1 files changed, 180 insertions, 0 deletions
diff --git a/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java b/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java
new file mode 100644
index 00000000..aa2f055a
--- /dev/null
+++ b/api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java
@@ -0,0 +1,180 @@
+/*
+ * Copyright 2017, OpenCensus 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
+ *
+ *     http://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 io.opencensus.trace;
+
+import io.grpc.Context;
+import io.opencensus.common.Scope;
+import io.opencensus.trace.unsafe.ContextUtils;
+import java.util.concurrent.Callable;
+import javax.annotation.Nullable;
+
+/** Util methods/functionality to interact with the {@link Span} in the {@link io.grpc.Context}. */
+final class CurrentSpanUtils {
+  // No instance of this class.
+  private CurrentSpanUtils() {}
+
+  /**
+   * Returns The {@link Span} from the current context.
+   *
+   * @return The {@code Span} from the current context.
+   */
+  @Nullable
+  static Span getCurrentSpan() {
+    return ContextUtils.CONTEXT_SPAN_KEY.get();
+  }
+
+  /**
+   * Enters the scope of code where the given {@link Span} is in the current context, and returns an
+   * object that represents that scope. The scope is exited when the returned object is closed.
+   *
+   * <p>Supports try-with-resource idiom.
+   *
+   * @param span The {@code Span} to be set to the current context.
+   * @param endSpan if {@code true} the returned {@code Scope} will close the {@code Span}.
+   * @return An object that defines a scope where the given {@code Span} is set to the current
+   *     context.
+   */
+  static Scope withSpan(Span span, boolean endSpan) {
+    return new ScopeInSpan(span, endSpan);
+  }
+
+  /**
+   * Wraps a {@link Runnable} so that it executes with the {@code span} as the current {@code Span}.
+   *
+   * @param span the {@code Span} to be set as current.
+   * @param endSpan if {@code true} the returned {@code Runnable} will close the {@code Span}.
+   * @param runnable the {@code Runnable} to run in the {@code Span}.
+   * @return the wrapped {@code Runnable}.
+   */
+  static Runnable withSpan(Span span, boolean endSpan, Runnable runnable) {
+    return new RunnableInSpan(span, runnable, endSpan);
+  }
+
+  /**
+   * Wraps a {@link Callable} so that it executes with the {@code span} as the current {@code Span}.
+   *
+   * @param span the {@code Span} to be set as current.
+   * @param endSpan if {@code true} the returned {@code Runnable} will close the {@code Span}.
+   * @param callable the {@code Callable} to run in the {@code Span}.
+   * @return the wrapped {@code Callable}.
+   */
+  static <C> Callable<C> withSpan(Span span, boolean endSpan, Callable<C> callable) {
+    return new CallableInSpan<C>(span, callable, endSpan);
+  }
+
+  // Defines an arbitrary scope of code as a traceable operation. Supports try-with-resources idiom.
+  private static final class ScopeInSpan implements Scope {
+    private final Context origContext;
+    private final Span span;
+    private final boolean endSpan;
+
+    /**
+     * Constructs a new {@link ScopeInSpan}.
+     *
+     * @param span is the {@code Span} to be added to the current {@code io.grpc.Context}.
+     */
+    private ScopeInSpan(Span span, boolean endSpan) {
+      this.span = span;
+      this.endSpan = endSpan;
+      origContext = Context.current().withValue(ContextUtils.CONTEXT_SPAN_KEY, span).attach();
+    }
+
+    @Override
+    public void close() {
+      Context.current().detach(origContext);
+      if (endSpan) {
+        span.end();
+      }
+    }
+  }
+
+  private static final class RunnableInSpan implements Runnable {
+    // TODO(bdrutu): Investigate if the extra private visibility increases the generated bytecode.
+    private final Span span;
+    private final Runnable runnable;
+    private final boolean endSpan;
+
+    private RunnableInSpan(Span span, Runnable runnable, boolean endSpan) {
+      this.span = span;
+      this.runnable = runnable;
+      this.endSpan = endSpan;
+    }
+
+    @Override
+    public void run() {
+      Context origContext =
+          Context.current().withValue(ContextUtils.CONTEXT_SPAN_KEY, span).attach();
+      try {
+        runnable.run();
+      } catch (Throwable t) {
+        setErrorStatus(span, t);
+        if (t instanceof RuntimeException) {
+          throw (RuntimeException) t;
+        } else if (t instanceof Error) {
+          throw (Error) t;
+        }
+        throw new RuntimeException("unexpected", t);
+      } finally {
+        Context.current().detach(origContext);
+        if (endSpan) {
+          span.end();
+        }
+      }
+    }
+  }
+
+  private static final class CallableInSpan<V> implements Callable<V> {
+    private final Span span;
+    private final Callable<V> callable;
+    private final boolean endSpan;
+
+    private CallableInSpan(Span span, Callable<V> callable, boolean endSpan) {
+      this.span = span;
+      this.callable = callable;
+      this.endSpan = endSpan;
+    }
+
+    @Override
+    public V call() throws Exception {
+      Context origContext =
+          Context.current().withValue(ContextUtils.CONTEXT_SPAN_KEY, span).attach();
+      try {
+        return callable.call();
+      } catch (Exception e) {
+        setErrorStatus(span, e);
+        throw e;
+      } catch (Throwable t) {
+        setErrorStatus(span, t);
+        if (t instanceof Error) {
+          throw (Error) t;
+        }
+        throw new RuntimeException("unexpected", t);
+      } finally {
+        Context.current().detach(origContext);
+        if (endSpan) {
+          span.end();
+        }
+      }
+    }
+  }
+
+  private static void setErrorStatus(Span span, Throwable t) {
+    span.setStatus(
+        Status.UNKNOWN.withDescription(
+            t.getMessage() == null ? t.getClass().getSimpleName() : t.getMessage()));
+  }
+}