From 21f16fa3a21d7000bfc401f808a42909f64a7c27 Mon Sep 17 00:00:00 2001
From: Hannes Wellmann <wellmann.hannes1@gmx.net>
Date: Sun, 23 Oct 2022 13:03:09 +0200
Subject: [PATCH] Add ServiceCaller.use() methods to simply obtain rarely used
 services

---
 .../eclipse/core/runtime/ServiceCaller.java   | 123 ++++++++++++++++++
 1 file changed, 123 insertions(+)

diff --git a/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/ServiceCaller.java b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/ServiceCaller.java
index 1fbb3107776..c36be8408b4 100644
--- a/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/ServiceCaller.java
+++ b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/ServiceCaller.java
@@ -13,11 +13,14 @@
  *******************************************************************************/
 package org.eclipse.core.runtime;
 
+import java.lang.StackWalker.Option;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.function.Consumer;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
 import org.osgi.framework.*;
 import org.osgi.util.tracker.ServiceTracker;
 
@@ -96,6 +99,9 @@
  * @since 3.13
  */
 public class ServiceCaller<S> {
+
+	private static final StackWalker STACK_WALKER = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE);
+
 	/**
 	 * Calls an OSGi service by dynamically looking it up and passing it to the
 	 * given consumer.
@@ -160,6 +166,123 @@ public static <S> boolean callOnce(Class<?> caller, Class<S> serviceType, String
 		}).orElse(Boolean.FALSE);
 	}
 
+	/**
+	 * Not thread save.
+	 * <p>
+	 * Service registrations are obtained upon creation, service instances are get
+	 * on the first request (i.e. the first instance when {@link #first()} or
+	 * {@link #all()} is called. Services that are unregistered in the meantime are
+	 * discarded and newly registered services are ignored.
+	 * </p>
+	 * 
+	 * @param <S> the service type for this caller
+	 * @since 3.17
+	 */
+	public interface ServiceUsageScope<S> extends AutoCloseable { // TODO:? , Supplier<S>
+
+		/**
+		 * Gets the first available service implementation.
+		 */
+		Optional<S> first();
+
+		Stream<S> all();
+
+		@Override
+		void close(); // do not throw (checked) exception
+	}
+
+	/**
+	 * @since 3.17
+	 */
+	public static <T> ServiceUsageScope<T> use(Class<T> service) {
+		Class<?> callerClass = STACK_WALKER.getCallerClass();
+		try {
+			return useService(callerClass, service, null);
+		} catch (InvalidSyntaxException e) {
+			throw new AssertionError("Impossible exception was thrown"); //$NON-NLS-1$
+		}
+	}
+
+	/**
+	 * @since 3.17
+	 */
+	public static <S> ServiceUsageScope<S> use(Class<S> service, String filter) throws InvalidSyntaxException {
+		Class<?> callerClass = STACK_WALKER.getCallerClass();
+		return useService(callerClass, service, filter);
+	}
+
+	private static <S> ServiceUsageScope<S> useService(Class<?> caller, Class<S> serviceType, String filter)
+			throws InvalidSyntaxException {
+		Bundle bundle = FrameworkUtil.getBundle(caller);
+		if (bundle == null) {
+			throw new IllegalStateException(); // TODO: handle differently?
+		}
+		BundleContext ctx = bundle.getBundleContext();
+		if (ctx == null) {
+			throw new IllegalStateException(); // TODO: handle differently?
+		}
+		return use(serviceType, filter, ctx);
+	}
+
+	/**
+	 * @since 3.17
+	 */
+	public static <S> ServiceUsageScope<S> use(Class<S> service, BundleContext context) {
+		try {
+			return use(service, null, context);
+		} catch (InvalidSyntaxException e) {
+			throw new AssertionError("Impossible exception was thrown"); //$NON-NLS-1$
+		}
+	}
+
+	/**
+	 * @since 3.17
+	 */
+	public static <S> ServiceUsageScope<S> use(Class<S> service, String filter, BundleContext context)
+			throws InvalidSyntaxException {
+		ServiceReference<?>[] references = context.getServiceReferences(service.getName(), filter);
+		Object[] instances = new Object[references.length];
+		return new ServiceUsageScope<>() {
+			private Optional<S> first;
+
+			@Override
+			public Optional<S> first() {
+				if (first == null) {
+					first = references.length == 0 ? Optional.empty() : all().findFirst();
+				}
+				return first;
+				// TODO: if the ServiceUsageScope itself would be the 'Optional' the name of the
+				// missing service could be mentioned in the exception.
+//				throw new NoSuchElementException("Service '" + serviceName + "' is not available"); //$NON-NLS-1$//$NON-NLS-2$
+			}
+
+			@Override
+
+			public Stream<S> all() {
+				if (references.length == 0) {
+					return Stream.empty();
+				}
+				return IntStream.range(0, references.length).mapToObj(i -> {
+					if (instances[i] == null) {
+						instances[i] = context.getService(references[i]);
+					}
+					@SuppressWarnings("unchecked")
+					S instance = (S) instances[i];
+					return instance;
+				}).filter(Objects::nonNull);
+			}
+
+			@Override
+			public void close() {
+				for (int i = 0; i < references.length; i++) {
+					if (instances[i] != null) {
+						context.ungetService(references[i]);
+					}
+				}
+			}
+		};
+	}
+
 	private static int getRank(ServiceReference<?> ref) {
 		Object rank = ref.getProperty(Constants.SERVICE_RANKING);
 		if (rank instanceof Integer) {