De-singleton ZPageServer implementation (#4935)

* remove the static/singleton nature from ZPageServer

* add convenience method for creating zpages-based sdktracerprovider

* update readme for zpageserver

* oh checkstyle.

* overload build and add test

sdk-extensions/incubator/README.md

@@ -108,30 +108,37 @@ make sure your
 version of the JDK includes this package.
 
 To setup the zPages, register zPages with your `OpenTelemetrySdk` and
-call `ZPageServer.startHttpServerAndRegisterAllPages(int port)`:
+call `startHttpServerAndRegisterAllPages(int port)` on your ZPageServer instance:
 
 ```java
 public class MyMainClass {
   public static void main(String[] args) throws Exception {
+    // Create a new ZPageServer
+    ZPageServer zpageServer = ZPageServer.create();
     // Configure OpenTelemetrySdk with zPages
-    OpenTelemetry openTelemetry = OpenTelemetrySdk.builder()
-        .setTracerProvider(
-            SdkTracerProvider.builder()
-                .addSpanProcessor(ZPageServer.getSpanProcessor())
-                .setSpanLimits(ZPageServer.getTracezTraceConfigSupplier())
-                .setSampler(ZPageServer.getTracezSampler())
-                .build())
-        .build();
+    OpenTelemetry openTelemetry =
+        OpenTelemetrySdk.builder().setTracerProvider(zpageServer.buildSdkTracerProvider()).build();
 
     // Start zPages server
-    ZPageServer.startHttpServerAndRegisterAllPages(8080);
-    // ... do work
+    zpageServer.startHttpServerAndRegisterAllPages(8080);
+    // ...Do work (this is just an example)
+    long count = 0;
+    while (true) {
+      Tracer tracer = openTelemetry.getTracer("demo");
+      Span span = tracer.spanBuilder("exampleSpan" + ++count).startSpan();
+      try (Scope scope = span.makeCurrent()) {
+        System.out.println("Inside a span...");
+        TimeUnit.SECONDS.sleep(2);
+      }
+      span.end();
+    }
   }
 }
 ```
 
-Alternatively, you can call `ZPageServer.registerAllPagesToHttpServer(HttpServer server)` to
-register the zPages to a shared server:
+Note that `startHttpServerAndRegisterAllPages()` will create a new `HttpServer` and register the zPages
+with it. If you already have an existing or shared `HttpServer`, you can instead call
+`registerAllPagesToHttpServer(HttpServer server)`:
 
 ```java
 public class MyMainClass {
@@ -140,7 +147,7 @@ public class MyMainClass {
 
     // Start zPages server
     HttpServer server = HttpServer.create(new InetSocketAddress(8000), 10);
-    ZPageServer.registerAllPagesToHttpServer(server);
+    zPageServer.registerAllPagesToHttpServer(server);
     server.start();
     // ... do work
   }

sdk-extensions/incubator/src/main/java/io/opentelemetry/sdk/extension/incubator/trace/zpages/ZPageServer.java

@@ -7,6 +7,8 @@
 
 import com.sun.net.httpserver.HttpServer;
 import io.opentelemetry.api.internal.GuardedBy;
+import io.opentelemetry.sdk.trace.SdkTracerProvider;
+import io.opentelemetry.sdk.trace.SdkTracerProviderBuilder;
 import io.opentelemetry.sdk.trace.SpanLimits;
 import io.opentelemetry.sdk.trace.SpanProcessor;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
@@ -74,42 +76,46 @@ public final class ZPageServer {
   // Length of time to wait for the HttpServer to stop
   private static final int HTTPSERVER_STOP_DELAY = 1;
   // Tracez SpanProcessor and DataAggregator for constructing TracezZPageHandler
-  private static final TracezSpanProcessor tracezSpanProcessor =
-      TracezSpanProcessor.builder().build();
-  private static final TracezTraceConfigSupplier tracezTraceConfigSupplier =
+  private final TracezSpanProcessor tracezSpanProcessor = TracezSpanProcessor.builder().build();
+  private final TracezTraceConfigSupplier tracezTraceConfigSupplier =
       new TracezTraceConfigSupplier();
-  private static final TracezDataAggregator tracezDataAggregator =
+  private final TracezDataAggregator tracezDataAggregator =
       new TracezDataAggregator(tracezSpanProcessor);
   // Handler for /tracez page
-  private static final ZPageHandler tracezZPageHandler =
-      new TracezZPageHandler(tracezDataAggregator);
+  private final ZPageHandler tracezZPageHandler = new TracezZPageHandler(tracezDataAggregator);
   // Handler for /traceconfigz page
-  private static final ZPageHandler traceConfigzZPageHandler =
+  private final ZPageHandler traceConfigzZPageHandler =
       new TraceConfigzZPageHandler(tracezTraceConfigSupplier);
   // Handler for index page, **please include all available ZPageHandlers in the constructor**
-  private static final ZPageHandler indexZPageHandler =
+  private final ZPageHandler indexZPageHandler =
       new IndexZPageHandler(Arrays.asList(tracezZPageHandler, traceConfigzZPageHandler));
 
-  private static final Object mutex = new Object();
+  private final Object mutex = new Object();
 
   @GuardedBy("mutex")
   @Nullable
-  private static HttpServer server;
+  private HttpServer server;
+
+  private ZPageServer() {}
+
+  public static ZPageServer create() {
+    return new ZPageServer();
+  }
 
   /** Returns a supplier of {@link SpanLimits} which can be reconfigured using zpages. */
-  public static Supplier<SpanLimits> getTracezTraceConfigSupplier() {
+  public Supplier<SpanLimits> getTracezTraceConfigSupplier() {
     return tracezTraceConfigSupplier;
   }
 
   /** Returns a {@link Sampler} which can be reconfigured using zpages. */
-  public static Sampler getTracezSampler() {
+  public Sampler getTracezSampler() {
     return tracezTraceConfigSupplier;
   }
 
   /**
    * Returns a {@link SpanProcessor} which will allow processing of spans by {@link ZPageServer}.
    */
-  public static SpanProcessor getSpanProcessor() {
+  public SpanProcessor getSpanProcessor() {
     return tracezSpanProcessor;
   }
 
@@ -119,7 +125,7 @@ public static SpanProcessor getSpanProcessor() {
    *
    * @param server the {@link HttpServer} for the page to register to.
    */
-  static void registerIndexZPageHandler(HttpServer server) {
+  private void registerIndexZPageHandler(HttpServer server) {
     server.createContext(indexZPageHandler.getUrlPath(), new ZPageHttpHandler(indexZPageHandler));
   }
 
@@ -138,7 +144,7 @@ static void registerIndexZPageHandler(HttpServer server) {
    *
    * @param server the {@link HttpServer} for the page to register to.
    */
-  static void registerTracezZPageHandler(HttpServer server) {
+  private void registerTracezZPageHandler(HttpServer server) {
     server.createContext(tracezZPageHandler.getUrlPath(), new ZPageHttpHandler(tracezZPageHandler));
   }
 
@@ -154,7 +160,7 @@ static void registerTracezZPageHandler(HttpServer server) {
    *
    * @param server the {@link HttpServer} for the page to register to.
    */
-  static void registerTraceConfigzZPageHandler(HttpServer server) {
+  private void registerTraceConfigzZPageHandler(HttpServer server) {
     server.createContext(
         traceConfigzZPageHandler.getUrlPath(), new ZPageHttpHandler(traceConfigzZPageHandler));
   }
@@ -164,7 +170,7 @@ static void registerTraceConfigzZPageHandler(HttpServer server) {
    *
    * @param server the {@link HttpServer} for the page to register to.
    */
-  public static void registerAllPagesToHttpServer(HttpServer server) {
+  public void registerAllPagesToHttpServer(HttpServer server) {
     // For future zPages, register them to the server in here
     registerIndexZPageHandler(server);
     registerTracezZPageHandler(server);
@@ -173,7 +179,7 @@ public static void registerAllPagesToHttpServer(HttpServer server) {
   }
 
   /** Method for stopping the {@link HttpServer} {@code server}. */
-  private static void stop() {
+  private void stop() {
     synchronized (mutex) {
       if (server == null) {
         return;
@@ -183,6 +189,30 @@ private static void stop() {
     }
   }
 
+  /**
+   * Convenience method to return a new SdkTracerProvider that has been configured with our ZPage
+   * specific span processor, sampler, and limits.
+   *
+   * @return new SdkTracerProvider
+   */
+  public SdkTracerProvider buildSdkTracerProvider() {
+    return buildSdkTracerProvider(SdkTracerProvider.builder());
+  }
+
+  /**
+   * Convenience method to return a new SdkTracerProvider that has been configured with our ZPage
+   * specific span processor, sampler, and limits.
+   *
+   * @return new SdkTracerProvider
+   */
+  public SdkTracerProvider buildSdkTracerProvider(SdkTracerProviderBuilder builder) {
+    return builder
+        .addSpanProcessor(getSpanProcessor())
+        .setSpanLimits(getTracezTraceConfigSupplier())
+        .setSampler(getTracezSampler())
+        .build();
+  }
+
   /**
    * Starts a private {@link HttpServer} and registers all zPages to it. When the JVM shuts down the
    * server is stopped.
@@ -193,13 +223,13 @@ private static void stop() {
    * @throws IllegalStateException if the server is already started.
    * @throws IOException if the server cannot bind to the specified port.
    */
-  public static void startHttpServerAndRegisterAllPages(int port) throws IOException {
+  public void startHttpServerAndRegisterAllPages(int port) throws IOException {
     synchronized (mutex) {
       if (server != null) {
         throw new IllegalStateException("The HttpServer is already started.");
       }
       server = HttpServer.create(new InetSocketAddress(port), HTTPSERVER_BACKLOG);
-      ZPageServer.registerAllPagesToHttpServer(server);
+      registerAllPagesToHttpServer(server);
       server.start();
     }
 
@@ -208,10 +238,8 @@ public static void startHttpServerAndRegisterAllPages(int port) throws IOExcepti
             new Thread() {
               @Override
               public void run() {
-                ZPageServer.stop();
+                ZPageServer.this.stop();
               }
             });
   }
-
-  private ZPageServer() {}
 }

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/trace/zpages/ZPageServerTest.java

@@ -7,23 +7,38 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import io.opentelemetry.sdk.trace.SdkTracerProvider;
+import io.opentelemetry.sdk.trace.SpanLimits;
 import org.junit.jupiter.api.Test;
 
 class ZPageServerTest {
 
   @Test
   void spanProcessor() {
-    assertThat(ZPageServer.getSpanProcessor()).isInstanceOf(TracezSpanProcessor.class);
+    ZPageServer server = ZPageServer.create();
+    assertThat(server.getSpanProcessor()).isInstanceOf(TracezSpanProcessor.class);
   }
 
   @Test
   void traceConfigSupplier() {
-    assertThat(ZPageServer.getTracezTraceConfigSupplier())
-        .isInstanceOf(TracezTraceConfigSupplier.class);
+    ZPageServer server = ZPageServer.create();
+    assertThat(server.getTracezTraceConfigSupplier()).isInstanceOf(TracezTraceConfigSupplier.class);
   }
 
   @Test
   void testSampler() {
-    assertThat(ZPageServer.getTracezSampler()).isInstanceOf(TracezTraceConfigSupplier.class);
+    ZPageServer server = ZPageServer.create();
+    assertThat(server.getTracezSampler()).isInstanceOf(TracezTraceConfigSupplier.class);
+  }
+
+  @Test
+  void buildTracerProvider() {
+    ZPageServer server = ZPageServer.create();
+    SpanLimits expectedLimits = server.getTracezTraceConfigSupplier().get();
+
+    try (SdkTracerProvider provider = server.buildSdkTracerProvider()) {
+      assertThat(provider.getSpanLimits()).isEqualTo(expectedLimits);
+      assertThat(provider.getSampler()).isSameAs(server.getTracezSampler());
+    }
   }
 }