Save memory when test plan contains lots of HTTP Header Manager eleme…

…nts by sharing the managers across threads

bin/jmeter.properties

@@ -488,6 +488,15 @@ remote_hosts=127.0.0.1
 # RETURN_CUSTOM_STATUS.code=
 # RETURN_CUSTOM_STATUS.message=
 
+#---------------------------------------------------------------------------
+# HTTP Header Manager configuration
+#---------------------------------------------------------------------------
+# Save memory by sharing HTTP Header Manager across threads.
+# The drawback is that HTTP Header Manager's can't be modified in the runtime
+# as all the threads would notice the change.
+# If you need dynamic headers, consider using ${..} functions or variables
+#http.header_manager.is_shareable=true
+
 #---------------------------------------------------------------------------
 # Results file configuration
 #---------------------------------------------------------------------------

src/protocol/http/src/main/java/org/apache/jmeter/protocol/http/control/HeaderManager.java

@@ -29,18 +29,20 @@
 import java.util.List;
 
 import org.apache.jmeter.config.ConfigTestElement;
+import org.apache.jmeter.engine.util.NoThreadClone;
 import org.apache.jmeter.gui.Replaceable;
 import org.apache.jmeter.testelement.TestElement;
 import org.apache.jmeter.testelement.property.CollectionProperty;
 import org.apache.jmeter.testelement.property.JMeterProperty;
+import org.apache.jmeter.util.JMeterUtils;
 import org.apache.jorphan.util.JOrphanUtils;
 
 /**
  * This class provides an interface to headers file to pass HTTP headers along
  * with a request.
  *
  */
-public class HeaderManager extends ConfigTestElement implements Serializable, Replaceable {
+public class HeaderManager extends ConfigTestElement implements Serializable, Replaceable, NoThreadClone {
 
     private static final long serialVersionUID = 240L;
 
@@ -57,9 +59,24 @@ public HeaderManager() {
         setProperty(new CollectionProperty(HEADERS, new ArrayList<>()));
     }
 
+    @Override
+    public boolean isShareable() {
+        return JMeterUtils.getPropDefault("http.header_manager.is_shareable", true); // $NON-NLS-1$
+    }
+
+    private void assertMutable() {
+        if (isRunningVersion()) {
+            throw new IllegalStateException(
+                    "Cannot modify HeaderManager " + getName() + " while test is running. " +
+                            "If you need dynamic headers, prefer using ${...} functions in variables if you need dynamic headers."
+            );
+        }
+    }
+
     /** {@inheritDoc} */
     @Override
     public void clear() {
+        assertMutable();
         super.clear();
         setProperty(new CollectionProperty(HEADERS, new ArrayList<>()));
     }
@@ -160,13 +177,15 @@ public void addFile(String headerFile) throws IOException {
      * @param h {@link Header} to add
      */
     public void add(Header h) {
+        assertMutable();
         getHeaders().addItem(h);
     }
 
     /**
      * Add an empty header.
      */
     public void add() {
+        assertMutable();
         getHeaders().addItem(new Header());
     }
 
@@ -176,6 +195,7 @@ public void add() {
      * @param index index from the header to remove
      */
     public void remove(int index) {
+        assertMutable();
         getHeaders().remove(index);
     }
 
@@ -224,6 +244,7 @@ public Header getFirstHeaderNamed(final String name) {
      * @param name header name
      */
     public void removeHeaderNamed(String name) {
+        assertMutable();
         List<Integer> removeIndices = new ArrayList<>();
         for (int i = getHeaders().size() - 1; i >= 0; i--) {
             Header header = (Header) getHeaders().get(i).getObjectValue();
@@ -304,6 +325,7 @@ public HeaderManager merge(TestElement element) {
 
     @Override
     public int replace(String regex, String replaceBy, boolean caseSensitive) throws Exception {
+        assertMutable();
         final CollectionProperty hdrs = getHeaders();
         int totalReplaced = 0;
         for (int i = 0; i < hdrs.size(); i++) {

xdocs/changes.xml

@@ -75,6 +75,7 @@ Summary
 <h3>HTTP Samplers and Test Script Recorder</h3>
 <ul>
   <li><pr>5911</pr> Use Caffeine for caching HTTP headers instead of commons-collections4 LRUMap</li>
+  <li><pr>727</pr> Save memory when test plan contains lots of HTTP Header Manager elements by sharing the managers across threads (add NoThreadClone to HeaderManager)</li>
 </ul>
 
 <h3>Other samplers</h3>

xdocs/usermanual/properties_reference.xml

@@ -602,6 +602,23 @@ JMETER-SERVER</source>
 </property>
 </properties>
 </section>
+
+  <section name="&sect-num;.14 HTTP Header Manager configuration" anchor="http_header_manager">
+    <properties>
+      <property name="http.header_manager.is_shareable">
+        By default, HTTP Header Manager elements are shared between threads. It enables to save memory by not
+        cloning the elements for each thread, however, the drawback is that HTTP Header Manager's can't be
+        modified in the runtime.<br/>
+        However, HTTP Header Managers still support <code>${...}</code> functions and variables, so it is still
+        possible to have dynamic headers.
+        <br/>
+        Defaults to:
+        <code>true</code>
+      </property>
+    </properties>
+  </section>
+
+
 <section name="&sect-num;.15 Results file configuration" anchor="results_file_config">
 <properties>
 <property name="jmeter.save.saveservice.output_format">