Exception semantic conventions: Add example & more explanation for exception.escaped.

CHANGELOG.md

@@ -19,10 +19,12 @@ New:
   ([#606](https://github.com/open-telemetry/opentelemetry-specification/pull/606/))
 - Clarification of the behavior of the Trace API, re: context propagation, in
   the absence of an installed SDK
-- Add Span API and semantic conventions for recording exceptions
+- Add API and semantic conventions for recording exceptions as Span Events
   ([#697](https://github.com/open-telemetry/opentelemetry-specification/pull/697))
   * API was extended to allow adding arbitrary event attributes ([#874](https://github.com/open-telemetry/opentelemetry-specification/pull/874))
-  * `exception.escaped` was added ([#784](https://github.com/open-telemetry/opentelemetry-specification/pull/784))
+  * `exception.escaped` sematic span event attribute was added
+    ([#784](https://github.com/open-telemetry/opentelemetry-specification/pull/784),
+    [#946](https://github.com/open-telemetry/opentelemetry-specification/pull/946))
 
 Updates:
 

specification/trace/semantic_conventions/exceptions.md

@@ -16,6 +16,24 @@ exceptions.
 An exception SHOULD be recorded as an `Event` on the span during which it occurred.
 The name of the event MUST be `"exception"`.
 
+<a name="exception-end-example"></a>
+
+A typical template for an auto-instrumentation implementing this semantic convention
+using an [API-provided `recordException` method](../api.md#record-exception)
+could look like this (pseudo-Java):
+
+```java
+Span span = myTracer.startSpan(/*...*/);
+try {
+  // Code that does the actual work which the Span represents
+} catch (Throwable e) {
+  span.recordException(e, Attributes.of("exception.escaped", true));
+  throw e;
+} finally {
+  span.end();
+}
+```
+
 ## Attributes
 
 The table below indicates which attributes should be added to the `Event` and
@@ -26,7 +44,7 @@ their types.
 | exception.type       | String | The type of the exception (its fully-qualified class name, if applicable). The dynamic type of the exception should be preferred over the static type in languages that support it. E.g. "java.net.ConnectException", "OSError"                                                                                                                                                                                                     | One of `exception.type` or `exception.message` is required |
 | exception.message    | String | The exception message. E.g. `"Division by zero"`, `"Can't convert 'int' object to str implicitly"`                                                                                                                                                                                                                                                                                                                                  | One of `exception.type` or `exception.message` is required |
 | exception.stacktrace | String | A stacktrace as a string in the natural representation for the language runtime. The representation is to be determined and documented by each language SIG. E.g. `"Exception in thread \"main\" java.lang.RuntimeException: Test exception\n at com.example.GenerateTrace.methodB(GenerateTrace.java:13)\n at com.example.GenerateTrace.methodA(GenerateTrace.java:9)\n at com.example.GenerateTrace.main(GenerateTrace.java:5)"`. | No                                                         |
-| exception.escaped | Bool | SHOULD be set to true if the exception event is recorded at a point where it is known that the exception is escaping the scope of the span (e.g. if there is an exception active just before ending the span). Note that an exception may still leave the scope of the span even if this was not set or set to false, if the event was recorded at an earlier time. | No |
+| exception.escaped | Bool | SHOULD be set to true if the exception event is recorded at a point where it is known that the exception is escaping the scope of the span. See [explanation below](#escaped-exceptions). | No |
 
 ### Stacktrace Representation
 
@@ -57,3 +75,16 @@ grained information from a stacktrace, if necessary.
 [csharp-stacktrace]: https://docs.microsoft.com/en-us/dotnet/api/system.exception.tostring
 [go-stacktrace]: https://golang.org/pkg/runtime/debug/#Stack
 [telemetry-sdk-resource]: https://github.com/open-telemetry/opentelemetry-specification/tree/master/specification/resource/semantic_conventions#telemetry-sdk
+
+### Escaped exceptions
+
+An exception is considered to have escaped (or left) the scope of a span,
+if that span is ended while the exception is still "in flight".
+
+While it is usually not possible to determine whether some exception thrown
+now *will* escape the scope of a span, it is trivial to know that an exception
+will escape, if one checks for an active exception just before ending the span.
+See the [example above](#exception-end-example). It follows that an exception
+may still escape the scope of the span even if the `exception.escaped` attribute
+was not set or set to false, since that event might have been recorded at a time
+where it was not clear whether the exception will escape.