Add synchronization around use of JDT code formatter to prevent NPE/race condition (#6079)

* Add synchronization around use of JDT code formatter to prevent NPE/race condition

* Add changelog

Author: alextwoods

.changes/next-release/bugfix-AWSSDKforJavaV2-e335804.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java V2",
+    "contributor": "",
+    "description": "Add synchronization around use of JDT code formatter to prevent NPE/race condition during code generation."
+}

codegen-lite/src/main/java/software/amazon/awssdk/codegen/lite/emitters/JavaCodeFormatter.java

@@ -32,6 +32,7 @@
 public class JavaCodeFormatter implements CodeTransformer {
 
     private static final Map<String, Object> DEFAULT_FORMATTER_OPTIONS;
+    private static final Object lock = new Object();
 
     static {
         DEFAULT_FORMATTER_OPTIONS = DefaultCodeFormatterConstants.getEclipseDefaultSettings();
@@ -89,10 +90,16 @@ public JavaCodeFormatter(final Map<String, Object> overrideOptions) {
 
     @Override
     public String apply(String contents) {
-        TextEdit edit = codeFormatter.format(
+        TextEdit edit;
+        // There is a race condition in the org.eclipse.jdt.internal.formatter.DefaultCodeFormatter in version 3.10.0.
+        // The static PROBING_SCANNER can have its state changed by multiple threads.
+        // Synchronize our usage of that class to ensure we don't hit this.
+        synchronized (lock) {
+            edit = codeFormatter.format(
                 CodeFormatter.K_COMPILATION_UNIT
                 | CodeFormatter.F_INCLUDE_COMMENTS, contents, 0,
                 contents.length(), 0, System.lineSeparator());
+        }
 
         if (edit == null) {
             // TODO log a fatal or warning here. Throwing an exception is causing the actual freemarker error to be lost

codegen/src/main/java/software/amazon/awssdk/codegen/emitters/JavaCodeFormatter.java

@@ -33,6 +33,7 @@
 public class JavaCodeFormatter implements CodeTransformer {
 
     private static final Map<String, Object> DEFAULT_FORMATTER_OPTIONS;
+    private static final Object lock = new Object();
 
     static {
         DEFAULT_FORMATTER_OPTIONS = DefaultCodeFormatterConstants.getEclipseDefaultSettings();
@@ -90,10 +91,16 @@ public JavaCodeFormatter(final Map<String, Object> overrideOptions) {
 
     @Override
     public String apply(String contents) {
-        TextEdit edit = codeFormatter.format(
+        TextEdit edit;
+        // There is a race condition in the org.eclipse.jdt.internal.formatter.DefaultCodeFormatter in version 3.10.0.
+        // The static PROBING_SCANNER can have its state changed by multiple threads.
+        // Synchronize our usage of that class to ensure we don't hit this.
+        synchronized (lock) {
+            edit = codeFormatter.format(
                 CodeFormatter.K_COMPILATION_UNIT
                 | CodeFormatter.F_INCLUDE_COMMENTS, contents, 0,
                 contents.length(), 0, Constant.LF);
+        }
 
         if (edit == null) {
             // TODO log a fatal or warning here. Throwing an exception is causing the actual freemarker error to be lost