CMAKE-INSTRUMENTATION(7)

NAME
cmake-instrumentation - CMake Instrumentation

Added in version 4.0.

INTRODUCTION

Note: This feature is only available when experimental support for instrumentation has been enabled by the CMAKE_EXPERIMENTAL_INSTRUMENTATION gate.

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 Makefile Generators <#makefile-generators> or the Ninja Generators <#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 RULE_LAUNCH_COMPILE <#prop_gbl:RULE_LAUNCH_COMPILE>, RULE_LAUNCH_LINK <#prop_gbl:RULE_LAUNCH_LINK> and RULE_LAUNCH_CUSTOM <#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 CTestUseLaunchers <#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 <build>.

  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 cmake_instrumentation() <#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 CMAKE_CONFIG_DIR <#envvar:CMAKE_CONFIG_DIR> under <config_dir>/instrumentation/<version>/query/.

  Enabling Instrumentation for CDash Submissions

You can enable instrumentation when using CTest in Dashboard Client <#dashboard-client> mode by setting the CTEST_USE_INSTRUMENTATION <#envvar:CTEST_USE_INSTRUMENTATION> environment variable to the current UUID for the CMAKE_EXPERIMENTAL_INSTRUMENTATION feature. Doing so automatically enables the dynamicSystemInformation query.

The following table shows how each type of instrumented command gets mapped to a corresponding type of CTest XML file.
Snippet Role | CTest XML File
configure | Configure.xml
generate | Configure.xml
compile | Build.xml
link | Build.xml
custom | Build.xml
build | unused!
cmakeBuild | Build.xml
cmakeInstall | Build.xml
install | Build.xml
ctest | Build.xml
test | Test.xml

By default the command line reported to CDash is truncated at the first space. You can instead choose to report the full command line (including arguments) by setting CTEST_USE_VERBOSE_INSTRUMENTATION <#envvar:CTEST_USE_VERBOSE_INSTRUMENTATION> to 1.

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 cmake_instrumentation() <#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.

cdash/
    Holds temporary files used internally to generate XML content to be submitted to CDash.

  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:

        {
          "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-<timestamp>.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-<timestamp>.json and /usr/bin/cmake -P callback.cmake arg index-<timestamp>.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.

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>-<hash>-<timestamp>.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.

workingDir
    The working directory in which the command was executed.

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 compile or link.

targetType
    The TYPE <#prop_tgt:TYPE> of the target. Only included when role is link.

targetLabels
    The LABELS <#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:

        {
          "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 <build>.

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:

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

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