Added spring-cloud-task support

fixes gh-1903

spring-cloud-sleuth-api/src/main/java/org/springframework/cloud/sleuth/SpanAndScope.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2013-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth;
+
+/**
+ * Container object for {@link Span} and its corresponding {@link Tracer.SpanInScope}.
+ *
+ * @author Marcin Grzejszczak
+ * @since 3.1.0
+ */
+public class SpanAndScope {
+
+	private final Span span;
+
+	private final Tracer.SpanInScope scope;
+
+	public SpanAndScope(Span span, Tracer.SpanInScope scope) {
+		this.span = span;
+		this.scope = scope;
+	}
+
+	public Span getSpan() {
+		return this.span;
+	}
+
+	public Tracer.SpanInScope getScope() {
+		return this.scope;
+	}
+
+}

spring-cloud-sleuth-api/src/main/java/org/springframework/cloud/sleuth/ThreadLocalSpan.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2013-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth;
+
+import java.util.Deque;
+import java.util.NoSuchElementException;
+import java.util.concurrent.LinkedBlockingDeque;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * Represents a {@link Span} stored in thread local.
+ *
+ * @author Marcin Grzejszczak
+ * @since 3.1.0
+ */
+public class ThreadLocalSpan {
+
+	private static final Log log = LogFactory.getLog(ThreadLocalSpan.class);
+
+	private final ThreadLocal<SpanAndScope> threadLocalSpan = new ThreadLocal<>();
+
+	private final Deque<SpanAndScope> spans = new LinkedBlockingDeque<>();
+
+	private final Tracer tracer;
+
+	public ThreadLocalSpan(Tracer tracer) {
+		this.tracer = tracer;
+	}
+
+	/**
+	 * Sets given span and scope.
+	 * @param span - span to be put in scope
+	 */
+	public void set(Span span) {
+		Tracer.SpanInScope spanInScope = this.tracer.withSpan(span);
+		SpanAndScope newSpanAndScope = new SpanAndScope(span, spanInScope);
+		SpanAndScope scope = this.threadLocalSpan.get();
+		if (scope != null) {
+			this.spans.addFirst(scope);
+		}
+		this.threadLocalSpan.set(newSpanAndScope);
+	}
+
+	/**
+	 * @return currently stored span and scope
+	 */
+	public SpanAndScope get() {
+		return this.threadLocalSpan.get();
+	}
+
+	/**
+	 * Removes the current span from thread local and brings back the previous span to the
+	 * current thread local.
+	 */
+	public void remove() {
+		this.threadLocalSpan.remove();
+		if (this.spans.isEmpty()) {
+			return;
+		}
+		try {
+			SpanAndScope span = this.spans.removeFirst();
+			if (log.isDebugEnabled()) {
+				log.debug("Took span [" + span + "] from thread local");
+			}
+			this.threadLocalSpan.set(span);
+		}
+		catch (NoSuchElementException ex) {
+			if (log.isTraceEnabled()) {
+				log.trace("Failed to remove a span from the queue", ex);
+			}
+		}
+	}
+
+}