Java多线程死锁问题

刚才用jstack解决了一个进程死锁的问题。

流程大致如下：
（0）环境要求，JDK1.6及以上
（1）先找到进程的PID，Windows下，打开进程管理器，按照名字排序，可以找到叫做javaw.exe的进程（java虚拟机进程一律叫做javaw.exe），要找出哪个是你的进程，记住当前进程列表，然后重启你的进程，PID刷新过的那个即是你的进程。
（2）在CMD下运行：jstack pid，jstack会在console上打出一系列信息
（3）分析上述信息

"startQuertz_Worker-2" prio=6 tid=0x000000006201f000 nid=0x14b0 runnable [0x0000000068b9e000]
   java.lang.Thread.State: RUNNABLE
	at java.net.SocketInputStream.socketRead0(Native Method)
	at java.net.SocketInputStream.read(SocketInputStream.java:129)
	at com.sun.mail.util.TraceInputStream.read(TraceInputStream.java:97)
	at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
	at java.io.BufferedInputStream.read(BufferedInputStream.java:237)
	- locked <0x0000005896b7a708> (a java.io.BufferedInputStream)
	at com.sun.mail.iap.ResponseInputStream.read0(ResponseInputStream.java:81)
	at com.sun.mail.iap.ResponseInputStream.readResponse(ResponseInputStream.java:67)
	at com.sun.mail.iap.Response.<init>(Response.java:83)
	at com.sun.mail.imap.protocol.IMAPResponse.<init>(IMAPResponse.java:48)
	at com.sun.mail.imap.protocol.IMAPResponse.readResponse(IMAPResponse.java:122)
	at com.sun.mail.imap.protocol.IMAPProtocol.readResponse(IMAPProtocol.java:230)
	at com.sun.mail.iap.Protocol.command(Protocol.java:263)
	- locked <0x0000005896b74cb8> (a com.sun.mail.imap.protocol.IMAPProtocol)
	at com.sun.mail.imap.protocol.IMAPProtocol.fetch(IMAPProtocol.java:1234)
	at com.sun.mail.imap.protocol.IMAPProtocol.fetch(IMAPProtocol.java:1226)
	at com.sun.mail.imap.protocol.IMAPProtocol.fetchBody(IMAPProtocol.java:1028)
	at com.sun.mail.imap.protocol.IMAPProtocol.fetchBody(IMAPProtocol.java:1023)
	at com.sun.mail.imap.IMAPInputStream.fill(IMAPInputStream.java:101)
	- locked <0x0000005896bb77d0> (a java.lang.Object)
	at com.sun.mail.imap.IMAPInputStream.read(IMAPInputStream.java:158)
	- locked <0x0000005897da6540> (a com.sun.mail.imap.IMAPInputStream)
	at com.sun.mail.imap.IMAPInputStream.read(IMAPInputStream.java:184)
	at com.sun.mail.util.BASE64DecoderStream.getByte(BASE64DecoderStream.java:337)
	at com.sun.mail.util.BASE64DecoderStream.decode(BASE64DecoderStream.java:230)
	at com.sun.mail.util.BASE64DecoderStream.read(BASE64DecoderStream.java:135)
	at java.io.FilterInputStream.read(FilterInputStream.java:90)
	at javax.mail.internet.MimeBodyPart.saveFile(MimeBodyPart.java:805)
	at com.detao.dtma.email.EmailReciver.processAttachment(EmailReciver.java:244)
	at com.detao.dtma.email.EmailReciver.processMsg(EmailReciver.java:140)
	at com.detao.dtma.email.EmailReciver.processMsg(EmailReciver.java:93)
	at com.detao.dtma.email.EmailReciver.processMessages(EmailReciver.java:69)
	at com.detao.dtma.email.EmailReciver.processMessages(EmailReciver.java:50)
	at com.detao.dtma.email.EmailReciverMgr.run(EmailReciverMgr.java:31)
	at sun.reflect.GeneratedMethodAccessor2511.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:273)
	at org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean$MethodInvokingJob.executeInternal(MethodInvokingJobDetailFactoryBean.java:264)
	at org.springframework.scheduling.quartz.QuartzJobBean.execute(QuartzJobBean.java:86)
	at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
	at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)

"startQuertz_Worker-1" prio=6 tid=0x0000000064022800 nid=0x3a4 waiting for monitor entry [0x0000000068a9f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x0000005872f40648> (a java.lang.Object)
	at org.quartz.simpl.SimpleThreadPool.getNextRunnable(SimpleThreadPool.java:428)
	- locked <0x0000005872f40648> (a java.lang.Object)
	at org.quartz.simpl.SimpleThreadPool.access$000(SimpleThreadPool.java:47)
	at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:518)

"startQuertz_Worker-0" prio=6 tid=0x0000000060f15000 nid=0x13e8 waiting for monitor entry [0x000000006899f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x0000005872f40648> (a java.lang.Object)
	at org.quartz.simpl.SimpleThreadPool.getNextRunnable(SimpleThreadPool.java:428)
	- locked <0x0000005872f40648> (a java.lang.Object)
	at org.quartz.simpl.SimpleThreadPool.access$000(SimpleThreadPool.java:47)
	at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:518)

"Store userCache Spool Thread" daemon prio=6 tid=0x000000006194f000 nid=0x1354 waiting on condition [0x000000006889f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
	at java.lang.Thread.sleep(Native Method)
	at net.sf.ehcache.store.DiskStore.spoolAndExpiryThreadMain(DiskStore.java:634)
	at net.sf.ehcache.store.DiskStore.access$900(DiskStore.java:68)
	at net.sf.ehcache.store.DiskStore$SpoolAndExpiryThread.run(DiskStore.java:1110)

最后定位到错误行

at com.detao.dtma.email.EmailReciverMgr.run(EmailReciverMgr.java:31)

找到相应代码

public class EmailReciverMgr extends TimerTask {
	/* 邮件接收器 一个邮件接收器对应一个邮箱 */
	private java.util.List<EmailReciver> recivers;
	/* 程序是否正在进行 */
	private boolean running = false;

	public void setRecivers(java.util.List<EmailReciver> recivers) {
		this.recivers = recivers;
	}

	@Override
	public void run() {
		// 如果正在运行就返回，否则运行
		if (running) {
			return;
		}
		try {
			running = true;
			// 循环邮件接收器 
			for (EmailReciver reciver : recivers) {
				// 处理邮件
				reciver.processMessages();
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			// 运行完毕设置为false，以便进行下一次运行
			running = false;
		}

	}
}

程序本身没有问题，问题出现在了调用上，两个定时器都有自己的定时策略，分别调用了两次，造成相互等待，形成死锁。

此问题的难点在于问题的定位，问题的发生具有不确定性，有时候半月不发生，有时候一天发生多次，定位不到问题，后台没有任何报错，最后jstack，终于定位到了问题，找到问题之后，解决就好办了。