1 files changed, 45 insertions, 1 deletions

diff --git a/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java b/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
index 335f0636..0b417b06 100644
--- a/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
+++ b/language-web/src/main/java/tools/refinery/language/web/xtext/server/TransactionExecutor.java
@@ -1,7 +1,9 @@
 package tools.refinery.language.web.xtext.server;
 
 import java.lang.ref.WeakReference;
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.eclipse.emf.common.util.URI;
@@ -13,6 +15,8 @@ import org.eclipse.xtext.web.server.ISession;
 import org.eclipse.xtext.web.server.InvalidRequestException;
 import org.eclipse.xtext.web.server.InvalidRequestException.UnknownLanguageException;
 import org.eclipse.xtext.web.server.XtextServiceDispatcher;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import com.google.common.base.Strings;
 import com.google.inject.Injector;
@@ -27,6 +31,8 @@ import tools.refinery.language.web.xtext.server.push.PushWebDocument;
 import tools.refinery.language.web.xtext.servlet.SimpleServiceContext;
 
 public class TransactionExecutor implements IDisposable, PrecomputationListener {
+        private static final Logger LOG = LoggerFactory.getLogger(TransactionExecutor.class);
+
         private final ISession session;
 
         private final IResourceServiceProvider.Registry resourceServiceProviderRegistry;
@@ -35,6 +41,12 @@ public class TransactionExecutor implements IDisposable, PrecomputationListener
 
         private ResponseHandler responseHandler;
 
+        private Object callPendingLock = new Object();
+
+        private boolean callPending;
+
+        private List<XtextWebPushMessage> pendingPushMessages = new ArrayList<>();
+
         public TransactionExecutor(ISession session, IResourceServiceProvider.Registry resourceServiceProviderRegistry) {
                 this.session = session;
                 this.resourceServiceProviderRegistry = resourceServiceProviderRegistry;
@@ -51,6 +63,15 @@ public class TransactionExecutor implements IDisposable, PrecomputationListener
                         responseHandler.onResponse(new XtextWebOkResponse(request, new PongResult(ping)));
                         return;
                 }
+                synchronized (callPendingLock) {
+                        if (callPending) {
+                                LOG.error("Reentrant request detected");
+                        }
+                        if (!pendingPushMessages.isEmpty()) {
+                                LOG.error("{} push messages got stuck without a pending request", pendingPushMessages.size());
+                        }
+                        callPending = true;
+                }
                 try {
                         var injector = getInjector(serviceContext);
                         var serviceDispatcher = injector.getInstance(XtextServiceDispatcher.class);
@@ -61,13 +82,36 @@ public class TransactionExecutor implements IDisposable, PrecomputationListener
                         responseHandler.onResponse(new XtextWebErrorResponse(request, XtextWebErrorKind.REQUEST_ERROR, e));
                 } catch (RuntimeException e) {
                         responseHandler.onResponse(new XtextWebErrorResponse(request, XtextWebErrorKind.SERVER_ERROR, e));
+                } finally {
+                        synchronized (callPendingLock) {
+                                for (var message : pendingPushMessages) {
+                                        try {
+                                                responseHandler.onResponse(message);
+                                        } catch (ResponseHandlerException | RuntimeException e) {
+                                                LOG.error("Error while flushing push message", e);
+                                        }
+                                }
+                                pendingPushMessages.clear();
+                                callPending = false;
+                        }
                 }
         }
 
         @Override
         public void onPrecomputedServiceResult(String resourceId, String stateId, String serviceName,
                         IServiceResult serviceResult) throws ResponseHandlerException {
-                responseHandler.onResponse(new XtextWebPushMessage(resourceId, stateId, serviceName, serviceResult));
+                var message = new XtextWebPushMessage(resourceId, stateId, serviceName, serviceResult);
+                synchronized (callPendingLock) {
+                        // If we're currently responding to a call we must delay any push messages until
+                        // the reply is sent, because push messages relating to the new state id must be
+                        // sent after the response with the new state id so that the client knows about
+                        // the new state when it receives the push message.
+                        if (callPending) {
+                                pendingPushMessages.add(message);
+                        } else {
+                                responseHandler.onResponse(message);
+                        }
+                }
         }
 
         @Override