Refactored code to allow the use of a custom ExecutorService

simpleclient_httpserver/src/main/java/io/prometheus/client/exporter/HTTPServer.java

@@ -199,6 +199,7 @@ public static class Builder {
         private InetAddress inetAddress = null;
         private InetSocketAddress inetSocketAddress = null;
         private HttpServer httpServer = null;
+        private ExecutorService executorService = null;
         private CollectorRegistry registry = CollectorRegistry.defaultRegistry;
         private boolean daemon = false;
         private Predicate<String> sampleNameFilter;
@@ -248,13 +249,26 @@ public Builder withInetSocketAddress(InetSocketAddress address) {
         /**
          * Use this httpServer. The {@code httpServer} is expected to already be bound to an address.
          * Must not be called together with {@link #withPort(int)}, or {@link #withHostname(String)},
-         * or {@link #withInetAddress(InetAddress)}, or {@link #withInetSocketAddress(InetSocketAddress)}.
+         * or {@link #withInetAddress(InetAddress)}, or {@link #withInetSocketAddress(InetSocketAddress)},
+         * or {@link #withExecutorService(ExecutorService)}.
          */
         public Builder withHttpServer(HttpServer httpServer) {
             this.httpServer = httpServer;
             return this;
         }
 
+        /**
+         * Optional: ExecutorService used by the {@code httpServer}.
+         * Must not be called together with the {@link #withHttpServer(HttpServer)}.
+         *
+         * @param executorService
+         * @return
+         */
+        public Builder withExecutorService(ExecutorService executorService) {
+            this.executorService = executorService;
+            return this;
+        }
+
         /**
          * By default, the {@link HTTPServer} uses non-daemon threads. Set this to {@code true} to
          * run the {@link HTTPServer} with daemon threads.
@@ -323,12 +337,13 @@ public HTTPServer build() throws IOException {
             }
 
             if (httpServer != null) {
+                assertNull(executorService, "cannot configure 'httpServer' and `executorService'");
                 assertZero(port, "cannot configure 'httpServer' and 'port' at the same time");
                 assertNull(hostname, "cannot configure 'httpServer' and 'hostname' at the same time");
                 assertNull(inetAddress, "cannot configure 'httpServer' and 'inetAddress' at the same time");
                 assertNull(inetSocketAddress, "cannot configure 'httpServer' and 'inetSocketAddress' at the same time");
                 assertNull(httpsConfigurator, "cannot configure 'httpServer' and 'httpsConfigurator' at the same time");
-                return new HTTPServer(httpServer, registry, daemon, sampleNameFilterSupplier, authenticator);
+                return new HTTPServer(executorService, httpServer, registry, daemon, sampleNameFilterSupplier, authenticator);
             } else if (inetSocketAddress != null) {
                 assertZero(port, "cannot configure 'inetSocketAddress' and 'port' at the same time");
                 assertNull(hostname, "cannot configure 'inetSocketAddress' and 'hostname' at the same time");
@@ -350,7 +365,7 @@ public HTTPServer build() throws IOException {
                 httpServer = HttpServer.create(inetSocketAddress, 3);
             }
 
-            return new HTTPServer(httpServer, registry, daemon, sampleNameFilterSupplier, authenticator);
+            return new HTTPServer(executorService, httpServer, registry, daemon, sampleNameFilterSupplier, authenticator);
         }
 
         private void assertNull(Object o, String msg) {
@@ -371,7 +386,7 @@ private void assertZero(int i, String msg) {
      * The {@code httpServer} is expected to already be bound to an address
      */
     public HTTPServer(HttpServer httpServer, CollectorRegistry registry, boolean daemon) throws IOException {
-        this(httpServer, registry, daemon, null, null);
+        this(null, httpServer, registry, daemon, null, null);
     }
 
     /**
@@ -416,7 +431,7 @@ public HTTPServer(String host, int port) throws IOException {
         this(new InetSocketAddress(host, port), CollectorRegistry.defaultRegistry, false);
     }
 
-    private HTTPServer(HttpServer httpServer, CollectorRegistry registry, boolean daemon, Supplier<Predicate<String>> sampleNameFilterSupplier, Authenticator authenticator) {
+    private HTTPServer(ExecutorService executorService, HttpServer httpServer, CollectorRegistry registry, boolean daemon, Supplier<Predicate<String>> sampleNameFilterSupplier, Authenticator authenticator) {
         if (httpServer.getAddress() == null)
             throw new IllegalArgumentException("HttpServer hasn't been bound to an address");
 
@@ -434,8 +449,12 @@ private HTTPServer(HttpServer httpServer, CollectorRegistry registry, boolean da
         if (authenticator != null) {
             mContext.setAuthenticator(authenticator);
         }
-        executorService = Executors.newFixedThreadPool(5, NamedDaemonThreadFactory.defaultThreadFactory(daemon));
-        server.setExecutor(executorService);
+        if (executorService != null) {
+            this.executorService = executorService;
+        } else {
+            this.executorService = Executors.newFixedThreadPool(5, NamedDaemonThreadFactory.defaultThreadFactory(daemon));
+        }
+        server.setExecutor(this.executorService);
         start(daemon);
     }
 

simpleclient_httpserver/src/test/java/io/prometheus/client/exporter/TestHTTPServer.java

@@ -30,6 +30,8 @@
 import java.security.GeneralSecurityException;
 import java.security.KeyStore;
 import java.security.cert.X509Certificate;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 import static org.assertj.core.api.Java6Assertions.assertThat;
 
@@ -451,6 +453,53 @@ public void testHEADRequestWithSSLAndBasicAuthWrongCredentials() throws GeneralS
     }
   }
 
+  @Test
+  public void testExecutorService() throws IOException {
+    ExecutorService executorService = Executors.newFixedThreadPool(20);
+
+    HTTPServer httpServer = new HTTPServer.Builder()
+            .withExecutorService(executorService)
+            .withRegistry(registry)
+            .build();
+
+    Assert.assertEquals(httpServer.executorService, executorService);
+
+    try {
+      String body = createHttpRequestBuilder(httpServer, "/metrics").build().execute().getBody();
+      assertThat(body).contains("a 0.0");
+      assertThat(body).contains("b 0.0");
+      assertThat(body).contains("c 0.0");
+    } finally {
+      httpServer.close();
+    }
+  }
+
+  @Test(expected = IllegalStateException.class)
+  public void testExecutorServiceWithHttpServer() throws IOException {
+    InetSocketAddress inetSocketAddress = new InetSocketAddress("localhost", 0);
+
+    HttpServer externalHttpServer = HttpServer.create(inetSocketAddress, 0);
+    externalHttpServer.createContext("/metrics", new HTTPServer.HTTPMetricHandler(registry));
+    externalHttpServer.start();
+
+    ExecutorService executorService = Executors.newFixedThreadPool(20);
+
+    HTTPServer httpServer = new HTTPServer.Builder()
+            .withExecutorService(executorService)
+            .withHttpServer(externalHttpServer)
+            .withRegistry(registry)
+            .build();
+
+    try {
+      String body = createHttpRequestBuilder(httpServer, "/metrics").build().execute().getBody();
+      assertThat(body).contains("a 0.0");
+      assertThat(body).contains("b 0.0");
+      assertThat(body).contains("c 0.0");
+    } finally {
+      httpServer.close();
+    }
+  }
+
   /**
    * Encodes authorization credentials
    *