Lazy init Writer from config to avoid premature resource allocation.

dd-trace-ot/src/main/java/datadog/opentracing/DDTracer.java

@@ -97,27 +97,20 @@ public class DDTracer implements io.opentracing.Tracer, Closeable, datadog.trace
   private final HttpCodec.Extractor extractor;
 
   public static class Builder {
+
     public Builder() {
       // Apply the default values from config.
-      withConfig(Config.get());
-    }
-
-    public Builder writer(final Writer writer) {
-      if (this.writer != null && this.writer != writer) {
-        // Try to avoid leaking resources
-        this.writer.close();
-      }
-      this.writer = writer;
-      return this;
+      config(Config.get());
     }
 
     public Builder withProperties(final Properties properties) {
-      return withConfig(Config.get(properties));
+      return config(Config.get(properties));
     }
 
-    public Builder withConfig(final Config config) {
+    public Builder config(final Config config) {
+      this.config = config;
       serviceName(config.getServiceName());
-      writer(Writer.Builder.forConfig(config));
+      // Explicitly skip setting writer to avoid allocating resources prematurely.
       sampler(Sampler.Builder.forConfig(config));
       injector(HttpCodec.createInjector(config));
       extractor(HttpCodec.createExtractor(config, config.getHeaderTags()));
@@ -259,6 +252,7 @@ public class DDTracer implements io.opentracing.Tracer, Closeable, datadog.trace
       final Map<String, String> taggedHeaders,
       final int partialFlushMinSpans) {
     this(
+        Config.get(),
         serviceName,
         writer,
         sampler,
@@ -274,6 +268,7 @@ public class DDTracer implements io.opentracing.Tracer, Closeable, datadog.trace
   @lombok.Builder(builderClassName = "Builder")
   // These field names must be stable to ensure the builder api is stable.
   private DDTracer(
+      final Config config,
       final String serviceName,
       final Writer writer,
       final Sampler sampler,
@@ -285,14 +280,17 @@ public class DDTracer implements io.opentracing.Tracer, Closeable, datadog.trace
       final Map<String, String> taggedHeaders,
       final int partialFlushMinSpans) {
 
-    assert writer != null;
     assert localRootSpanTags != null;
     assert defaultSpanTags != null;
     assert serviceNameMappings != null;
     assert taggedHeaders != null;
 
     this.serviceName = serviceName;
+    if (writer == null) {
+      this.writer = Writer.Builder.forConfig(config);
+    } else {
       this.writer = writer;
+    }
     this.sampler = sampler;
     this.injector = injector;
     this.extractor = extractor;

dd-trace-ot/src/main/java/datadog/opentracing/resolver/DDTracerResolver.java

@@ -16,7 +16,7 @@ public class DDTracerResolver extends TracerResolver {
   Tracer resolve(final Config config) {
     if (config.isTraceResolverEnabled()) {
       log.info("Creating DDTracer with DDTracerResolver");
-      return DDTracer.builder().withConfig(config).build();
+      return DDTracer.builder().config(config).build();
     } else {
       log.info("DDTracerResolver disabled");
       return null;

dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanBuilderTest.groovy

@@ -458,7 +458,7 @@ class DDSpanBuilderTest extends DDSpecification {
     setup:
     System.setProperty("dd.trace.span.tags", tagString)
     def config = new Config()
-    tracer = DDTracer.builder().withConfig(config).writer(writer).build()
+    tracer = DDTracer.builder().config(config).writer(writer).build()
     def span = tracer.buildSpan("op name").withServiceName("foo").start()
 
     expect:

dd-trace-ot/src/test/groovy/datadog/opentracing/PendingTraceTest.groovy

@@ -195,7 +195,7 @@ class PendingTraceTest extends DDSpecification {
     def properties = new Properties()
     properties.setProperty(PARTIAL_FLUSH_MIN_SPANS, "1")
     def config = Config.get(properties)
-    def tracer = DDTracer.builder().withConfig(config).writer(writer).build()
+    def tracer = DDTracer.builder().config(config).writer(writer).build()
     def trace = new PendingTrace(tracer, traceId, [:])
     def rootSpan = SpanFactory.newSpanOf(trace)
     def child1 = tracer.buildSpan("child1").asChildOf(rootSpan).start()
@@ -241,7 +241,7 @@ class PendingTraceTest extends DDSpecification {
     def properties = new Properties()
     properties.setProperty(PARTIAL_FLUSH_MIN_SPANS, "1")
     def config = Config.get(properties)
-    def tracer = DDTracer.builder().withConfig(config).writer(writer).build()
+    def tracer = DDTracer.builder().config(config).writer(writer).build()
     def trace = new PendingTrace(tracer, traceId, [:])
     def rootSpan = SpanFactory.newSpanOf(trace)
     def child1 = tracer.buildSpan("child1").asChildOf(rootSpan).start()

dd-trace-ot/src/test/groovy/datadog/trace/DDTracerTest.groovy

@@ -63,7 +63,7 @@ class DDTracerTest extends DDSpecification {
     System.setProperty(PREFIX + HEALTH_METRICS_ENABLED, "true")
 
     when:
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
 
     then:
     tracer.writer.monitor instanceof Monitor.StatsD
@@ -75,7 +75,7 @@ class DDTracerTest extends DDSpecification {
     setup:
     System.setProperty(PREFIX + PRIORITY_SAMPLING, "false")
     when:
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
     then:
     tracer.sampler instanceof AllSampler
   }
@@ -85,7 +85,7 @@ class DDTracerTest extends DDSpecification {
     System.setProperty(PREFIX + WRITER_TYPE, "LoggingWriter")
 
     when:
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
 
     then:
     tracer.writer instanceof LoggingWriter
@@ -98,7 +98,7 @@ class DDTracerTest extends DDSpecification {
     System.setProperty(PREFIX + HEADER_TAGS, mapString)
 
     when:
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
     // Datadog extractor gets placed first
     def taggedHeaders = tracer.extractor.extractors[0].taggedHeaders
 
@@ -116,7 +116,7 @@ class DDTracerTest extends DDSpecification {
   def "verify overriding host"() {
     when:
     System.setProperty(PREFIX + key, value)
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
 
     then:
     tracer.writer instanceof DDAgentWriter
@@ -131,7 +131,7 @@ class DDTracerTest extends DDSpecification {
   def "verify overriding port"() {
     when:
     System.setProperty(PREFIX + key, value)
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
 
     then:
     tracer.writer instanceof DDAgentWriter
@@ -147,7 +147,7 @@ class DDTracerTest extends DDSpecification {
   def "Writer is instance of LoggingWriter when property set"() {
     when:
     System.setProperty(PREFIX + "writer.type", "LoggingWriter")
-    def tracer = DDTracer.builder().withConfig(new Config()).build()
+    def tracer = DDTracer.builder().config(new Config()).build()
 
     then:
     tracer.writer instanceof LoggingWriter