ejb与java序列化(1) 发现并解析问题[Java编程]

这是加入新公司后接办的第一个项目,利用weblogic9.2 + ejb2.0,压力测试时发现速度非常慢,呼应时间很不睬想,查抄日记发现,某些ejb彼此调用时办法调用的时间非常长,高达300-500毫秒.非常浮夸,因为两个日记之间只是隔断了一个ejb调用.通过thread dump解析后发现有相当多的线程在wait,查抄线程调用绽发现是在将参数举行序列化时,线程试图加锁但是锁被占用,因此处于等候状况.考虑到thread dump的这一刹时,有多达30-50个线程都在同时试图在同一个锁上加锁,很明显这里的锁竞争非常严重.

因此激烈猜疑是java的序列化机制招致的问题,由于weblogic/ejb之类的太复杂不便利测试,因此单独写了一个类来模拟这种场景:
1.有大量线程在运行,期间都有序列化的操作
2.被序列化的对象对比大,有大量子对象（子对象的子对象...)

运行测试代码,问题重现,测试用开了50个线程,thread dump并解析thread dump信息,发现49个线程处于waiting 状况,只有一个线程在干活!因此抛开weblogic/ejb单独解析java的序列化机制,首先看thread dump的线程信息:

占据锁的线程:

"testthread21" prio=6 tid=0x0ad2d3b8 nid=0x224 runnable [0x0b48f000..0x0b48fce4]
at java.io.ObjectStreamClass.processQueue(Unknown Source)
at java.io.ObjectStreamClass.lookup(Unknown Source)
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at java.util.ArrayList.writeObject(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeWriteObject(Unknown Source)
at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at test.Test.test(Test.java:68)
at test.Test.run(Test.java:53)
at java.lang.Thread.run(Unknown Source)

等候加锁的线程之一: "testthread49" prio=6 tid=0x0ad9a508 nid=0xa9c waiting for monitor entry [0x0bb8f000..0x0bb8fbe4]
at java.lang.ref.ReferenceQueue.poll(Unknown Source)
- waiting to lock <0x02fb1d40> (a java.lang.ref.ReferenceQueue$Lock)
at java.io.ObjectStreamClass.processQueue(Unknown Source)
at java.io.ObjectStreamClass.lookup(Unknown Source)
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at java.util.ArrayList.writeObject(Unknown Source)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeWriteObject(Unknown Source)
at java.io.ObjectOutputStream.writeSerialData(Unknown Source)
at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
at java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.io.ObjectOutputStream.writeObject(Unknown Source)
at test.Test.test(Test.java:68)
at test.Test.run(Test.java:53)
at java.lang.Thread.run(Unknown Source)

可以发现问题发生在类java.io.ObjectStreamClass中的办法processQueue()办法中: static void processQueue(ReferenceQueue<Class<?>> queue,
ConcurrentMap<? extends
WeakReference<Class<?>>, ?> map)
{
Reference<? extends Class<?>> ref;
while((ref = queue.poll()) != null) {
map.remove(ref);
}
}

这里的queue.poll()有加锁,持续跟进poll()的代码: public Reference<? extends T> poll() {
if(queueEmpty) return null;
synchronized (lock) {
return reallyPoll();
}
}

　　以上是“ejb与java序列化(1) 发现并解析问题[Java编程]”的内容，如果你对以上该文章内容感兴趣，你可以看看七道奇为您推荐以下文章：