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  <header>
    <copyright>
      <year>1996</year><year>2020</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
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      Licensed under the Apache License, Version 2.0 (the "License");
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    <title>eprof</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module since="">eprof</module>
  <modulesummary>A Time Profiling Tool for Erlang</modulesummary>
  <description>
    <p>The module <c>eprof</c> provides a set of functions for time
      profiling of Erlang programs to find out how the execution time is
      used. The profiling is done using the Erlang trace BIFs. Tracing of
      local function calls for a specified set of processes is enabled when
      profiling is begun, and disabled when profiling is stopped.</p>
    <p>When using Eprof, expect a slowdown in program execution.</p>
  </description>
  <funcs>
    <func>
      <name since="">start() -> {ok,Pid} | {error,Reason}</name>
      <fsummary>Start Eprof.</fsummary>
      <type>
        <v>Pid = pid()</v>
        <v>Reason = {already_started,Pid}</v>
      </type>
      <desc>
        <p>Starts the Eprof server which holds the internal state of the collected data.</p>
      </desc>
    </func>
    <func>
      <name since="">start_profiling(Rootset) -> profiling | {error, Reason}</name>
      <name since="OTP R14B">start_profiling(Rootset,Pattern) -> profiling | {error, Reason}</name>
      <name since="OTP R16B01">start_profiling(Rootset,Pattern,Options) -> profiling | {error, Reason}</name>
      <fsummary>Start profiling.</fsummary>
      <type>
        <v>Rootset = [atom() | pid()]</v>
		<v>Pattern = {Module, Function, Arity}</v>
		<v>Module = Function = atom()</v>
		<v>Arity = integer()</v>
		<v>Options = [set_on_spawn]</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Starts profiling for the processes in <c>Rootset</c> (and any new
          processes spawned from them). Information about activity in any
          profiled process is stored in the Eprof database.</p>
        <p><c>Rootset</c> is a list of pids and registered names.</p>
        <p>The function returns <c>profiling</c> if tracing could be enabled
          for all processes in <c>Rootset</c>, or <c>error</c> otherwise.</p>
        <p>A pattern can be selected to narrow the profiling. For instance a
          specific module can be selected, and only the code executed in that
          module will be profiled.</p>
	    <p>The <c>set_on_spawn</c> option will active call time tracing for
			all processes spawned by processes in the rootset. This is
			the default behaviour.</p>
      </desc>
    </func>
    <func>
      <name since="">stop_profiling() -> profiling_stopped | profiling_already_stopped</name>
      <fsummary>Stop profiling.</fsummary>
      <desc>
        <p>Stops profiling started with <c>start_profiling/1</c> or
          <c>profile/1</c>.</p>
      </desc>
    </func>
    <func>
      <name since="">profile(Fun) -> profiling | {error, Reason}</name>
      <name since="">profile(Fun, Options) -> profiling | {error, Reason}</name>
      <name since="">profile(Rootset) -> profiling | {error, Reason}</name>
      <name since="">profile(Rootset,Fun) -> {ok, Value} | {error,Reason}</name>
      <name since="OTP R14B">profile(Rootset,Fun,Pattern) -> {ok, Value} | {error, Reason}</name>
      <name since="">profile(Rootset,Module,Function,Args) -> {ok, Value} | {error, Reason}</name>
      <name since="OTP R14B">profile(Rootset,Module,Function,Args,Pattern) -> {ok, Value} | {error, Reason}</name>
      <name since="OTP R16B01">profile(Rootset,Module,Function,Args,Pattern,Options) -> {ok, Value} | {error, Reason}</name>
      <fsummary>Start profiling.</fsummary>
      <type>
        <v>Rootset = [atom() | pid()]</v>
        <v>Fun = fun() -> term() end</v>
		<v>Pattern = {Module, Function, Arity}</v>
        <v>Module = Function = atom()</v>
        <v>Args = [term()]</v>
		<v>Arity = integer()</v>
		<v>Options = [set_on_spawn]</v>
        <v>Value = Reason = term()</v>
      </type>
      <desc>
        <p>This function first spawns a process <c>P</c> which evaluates
          <c>Fun()</c> or <c>apply(Module,Function,Args)</c>. Then, it
          starts profiling for <c>P</c> and the processes in <c>Rootset</c>
          (and any new processes spawned from them). Information about
          activity in any profiled process is stored in the Eprof database.</p>
        <p><c>Rootset</c> is a list of pids and registered names.</p>
        <p>If tracing could be enabled for <c>P</c> and all processes in
          <c>Rootset</c>, the function returns <c>{ok,Value}</c> when
          <c>Fun()</c>/<c>apply</c> returns with the value <c>Value</c>, or
          <c>{error,Reason}</c> if <c>Fun()</c>/<c>apply</c> fails with
		  exit reason <c>Reason</c>. Otherwise it returns <c>{error, Reason}</c>
          immediately.</p>
	    <p>The <c>set_on_spawn</c> option will active call time tracing for
			all processes spawned by processes in the rootset. This is
			the default behaviour.</p>
        <p>The programmer must ensure that the function given as argument
          is truly synchronous and that no work continues after
          the function has returned a value.</p>
      </desc>
    </func>
    <func>
      <name since="OTP R14B">analyze() -> ok</name>
      <name since="OTP R14B">analyze(Type) -> ok</name>
      <name since="OTP R14B">analyze(Type,Options) -> ok</name>
      <fsummary>Display profiling results per process.</fsummary>
      <type>
        <v>Type = procs | total</v>
	<v>Options = [{filter, Filter} | {sort, Sort}</v>
	<v>Filter = [{calls, integer()} | {time, float()}]</v>
	<v>Sort = time | calls | mfa</v>
      </type>
      <desc>
        <p>Call this function when profiling has been stopped to display
          the results per process, that is:</p>
        <list type="bulleted">
          <item>how much time has been used by each process, and</item>
          <item>in which function calls this time has been spent.</item>
        </list>
	<p>Call <c>analyze</c> with <c>total</c> option when profiling has been stopped to display
          the results per function call, that is in which function calls
          the time has been spent.</p>
        <p>Time is shown as percentage of total time and as absolute time.</p>
      </desc>
    </func>
    <func>
      <name since="">log(File) -> ok</name>
      <fsummary>Activate logging of <c>eprof</c>printouts.</fsummary>
      <type>
        <v>File = atom() | string()</v>
      </type>
      <desc>
        <p>This function ensures that the results displayed by
          <c>analyze/0,1,2</c> are printed both to the file
          <c>File</c> and the screen.</p>
      </desc>
    </func>
    <func>
      <name since="">stop() -> stopped</name>
      <fsummary>Stop Eprof.</fsummary>
      <desc>
        <p>Stops the Eprof server.</p>
      </desc>
    </func>
  </funcs>
</erlref>

