commons-lang2.6在高并发下使用ExceptionUtils.getFullStackTrace()获取异常详情导致的性能下降

某天，在不知情的情况下，实施私自接入了某其他平台数据，由于数据不规范，导致生产出现阶段性大面积异常报错，有大量线程阻塞，处于BLOCKED状态，应用性能下降一倍。通过线程堆栈日志定位到：阻塞线程都阻塞在org.apache.commons.lang.exception.ExceptionUtils.getCause()处，并且在等待的是一个对象锁，查看源码（commons-lang的2.6版本）发现getCause中会先获取锁，然后通过反射的方式获取异常的详情，反射存在性能问题，在高并发下，导致大量线程阻塞。

通过如下案例进行模拟

创建一个2000个核心线程数的线程池，线程名命名为：test-exception-，在线程池中跑着会抛出类型转换异常的线程，在对异常进行捕获的时候使用ExceptionUtils.getFullStackTrace(e)获取异常的详情信息。

import org.apache.commons.lang.exception.ExceptionUtils;
import org.springframework.scheduling.concurrent.CustomizableThreadFactory;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class TestException {

    public static void main(String[] args) {
        CustomizableThreadFactory customizableThreadFactory = new CustomizableThreadFactory("test-exception-");
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2000, 2000, 0L,
                TimeUnit.MILLISECONDS, new LinkedBlockingQueue(), customizableThreadFactory);
        for(int i=0; i<20000; i++) {
            Run run = new Run();
            threadPoolExecutor.submit(run);
        }
    }

    public static class Run implements Runnable {
        @Override
        public void run() {
            try {
                Map map = new HashMap();
                map.put("key", "3");
                Integer value = (Integer) map.get("key");
            } catch (Exception e) {
                System.out.println(Thread.currentThread().getName() + ExceptionUtils.getFullStackTrace(e));
            }
        }
    }
}

启动程序，打印dump日志，通过dump日志可以清晰地看到如下日志内容，在线程test-exception-1539运行的时候，获取到对象锁0x00000000dc112b90：- locked <0x00000000dc112b90> (a java.lang.Object)，此时其他线程会被阻塞，处于BLOCKED状态，等待锁0x00000000dc112b90：- waiting to lock <0x00000000de112b90> (a java.lang.Object)

"test-exception-1543" #1553 prio=5 os_prio=0 tid=0x000000005c4bf800 nid=0xe338 waiting for monitor entry [0x000000007cffe000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.apache.commons.lang.exception.ExceptionUtils.getCause(ExceptionUtile.java:282]]
    - waiting to lock <0x00000000de112b90> (a java.lang.Object)
    at org. apache.commons.lang.exception.ExceptionUtils.getThrowableList(ExceptionUtils.java:571)
    at org.apache.commons.lang.exception.ExceptionUtils.getThrowables(ExceptionUtils.java:544)
    at org.apache.commons.lang.exception.ExceptionUtils.getFullStackTrace(ExceptionUtils.java:870)
    at ExceptionTest$Run.run(ExceptionTest.java:36)
    at java.util.concurrent.Executora$RunnableAdapter.call(Executora.java:511)
    at at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent .ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

"test-exception-1540" #1550 prio=5 os_prio=0 tid=0x000000005c4c4000 nid=0xe32c waiting for monitor entry [0x000000007ccfe000]
   java.lang.Thread.State: BLOCKED(on object monitor)
   at org.apache.commons.lang.exception.ExceptionUtils.getCause(ExceptionUtile.java:282)
   - waiting to lock <0x00000000de112b90> (a java.lang.Object)
   at org.apache.commons.lang.exception.ExceptionUtils.getThrowableList(ExceptionUtils.java:571)
   at org.apache.commons.lang.exception.ExceptionUtils.getThrowables(ExceptionUtils.java:544)
   at org.apache.commons.lang.exception.ExceptionUtils.getFullStackTrace(ExceptionUtils.java:870)
   at ExceptionTest$Run.run(ExceptionTest.java:36)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
   at java.util.concurrent.FutureTask.run(FutureTask.java:266)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
   at java.lang.Thread.run(Thread.java:745)
"test-exception-1539" #1549 prio=5 os prio=0 tid=0x000000005c4c2800 nid=0xe328 runnable [0x000000007cbfe000]
   java.lang.Thread.State: RUNNABLE
   at java.lang.Class.getMethod0(Class.java: 3017)
   at java.lang.Class.getMethod(Class.java:1784)
   at org.apache.commons.lang.exception.ExceptionUtils.getCauseUsingMethodName(ExceptionUtils.java:386)
   at org.apache.commons.lang.exception.ExceptionUtils.getCause(ExceptionUtils.java:318)
   org.apache.commons.lang.exception.ExceptionUtils.getCause(ExceptionUtila.java:282)
   - locked <0x00000000dc112b90> (a java.lang.Object)
   at org.apache.commons.lang.exception.ExceptionUtils.getThrowableList(ExceptionUtils.java:571)
   at org.apache.commons .lang.exception.ExceptionUtils.getThrowables(ExceptionUtils.java: 544)
   at org.apache.commons.lang.exception.ExceptionUtils.getFullStackTrace(ExceptionUtile.java:870)
   at ExceptionTestSRun.run(ExceptionTest.java:36)
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
   at java.util.concurrent.FutureTask.run(FutureTaak.java:266)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)

所以在高并发的情况下，遇到异常之后，大量线程中只有其中一个线程能得到执行，其他线程处于BLOCKED状态，而且这只是一个辅助功能，在一些对主业务没有影响的异常大量发生的情况下，会导致应用性能的下降。

在ExceptionUtils的getCause()方法内会先锁住CAUSE_METHOD_NAMES_LOCK对象，synchronized(CAUSE_METHOD_NAMES_LOCK)，CAUSE_METHOD_NAMES_LOCK是一个Object对象，获取都对象锁之后，在getCauseUsingMethodName方法里通过throwable.getClass().getMethod(methodName, null)反射的方式获取方法Method，由于JIT编译无法优化等一些原因，导致反射效率比较低，造成了getCause(throwable, CAUSE_METHOD_NAMES)耗时较多，从而在高并发情况下，会导致大量的线程阻塞。

public class ExceptionUtils {
    
    // Lock object for CAUSE_METHOD_NAMES
    private static final Object CAUSE_METHOD_NAMES_LOCK = new Object();
    
    private static String[] CAUSE_METHOD_NAMES = {
        "getCause", "getNextException", "getTargetException", "getException",
        "getSourceException", "getRootCause","getCausedByException","getThrowable",
        "getNested", "getLinkedException", "getNestedException", "getLinkedCause",
    };


    public static String getFullStackTrace(Throwable throwable) {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter(sw, true);
        Throwable[] ts = getThrowables(throwable);
        for (int i = 0; i < ts.length; i++) {
            ts[i].printStackTrace(pw);
            if (isNestedThrowable(ts[i])) {
                break;
            }
        }
        return sw.getBuffer().toString();
    }

    public static Throwable[] getThrowables(Throwable throwable) {
        List list = getThrowableList(throwable);
        return (Throwable[]) list.toArray(new Throwable[list.size()]);
    }

    public static List getThrowableList(Throwable throwable) {
        List list = new ArrayList();
        while (throwable != null && list.contains(throwable) == false) {
            list.add(throwable);
            throwable = ExceptionUtils.getCause(throwable);
        }
        return list;
    }

    public static Throwable getCause(Throwable throwable) {
        synchronized(CAUSE_METHOD_NAMES_LOCK) {
            return getCause(throwable, CAUSE_METHOD_NAMES);
        }
    }

    public static Throwable getCause(Throwable throwable, String[] methodNames) {
        if (throwable == null) {
            return null;
        }
        Throwable cause = getCauseUsingWellKnownTypes(throwable);
        if (cause == null) {
            if (methodNames == null) {
                synchronized(CAUSE_METHOD_NAMES_LOCK) {
                    methodNames = CAUSE_METHOD_NAMES;
                }
            }
            for (int i = 0; i < methodNames.length; i++) {
                String methodName = methodNames[i];
                if (methodName != null) {
                    cause = getCauseUsingMethodName(throwable, methodName);
                    if (cause != null) {
                        break;
                    }
                }
            }

            if (cause == null) {
                cause = getCauseUsingFieldName(throwable, "detail");
            }
        }
        return cause;
    }

    private static Throwable getCauseUsingMethodName(Throwable throwable, String methodName) {
        Method method = null;
        try {
            method = throwable.getClass().getMethod(methodName, null);
        } catch (NoSuchMethodException ignored) {
            // exception ignored
        } catch (SecurityException ignored) {
            // exception ignored
        }

        if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) {
            try {
                return (Throwable) method.invoke(throwable, ArrayUtils.EMPTY_OBJECT_ARRAY);
            } catch (IllegalAccessException ignored) {
                // exception ignored
            } catch (IllegalArgumentException ignored) {
                // exception ignored
            } catch (InvocationTargetException ignored) {
                // exception ignored
            }
        }
        return null;
    }
}

解决方法：该问题在commons-lang3中已经不存在，把依赖升级为3，并且获取异常堆栈信息改为使用org.apache.commons.lang3.exception.ExceptionUtils.getStackTrace(e)即可。

maven

    org.apache.commons
    commons-lang3
    3.11