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Remove inconsistent synchronization from EmbeddedWebApplicationContext 

Previously, EmbeddedWebApplicationContext used synchronized, but did
not do so consistently. It also synchronized on this so its lock was
exposed outside of the class, creating a risk of deadlock if a caller
synchronized incorrectly. Furthermore, not all fields on the class
were sychronized so the class wasn't truly thread-safe.

This commit attempts to rectify some of the problems above. The use
of synchronized has been dropped in favour of using a volatile field
for the embedded servlet container. Whenever this field is accessed,
a local variable is used to "cache" the value thereby preventing a
change on another thread from causing unwanted behaviour such as an
NPE.

Closes gh-4593
This commit is contained in:
Andy Wilkinson 2015-12-01 14:55:53 +00:00
parent 9bffdc80ff
commit 0214fe4b82
1 changed files with 20 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
spring-boot/src/main/java/org/springframework/boot/context/embedded/EmbeddedWebApplicationContext.java
View File

@ -95,7 +95,7 @@ public class EmbeddedWebApplicationContext extends GenericWebApplicationContext
*/ */
public static final String DISPATCHER_SERVLET_NAME = ServletContextInitializerBeans.DISPATCHER_SERVLET_NAME; public static final String DISPATCHER_SERVLET_NAME = ServletContextInitializerBeans.DISPATCHER_SERVLET_NAME;
private EmbeddedServletContainer embeddedServletContainer; private volatile EmbeddedServletContainer embeddedServletContainer;
private ServletConfig servletConfig; private ServletConfig servletConfig;
@ -138,10 +138,10 @@ public class EmbeddedWebApplicationContext extends GenericWebApplicationContext
@Override @Override
protected void finishRefresh() { protected void finishRefresh() {
super.finishRefresh(); super.finishRefresh();
startEmbeddedServletContainer(); EmbeddedServletContainer localContainer = startEmbeddedServletContainer();
if (this.embeddedServletContainer != null) { if (localContainer != null) {
publishEvent(new EmbeddedServletContainerInitializedEvent(this, publishEvent(
this.embeddedServletContainer)); new EmbeddedServletContainerInitializedEvent(this, localContainer));
} }
} }
@ -151,15 +151,17 @@ public class EmbeddedWebApplicationContext extends GenericWebApplicationContext
stopAndReleaseEmbeddedServletContainer(); stopAndReleaseEmbeddedServletContainer();
} }
private synchronized void createEmbeddedServletContainer() { private void createEmbeddedServletContainer() {
if (this.embeddedServletContainer == null && getServletContext() == null) { EmbeddedServletContainer localContainer = this.embeddedServletContainer;
ServletContext localServletContext = getServletContext();
if (localContainer == null && localServletContext == null) {
EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory(); EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
this.embeddedServletContainer = containerFactory this.embeddedServletContainer = containerFactory
.getEmbeddedServletContainer(getSelfInitializer()); .getEmbeddedServletContainer(getSelfInitializer());
} }
else if (getServletContext() != null) { else if (localServletContext != null) {
try { try {
getSelfInitializer().onStartup(getServletContext()); getSelfInitializer().onStartup(localServletContext);
} }
catch (ServletException ex) { catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", throw new ApplicationContextException("Cannot initialize servlet context",
@ -284,16 +286,19 @@ public class EmbeddedWebApplicationContext extends GenericWebApplicationContext
} }
} }
private void startEmbeddedServletContainer() { private EmbeddedServletContainer startEmbeddedServletContainer() {
if (this.embeddedServletContainer != null) { EmbeddedServletContainer localContainer = this.embeddedServletContainer;
this.embeddedServletContainer.start(); if (localContainer != null) {
localContainer.start();
} }
return localContainer;
} }
private synchronized void stopAndReleaseEmbeddedServletContainer() { private void stopAndReleaseEmbeddedServletContainer() {
if (this.embeddedServletContainer != null) { EmbeddedServletContainer localContainer = this.embeddedServletContainer;
if (localContainer != null) {
try { try {
this.embeddedServletContainer.stop(); localContainer.stop();
this.embeddedServletContainer = null; this.embeddedServletContainer = null;
} }
catch (Exception ex) { catch (Exception ex) {