fix pool metrics for tainted connections

In case of a tainted connection, the metrics were not ended properly.
This commit fixes that while retaining idempotency of `PooledRedisConnection.close()`.

src/main/java/io/vertx/redis/client/impl/PooledRedisConnection.java

@@ -10,6 +10,7 @@
 import io.vertx.redis.client.Response;
 
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * A pooled Redis connection
@@ -20,6 +21,7 @@ public class PooledRedisConnection implements RedisConnection {
   private final RedisConnectionInternal connection;
   private final PoolMetrics metrics;
   private final Object metric;
+  private final AtomicBoolean ended = new AtomicBoolean();
 
   public PooledRedisConnection(Lease<RedisConnectionInternal> lease, PoolMetrics<?> poolMetrics, Object metric) {
     this.lease = lease;
@@ -88,7 +90,9 @@ public RedisConnection endHandler(@Nullable Handler<Void> endHandler) {
   public Future<Void> close() {
     if (connection.reset()) {
       lease.recycle();
+    }
 
+    if (ended.compareAndSet(false, true)) {
       if (metrics != null) {
         metrics.end(metric, true);
       }

src/test/java/io/vertx/redis/client/test/RedisPoolMetricsTest.java

@@ -99,6 +99,36 @@ public void simpleTest(TestContext should) {
       });
   }
 
+  @Test
+  public void taintedConnection(TestContext test) {
+    Async async = test.async();
+
+    Redis client = Redis.createClient(rule.vertx(), new RedisOptions().setConnectionString(redis.getRedisUri()));
+    client.connect()
+      .compose(conn -> {
+        test.assertEquals(0, getMetrics().numberOfWaitingTasks());
+        test.assertEquals(1, getMetrics().numberOfRunningTasks());
+
+        return conn.send(Request.cmd(Command.SELECT).arg(7)) // taints the connection
+          .compose(response -> {
+            test.assertEquals(0, getMetrics().numberOfWaitingTasks());
+            test.assertEquals(1, getMetrics().numberOfRunningTasks());
+
+            return conn.close();
+          }).onComplete(test.asyncAssertSuccess(ignored -> {
+            test.assertEquals(0, getMetrics().numberOfWaitingTasks());
+            test.assertEquals(0, getMetrics().numberOfRunningTasks());
+          }));
+      })
+      .map(ignored -> {
+        client.close();
+        return null;
+      })
+      .onComplete(test.asyncAssertSuccess(ignored -> {
+        async.complete();
+      }));
+  }
+
   @Test
   public void testLifecycle(TestContext should) {
     final Async test = should.async();