How to lock a (IMAP) Folder or Message?

Question

I am working on a program that reads and processes email messages from a IMAP folder. Because there might be huge volume of messages to be processed, multiple processes of this program may run on different machines. Since a single message can only be processed once, I need a lock mechanism that guarantees that no message can be read by more than one processes at any time.
Can anyone tell me how to do that by using JavaMail APIs? Thanks a lot.

Answer 1

Thanks. I tried using flag but got duplicated messages. There is a method doCommand(IMAPFolder.ProtocolCommand cmd) in class IMAPFolder. The document says that it "Execute a user-supplied IMAP command. The command is executed in the appropriate context with the necessary locks held and using the appropriate IMAPProtocol object. " I tried to use it. But it seems that there was still a race condition. Below is my code:
protected Message getNextMessage(IMAPFolder folder) throws Exception {
if (! folder.isOpen())
folder.open(Folder.READ_WRITE);
//curImapFolder is a class member variable
curImapFolder = folder;
Object val = folder.doCommand(new IMAPFolder.ProtocolCommand() {
public Object doCommand(IMAPProtocol p) throws ProtocolException {
Flags searchflags = new Flags(Flags.Flag.FLAGGED);
searchflags.add(Flags.Flag.DELETED);
FlagTerm term = new FlagTerm(searchflags, false);
int[] ids = null;
try {
ids = p.search(term);
} catch (SearchException se) {
return null;
if ((null == ids) || (ids.length <= 0))
return null;
Message msg = null;
try {
//get the first fresh message
msg = curImapFolder.getMessage(ids[0]);
} catch (MessagingException me) {
msg = null;
if (null != msg) {
//set message not fresh
Flags checkedflags = new Flags(Flags.Flag.FLAGGED);
p.storeFlags(ids[0], checkedflags, true);
return msg;
else
return null;
return (Message)val;
}