BcelTypeMunger.mungeMethodDelegate: only use 'synchronized' when necessary

Relates to #198. Now, we create a delegate method body which basically
looks as follows:

public void methodOne() {
  if (this.ajc$instance$MyAspect$MyMixin == null) {
    synchronized(this) {
      if (this.ajc$instance$MyAspect$MyMixin == null) {
        this.ajc$instance$MyAspect$MyMixin = MyAspect.aspectOf().createImplementation(this);
      }
    }
  }
  this.ajc$instance$MyAspect$MyMixin.methodOne();
}

The idea for the outer null check is from @aclement, see
https://github.com/eclipse/org.aspectj/pull/205#issuecomment-1371556080.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

diff --git a/tests/features164/declareMixin/CaseEConcurrent.java b/tests/features164/declareMixin/CaseEConcurrent.java
index df1e1377418d3eda28ded5bb84b5e3cf79ed6179..874f249d54f2cadc9b84ffd3696cdbd21c3cc9c3 100644 (file)
--- a/tests/features164/declareMixin/CaseEConcurrent.java
+++ b/tests/features164/declareMixin/CaseEConcurrent.java
@@ -39,9 +39,11 @@ public class CaseEConcurrent {
   // the byte code, e.g. with JDK tool 'javap -v'.
   /*
   public void doSomething() {
-    synchronized (this) {
-      if (id == null)
-        id = "doing something";
+    if (id == null) {
+      synchronized (this) {
+        if (id == null)
+          id = "doing something";
+      }
     }
     callMe(id);
   }

diff --git a/weaver/src/main/java/org/aspectj/weaver/bcel/BcelTypeMunger.java b/weaver/src/main/java/org/aspectj/weaver/bcel/BcelTypeMunger.java
index 0ecad3606ab3336903d77d0d8cf0321550ab15ec..3463d444aebcf9c4d24982f6045243d475ceecfd 100644 (file)
--- a/weaver/src/main/java/org/aspectj/weaver/bcel/BcelTypeMunger.java
+++ b/weaver/src/main/java/org/aspectj/weaver/bcel/BcelTypeMunger.java
@@ -1436,6 +1436,26 @@ public class BcelTypeMunger extends ConcreteTypeMunger {
                        InstructionList body = new InstructionList();
                        InstructionFactory fact = gen.getFactory();
 
+                       // Create a delegate method body which basically looks as follows:
+                       //
+                       // public void methodOne() {
+                       //   if (this.ajc$instance$MyAspect$MyMixin == null) {
+                       //     synchronized(this) {
+                       //       if (this.ajc$instance$MyAspect$MyMixin == null) {
+                       //         this.ajc$instance$MyAspect$MyMixin = MyAspect.aspectOf().createImplementation(this);
+                       //       }
+                       //     }
+                       //   }
+                       //   this.ajc$instance$MyAspect$MyMixin.methodOne();
+                       // }
+
+                       // Before synchronising on 'this', perform a preliminary null check on the delegate field. Only if it is null,
+                       // it makes sense to synchronise, then check for null again and initialise the delegate, if null.
+                       body.append(InstructionConstants.ALOAD_0);
+                       body.append(Utility.createGet(fact, munger.getDelegate(weaver.getLazyClassGen().getType())));
+                       InstructionBranch outerIfNonNull = InstructionFactory.createBranchInstruction(Constants.IFNONNULL, null);
+                       body.append(outerIfNonNull);
+
                        // Wrap delegate field initialisation in 'synchronized(this)' block - MONITORENTER (beginning of 'try')
                        body.append(InstructionConstants.ALOAD_0);
                        body.append(InstructionConstants.MONITORENTER);
@@ -1444,8 +1464,8 @@ public class BcelTypeMunger extends ConcreteTypeMunger {
                        // synchronized block, see https://docs.oracle.com/javase/specs/jvms/se17/html/jvms-3.html#jvms-3.14.
                        InstructionHandle tryStart = body.append(InstructionConstants.ALOAD_0);
                        body.append(Utility.createGet(fact, munger.getDelegate(weaver.getLazyClassGen().getType())));
-                       InstructionBranch ifNonNull = InstructionFactory.createBranchInstruction(Constants.IFNONNULL, null);
-                       body.append(ifNonNull);
+                       InstructionBranch innerIfNonNull = InstructionFactory.createBranchInstruction(Constants.IFNONNULL, null);
+                       body.append(innerIfNonNull);
 
                        // Create and store a new instance
                        body.append(InstructionConstants.ALOAD_0); // 'this' is where we'll store the field value
@@ -1494,7 +1514,7 @@ public class BcelTypeMunger extends ConcreteTypeMunger {
 
                        // Wrap delegate field initialisation in 'synchronized(this)' block - MONITOREXIT (end of 'try')
                        InstructionHandle ifNonNullElse = body.append(InstructionConstants.ALOAD_0);
-                       ifNonNull.setTarget(ifNonNullElse);
+                       innerIfNonNull.setTarget(ifNonNullElse);
                        body.append(InstructionConstants.MONITOREXIT);
 
                        // There was no error in the 'synchronized(this)' block -> jump to first instruction after exception handler
@@ -1519,6 +1539,8 @@ public class BcelTypeMunger extends ConcreteTypeMunger {
                        InstructionHandle afterTryCatch = body.append(InstructionConstants.ALOAD_0);
                        // Tell 'gotoAfterTryCatch' where to find the first statement after the exception handler
                        gotoAfterTryCatch.setTarget(afterTryCatch);
+                       // The outer delegate field null check should also jump to the same place, if the delegate field is not null
+                       outerIfNonNull.setTarget(afterTryCatch);
                        body.append(Utility.createGet(fact, munger.getDelegate(weaver.getLazyClassGen().getType())));
 
                        // args