Use Java Application class data sharing (AppCDS).

- Boost startup performance using AppCDS
- Enable by default (auto) only for insiders & pre-release versions
- Use java.jdt.ls.appcds.enabled to control the setting

Signed-off-by: Roland Grunberg <rgrunber@redhat.com>

Author: rgrunber

README.md

@@ -257,6 +257,9 @@ The following settings are supported:
 * `java.completion.engine`: [Experimental] Select code completion engine. Defaults to `ecj`.
 * `java.references.includeDeclarations`: Include declarations when finding references. Defaults to `true`
 
+New in 1.44.0
+* `java.jdt.ls.appcds.enabled` : [Experimental] Enable Java AppCDS (Application Class Data Sharing) for improvements to extension activation. When set to `auto`, AppCDS will be enabled in Visual Studio Code - Insiders, and for pre-release versions.
+
 Semantic Highlighting
 ===============
 [Semantic Highlighting](https://github.com/redhat-developer/vscode-java/wiki/Semantic-Highlighting) fixes numerous syntax highlighting issues with the default Java Textmate grammar. However, you might experience a few minor issues, particularly a delay when it kicks in, as it needs to be computed by the Java Language server, when opening a new file or when typing. Semantic highlighting can be disabled for all languages using the `editor.semanticHighlighting.enabled` setting, or for Java only using [language-specific editor settings](https://code.visualstudio.com/docs/getstarted/settings#_languagespecific-editor-settings).

package.json

@@ -420,6 +420,18 @@
             "scope": "window",
             "order": 95
           },
+          "java.jdt.ls.appcds.enabled": {
+            "type": "string",
+            "enum": [
+              "auto",
+              "on",
+              "off"
+            ],
+            "default": "auto",
+            "markdownDescription": "[Experimental] Enable Java AppCDS (Application Class Data Sharing) for improvements to extension activation. When set to `auto`, AppCDS will be enabled in Visual Studio Code - Insiders, and for pre-release versions.",
+            "scope": "machine-overridable",
+            "order": 100
+          },
           "java.trace.server": {
             "type": "string",
             "enum": [

src/javaServerStarter.ts

@@ -36,6 +36,11 @@ export const HEAP_DUMP = '-XX:+HeapDumpOnOutOfMemoryError';
 const DEPENDENCY_COLLECTOR_IMPL= '-Daether.dependencyCollector.impl=';
 const DEPENDENCY_COLLECTOR_IMPL_BF= 'bf';
 
+const UNLOCK_DIAGNOSTIC_VM_OPTIONS= '-XX:+UnlockDiagnosticVMOptions';
+const ALLOW_ARCHIVING_WITH_JAVA_AGENT= '-XX:+AllowArchivingWithJavaAgent';
+const AUTO_CREATE_SHARED_ARCHIVE= '-XX:+AutoCreateSharedArchive';
+const SHARED_ARCHIVE_FILE_LOC= '-XX:SharedArchiveFile=';
+
 export function prepareExecutable(requirements: RequirementsData, workspacePath, context: ExtensionContext, isSyntaxServer: boolean): Executable {
 	const executable: Executable = Object.create(null);
 	const options: ExecutableOptions = Object.create(null);
@@ -224,6 +229,23 @@ function prepareParams(requirements: RequirementsData, workspacePath, context: E
 		if (sharedIndexLocation) {
 			params.push(`-Djdt.core.sharedIndexLocation=${sharedIndexLocation}`);
 		}
+
+		const hasJDWP = params.find((param: string) => param.includes('jdwp')) !== undefined;
+		const isInsider: boolean = version.includes("insider");
+		const extVersion = getVersion(context.extensionPath);
+		const isPreReleaseVersion = /^\d+\.\d+\.\d{10}/.test(extVersion);
+		const globalStoragePath = path.resolve(context.globalStorageUri?.fsPath, extVersion); // .../Code/User/globalStorage/redhat.java/1.42.0/
+		const appCDSMode = workspace.getConfiguration().get('java.jdt.ls.appcds.enabled');
+		const useAppCDS = (appCDSMode === 'on') || (appCDSMode === 'auto' && (isInsider || isPreReleaseVersion));
+
+		ensureExists(globalStoragePath);
+		const sharedArchiveLocation = path.join(globalStoragePath, "jdtls.jsa");
+		if (useAppCDS && vmargs.indexOf(SHARED_ARCHIVE_FILE_LOC) < 0 && !hasJDWP) {
+			params.push(UNLOCK_DIAGNOSTIC_VM_OPTIONS);
+			params.push(ALLOW_ARCHIVING_WITH_JAVA_AGENT); // required due to use of '-javaagent'
+			params.push(AUTO_CREATE_SHARED_ARCHIVE);
+			params.push(`${SHARED_ARCHIVE_FILE_LOC}${sharedArchiveLocation}`);
+		}
 	}
 
 	// "OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify

src/settings.ts

@@ -139,7 +139,8 @@ function hasJavaConfigChanged(oldConfig: WorkspaceConfiguration, newConfig: Work
 		|| hasConfigKeyChanged('transport', oldConfig, newConfig)
 		|| hasConfigKeyChanged('diagnostic.filter', oldConfig, newConfig)
 		|| hasConfigKeyChanged('jdt.ls.javac.enabled', oldConfig, newConfig)
-		|| hasConfigKeyChanged('completion.engine', oldConfig, newConfig);
+		|| hasConfigKeyChanged('completion.engine', oldConfig, newConfig)
+		|| hasConfigKeyChanged('jdt.ls.appcds.enabled', oldConfig, newConfig);
 }
 
 function hasConfigKeyChanged(key, oldConfig, newConfig) {