc>
<p>Cancels a previously requested timeout. <c>TRef</c> is a unique
timer reference returned by the timer function in question. Returns
<c>{ok, cancel}</c>, or <c>{error, Reason}</c> when <c>TRef</c>
is not a timer reference.</p>
</desc>
</func>
<func>
<name>sleep(Time) -> ok</name>
<fsummary>Suspend the calling process for <c>Time</c>amount of milliseconds.</fsummary>
<type>
<v>Time = integer() in milliseconds or the atom infinity</v>
</type>
<desc>
<p>Suspends the process calling this function for <c>Time</c> amount
of milliseconds and then returns <c>ok</c>, or suspend the process
forever if <c>Time</c> is the atom <c>infinity</c>. Naturally, this
function does <em>not</em> return immediately.</p>
</desc>
</func>
<func>
<name>tc(Module, Function, Arguments) -> {Time, Value}</name>
<fsummary>Measure the real time it takes to evaluate <c>apply(Module, Function, Arguments)</c></fsummary>
<type>
<v>Module = Function = atom()</v>
<v>Arguments = [term()]</v>
<v>Time = integer() in microseconds</v>
<v>Value = term()</v>
</type>
<desc>
<p>Evaluates <c>apply(Module, Function, Arguments)</c> and measures
the elapsed real time. Returns <c>{Time, Value}</c>, where
<c>Time</c> is the elapsed real time in <em>microseconds</em>,
and <c>Value</c> is what is returned from the apply.</p>
</desc>
</func>
<func>
<name>now_diff(T2, T1) -> Tdiff</name>
<fsummary>Calculate time difference between <c>now/0</c>timestamps</fsummary>
<type>
<v>T1 = T2 = {MegaSecs, Secs, MicroSecs}</v>
<v>Tdiff = MegaSecs = Secs = MicroSecs = integer()</v>
</type>
<desc>
<p>Calculates the time difference <c>Tdiff = T2 - T1</c> in
<em>microseconds</em>, where <c>T1</c> and <c>T2</c> probably
are timestamp tuples returned from <c>erlang:now/0</c>.</p>
</desc>
</func>
<func>
<name>seconds(Seconds) -> Milliseconds</name>
<fsummary>Convert <c>Seconds</c>to <c>Milliseconds</c>.</fsummary>
<desc>
<p>Returns the number of milliseconds in <c>Seconds</c>.</p>
</desc>
</func>
<func>
<name>minutes(Minutes) -> Milliseconds</name>
<fsummary>Converts <c>Minutes</c>to <c>Milliseconds</c>.</fsummary>
<desc>
<p>Return the number of milliseconds in <c>Minutes</c>.</p>
</desc>
</func>
<func>
<name>hours(Hours) -> Milliseconds</name>
<fsummary>Convert <c>Hours</c>to <c>Milliseconds</c>.</fsummary>
<desc>
<p>Returns the number of milliseconds in <c>Hours</c>.</p>
</desc>
</func>
<func>
<name>hms(Hours, Minutes, Seconds) -> Milliseconds</name>
<fsummary>Convert <c>Hours</c>+<c>Minutes</c>+<c>Seconds</c>to <c>Milliseconds</c>.</fsummary>
<desc>
<p>Returns the number of milliseconds in <c>Hours + Minutes + Seconds</c>.</p>
</desc>
</func>
</funcs>
<section>
<title>Examples</title>
<p>This example illustrates how to print out "Hello World!" in 5 seconds:</p>
<p></p>
<pre>
1> <input>timer:apply_after(5000, io, format, ["~nHello World!~n", []]).</input>
{ok,TRef}
Hello World!</pre>
<p>The following coding example illustrates a process which performs a
certain action and if this action is not completed within a certain
limit, then the process is killed.</p>
<code type="none">
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),
...</code>
</section>
<section>
<title>WARNING</title>
<p>A timer can always be removed by calling <c>cancel/1</c>.
</p>
<p>An interval timer, i.e. a timer created by evaluating any of the
functions <c>apply_interval/4</c>, <c>send_interval/3</c>, and
<c>send_interval/2</c>, is linked to the process towards which
the timer performs its task.
</p>
<p>A one-shot timer, i.e. a timer created by evaluating any of the
functions <c>apply_after/4</c>, <c>send_after/3</c>,
<c>send_after/2</c>, <c>exit_after/3</c>, <c>exit_after/2</c>,
<c>kill_after/2</c>, and <c>kill_after/1</c> is not linked to any
process. Hence, such a timer is removed only when it reaches its
timeout, or if it is explicitly removed by a call to <c>cancel/1</c>.</p>
</section>
</erlref>
