add span stacktrace config option

span-stacktrace/README.md

@@ -40,6 +40,22 @@ SdkTracerProvider tracerProvider = SdkTracerProvider.builder()
 OpenTelemetrySdk sdk = OpenTelemetrySdk.builder().setTracerProvider(tracerProvider).build();
 ```
 
+### Configuration
+
+Even if autoconfiguration is not yet supported, usages of this module must use the
+`otel.span.stacktrace.min.duration` configuration option (defaults to 5ms) to
+allow consistent configuration across usages.
+
+The following constants are provided as a convenience:
+
+- `StackTraceSpanProcessor.CONFIG_MIN_DURATION`
+- `StackTraceSpanProcessor.CONFIG_MIN_DURATION_DEFAULT`
+
+This means the default for this feature will capture a stacktrace for all spans that last 5ms or more,
+disabling it must be allowed by setting a negative value to `otel.span.stacktrace.min.duration`.
+Setting `otel.span.stacktrace.min.duration` to zero means a stacktrace will be captured for all
+spans.
+
 ## Component owners
 
 - [Jack Shirazi](https://github.com/jackshirazi), Elastic

span-stacktrace/src/main/java/io/opentelemetry/contrib/stacktrace/StackTraceSpanProcessor.java

@@ -12,12 +12,16 @@
 import io.opentelemetry.sdk.trace.SpanProcessor;
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import java.time.Duration;
 import java.util.function.Predicate;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
 public class StackTraceSpanProcessor extends AbstractSimpleChainingSpanProcessor {
 
+  public static final String CONFIG_MIN_DURATION = "otel.span.stacktrace.min.duration";
+  public static final Duration CONFIG_MIN_DURATION_DEFAULT = Duration.ofMillis(5);
+
   // inlined incubating attribute to prevent direct dependency on incubating semconv
   private static final AttributeKey<String> SPAN_STACKTRACE =
       AttributeKey.stringKey("code.stacktrace");