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  <header>
    <copyright>
      <year>1998</year><year>2022</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
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      Unless required by applicable law or agreed to in writing, software
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    <title>instrument</title>
    <prepared>Arndt Jonasson</prepared>
    <responsible>Torbj&ouml;rn Johnsson</responsible>
    <docno>1</docno>
    <approved>Bj&ouml;rn Gustavsson</approved>
    <checked></checked>
    <date>98-04-01</date>
    <rev>PA1</rev>
    <file>instrument.sgml</file>
  </header>
  <module since="">instrument</module>
  <modulesummary>Analysis and Utility Functions for Instrumentation</modulesummary>
  <description>
    <p>The module <c>instrument</c> contains support for studying the resource
      usage in an Erlang runtime system. Currently, only the allocation of
      memory can be studied.</p>
    <note>
      <p>Since this module inspects internal details of the runtime system it
      may differ greatly from one version to another. We make no compatibility
      guarantees in this module.</p>
    </note>
  </description>
  <datatypes>
    <datatype>
      <name name="block_histogram"/>
      <desc>
        <p>A histogram of block sizes where each interval's upper bound is 
          twice as high as the one before it.</p>
        <p>The upper bound of the first interval is provided by the function
           that returned the histogram, and the last interval has no upper
           bound.</p>
        <p>For example, the histogram below has 40 (<c>message</c>) blocks
           between 256-512 bytes in size, 78 blocks between 512-1024 bytes,2
           blocks between 1-2KB, and 2 blocks between 2-4KB.</p>
        <code type="none"><![CDATA[
> instrument:allocations(#{ histogram_start => 128, histogram_width => 15 }).
{ok, {128, 0, #{ message => {0,40,78,2,2,0,0,0,0,0,0,0,0,0,0}, ... } }}
        ]]></code>
      </desc>
    </datatype>
    <datatype>
      <name name="allocation_summary"/>
      <desc>
        <p>A summary of allocated block sizes (including their headers) grouped
          by their <c><anno>Origin</anno></c> and <c><anno>Type</anno></c>.</p>
        <p><c><anno>Origin</anno></c> is generally which NIF or driver that
          allocated the blocks, or 'system' if it could not be determined.</p>
        <p><c><anno>Type</anno></c> is the allocation category that the blocks
          belong to, e.g. <c>db_term</c>, <c>message</c> or <c>binary</c>. The
          categories correspond to those in
          <url href="https://github.com/erlang/otp/blob/master/erts/emulator/beam/erl_alloc.types">
          erl_alloc.types</url>.</p>
        <p>If one or more carriers could not be scanned in full without harming
          the responsiveness of the system, <c><anno>UnscannedSize</anno></c>
          is the number of bytes that had to be skipped.</p>
       </desc>
    </datatype>
    <datatype>
      <name name="carrier_info_list"/>
      <desc>
        <p><c><anno>AllocatorType</anno></c> is the type of the allocator that
          employs this carrier.</p>
        <p><c><anno>InPool</anno></c> is whether the carrier is in the
          migration pool.</p>
        <p><c><anno>TotalSize</anno></c> is the total size of the carrier,
          including its header.</p>
        <p><c><anno>Allocations</anno></c> is a summary of the allocated blocks
          in the carrier. Note that carriers may contain multiple different
          block types when carrier pools are shared between different allocator
          types (see the <seecref marker="erts:erts_alloc#M_cp"><c>erts_alloc</c>
          </seecref> documentation for more details).</p>
        <p><c><anno>FreeBlocks</anno></c> is a histogram of the free block
          sizes in the carrier.</p>
        <p>If the carrier could not be scanned in full without harming the
          responsiveness of the system, <c><anno>UnscannedSize</anno></c> is
          the number of bytes that had to be skipped.</p>
       </desc>
    </datatype>
  </datatypes>
  <funcs>

    <func>
      <name name="allocations" arity="0" since="OTP 21.0"/>
      <fsummary>Return a summary of all allocations in the system.</fsummary>
      <desc>
        <p>Shorthand for
          <seemfa marker="#allocations/1"><c>allocations(#{})</c>.</seemfa></p>
      </desc>
    </func>

    <func>
      <name name="allocations" arity="1" since="OTP 21.0"/>
      <fsummary>Return a summary of all allocations filtered by allocator type
        and scheduler id.</fsummary>
      <desc>
        <p>Returns a summary of all tagged allocations in the system,
          optionally filtered by allocator type and scheduler id.</p>
        <p>Only binaries and allocations made by NIFs and drivers are tagged by
          default, but this can be configured an a per-allocator basis with the
          <seecref marker="erts:erts_alloc#M_atags"><c>+M&lt;S&gt;atags</c>
          </seecref> emulator option.</p>
        <p>If the specified allocator types are not enabled, the call will fail
          with <c>{error, not_enabled}</c>.</p>
        <p>The following options can be used:</p>
        <taglist>
          <tag><c>allocator_types</c></tag>
          <item>
            <p>The allocator types that will be searched.</p>
            <p>Specifying a specific allocator type may lead to strange results
              when carrier migration between different allocator types has been
              enabled: you may see unexpected types (e.g. process heaps when
              searching binary_alloc), or fewer blocks than expected if the
              carriers the blocks are on have been migrated out to an allocator
              of a different type.</p>
            <p>Defaults to all <c>alloc_util</c> allocators.</p>
          </item>
          <tag><c>scheduler_ids</c></tag>
          <item>
            <p>The scheduler ids whose allocator instances will be searched. A
              scheduler id of 0 will refer to the global instance that is not
              tied to any particular scheduler. Defaults to all schedulers and
              the global instance.</p>
          </item>
          <tag><c>histogram_start</c></tag>
          <item>
            <p>The upper bound of the first interval in the allocated block
              size histograms. Defaults to 128.</p>
          </item>
          <tag><c>histogram_width</c></tag>
          <item>
            <p>The number of intervals in the allocated block size histograms.
              Defaults to 18.</p>
          </item>
        </taglist>
        <p><em>Example:</em></p>
        <code type="none"><![CDATA[
> instrument:allocations(#{ histogram_start => 128, histogram_width => 15 }).
{ok,{128,0,
     #{udp_inet =>
           #{driver_event_state => {0,0,0,0,0,0,0,0,0,1,0,0,0,0,0}},
       system =>
           #{heap => {0,0,0,0,20,4,2,2,2,3,0,1,0,0,1},
             db_term => {271,3,1,52,80,1,0,0,0,0,0,0,0,0,0},
             code => {0,0,0,5,3,6,11,22,19,20,10,2,1,0,0},
             binary => {18,0,0,0,7,0,0,1,0,0,0,0,0,0,0},
             message => {0,40,78,2,2,0,0,0,0,0,0,0,0,0,0},
             ... }
       spawn_forker =>
           #{driver_select_data_state =>
                 {1,0,0,0,0,0,0,0,0,0,0,0,0,0,0}},
       ram_file_drv => #{drv_binary => {0,0,0,0,0,0,1,0,0,0,0,0,0,0,0}},
       prim_file =>
           #{process_specific_data => {2,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
             nif_trap_export_entry => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0},
             monitor_extended => {0,1,0,0,0,0,0,0,0,0,0,0,0,0,0},
             drv_binary => {0,0,0,0,0,0,1,0,3,5,0,0,0,1,0},
             binary => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0}},
       prim_buffer =>
           #{nif_internal => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0},
             binary => {0,4,0,0,0,0,0,0,0,0,0,0,0,0,0}}}}}
     ]]></code>
      </desc>
    </func>

    <func>
      <name name="carriers" arity="0" since="OTP 21.0"/>
      <fsummary>Return a list of all carriers in the system.</fsummary>
      <desc>
        <p>Shorthand for
          <seemfa marker="#carriers/1"><c>carriers(#{})</c>.</seemfa></p>
      </desc>
    </func>

    <func>
      <name name="carriers" arity="1" since="OTP 21.0"/>
      <fsummary>Return a list of all carriers filtered by allocator type and
        scheduler id.</fsummary>
      <desc>
        <p>Returns a summary of all carriers in the system, optionally filtered
          by allocator type and scheduler id.</p>
        <p>If the specified allocator types are not enabled, the call will fail
          with <c>{error, not_enabled}</c>.</p>
        <p>The following options can be used:</p>
        <taglist>
          <tag><c>allocator_types</c></tag>
          <item>
            <p>The allocator types that will be searched. Defaults to all
              <c>alloc_util</c> allocators.</p>
          </item>
          <tag><c>scheduler_ids</c></tag>
          <item>
            <p>The scheduler ids whose allocator instances will be searched. A
              scheduler id of 0 will refer to the global instance that is not
              tied to any particular scheduler. Defaults to all schedulers and
              the global instance.</p>
          </item>
          <tag><c>histogram_start</c></tag>
          <item>
            <p>The upper bound of the first interval in the free block size
              histograms. Defaults to 512.</p>
          </item>
          <tag><c>histogram_width</c></tag>
          <item>
            <p>The number of intervals in the free block size histograms.
              Defaults to 14.</p>
          </item>
        </taglist>
        <p><em>Example:</em></p>
        <code type="none"><![CDATA[
> instrument:carriers(#{ histogram_start => 512, histogram_width => 8 }).
{ok,{512,
     [{driver_alloc,false,262144,0,
                    [{driver_alloc,1,32784}],
                    {0,0,0,0,0,0,0,1}},
      {binary_alloc,false,32768,0,
                    [{binary_alloc,15,4304}],
                    {3,0,0,0,1,0,0,0}},
      {...}|...]}}
     ]]></code>
      </desc>
    </func>

  </funcs>

  <section>
    <title>See Also</title>
    <p><seecref marker="erts:erts_alloc">erts_alloc(3)</seecref>,
      <seecom marker="erts:erl">erl(1)</seecom></p>
  </section>
</erlref>

