Do not automatically detect JVMs on CI systems

Automatic detection on CI systems can cause a lot of trouble (e.g.
memory consumption, time to read the jvms, old jvms lingering around)
and is generally not useful as a CI has usually a dedicated and fixed
setup to run with.

This adds a check for the common 'CI' environment variable that is
usually defined by all usual CI/CD pipelines to indicate a job is
running on a CI server to skip the detection regardless of preferences
configuration. If one absolutely want the feature even for CI, the
system-property 'DetectVMInstallationsJob.disabled' can be set to false
to restore previous behavior.

Author: laeubi

org.eclipse.jdt.launching/launching/org/eclipse/jdt/internal/launching/DetectVMInstallationsJob.java

@@ -46,6 +46,11 @@
  */
 public class DetectVMInstallationsJob extends Job {
 
+	/**
+	 * CI is a common variable defined in CI/CDI servers like Jenkins, Gitlab, Github, ... to indicate it is a CI environment
+	 */
+	private static final String ENV_CI = "CI"; //$NON-NLS-1$
+	private static final String PROPERTY_DETECT_VM_INSTALLATIONS_JOB_DISABLED = "DetectVMInstallationsJob.disabled"; //$NON-NLS-1$
 	private static final Object FAMILY = DetectVMInstallationsJob.class;
 
 	public DetectVMInstallationsJob() {
@@ -222,11 +227,20 @@ public boolean belongsTo(Object family) {
 	}
 
 	public static void initialize() {
-		boolean forcedDisableVMDetection = Boolean.getBoolean("DetectVMInstallationsJob.disabled"); //$NON-NLS-1$
+		boolean forcedDisableVMDetection = Boolean.getBoolean(PROPERTY_DETECT_VM_INSTALLATIONS_JOB_DISABLED);
+		if (forcedDisableVMDetection) {
+			// early exit no need to read preferences!
+			return;
+		}
+		if (System.getProperty(PROPERTY_DETECT_VM_INSTALLATIONS_JOB_DISABLED) == null && Boolean.parseBoolean(System.getenv(ENV_CI))) {
+			// exit because no explicit value for the property was given and we are running in a CI environment
+			return;
+		}
+		// finally look what is defined in the preferences
 		IEclipsePreferences instanceNode = InstanceScope.INSTANCE.getNode(LaunchingPlugin.getDefault().getBundle().getSymbolicName());
 		IEclipsePreferences defaultNode = DefaultScope.INSTANCE.getNode(LaunchingPlugin.getDefault().getBundle().getSymbolicName());
 		boolean defaultValue = defaultNode.getBoolean(LaunchingPlugin.PREF_DETECT_VMS_AT_STARTUP, true);
-		if (!forcedDisableVMDetection && instanceNode.getBoolean(LaunchingPlugin.PREF_DETECT_VMS_AT_STARTUP, defaultValue)) {
+		if (instanceNode.getBoolean(LaunchingPlugin.PREF_DETECT_VMS_AT_STARTUP, defaultValue)) {
 			new DetectVMInstallationsJob().schedule();
 		}
 	}