[isis] branch master updated: ISIS-2158: refactors one-shot idiom into a 'commons' utility

[ah...@apache.org]

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ahuber pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/isis.git


The following commit(s) were added to refs/heads/master by this push:
     new 8759334  ISIS-2158: refactors one-shot idiom into a 'commons' utility
8759334 is described below

commit 8759334412b72530ea3a804c50495d22dd745ab6
Author: Andi Huber <ah...@apache.org>
AuthorDate: Fri Jan 10 16:20:53 2020 +0100

    ISIS-2158: refactors one-shot idiom into a 'commons' utility
---
 .../isis/commons/internal/base/_Oneshot.java       | 64 ++++++++++++++++++++++
 .../webappctx/IsisWebAppContextInitializer.java    | 15 +++--
 2 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/core/commons/src/main/java/org/apache/isis/commons/internal/base/_Oneshot.java b/core/commons/src/main/java/org/apache/isis/commons/internal/base/_Oneshot.java
new file mode 100644
index 0000000..c2c006a
--- /dev/null
+++ b/core/commons/src/main/java/org/apache/isis/commons/internal/base/_Oneshot.java
@@ -0,0 +1,64 @@
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one
+ *  or more contributor license agreements.  See the NOTICE file
+ *  distributed with this work for additional information
+ *  regarding copyright ownership.  The ASF licenses this file
+ *  to you under the Apache License, Version 2.0 (the
+ *  "License"); you may not use this file except in compliance
+ *  with the License.  You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing,
+ *  software distributed under the License is distributed on an
+ *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ *  KIND, either express or implied.  See the License for the
+ *  specific language governing permissions and limitations
+ *  under the License.
+ */
+package org.apache.isis.commons.internal.base;
+
+import java.io.Serializable;
+
+/**
+ * <h1>- internal use only -</h1>
+ * <p>
+ * One-shot idiom helper utility, thread-safe and serializable
+ * <p>
+ * <b>WARNING</b>: Do <b>NOT</b> use any of the classes provided by this package! <br/>
+ * These may be changed or removed without notice!
+ *
+ * @since 2.0
+ *
+ */
+public final class _Oneshot implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    private final Object $lock = new Object[0]; // serializable lock
+    
+    private int shotCount = 0;
+
+    /**
+     * @return whether the shot actually happened (was allowed)
+     */
+    public boolean shoot() {
+        synchronized ($lock) {
+            if(shotCount==0) {
+                ++ shotCount;
+                return true;
+            }
+            return false;    
+        }
+    }
+
+    /**
+     * resets to initial condition, that is it allows one more shot
+     */
+    public void reset() {
+        synchronized ($lock) {
+            shotCount = 0;
+        }
+    }
+    
+}
diff --git a/core/webapp/src/main/java/org/apache/isis/webapp/webappctx/IsisWebAppContextInitializer.java b/core/webapp/src/main/java/org/apache/isis/webapp/webappctx/IsisWebAppContextInitializer.java
index 2a9507b..8324f32 100644
--- a/core/webapp/src/main/java/org/apache/isis/webapp/webappctx/IsisWebAppContextInitializer.java
+++ b/core/webapp/src/main/java/org/apache/isis/webapp/webappctx/IsisWebAppContextInitializer.java
@@ -19,9 +19,9 @@
 package org.apache.isis.webapp.webappctx;
 
 import java.util.EventListener;
-import java.util.concurrent.atomic.LongAdder;
 
 import javax.inject.Inject;
+import javax.inject.Singleton;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletContextListener;
@@ -31,6 +31,7 @@ import org.springframework.boot.web.servlet.ServletContextInitializer;
 import org.springframework.stereotype.Component;
 
 import org.apache.isis.applib.services.registry.ServiceRegistry;
+import org.apache.isis.commons.internal.base._Oneshot;
 import org.apache.isis.commons.internal.context._Context;
 import org.apache.isis.config.IsisConfiguration;
 import org.apache.isis.config.viewer.wicket.WebAppContextPath;
@@ -59,7 +60,7 @@ import lombok.extern.log4j.Log4j2;
 @Log4j2
 public class IsisWebAppContextInitializer implements ServletContextInitializer {
     
-    private final static LongAdder instanceCount = new LongAdder();
+    private final static _Oneshot oneshot = new _Oneshot();
     
     @Inject private ServiceRegistry serviceRegistry; // this dependency ensures Isis has been initialized/provisioned
     @Inject private IsisConfiguration isisConfiguration;
@@ -70,11 +71,9 @@ public class IsisWebAppContextInitializer implements ServletContextInitializer {
     @Override
     public void onStartup(ServletContext servletContext) throws ServletException {
 
-        { // onStartup(...) must be a one shot, otherwise just ignore 
-            if(instanceCount.intValue() > 0) {
-                return;
-            }
-            instanceCount.increment();
+        // onStartup(...) must be a one shot, otherwise just ignore 
+        if(!oneshot.shoot()) {
+            return;
         }
         
         if(!isIsisProvisioned()) {
@@ -109,7 +108,7 @@ public class IsisWebAppContextInitializer implements ServletContextInitializer {
             log.info("about to destroy the context");
             webModuleContext.shutdown(event);
         }
-        instanceCount.reset();
+        oneshot.reset();
         log.info("context destroyed");
     }