Refactor flashlight-agent attachment code to simplify it.

Author: OndroMih

nucleus/flashlight/framework/src/main/java/org/glassfish/flashlight/FlashlightLoggerInfo.java

@@ -132,11 +132,6 @@ public static Logger getLogger() {
             level = "WARNING")
     public static final String NO_ATTACH_API = LOGMSG_PREFIX + "-00510";
 
-    @LogMessageInfo(
-            message = "Error while getting Instrumentation object from ProbeAgentMain",
-            level = "WARNING")
-    public static final String NO_ATTACH_GET = LOGMSG_PREFIX + "-00511";
-
     @LogMessageInfo(
             message = "DTrace is not available.",
             cause="This is caused if following are missing: \n1. JDK 7 is required to run DTrace\n2. glassfish-dtrace.jar value-add is required for DTrace",

nucleus/flashlight/framework/src/main/java/org/glassfish/flashlight/cli/EnableMonitoring.java

@@ -126,7 +126,7 @@ public void execute(AdminCommandContext context) {
          if (!AgentAttacher.attachAgent(pidInt, options)) {
             ActionReport.MessagePart part = report.getTopMessagePart().addChild();
             part.setMessage(localStrings.getLocalString("attach.agent.exception",
-                    "Can't attach the agent to the JVM. Restart with the flash-light agent attached by the -javaagent command line parameter"));
+                    "Can't attach the monitoring agent to the JVM. Restart with the flashlight-agent.jar attached by the -javaagent command line parameter"));
             report.setActionExitCode(ActionReport.ExitCode.FAILURE);
             return;
         }

nucleus/flashlight/framework/src/main/java/org/glassfish/flashlight/impl/client/AgentAttacher.java

@@ -13,51 +13,88 @@
  *
  * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
  */
-
 package org.glassfish.flashlight.impl.client;
 
+import java.lang.instrument.Instrumentation;
+import java.lang.reflect.Method;
+import java.util.Optional;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import org.glassfish.flashlight.FlashlightLoggerInfo;
+
+
 /**
  * created May 26, 2011
+ *
  * @author Byron Nevins
  */
 public final class AgentAttacher {
+
+    private static final String AGENT_CLASSNAME = "org.glassfish.flashlight.agent.ProbeAgentMain";
+
+    private static final Logger logger = FlashlightLoggerInfo.getLogger();
+
+    public static Optional<Instrumentation> getInstrumentation() {
+        try {
+            Class agentMainClass = null;
+            ClassLoader classLoader = ClassLoader.getSystemClassLoader();
+
+            try {
+                agentMainClass = classLoader.loadClass(AGENT_CLASSNAME);
+            } catch (Throwable t) {
+                // need throwable, not Exception - it may throw an Error!
+                // try one more time after attempting to attach.
+                AgentAttacher.attachAgent();
+                // might throw
+                agentMainClass = classLoader.loadClass(AGENT_CLASSNAME);
+            }
+
+            Method mthd = agentMainClass.getMethod("getInstrumentation", null);
+            return Optional.ofNullable((Instrumentation) mthd.invoke(null, null));
+        } catch (Throwable throwable) {
+            logger.log(Level.WARNING, "Error while getting Instrumentation object from ProbeAgentMain", throwable);
+            return Optional.empty();
+        }
+    }
+
     public synchronized static boolean canAttach() {
         return canAttach;
     }
 
     public synchronized static boolean isAttached() {
         try {
-            if (!canAttach)
+            if (!canAttach) {
                 return false;
+            }
 
             return AgentAttacherInternal.isAttached();
-        }
-        catch (Throwable t) {
+        } catch (Throwable t) {
             return false;
         }
     }
 
     public synchronized static boolean attachAgent() {
 
         try {
-            if (!canAttach)
+            if (!canAttach) {
                 return false;
+            }
 
             return attachAgent(-1, "");
-        }
-        catch (Throwable t) {
+        } catch (Throwable t) {
             return false;
         }
     }
 
     public synchronized static boolean attachAgent(int pid, String options) {
         try {
-            if (!canAttach)
+            if (!canAttach) {
                 return false;
+            }
 
             return AgentAttacherInternal.attachAgent(pid, options);
-        }
-        catch (Throwable t) {
+        } catch (Throwable t) {
             return false;
         }
     }
@@ -71,8 +108,7 @@ public synchronized static boolean attachAgent(int pid, String options) {
             // this is a distinct possibility in embedded mode.
             AgentAttacherInternal.isAttached();
             b = true;
-        }
-        catch (Throwable t) {
+        } catch (Throwable t) {
             b = false;
         }
         canAttach = b;

nucleus/flashlight/framework/src/main/java/org/glassfish/flashlight/impl/client/AgentAttacherInternal.java

@@ -48,7 +48,6 @@ static boolean attachAgent() {
         return attachAgent(-1, "");
     }
 
-    private static final String AGENT_CLASSNAME = "org.glassfish.flashlight.agent.ProbeAgentMain";
     static boolean attachAgent(long pid, String options) {
         try {
             if (isAttached) {
@@ -57,11 +56,9 @@ static boolean attachAgent(long pid, String options) {
 
             if (pid < 0) {
 
-                try {
-                    ClassLoader.getSystemClassLoader().loadClass(AGENT_CLASSNAME);
+                if (AgentAttacher.getInstrumentation().isPresent()) {
                     isAttached = true;
                     return true;
-                } catch (Throwable t) {
                 }
 
                 pid = ProcessHandle.current().pid();

nucleus/flashlight/framework/src/main/java/org/glassfish/flashlight/impl/client/ProbeProviderClassFileTransformer.java

@@ -48,7 +48,6 @@
 
 import static org.glassfish.embeddable.GlassFishVariable.INSTALL_ROOT;
 import static org.glassfish.flashlight.FlashlightLoggerInfo.NO_ATTACH_API;
-import static org.glassfish.flashlight.FlashlightLoggerInfo.NO_ATTACH_GET;
 import static org.glassfish.flashlight.FlashlightLoggerInfo.REGISTRATION_ERROR;
 import static org.glassfish.flashlight.FlashlightLoggerInfo.RETRANSFORMATION_ERROR;
 import static org.glassfish.flashlight.FlashlightLoggerInfo.WRITE_ERROR;
@@ -82,7 +81,6 @@ public class ProbeProviderClassFileTransformer implements ClassFileTransformer {
     private static final Instrumentation instrumentation;
     private static boolean _debug = Boolean.parseBoolean(Utility.getEnvOrProp("AS_DEBUG"));
     private static boolean emittedAttachUnavailableMessageAlready = false;
-    private static final String AGENT_CLASSNAME = "org.glassfish.flashlight.agent.ProbeAgentMain";
     private static final Logger logger = FlashlightLoggerInfo.getLogger();
 
     private ProbeProviderClassFileTransformer(Class providerClass) {
@@ -494,28 +492,7 @@ private Method getMethod(FlashlightProbe probe) throws NoSuchMethodException {
         if (AgentAttacher.canAttach()) {
             canAttach = true;
 
-            try {
-                ClassLoader classLoader = ClassLoader.getSystemClassLoader();
-
-                try {
-                    agentMainClass = classLoader.loadClass(AGENT_CLASSNAME);
-                }
-                catch (Throwable t) {
-                    // need throwable, not Exception - it may throw an Error!
-                    // try one more time after attempting to attach.
-                    AgentAttacher.attachAgent();
-                    // might throw
-                    agentMainClass = classLoader.loadClass(AGENT_CLASSNAME);
-                }
-
-                Method mthd = agentMainClass.getMethod("getInstrumentation", null);
-                nonFinalInstrumentation = (Instrumentation) mthd.invoke(null, null);
-            }
-            catch (Throwable t) {
-                nonFinalInstrumentation = null;
-                // save it for nice neat message code below
-                throwable = t;
-            }
+            nonFinalInstrumentation = AgentAttacher.getInstrumentation().orElse(null);
         }
         // set the final
         instrumentation = nonFinalInstrumentation;
@@ -525,7 +502,7 @@ private Method getMethod(FlashlightProbe probe) throws NoSuchMethodException {
         } else if (instrumentation != null) {
             Log.info("yes.attach.api", instrumentation);
         } else {
-            logger.log(Level.WARNING, NO_ATTACH_GET, throwable);
+            logger.log(Level.WARNING, "Could not attach agent");
         }
     }
 }