Index: java/org/apache/catalina/core/ContainerBase.java
===================================================================
--- java/org/apache/catalina/core/ContainerBase.java	(revision 1611495)
+++ java/org/apache/catalina/core/ContainerBase.java	(working copy)
@@ -1335,14 +1335,28 @@
 
         @Override
         public void run() {
-            while (!threadDone) {
-                try {
-                    Thread.sleep(backgroundProcessorDelay * 1000L);
-                } catch (InterruptedException e) {
-                    // Ignore
+            Throwable t = null;
+            String unexpectedDeathMessage = sm.getString(
+                    "containerBase.backgroundProcess.unexpectedThreadDeath",
+                    Thread.currentThread().getName());
+            try {
+                while (!threadDone) {
+                    try {
+                        Thread.sleep(backgroundProcessorDelay * 1000L);
+                    } catch (InterruptedException e) {
+                        // Ignore
+                    }
+                    if (!threadDone) {
+                        processChildren(ContainerBase.this);
+                    }
                 }
+            } catch (RuntimeException|Error e) {
+                t = e;
+                throw e;
+            } finally {
+                thread = null;
                 if (!threadDone) {
-                    processChildren(ContainerBase.this);
+                    log.error(unexpectedDeathMessage, t);
                 }
             }
         }
Index: java/org/apache/catalina/core/LocalStrings.properties
===================================================================
--- java/org/apache/catalina/core/LocalStrings.properties	(revision 1611495)
+++ java/org/apache/catalina/core/LocalStrings.properties	(working copy)
@@ -81,6 +81,7 @@
 containerBase.backgroundProcess.cluster=Exception processing cluster {0} background process
 containerBase.backgroundProcess.realm=Exception processing realm {0} background process
 containerBase.backgroundProcess.valve=Exception processing valve {0} background process
+containerBase.backgroundProcess.unexpectedThreadDeath=Unexpected death of background thread {0}
 defaultInstanceManager.invalidInjection=Invalid method resource injection annotation
 filterChain.filter=Filter execution threw an exception
 filterChain.servlet=Servlet execution threw an exception
Index: webapps/docs/changelog.xml
===================================================================
--- webapps/docs/changelog.xml	(revision 1611495)
+++ webapps/docs/changelog.xml	(working copy)
@@ -64,6 +64,10 @@
         <code>MapperListener</code> during repeated starts of embedded Tomcat.
         (kkolinko)
       </fix>
+      <add>
+        <bug>56724</bug>: Write an error message to Tomcat logs if container
+        background thread is aborted unexpectedly. (kkolinko)
+      </add>
     </changelog>
   </subsection>
   <subsection name="Coyote">