ppkarwasz commented on code in PR #3418:
URL: https://github.com/apache/logging-log4j2/pull/3418#discussion_r1932333472
##########
log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/InternalLoggerRegistry.java:
##########
@@ -147,44 +147,43 @@ public Logger computeIfAbsent(
return logger;
}
+ // Creating a logger is expensive and might cause lookups and locks,
possibly deadlocks:
+ // https://github.com/apache/logging-log4j2/issues/3252
+ // https://github.com/apache/logging-log4j2/issues/3399
+ //
+ // Creating loggers without a lock, allows multiple threads to create
loggers in parallel, which also
+ // improves performance.
+ // Since all loggers with the same parameters are equivalent, we can
safely return the logger from the
+ // thread that finishes first.
+ Logger newLogger = loggerSupplier.apply(name, messageFactory);
+
+ // Report name and message factory mismatch if there are any
+ final String loggerName = newLogger.getName();
+ final MessageFactory loggerMessageFactory =
newLogger.getMessageFactory();
+ if (!loggerName.equals(name) ||
!loggerMessageFactory.equals(messageFactory)) {
+ StatusLogger.getLogger()
+ .error(
+ "Newly registered logger with name `{}` and
message factory `{}`, is requested to be associated with a different name `{}`
or message factory `{}`.\n"
+ + "Effectively the message factory of the
logger will be used and the other one will be ignored.\n"
+ + "This generally hints a problem at the
logger context implementation.\n"
+ + "Please report this using the Log4j
project issue tracker.",
+ loggerName,
+ loggerMessageFactory,
+ name,
+ messageFactory);
+ }
+
// Write lock slow path: Insert the logger
writeLock.lock();
try {
- // See if the logger is created by another thread in the meantime
- final Map<String, WeakReference<Logger>> loggerRefByName =
-
loggerRefByNameByMessageFactory.computeIfAbsent(messageFactory, ignored -> new
HashMap<>());
- WeakReference<Logger> loggerRef = loggerRefByName.get(name);
- if (loggerRef != null && (logger = loggerRef.get()) != null) {
- return logger;
- }
-
- // Create the logger
- logger = loggerSupplier.apply(name, messageFactory);
-
- // Report name and message factory mismatch if there are any
- final String loggerName = logger.getName();
- final MessageFactory loggerMessageFactory =
logger.getMessageFactory();
- if (!loggerMessageFactory.equals(messageFactory)) {
- StatusLogger.getLogger()
- .error(
- "Newly registered logger with name `{}` and
message factory `{}`, is requested to be associated with a different name `{}`
or message factory `{}`.\n"
- + "Effectively the message factory of
the logger will be used and the other one will be ignored.\n"
- + "This generally hints a problem at
the logger context implementation.\n"
- + "Please report this using the Log4j
project issue tracker.",
- loggerName,
- loggerMessageFactory,
- name,
- messageFactory);
- // Register logger under alternative keys
- loggerRefByNameByMessageFactory
- .computeIfAbsent(loggerMessageFactory, ignored -> new
HashMap<>())
- .putIfAbsent(loggerName, new WeakReference<>(logger));
- }
-
- // Insert the logger
- loggerRefByName.put(name, new WeakReference<>(logger));
- return logger;
+ Logger currentLogger = loggerRefByNameByMessageFactory
+ .computeIfAbsent(messageFactory, ignored -> new
HashMap<>())
+ .computeIfAbsent(name, ignored -> new
WeakReference<>(newLogger))
+ .get();
+ // A replacement for Reference.reachabilityFence() from Java 9.
+ // Prevents `newLogger` to become unreachable in the lines above.
+ return currentLogger != null ? currentLogger : newLogger;
Review Comment:
You might be right, but I am not eager to risk another `2.24.1` :smile:
My reasoning was:
- We get a `WR` to `newLogger`.
- At that point in code `newLogger` has already been referenced for the last
time. The `() -> new WeakReference<>(newLogger)` has already been used and can
be reclaimed.
- If a GC occurs just before the `WR.get()`, the reference might be emptied.
Since I reference `newLogger` on line 186, `currentLogger` will never be
`null`.
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