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Add GlobalTracer #1270

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Add GlobalTracer #1270

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felixbarny
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@felixbarny felixbarny commented Jul 2, 2020 •
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What does this PR do?

Depends on #1230

Removes the need for tedious if (tracer != null) checks.

The separation of ElasticApmInstrumentation from TracerAwareElasticApmInstrumentation is a preparation step for creating a apm-agent-plugin-sdk module needed for #937.

Checklist

  • This is an enhancement of existing features, or a new feature in existing plugins
    • I have updated CHANGELOG.asciidoc
    • I have added tests that prove my fix is effective or that my feature works
    • Added an API method or config option? Document in which version this will be introduced
    • I have made corresponding changes to the documentation
  • This is a bugfix
  • This is a new plugin
    • I have updated CHANGELOG.asciidoc
    • My code follows the style guidelines of this project
    • I have made corresponding changes to the documentation
    • I have added tests that prove my fix is effective or that my feature works
    • New and existing unit tests pass locally with my changes
    • I have updated CHANGELOG.asciidoc
    • I have updated supported-technologies.asciidoc
    • Added an API method or config option? Document in which version this will be introduced
    • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
  • This is something else

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apmmachine commented Jul 2, 2020 •
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💚 Build Succeeded

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Build stats

  • Build Cause: [Pull request #1270 updated]

  • Start Time: 2020-07-02T14:02:17.288+0000

  • Duration: 43 min 22 sec

Test stats 🧪

Test Results
Failed 0
Passed 1459
Skipped 11
Total 1470

@felixbarny felixbarny requested a review from SylvainJuge July 2, 2020 12:54
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felixbarny commented Jul 2, 2020 •
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Hints for reviewers:
I've based this on #1230 as both touch lots of plugins and rebasing one on the other would be near impossible. Only commit 0e20bf0 is relevant currently.
Most of the interesting changes are in the core plugin. This touches most plugins but there are no significant logic changes other than removed null checks that are not necessary anymore.

EDIT: rebased on master and force-pushed

@felixbarny
Add GlobalTracer
834a732 
bye bye tracer null checks
felixbarny
felixbarny commented Jul 3, 2020
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apm-agent-core/src/main/java/co/elastic/apm/agent/impl/GlobalTracer.java
private static final Logger logger = LoggerFactory.getLogger(GlobalTracer.class);

private static final GlobalTracer INSTANCE = new GlobalTracer();
private volatile Tracer tracer = NoopTracer.INSTANCE;
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Currently, we don't declare the tracer volatile as it's usually created once on startup and never changed in non-test scenarios.

SylvainJuge
SylvainJuge approved these changes Jul 6, 2020
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LGTM, only few minor questions & comments.

apm-agent-core/src/main/java/co/elastic/apm/agent/impl/GlobalTracer.java Outdated Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/bci/ElasticApmAgent.java Outdated Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/bci/ElasticApmAgent.java Outdated Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/bci/ElasticApmAgent.java Outdated Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/impl/Tracer.java Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/bci/TracerAwareElasticApmInstrumentation.java Outdated Show resolved Hide resolved
apm-agent-core/src/main/java/co/elastic/apm/agent/impl/GlobalTracer.java Outdated Show resolved Hide resolved
...c/main/java/co/elastic/apm/agent/asynchttpclient/AbstractAsyncHttpClientInstrumentation.java
@@ -175,8 +183,8 @@ protected AbstractAsyncHandlerInstrumentation(ElementMatcher<? super MethodDescr

public static class AsyncHandlerOnCompletedInstrumentation extends AbstractAsyncHandlerInstrumentation {

public AsyncHandlerOnCompletedInstrumentation() {
super(named("onCompleted").and(takesArguments(0)));
public AsyncHandlerOnCompletedInstrumentation(ElasticApmTracer tracer) {
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Why do we have to provide tracer explicitly here ? shouldn't we use make AsyncHandlerOnCompletedInstrumentation extend TracerAwareElasticApmInstrumentation ?

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It's because co.elastic.apm.agent.bci.HelperClassManager.ForAnyClassLoader requires a ElasticApmTracer

...lugin/src/main/java/co/elastic/apm/agent/opentracing/impl/ApmSpanBuilderInstrumentation.java
@@ -92,6 +93,7 @@ public static Object createSpan(@Advice.Argument(value = 0, typing = Assigner.Ty
String operationName, long microseconds,
@Nullable Iterable<Map.Entry<String, String>> baggage, ClassLoader applicationClassLoader) {
AbstractSpan<?> result = null;
ElasticApmTracer tracer = GlobalTracer.getTracerImpl();
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Why can't we use GlobalTracer.get() here instead ?

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Because Tracer#startSpan is not part of the Tracer interface. That is because it returns a non-null span but because the NoopTracer only returns nulls, we can't add it to the interface. Normally it's not an issue because spans are started via getActive().createSpan

.../src/main/java/co/elastic/apm/agent/opentracing/impl/ExternalSpanContextInstrumentation.java
@@ -121,6 +123,7 @@ public static String onExit(@Advice.FieldValue(value = "childTraceContext", typi
@VisibleForAdvice
@Nullable
public static TraceContext parseTextMap(Iterable<Map.Entry<String, String>> textMap) {
ElasticApmTracer tracer = GlobalTracer.getTracerImpl();
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as previous, why not use GlobalTracer.get() ?

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Similar reason: because TraceContext needs a ElasticApmTracer instance so it can start spans.

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Merged on the command line via dd3e45f

@felixbarny felixbarny closed this Jul 6, 2020
@felixbarny felixbarny deleted the global-tracer branch July 6, 2020 14:00
@felixbarny felixbarny mentioned this pull request Jul 8, 2020
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@SylvainJuge SylvainJuge SylvainJuge approved these changes

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@felixbarny @apmmachine @SylvainJuge