[jboss-jira] [JBoss JIRA] (JGRP-1416) NAKACK / NAKACK2: shorten scope of seqno_lock
Bela Ban created JGRP-1416:
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Summary: NAKACK / NAKACK2: shorten scope of seqno_lock
Key: JGRP-1416
URL: https://issues.jboss.org/browse/JGRP-1416
Project: JGroups
Issue Type: Enhancement
Reporter: Bela Ban
Assignee: Bela Ban
Priority: Minor
Fix For: 3.0.3, 3.1
The code in NAKACK/NAKACK2.send() acquires seqno_lock like this:
{code:title=NAKACK.send()|borderStyle=solid}
seqno_lock.lock();
try {
try { // incrementing seqno and adding the msg to sent_msgs needs to be
atomic
msg_id=seqno +1;
msg.putHeader(this.id, NakAckHeader.createMessageHeader(msg_id));
win.add(msg_id, msg);
seqno=msg_id;
}
catch(Throwable t) {
throw new RuntimeException("failure adding msg " + msg + "
to the retransmit table for " + local_addr, t);
}
}
finally {
seqno_lock.unlock();
}
{code}
This slows concurrent sender threads down if add() takes a while. Method add() can take a
while if we have many concurrent adds and removes.
The reason we use seqno_lock is to prevent gaps in the sequence numbers, e.g. if we have
an exception in add().
SOLUTION:
- Assign a new msg_id by incrementing seqno *atomically* (seqno_lock is now de-scoped to
only increment seqno, might replace this with an AtomicLong anyway)
- In a loop: add the message (calling add()), until add() returns successfully, then
break
Example:
{code}
msg_id=seqno.incrementAndGet(); // uses an AtomicLong
while(running) { // maybe bound with a counter
try {
msg.adddHeader(...);
add();
break;
}
catch(Throwable t) {
// log
}
}
{code}
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