CMake/Help/manual/cmake-instrumentation.7.rst

.. cmake-manual-description: CMake Instrumentation

cmake-instrumentation(7)
************************

.. versionadded:: 4.0

.. only:: html

  .. contents::

Introduction
============

The CMake Instrumentation API allows for the collection of timing data, target
information and system diagnostic information during the configure, generate,
build, test and install steps for a CMake project.

This feature is only available for projects using the :ref:`Makefile Generators`
or the :ref:`Ninja Generators`.

All interactions with the CMake instrumentation API must specify both an API
version and a Data version. At this time, there is only one version for each of
these: the `API v1`_ and `Data v1`_.

Data Collection
---------------

Whenever a command is executed with
instrumentation enabled, a `v1 Snippet File`_ is created in the project build
tree with data specific to that command. These files remain until after
`Indexing`_ occurs.

CMake sets the :prop_gbl:`RULE_LAUNCH_COMPILE`, :prop_gbl:`RULE_LAUNCH_LINK` and
:prop_gbl:`RULE_LAUNCH_CUSTOM` global properties to use the
``ctest --instrument`` launcher in order to capture details of each compile, link
and custom command respectively. If the project has been configured with :module:`CTestUseLaunchers`,
``ctest --instrument`` will also include the behavior usually performed by
``ctest --launch``.

Indexing
--------

Indexing is the process of collating generated instrumentation data. Indexing
occurs at specific intervals called hooks, such as after every build. These
hooks are configured as part of the `v1 Query Files`_. Whenever a hook is
triggered, an index file is generated containing a list of snippet files newer
than the previous indexing.

Indexing and can also be performed by manually invoking
``ctest --collect-instrumentation``.

Callbacks
---------

As part of the `v1 Query Files`_, users can provide a list of callbacks
intended to handle data collected by this feature.

Whenever `Indexing`_ occurs, each provided callback is executed, passing the
path to the generated index file as an argument.

These callbacks, defined either at the user-level or project-level should read
the instrumentation data and perform any desired handling of it. The index file
and its listed snippets are automatically deleted by CMake once all callbacks
have completed. Note that a callback should never move or delete these data
files manually as they may be needed by other callbacks.

Enabling Instrumentation
========================

Instrumentation can be enabled either for an individual CMake project, or
for all CMake projects configured and built by a user. For both cases,
see the `v1 Query Files`_ for details on configuring this feature.

Enabling Instrumentation at the Project-Level
---------------------------------------------

Project code can contain instrumentation queries with the
:command:`cmake_instrumentation` command.

In addition, query files can be placed manually under
``<build>/.cmake/instrumentation/<version>/query/`` at the top of a build tree.
This version of CMake supports only one version schema, `API v1`_.

Enabling Instrumentation at the User-Level
------------------------------------------

Instrumentation can be configured at the user-level by placing query files in
the :envvar:`CMAKE_CONFIG_DIR` under
``<config_dir>/instrumentation/<version>/query/``.

.. _`cmake-instrumentation API v1`:

API v1
======

The API version specifies both the subdirectory layout of the instrumentation data,
and the format of the query files.

The Instrumentation API v1 is housed  in the ``instrumentation/v1/`` directory
under either ``<build>/.cmake/`` for output data and project-level queries, or
``<config_dir>/`` for user-level queries. The ``v1`` component of this
directory is what signifies the API version. It has the following
subdirectories:

``query/``
  Holds query files written by users or clients. Any file with the ``.json``
  file extension will be recognized as a query file. These files are owned by
  whichever client or user creates them.

``query/generated/``
  Holds query files generated by a CMake project with the
  :command:`cmake_instrumentation` command. These files are owned by CMake and
  are deleted and regenerated automatically during the CMake configure step.

``data/``
  Holds instrumentation data collected on the project. CMake owns all data
  files, they should never be removed by other processes. Data collected here
  remains until after `Indexing`_ occurs and all `Callbacks`_ are executed.

.. _`cmake-instrumentation v1 Query Files`:

v1 Query Files
--------------

Any file with the ``.json`` extension under the ``instrumentation/v1/query/``
directory is recognized as a query for instrumentation data.

These files must contain a JSON object with the following keys. The ``version``
key is required, but all other fields are optional.

``version``
  The Data version of snippet file to generate, an integer. Currently the only
  supported version is ``1``.

``callbacks``
  A list of command-line strings for `Callbacks`_ to handle collected
  instrumentation data. Whenever these callbacks are executed, the full path to
  a `v1 Index File`_ is appended to the arguments included in the string.

``hooks``
  A list of strings specifying when `Indexing`_ should occur automatically.
  These are the intervals when instrumentation data should be collated and user
  `Callbacks`_ should be invoked to handle the data. Elements in this list
  should be one of the following:

  * ``postGenerate``
  * ``preBuild`` (called when ``ninja``  or ``make`` is invoked; unavailable on Windows)
  * ``postBuild`` (called when ``ninja`` or ``make`` completes; unavailable on Windows)
  * ``preCMakeBuild`` (called when ``cmake --build`` is invoked)
  * ``postCMakeBuild`` (called when ``cmake --build`` completes)
  * ``postInstall``
  * ``postTest``

``queries``
  A list of strings specifying additional optional data to collect during
  instrumentation. Elements in this list should be one of the following:

    ``staticSystemInformation``
      Enables collection of the static information about the host machine CMake
      is being run from. This data is collected during `Indexing`_ and is
      included in the generated `v1 Index File`_.

    ``dynamicSystemInformation``
      Enables collection of the dynamic information about the host machine
      CMake is being run from. Data is collected for every `v1 Snippet File`_
      generated by CMake, and includes information from immediately before and
      after the command is executed.

The ``callbacks`` listed will be invoked during the specified hooks
*at a minimum*. When there are multiple query files, the ``callbacks``,
``hooks`` and ``queries`` between them will be merged. Therefore, if any query
file includes any ``hooks``, every ``callback`` across all query files will be
executed at every ``hook`` across all query files. Additionally, if any query
file includes any optional ``queries``, the optional query data will be present
in all data files.

Example:

.. code-block:: json

  {
    "version": 1,
    "callbacks": [
      "/usr/bin/python callback.py",
      "/usr/bin/cmake -P callback.cmake arg",
    ],
    "hooks": [
      "postCMakeBuild",
      "postInstall"
    ],
    "queries": [
      "staticSystemInformation",
      "dynamicSystemInformation"
    ]
  }

In this example, after every ``cmake --build`` or ``cmake --install``
invocation, an index file ``index-<hash>.json`` will be generated in
``<build>/.cmake/instrumentation/v1/data`` containing a list of data snippet
files created since the previous indexing. The commands
``/usr/bin/python callback.py index-<hash>.json`` and
``/usr/bin/cmake -P callback.cmake arg index-<hash>.json`` will be executed in
that order. The index file will contain the ``staticSystemInformation`` data and
each snippet file listed in the index will contain the
``dynamicSystemInformation`` data. Once both callbacks have completed, the index
file and all snippet files listed by it will be deleted from the project build
tree.

.. _`cmake-instrumentation Data v1`:

Data v1
=======

Data version specifies the contents of the output files generated by the CMake
instrumentation API as part of the `Data Collection`_ and `Indexing`_. There are
two types of data files generated: the `v1 Snippet File`_ and `v1 Index File`_.
When using the `API v1`_, these files live in
``<build>/.cmake/instrumentation/v1/data/`` under the project build tree.

v1 Snippet File
---------------

Snippet files are generated for every compile, link and custom command invoked
as part of the CMake build or install step and contain instrumentation data about
the command executed. Additionally, snippet files are created for the following:

* The CMake configure step
* The CMake generate step
* Entire build step (executed with ``cmake --build``)
* Entire install step (executed with ``cmake --install``)
* Each ``ctest`` invocation
* Each individual test executed by ``ctest``.

These files remain in the build tree until after `Indexing`_ occurs and any
user-specified `Callbacks`_ are executed.

Snippet files have a filename with the syntax ``<role>-<timestamp>-<hash>.json``
and contain the following data:

  ``version``
    The Data version of the snippet file, an integer. Currently the version is
    always ``1``.

  ``command``
    The full command executed. Excluded when ``role`` is ``build``.

  ``result``
    The exit-value of the command, an integer.

  ``role``
    The type of command executed, which will be one of the following values:

    * ``configure``: the CMake configure step
    * ``generate``: the CMake generate step
    * ``compile``: an individual compile step invoked during the build
    * ``link``: an individual link step invoked during the build
    * ``custom``: an individual custom command invoked during the build
    * ``build``: a complete ``make`` or ``ninja`` invocation. Only generated if ``preBuild`` or ``postBuild`` hooks are enabled.
    * ``cmakeBuild``: a complete ``cmake --build`` invocation
    * ``cmakeInstall``: a complete ``cmake --install`` invocation
    * ``install``: an individual ``cmake -P cmake_install.cmake`` invocation
    * ``ctest``: a complete ``ctest`` invocation
    * ``test``: a single test executed by CTest

  ``target``
    The CMake target associated with the command. Only included when ``role`` is
    one of ``compile``, ``link``, ``custom``.

  ``targetType``
    The :prop_tgt:`TYPE` of the target. Only included when ``role`` is
    ``link``.

  ``targetLabels``
    The :prop_tgt:`LABELS` of the target. Only included when ``role`` is
    ``link``.

  ``timeStart``
    Time at which the command started, expressed as the number of milliseconds
    since the system epoch.

  ``duration``
    The duration that the command ran for, expressed in milliseconds.

  ``outputs``
    The command's output file(s), an array. Only included when ``role`` is one
    of: ``compile``, ``link``, ``custom``.

  ``outputSizes``
    The size(s) in bytes of the ``outputs``, an array. For files which do not
    exist, the size is 0. Included under the same conditions as the ``outputs``
    field.

  ``source``
    The source file being compiled. Only included when ``role`` is ``compile``.

  ``language``
    The language of the source file being compiled. Only included when ``role`` is
    ``compile``.

  ``testName``
    The name of the test being executed. Only included when ``role`` is ``test``.

  ``config``
    The type of build, such as ``Release`` or ``Debug``. Only included when
    ``role`` is ``compile``, ``link`` or ``test``.

  ``dynamicSystemInformation``
    Specifies the dynamic information collected about the host machine
    CMake is being run from. Data is collected for every snippet file
    generated by CMake, with data immediately before and after the command is
    executed. Only included when enabled by the `v1 Query Files`_.

    ``beforeHostMemoryUsed``
      The Host Memory Used in KiB at ``timeStart``.

    ``afterHostMemoryUsed``
      The Host Memory Used in KiB at ``timeStop``.

    ``beforeCPULoadAverage``
      The Average CPU Load at ``timeStart``.

    ``afterCPULoadAverage``
      The Average CPU Load at ``timeStop``.

Example:

.. code-block:: json

  {
    "version": 1,
    "command" : "/usr/bin/c++ -MD -MT CMakeFiles/main.dir/main.cxx.o -MF CMakeFiles/main.dir/main.cxx.o.d -o CMakeFiles/main.dir/main.cxx.o -c <src>/main.cxx",
    "role" : "compile",
    "return" : 1,
    "target": "main",
    "language" : "C++",
    "outputs" : [ "CMakeFiles/main.dir/main.cxx.o" ],
    "outputSizes" : [ 0 ],
    "source" : "<src>/main.cxx",
    "config" : "Debug",
    "dynamicSystemInformation" :
    {
      "afterCPULoadAverage" : 2.3500000000000001,
      "afterHostMemoryUsed" : 6635680.0
      "beforeCPULoadAverage" : 2.3500000000000001,
      "beforeHostMemoryUsed" : 6635832.0
    },
    "timeStart" : 1737053448177,
    "duration" : 31
  }

v1 Index File
-------------

Index files contain a list of `v1 Snippet File`_. It serves as an entry point
for navigating the instrumentation data. They are generated whenever `Indexing`_
occurs and deleted after any user-specified `Callbacks`_ are executed.

``version``
  The Data version of the index file, an integer. Currently the version is
  always ``1``.

``buildDir``
  The build directory of the CMake project.

``dataDir``
  The full path to the ``<build>/.cmake/instrumentation/v1/data/`` directory.

``hook``
  The name of the hook responsible for generating the index file. In addition
  to the hooks that can be specified by one of the `v1 Query Files`_, this value may
  be set to ``manual`` if indexing is performed by invoking
  ``ctest --collect-instrumentation``.

``snippets``
  Contains a list of `v1 Snippet File`_. This includes all snippet files
  generated since the previous index file was created. The file paths are
  relative to ``dataDir``.

``staticSystemInformation``
  Specifies the static information collected about the host machine
  CMake is being run from. Only included when enabled by the `v1 Query Files`_.

  * ``OSName``
  * ``OSPlatform``
  * ``OSRelease``
  * ``OSVersion``
  * ``familyId``
  * ``hostname``
  * ``is64Bits``
  * ``modelId``
  * ``numberOfLogicalCPU``
  * ``numberOfPhysicalCPU``
  * ``processorAPICID``
  * ``processorCacheSize``
  * ``processorClockFrequency``
  * ``processorName``
  * ``totalPhysicalMemory``
  * ``totalVirtualMemory``
  * ``vendorID``
  * ``vendorString``

Example:

.. code-block:: json

  {
    "version": 1,
    "hook": "manual",
    "buildDir": "<build>",
    "dataDir": "<build>/.cmake/instrumentation/v1/data",
    "snippets": [
      "configure-<timestamp>-<hash>.json",
      "generate-<timestamp>-<hash>.json",
      "compile-<timestamp>-<hash>.json",
      "compile-<timestamp>-<hash>.json",
      "link-<timestamp>-<hash>.json",
      "install-<timestamp>-<hash>.json",
      "ctest-<timestamp>-<hash>.json",
      "test-<timestamp>-<hash>.json",
      "test-<timestamp>-<hash>.json",
    ]
  }