Just for reference, few methods which were synchronized earlier in log4j1.x but
not anymore in log4j1.x bridge.
1. public void addAppender(final Appender appender)
2. public Appender getAppender(final String name)
3. public void removeAppender(final Appender appender)
4. public void removeAllAppenders()
I suspect the methods relating to configuration or getting appenders would only
be problematic at initialization time.
The methods we might need to watch for are ones relating to the runtime logging
methods (e.g. info() warn()). May be the methods chained to in log4j2 are not
threadsafe. But maybe the bridge itself has some thread safety issues.
Pasting sample code here (Please Note that in this test program, class
CustomLogger is a dummy class, which you would need to replace with your logger)
package test.common;
import org.apache.log4j.Logger;
import sun.management.VMManagement;
import java.io.BufferedWriter;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
class CustomLogger extends Logger {
protected CustomLogger(String name) {
super(name);
}
public static void LogError(String s, Object o) {
}
}
public class JavaLoggingMultiThTest {
public int pid;
private class LoggerTask implements Callable<LoggerTask> {
public synchronized void run() {
int logMsgWrittenPerThread;
int maxLogMsgsPerThread = 52224;
for(logMsgWrittenPerThread = 1; logMsgWrittenPerThread <=
maxLogMsgsPerThread; logMsgWrittenPerThread++) {
CustomLogger.LogError("p:" + pid + ", LM:" +
Integer.toString(logMsgWrittenPerThread), null);
}
}
@Override public synchronized LoggerTask call() {
run();
return this;
}
}
public synchronized void runLoggerTaskMultipleThreads() {
int numThreads = 20;
ArrayList<LoggerTask> loggerTaskList = new ArrayList<LoggerTask>();
for(int i=0; i< numThreads; i++) {
loggerTaskList.add(new LoggerTask());
}
ExecutorService pool = Executors.newFixedThreadPool(numThreads);
try {
Instant startTS = Instant.now();
List<Future<LoggerTask>> waiters = pool.invokeAll(loggerTaskList);
boolean allEnded = false;
for (Future waiter : waiters) {
try {
waiter.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
do {
try {
pool.shutdown();
allEnded = pool.awaitTermination(1, TimeUnit.MINUTES);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("Interrupted, for some reason");
}
if (!allEnded)
System.out.println("Not ending cleanly");
} while (!allEnded);
Instant endTS = Instant.now();
Duration elapsed = Duration.between(startTS, endTS);
System.out.println("Time taken by current process" + elapsed);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private static int getCurrrentProcessId() throws Exception {
RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
Field jvm = runtime.getClass().getDeclaredField("jvm");
jvm.setAccessible(true);
VMManagement management = (VMManagement) jvm.get(runtime);
Method method = management.getClass().getDeclaredMethod("getProcessId");
method.setAccessible(true);
return (Integer) method.invoke(management);
}
public static void main(String[] args) throws IOException {
BufferedWriter writer =
Files.newBufferedWriter(Paths.get("C:\\Users\\Pooja.Pandey\\vdrws.log"));
writer.write("");
writer.flush();
JavaLoggingMultiThTest javaLoggingMultiThTest = new
JavaLoggingMultiThTest();
try {
javaLoggingMultiThTest.pid = getCurrrentProcessId();
} catch (Exception e) {
e.printStackTrace();
}
javaLoggingMultiThTest.runLoggerTaskMultipleThreads();
}
}
From: Pooja Pandey <pooja.pan...@asg.com.INVALID>
Sent: Friday, March 25, 2022 4:37 AM
To: Log4J Users List <log4j-user@logging.apache.org>
Subject: Synchronization issue in multithreading (Losing huge data in
multithreading) with log4j 1.x bridge (2.17.2)
*** External email: Verify sender before opening attachments or links ***
Hi,
In our application we have migrated from log4j1.x to log4j1.x bridge. With
Log4j1.x there was no issue with multithreading but with log4j 1.x bridge we
have noticed that in multithreading environment there is a huge data loss while
logging, however single thread works fine. I see that in Category.java which
Logger extends; many methods are not synchronized any more in log4j1.x bridge
however which were in case of log4j1.x. I suspect this could be root cause of
this multithreading problem. Please let me know if you have any idea.
I have compared Category.java which is a kind of core class for logging
functionality in Log4j1.x and Log4j1.x bridge and I see that many methods which
we are using were synchronized in log4j1.x but NOT in log4j1.x bridge. I think
this could be one of the root causes leading to this problem.
[cid:image001.png@01D84001.E6BD9A00]
Log4j1.x: synchronized public Appender getAppender(String name)
Log4j1.x bridge: public Appender getAppender(final String name)
[cid:image002.png@01D84001.E6BD9A00]
package test.common;
import org.apache.log4j.Logger;
import sun.management.VMManagement;
import java.io.BufferedWriter;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
class CustomLogger extends Logger {
protected CustomLogger(String name) {
super(name);
}
public static void LogError(String s, Object o) {
}
}
public class JavaLoggingMultiThTest {
public int pid;
private class LoggerTask implements Callable<LoggerTask> {
public synchronized void run() {
int logMsgWrittenPerThread;
int maxLogMsgsPerThread = 52224;
for(logMsgWrittenPerThread = 1; logMsgWrittenPerThread <=
maxLogMsgsPerThread; logMsgWrittenPerThread++) {
CustomLogger.LogError("p:" + pid + ", LM:" +
Integer.toString(logMsgWrittenPerThread), null);
}
}
@Override public synchronized LoggerTask call() {
run();
return this;
}
}
public synchronized void runLoggerTaskMultipleThreads() {
int numThreads = 20;
ArrayList<LoggerTask> loggerTaskList = new ArrayList<LoggerTask>();
for(int i=0; i< numThreads; i++) {
loggerTaskList.add(new LoggerTask());
}
ExecutorService pool = Executors.newFixedThreadPool(numThreads);
try {
Instant startTS = Instant.now();
List<Future<LoggerTask>> waiters = pool.invokeAll(loggerTaskList);
boolean allEnded = false;
for (Future waiter : waiters) {
try {
waiter.get();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
do {
try {
pool.shutdown();
allEnded = pool.awaitTermination(1, TimeUnit.MINUTES);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("Interrupted, for some reason");
}
if (!allEnded)
System.out.println("Not ending cleanly");
} while (!allEnded);
Instant endTS = Instant.now();
Duration elapsed = Duration.between(startTS, endTS);
System.out.println("Time taken by current process" + elapsed);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private static int getCurrrentProcessId() throws Exception {
RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
Field jvm = runtime.getClass().getDeclaredField("jvm");
jvm.setAccessible(true);
VMManagement management = (VMManagement) jvm.get(runtime);
Method method = management.getClass().getDeclaredMethod("getProcessId");
method.setAccessible(true);
return (Integer) method.invoke(management);
}
public static void main(String[] args) throws IOException {
BufferedWriter writer =
Files.newBufferedWriter(Paths.get("C:\\Users\\Pooja.Pandey\\vdrws.log"));
writer.write("");
writer.flush();
JavaLoggingMultiThTest javaLoggingMultiThTest = new
JavaLoggingMultiThTest();
try {
javaLoggingMultiThTest.pid = getCurrrentProcessId();
} catch (Exception e) {
e.printStackTrace();
}
javaLoggingMultiThTest.runLoggerTaskMultipleThreads();
}
}
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