Fixes #2500

Author: jfarcand

modules/cpr/src/main/java/org/atmosphere/cpr/AtmosphereRequestImpl.java

@@ -395,13 +395,15 @@ public String getHeader(String s, boolean checkCase) {
     public String getParameter(String s) {
         String name = isNotNoOps() ? b.request.getParameter(s) : null;
         if (name == null) {
-            if (b.queryStrings.get(s) != null) {
-                return b.queryStrings.get(s)[0];
+            String[] values = b.queryStrings.get(s);
+            if (values != null) {
+                return values[0];
             }
         }
         return name;
     }
 
+
     @Override
     public Map<String, String[]> getParameterMap() {
         if (!queryComputed) {

modules/cpr/src/test/java/org/atmosphere/cpr/AtmosphereRequestTest.java

@@ -31,6 +31,9 @@
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 
 import static org.mockito.Mockito.mock;
@@ -40,6 +43,7 @@
 import static org.testng.Assert.assertNotNull;
 import static org.testng.Assert.assertNull;
 import static org.testng.Assert.assertTrue;
+import static org.testng.AssertJUnit.fail;
 
 public class AtmosphereRequestTest {
     private AtmosphereFramework framework;
@@ -351,5 +355,41 @@ public void testWrapMethodWithNullAttributeValue() throws IOException, ServletEx
         assertNull(wrappedRequest.getAttribute("org.eclipse.jetty.multipartConfig"), "Attribute value should be null");
     }
 
+    public class AtmosphereRequestImplTest {
+
+        @Test
+        public void testGetParameterRaceCondition() throws InterruptedException {
+            final Map<String, String[]> queryStrings = Collections.synchronizedMap(new HashMap<>());
+            queryStrings.put("testParam", new String[]{"testValue"});
+
+            AtmosphereRequestImpl.Builder builder = new AtmosphereRequestImpl.Builder();
+            builder.queryStrings(queryStrings);
+
+            final AtmosphereRequest request = builder.build();
+
+            Runnable addAndRemove = () -> {
+                queryStrings.put("testParam", new String[]{"testValue"});
+                queryStrings.remove("testParam");
+            };
+
+            Runnable getParameter = () -> {
+                try {
+                    request.getParameter("testParam");
+                } catch (NullPointerException e) {
+                    fail("NullPointerException occurred");
+                }
+            };
+
+            ExecutorService executor = Executors.newFixedThreadPool(2);
+            for (int i = 0; i < 10000; i++) {
+                executor.execute(addAndRemove);
+                executor.execute(getParameter);
+            }
+
+            executor.shutdown();
+            executor.awaitTermination(1, TimeUnit.MINUTES);
+        }
+    }
+
 
 }