/**
* Invoked upon receiving a MERGE event from the MERGE layer. Starts the merge protocol. See
* description of protocol in DESIGN.
*
* @param views A List of <em>different</em> views detected by the merge protocol
*/
public void merge(Map<Address, View> views) {
if (isMergeInProgress()) {
if (log.isTraceEnabled())
log.trace(gms.local_addr + ": merge is already running (merge_id=" + merge_id + ")");
return;
}
// we need the merge *coordinators* not merge participants because not everyone can lead a merge
// !
Collection<Address> coords = Util.determineMergeCoords(views);
Collection<Address> merge_participants = Util.determineMergeParticipants(views);
Membership tmp =
new Membership(coords); // establish a deterministic order, so that coords can elect leader
tmp.sort();
Address merge_leader = tmp.elementAt(0);
if (log.isDebugEnabled()) log.debug("determining merge leader from " + merge_participants);
if (merge_leader.equals(gms.local_addr)) {
if (log.isDebugEnabled())
log.debug(
"I ("
+ gms.local_addr
+ ") will be the leader. Starting the merge task for "
+ merge_participants);
merge_task.start(views);
} else {
if (log.isDebugEnabled())
log.debug(
"I ("
+ gms.local_addr
+ ") am not the merge leader, "
+ "waiting for merge leader ("
+ merge_leader
+ ") to initiate merge");
}
}
/** Checks whether the potential_new_coord would be the new coordinator (2nd in line) */
protected boolean wouldBeNewCoordinator(Address potential_new_coord) {
if (potential_new_coord == null) return false;
synchronized (members) {
if (members.size() < 2) return false;
Address new_coord = members.elementAt(1); // member at 2nd place
return new_coord != null && new_coord.equals(potential_new_coord);
}
}
/**
* Merge all MergeData. All MergeData elements should be disjunct (both views and digests).
* However, this method is prepared to resolve duplicate entries (for the same member).
* Resolution strategy for views is to merge only 1 of the duplicate members. Resolution
* strategy for digests is to take the higher seqnos for duplicate digests.
*
* <p>After merging all members into a Membership and subsequent sorting, the first member of
* the sorted membership will be the new coordinator. This method has a lock on merge_rsps.
*
* @param merge_rsps A list of MergeData items. Elements with merge_rejected=true were removed
* before. Is guaranteed not to be null and to contain at least 1 member.
*/
private MergeData consolidateMergeData(Vector<MergeData> merge_rsps) {
long logical_time = 0; // for new_vid
Membership new_mbrs = new Membership();
Vector<View> subgroups =
new Vector<View>(11); // contains a list of Views, each View is a subgroup
for (MergeData tmp_data : merge_rsps) {
View tmp_view = tmp_data.getView();
if (tmp_view != null) {
ViewId tmp_vid = tmp_view.getVid();
if (tmp_vid != null) {
// compute the new view id (max of all vids +1)
logical_time = Math.max(logical_time, tmp_vid.getId());
}
// merge all membership lists into one (prevent duplicates)
new_mbrs.add(tmp_view.getMembers());
subgroups.addElement((View) tmp_view.clone());
}
}
// the new coordinator is the first member of the consolidated & sorted membership list
new_mbrs.sort();
Address new_coord = new_mbrs.size() > 0 ? new_mbrs.elementAt(0) : null;
if (new_coord == null) {
if (log.isErrorEnabled()) log.error("new_coord == null");
return null;
}
// should be the highest view ID seen up to now plus 1
ViewId new_vid = new ViewId(new_coord, logical_time + 1);
// determine the new view
MergeView new_view = new MergeView(new_vid, new_mbrs.getMembers(), subgroups);
// determine the new digest
Digest new_digest = consolidateDigests(merge_rsps, new_mbrs.size());
if (new_digest == null) {
if (log.isErrorEnabled())
log.error("Merge leader " + gms.local_addr + ": could not consolidate digest for merge");
return null;
}
if (log.isDebugEnabled())
log.debug(
"Merge leader "
+ gms.local_addr
+ ": consolidated view="
+ new_view
+ "\nconsolidated digest="
+ new_digest);
return new MergeData(gms.local_addr, new_view, new_digest);
}
protected Address determineCoordinator() {
synchronized (members) {
return members.size() > 0 ? members.elementAt(0) : null;
}
}
