[GitHub] [logging-log4j2] carterkozak commented on a change in pull request #289: LOG4J2-2644 - Improve performance of getting location info

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carterkozak commented on a change in pull request #289: LOG4J2-2644 - Improve performance of getting location info
URL: https://github.com/apache/logging-log4j2/pull/289#discussion_r298841455
 
 

 ##########
 File path: log4j-api-java9/src/main/java/org/apache/logging/log4j/util/StackLocator.java
 ##########
 @@ -72,15 +78,40 @@ private StackLocator() {
     }
 
     public StackTraceElement calcLocation(final String fqcnOfLogger) {
-        return stackWalker.walk(
-                s -> s.dropWhile(f -> !f.getClassName().equals(fqcnOfLogger)) // drop the top frames until we reach the logger
-                        .dropWhile(f -> f.getClassName().equals(fqcnOfLogger)) // drop the logger frames
-                        .findFirst())
-                .get()
-                .toStackTraceElement();
+        return walker.walk(s -> s.filter(LOCATOR.get().setFqcn(fqcnOfLogger)).findFirst()).get().toStackTraceElement();
 
 Review comment:
   We may want `CallerLocator` to implement `Function<Stream<StackWalker.StackFrame>, Optional<StackWalker.StackFrame>>` to avoid the lambda allocation for `s -> s.filter(LOCATOR.get().setFqcn(fqcnOfLogger)).findFirst()`
   ```suggestion
           return walker.walk(LOCATOR.get().setFqcn(fqcnOfLogger)).get().toStackTraceElement();
   ```
   
   using something like this:
   
   ```java
   static final class CallerLocator implements Predicate<StackWalker.StackFrame>,
           Function<Stream<StackWalker.StackFrame>, Optional<StackWalker.StackFrame>> {
   
       private String fqcn;
   
       private boolean foundFqcn = false;
       private boolean foundLogger = false;
   
       CallerLocator setFqcn(String fqcn) {
           this.fqcn = fqcn;
           this.foundFqcn = false;
           this.foundLogger = false;
           return this;
       }
   
       @Override
       public boolean test(StackWalker.StackFrame t) {
           final String className = t.getClassName();
           if (!foundLogger) {
               if (!foundFqcn) {
                   foundFqcn = className.equals(fqcn);
                   return false;
               } else if (!className.equals(fqcn)) {
                   foundLogger = true;
                   return true;
               }
           }
           return false;
       }
   
       @Override
       public Optional<StackWalker.StackFrame> apply(Stream<StackWalker.StackFrame> stackFrameStream) {
           return stackFrameStream.filter(this).findFirst();
       }
   }
   ```
   
   I'm not sure how much that helps if at all, I haven't looked into how much allocation StackWalker does internally.

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