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_r298841873
##########
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();
}
public StackTraceElement getStackTraceElement(final int depth) {
return stackWalker.walk(s ->
s.skip(depth).findFirst()).get().toStackTraceElement();
}
+
+ static final class CallerLocator implements
Predicate<StackWalker.StackFrame> {
+
+ private String fqcn;
+
+ private boolean foundFqcn = false;
+ private boolean foundLogger = false;
+
+ public 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;
+ }
Review comment:
It took me a few reads through to understand how this works, would you mind
adding a comment to make it easier to understand?
Maybe something along these lines (if I understand correctly)
```java
/**
* States:
* 1. foundFqcn=false, foundLogger=false Nested in logging code, we must
first
* work our way up to frames from the loggers fully qualified class name.
* 2. foundFqcn=true, foundLogger=false Once we've found the logger, the next
* class we encounter which does not match the loggers fully qualified
class
* name is the caller.
* 3. foundFqcn=true, foundLogger=true Terminal state, if execution
continues after
* the logger is found, the caller is doing something incorrectly.
*/
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;
}
}
// Unexpected usage, CallerLocator.test has been invoked after the
logger has been found.
return false;
}
```
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