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| <div class="section" id="unity-build"> |
| <span id="prop_tgt:UNITY_BUILD"></span><h1>UNITY_BUILD<a class="headerlink" href="#unity-build" title="Permalink to this headline">¶</a></h1> |
| <div class="versionadded"> |
| <p><span class="versionmodified added">New in version 3.16.</span></p> |
| </div> |
| <p>When this property is set to true, the target source files will be combined |
| into batches for faster compilation. This is done by creating a (set of) |
| unity sources which <code class="docutils literal notranslate"><span class="pre">#include</span></code> the original sources, then compiling these |
| unity sources instead of the originals. This is known as a <em>Unity</em> or <em>Jumbo</em> |
| build.</p> |
| <p>CMake provides different algorithms for selecting which sources are grouped |
| together into a <em>bucket</em>. Algorithm selection is decided by the |
| <span class="target" id="index-0-prop_tgt:UNITY_BUILD_MODE"></span><a class="reference internal" href="UNITY_BUILD_MODE.html#prop_tgt:UNITY_BUILD_MODE" title="UNITY_BUILD_MODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_MODE</span></code></a> target property, which has the following acceptable |
| values:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">BATCH</span></code> |
| When in this mode CMake determines which files are grouped together. |
| The <span class="target" id="index-0-prop_tgt:UNITY_BUILD_BATCH_SIZE"></span><a class="reference internal" href="UNITY_BUILD_BATCH_SIZE.html#prop_tgt:UNITY_BUILD_BATCH_SIZE" title="UNITY_BUILD_BATCH_SIZE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_BATCH_SIZE</span></code></a> property controls the upper limit on |
| how many sources can be combined per unity source file.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">GROUP</span></code> |
| When in this mode each target explicitly specifies how to group |
| source files. Each source file that has the same |
| <span class="target" id="index-0-prop_sf:UNITY_GROUP"></span><a class="reference internal" href="../prop_sf/UNITY_GROUP.html#prop_sf:UNITY_GROUP" title="UNITY_GROUP"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">UNITY_GROUP</span></code></a> value will be grouped together. Any sources |
| that don't have this property will be compiled individually. The |
| <span class="target" id="index-1-prop_tgt:UNITY_BUILD_BATCH_SIZE"></span><a class="reference internal" href="UNITY_BUILD_BATCH_SIZE.html#prop_tgt:UNITY_BUILD_BATCH_SIZE" title="UNITY_BUILD_BATCH_SIZE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_BATCH_SIZE</span></code></a> property is ignored when using |
| this mode.</p></li> |
| </ul> |
| <p>If no explicit <span class="target" id="index-1-prop_tgt:UNITY_BUILD_MODE"></span><a class="reference internal" href="UNITY_BUILD_MODE.html#prop_tgt:UNITY_BUILD_MODE" title="UNITY_BUILD_MODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_MODE</span></code></a> has been specified, CMake will |
| default to <code class="docutils literal notranslate"><span class="pre">BATCH</span></code>.</p> |
| <p>Unity builds are not currently supported for all languages. CMake version |
| 3.23.1 supports combining <code class="docutils literal notranslate"><span class="pre">C</span></code> and <code class="docutils literal notranslate"><span class="pre">CXX</span></code> source files. For targets that |
| mix source files from more than one language, CMake will separate the languages |
| such that each generated unity source file only contains sources for a single |
| language.</p> |
| <p>This property is initialized by the value of the <span class="target" id="index-0-variable:CMAKE_UNITY_BUILD"></span><a class="reference internal" href="../variable/CMAKE_UNITY_BUILD.html#variable:CMAKE_UNITY_BUILD" title="CMAKE_UNITY_BUILD"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_UNITY_BUILD</span></code></a> |
| variable when a target is created.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>Projects should not directly set the <code class="docutils literal notranslate"><span class="pre">UNITY_BUILD</span></code> property or its |
| associated <span class="target" id="index-1-variable:CMAKE_UNITY_BUILD"></span><a class="reference internal" href="../variable/CMAKE_UNITY_BUILD.html#variable:CMAKE_UNITY_BUILD" title="CMAKE_UNITY_BUILD"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_UNITY_BUILD</span></code></a> variable to true. Depending |
| on the capabilities of the build machine and compiler used, it might or |
| might not be appropriate to enable unity builds. Therefore, this feature |
| should be under developer control, which would normally be through the |
| developer choosing whether or not to set the <span class="target" id="index-2-variable:CMAKE_UNITY_BUILD"></span><a class="reference internal" href="../variable/CMAKE_UNITY_BUILD.html#variable:CMAKE_UNITY_BUILD" title="CMAKE_UNITY_BUILD"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_UNITY_BUILD</span></code></a> |
| variable on the <span class="target" id="index-0-manual:cmake(1)"></span><a class="reference internal" href="../manual/cmake.1.html#manual:cmake(1)" title="cmake(1)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">cmake(1)</span></code></a> command line or some other equivalent |
| method. However, it IS recommended to set the <code class="docutils literal notranslate"><span class="pre">UNITY_BUILD</span></code> target |
| property to false if it is known that enabling unity builds for the |
| target can lead to problems.</p> |
| </div> |
| <div class="section" id="odr-one-definition-rule-errors"> |
| <h2>ODR (One definition rule) errors<a class="headerlink" href="#odr-one-definition-rule-errors" title="Permalink to this headline">¶</a></h2> |
| <p>When multiple source files are included into one source file, as is done |
| for unity builds, it can potentially lead to ODR errors. CMake provides |
| a number of measures to help address such problems:</p> |
| <ul class="simple"> |
| <li><p>Any source file that has a non-empty <span class="target" id="index-0-prop_sf:COMPILE_OPTIONS"></span><a class="reference internal" href="../prop_sf/COMPILE_OPTIONS.html#prop_sf:COMPILE_OPTIONS" title="COMPILE_OPTIONS"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">COMPILE_OPTIONS</span></code></a>, |
| <span class="target" id="index-0-prop_sf:COMPILE_DEFINITIONS"></span><a class="reference internal" href="../prop_sf/COMPILE_DEFINITIONS.html#prop_sf:COMPILE_DEFINITIONS" title="COMPILE_DEFINITIONS"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">COMPILE_DEFINITIONS</span></code></a>, <span class="target" id="index-0-prop_sf:COMPILE_FLAGS"></span><a class="reference internal" href="../prop_sf/COMPILE_FLAGS.html#prop_sf:COMPILE_FLAGS" title="COMPILE_FLAGS"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">COMPILE_FLAGS</span></code></a>, or |
| <span class="target" id="index-0-prop_sf:INCLUDE_DIRECTORIES"></span><a class="reference internal" href="../prop_sf/INCLUDE_DIRECTORIES.html#prop_sf:INCLUDE_DIRECTORIES" title="INCLUDE_DIRECTORIES"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">INCLUDE_DIRECTORIES</span></code></a> source property will not be combined |
| into a unity source.</p></li> |
| <li><p>Projects can prevent an individual source file from being combined into |
| a unity source by setting its <span class="target" id="index-0-prop_sf:SKIP_UNITY_BUILD_INCLUSION"></span><a class="reference internal" href="../prop_sf/SKIP_UNITY_BUILD_INCLUSION.html#prop_sf:SKIP_UNITY_BUILD_INCLUSION" title="SKIP_UNITY_BUILD_INCLUSION"><code class="xref cmake cmake-prop_sf docutils literal notranslate"><span class="pre">SKIP_UNITY_BUILD_INCLUSION</span></code></a> |
| source property to true. This can be a more effective way to prevent |
| problems with specific files than disabling unity builds for an entire |
| target.</p></li> |
| <li><p>Projects can set <span class="target" id="index-0-prop_tgt:UNITY_BUILD_UNIQUE_ID"></span><a class="reference internal" href="UNITY_BUILD_UNIQUE_ID.html#prop_tgt:UNITY_BUILD_UNIQUE_ID" title="UNITY_BUILD_UNIQUE_ID"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_UNIQUE_ID</span></code></a> to cause a valid |
| C-identifier to be generated which is unique per file in a unity |
| build. This can be used to avoid problems with anonymous namespaces |
| in unity builds.</p></li> |
| <li><p>The <span class="target" id="index-0-prop_tgt:UNITY_BUILD_CODE_BEFORE_INCLUDE"></span><a class="reference internal" href="UNITY_BUILD_CODE_BEFORE_INCLUDE.html#prop_tgt:UNITY_BUILD_CODE_BEFORE_INCLUDE" title="UNITY_BUILD_CODE_BEFORE_INCLUDE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_CODE_BEFORE_INCLUDE</span></code></a> and |
| <span class="target" id="index-0-prop_tgt:UNITY_BUILD_CODE_AFTER_INCLUDE"></span><a class="reference internal" href="UNITY_BUILD_CODE_AFTER_INCLUDE.html#prop_tgt:UNITY_BUILD_CODE_AFTER_INCLUDE" title="UNITY_BUILD_CODE_AFTER_INCLUDE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_CODE_AFTER_INCLUDE</span></code></a> target properties can be used |
| to inject code into the unity source files before and after every |
| <code class="docutils literal notranslate"><span class="pre">#include</span></code> statement.</p></li> |
| <li><p>The order of source files added to the target via commands like |
| <span class="target" id="index-0-command:add_library"></span><a class="reference internal" href="../command/add_library.html#command:add_library" title="add_library"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">add_library()</span></code></a>, <span class="target" id="index-0-command:add_executable"></span><a class="reference internal" href="../command/add_executable.html#command:add_executable" title="add_executable"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">add_executable()</span></code></a> or |
| <span class="target" id="index-0-command:target_sources"></span><a class="reference internal" href="../command/target_sources.html#command:target_sources" title="target_sources"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">target_sources()</span></code></a> will be preserved in the generated unity source |
| files. This can be used to manually enforce a specific grouping based on |
| the <span class="target" id="index-2-prop_tgt:UNITY_BUILD_BATCH_SIZE"></span><a class="reference internal" href="UNITY_BUILD_BATCH_SIZE.html#prop_tgt:UNITY_BUILD_BATCH_SIZE" title="UNITY_BUILD_BATCH_SIZE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">UNITY_BUILD_BATCH_SIZE</span></code></a> target property.</p></li> |
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| <li><a class="reference internal" href="#">UNITY_BUILD</a><ul> |
| <li><a class="reference internal" href="#odr-one-definition-rule-errors">ODR (One definition rule) errors</a></li> |
| </ul> |
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