Is there any problem to use multiple threads to send email with JavaMail

Question

Dear all,
I am using JavaMail 1.3.2 to send emails with SMTP, it works very well for a long time.
But one day, I found that the email service hanged and I could never send email again until I restart the tomcat. I found that the reason was a deadlock had been created, the required resource for sending email had not been released.
I guess the error is due to multiple threads are sending email at the same time. I made a test to create seperate thread for sending each email. After few days, I found this deadlock happened again. So, my question is: Can I use JavaMail with multiple threads? If not, I may need to sychronized all the thread that using JavaMail. I would like to make sure this is the reason for causing the deadlock problem.
Here is part of my code for using JavaMail:
transport = session.getTransport("smtp");
transport.connect(email_host, smtp_user, smtp_pass);
message.saveChanges();
transport.sendMessage(message,message.getAllRecipients());
which is very standard call, and it worked well for a long time.
Here is part for my thread dump on tomcat:
(Thread-339)
- waiting to lock <0x5447c180> (a sun.nio.cs.StandardCharsets)
(Thread-342)
- locked <0x5447c180> (a sun.nio.cs.StandardCharsets)
It seems that these happened after call the method transport.sendMessage() or message.updateChanges()
, and the underlying implementation may require the JRE StandardCharsets object. But the object had been locked and never be released. So, the sendMessage() or updateChanges() can't be completed.
Please give me some helps if you have any idea about it.
Thanks very much!
Sirius

Answer 1

Note that the Nightly build gets updated daily (and sometimes more than once in case of a respin) and it is always possible that something goes wrong and it doesn't work properly, so be prepared for issues if you decide to stay with the Nightly build and make sure to have the current release with its own profile installed as well in case of problems.
See also:
* http://kb.mozillazine.org/Testing_pre-release_versions
*http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows
*http://kb.mozillazine.org/Shortcut_to_a_specific_profile
*http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox