Serialize nested BWC build tasks (#70428)

buildSrc/src/main/java/org/elasticsearch/gradle/internal/BwcSetupExtension.java

@@ -37,17 +37,20 @@ public class BwcSetupExtension {
 
     private static final String MINIMUM_COMPILER_VERSION_PATH = "buildSrc/src/main/resources/minimumCompilerVersion";
     private final Project project;
-
     private final Provider<BwcVersions.UnreleasedVersionInfo> unreleasedVersionInfo;
+    private final Provider<InternalDistributionBwcSetupPlugin.BwcTaskThrottle> bwcTaskThrottleProvider;
+
     private Provider<File> checkoutDir;
 
     public BwcSetupExtension(
         Project project,
         Provider<BwcVersions.UnreleasedVersionInfo> unreleasedVersionInfo,
+        Provider<InternalDistributionBwcSetupPlugin.BwcTaskThrottle> bwcTaskThrottleProvider,
         Provider<File> checkoutDir
     ) {
         this.project = project;
         this.unreleasedVersionInfo = unreleasedVersionInfo;
+        this.bwcTaskThrottleProvider = bwcTaskThrottleProvider;
         this.checkoutDir = checkoutDir;
     }
 
@@ -58,6 +61,7 @@ public class BwcSetupExtension {
     private TaskProvider<LoggedExec> createRunBwcGradleTask(Project project, String name, Action<LoggedExec> configAction) {
         return project.getTasks().register(name, LoggedExec.class, loggedExec -> {
             loggedExec.dependsOn("checkoutBwcBranch");
+            loggedExec.usesService(bwcTaskThrottleProvider);
             loggedExec.setSpoolOutput(true);
             loggedExec.setWorkingDir(checkoutDir.get());
             loggedExec.doFirst(t -> {

buildSrc/src/main/java/org/elasticsearch/gradle/internal/InternalDistributionBwcSetupPlugin.java

@@ -17,6 +17,8 @@ import org.gradle.api.Project;
 import org.gradle.api.Task;
 import org.gradle.api.provider.Provider;
 import org.gradle.api.provider.ProviderFactory;
+import org.gradle.api.services.BuildService;
+import org.gradle.api.services.BuildServiceParameters;
 import org.gradle.api.tasks.TaskProvider;
 import org.gradle.language.base.plugins.LifecycleBasePlugin;
 
@@ -39,6 +41,7 @@ import static java.util.Arrays.stream;
  */
 public class InternalDistributionBwcSetupPlugin implements InternalPlugin {
 
+    private static final String BWC_TASK_THROTTLE_SERVICE = "bwcTaskThrottle";
     private ProviderFactory providerFactory;
 
     @Inject
@@ -49,19 +52,26 @@ public class InternalDistributionBwcSetupPlugin implements InternalPlugin {
     @Override
     public void apply(Project project) {
         project.getRootProject().getPluginManager().apply(GlobalBuildInfoPlugin.class);
+        Provider<BwcTaskThrottle> bwcTaskThrottleProvider = project.getGradle()
+            .getSharedServices()
+            .registerIfAbsent(BWC_TASK_THROTTLE_SERVICE, BwcTaskThrottle.class, spec -> spec.getMaxParallelUsages().set(1));
         BuildParams.getBwcVersions()
             .forPreviousUnreleased(
                 (BwcVersions.UnreleasedVersionInfo unreleasedVersion) -> {
-                    configureBwcProject(project.project(unreleasedVersion.gradleProjectPath), unreleasedVersion);
+                    configureBwcProject(project.project(unreleasedVersion.gradleProjectPath), unreleasedVersion, bwcTaskThrottleProvider);
                 }
             );
     }
 
-    private void configureBwcProject(Project project, BwcVersions.UnreleasedVersionInfo versionInfo) {
+    private void configureBwcProject(
+        Project project,
+        BwcVersions.UnreleasedVersionInfo versionInfo,
+        Provider<BwcTaskThrottle> bwcTaskThrottleProvider
+    ) {
         Provider<BwcVersions.UnreleasedVersionInfo> versionInfoProvider = providerFactory.provider(() -> versionInfo);
         Provider<File> checkoutDir = versionInfoProvider.map(info -> new File(project.getBuildDir(), "bwc/checkout-" + info.branch));
         BwcSetupExtension bwcSetupExtension = project.getExtensions()
-            .create("bwcSetup", BwcSetupExtension.class, project, versionInfoProvider, checkoutDir);
+            .create("bwcSetup", BwcSetupExtension.class, project, versionInfoProvider, bwcTaskThrottleProvider, checkoutDir);
         BwcGitExtension gitExtension = project.getPlugins().apply(InternalBwcGitPlugin.class).getGitExtension();
         Provider<Version> bwcVersion = versionInfoProvider.map(info -> info.version);
         gitExtension.setBwcVersion(versionInfoProvider.map(info -> info.version));
@@ -252,7 +262,7 @@ public class InternalDistributionBwcSetupPlugin implements InternalPlugin {
         /**
          * can be removed once we don't build 7.10 anymore
          * from source for bwc tests.
-         * */
+         */
         @Deprecated
         final boolean expandedDistDirSupport;
         final DistributionProjectArtifact expectedBuildArtifact;
@@ -286,7 +296,7 @@ public class InternalDistributionBwcSetupPlugin implements InternalPlugin {
         /**
          * Newer elasticsearch branches allow building extracted bwc elasticsearch versions
          * from source without the overhead of creating an archive by using assembleExtracted instead of assemble.
-         * */
+         */
         public String getAssembleTaskName() {
             return extractedAssembleSupported ? "extractedAssemble" : "assemble";
         }
@@ -301,4 +311,6 @@ public class InternalDistributionBwcSetupPlugin implements InternalPlugin {
             this.expandedDistDir = expandedDistDir;
         }
     }
+
+    public abstract class BwcTaskThrottle implements BuildService<BuildServiceParameters.None> {}
 }