java mail: set

Problem: email thread is hanging at socket read

Today we found a email problem in production, all of the mail threads (3 threads) are hanging/sitting/blocking at same point

 

at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:129) at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) at java.io.BufferedInputStream.read(BufferedInputStream.java:237) - locked <0x9698d6c0> (a java.io.BufferedInputStream) at com.sun.mail.util.LineInputStream.readLine(LineInputStream.java:56) at com.sun.mail.smtp.SMTPTransport.readServerResponse(SMTPTransport.java:757) at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:673) at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:168) at javax.mail.Service.connect(Service.java:227) at javax.mail.Service.connect(Service.java:131) at javax.mail.Service.connect(Service.java:87) at com.sun.mail.smtp.SMTPTransport.connect(SMTPTransport.java:105) - locked <0x9698d6e0> (a com.sun.mail.smtp.SMTPTransport) at javax.mail.Transport.send0(Transport.java:162) at javax.mail.Transport.send(Transport.java:80) 

 

 

I search the "javax.mail.Transport.send" and "com.sun.mail.smtp.SMTPTransport.readServerResponse", got no hits.

while my colleague get answer from internet. 

 

http://jira.sakaiproject.org/browse/KNL-96

http://forums.sun.com/thread.jspa?forumID=43&threadID=474662

 

"I have a servlet which uses JavaMail to send out emails to a smtp server. During our peak access hours, we have many requests to send out emails, after a while my application went into CLOSE WAIT accumulation and finally my application server stops processing."

"ExecuteThread: '11' for queue: 'default'" daemon prio=5 tid=0x39fb28 nid=0x18 runnable [0xbf980000..0xbf981a38] at java.net.SocketInputStream.socketRead(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:85) at java.io.BufferedInputStream.fill(BufferedInputStream.java:181) at java.io.BufferedInputStream.read(BufferedInputStream.java:199) at com.sun.mail.util.LineInputStream.readLine(LineInputStream.java:56) at com.sun.mail.smtp.SMTPTransport.readServerResponse(SMTPTransport.java:929) at com.sun.mail.smtp.SMTPTransport.issueCommand(SMTPTransport.java:878) at com.sun.mail.smtp.SMTPTransport.finishData(SMTPTransport.java:820) at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:322) at javax.mail.Transport.send0(Transport.java:164) at javax.mail.Transport.send(Transport.java:81) 

 

Solution

"JavaMail send() method is synchronous call. If the smtp server does not return a response JavaMail may wait forever.

Therefore you should set the smtp timeout properties:
mail.smtp.connectiontimeout
mail.smtp.timeout"

Properties props = new Properties(); props.put("mail.smtp.host", hostid); props.put("mail.smtp.port", smtpPort); props.put("mail.smtp.connectiontimeout","600000");//timeout 10 mins props.put("mail.smtp.timeout","600000");//timeout 10 mins mysession = Session.getDefaultInstance(props); 

 

My postmortem 

1. try different search keywords in problem description : blocking, handing, never return. setting...

2. try different API:"javax.mail.Transport.send

"javax.mail.Transport.send" is abstract API.

"com.sun.mail.smtp.SMTPTransport.readServerResponse" is bottom.

Try a middle point: com.sun.mail.smtp.SMTPTransport.connect

3.We do not get the root cause: why 'CLOSE_WAIT ' accumulation.

   It means one peer of socket connection is closed, while the other do not.