- get rid of individual Peer locks
- hold Peers read (or write) lock and LocalPeer read lock while
performing route calculations
This eliminates the deadlock resulting from the inconsistent lock
acquisition order in route calculcation.
Fixes#643.
This makes for a more symmetric API - Peers.FetchWithDefault does the
increment and Peers.Dereference does the decrement, whereas previously
the latter was done by Peer.DecrementLocalRefCount.
This does increase lock granularity, i.e. modifying any ref count now
requires a write lock on Peers.
When we want a string representation of a Peer, we nearly always just
want the full name. So make String() return that and introduce Info()
to return expanded info.
Introduce an intermediary - GossipSender - between GossipChannel and
Connection. This accumulates gossip data (now represented by the new
GossipData interface) from the former until it can be passed onto the
latter, allowing the former to proceed when the latter may be blocked
on i/o.
This
1) prevents deadlocks that arise from cycles in the communication
topology
2) improves performance by allowing GossipChannel and its calling code
to proceed when connection i/o is blocked
3) improves performance by accumulating GossipData - the accumulated
data often is considerably more compact than the sum of all the
accumulated bits, and it is transmitted in a single communication
event.
In order to support accumulation, the GossipData interface has a Merge
method. Furthermore, encoding is deferred until the data can actually
be sent, since accumulation would be hard/impossible to encoded
data. This required changes on some interfaces, most notably Gossiper.
The implementation of GossipData for topology gossip is
TopologyGossipData. It carries a reference to Peers and a set of
PeerNames, indexing into Peers and referencing the Peer entries which
have changed. Previously updates were represented as a list of Peer
entries. The indirection via PeerNames allows Encode to omit entries
which have been removed. The change in representation required changes
to the signature of some methods on Peers.
Note that all the above only applies to the "periodic gossip" portion
of the Gossiper API, which topology gossip in fact uses for *all*
gossip. GossipUnicast and GossipBroadcast are unchanged, but could
conceivably receive the same treatment in the future.
Fixes#445.
Topology gossip can be received on a connection before that connection
has been marked as 'established'. If we do not include unestablished
connections in topology gossip, then parts of the topology can be
removed by gc, since they are deemed unreachable, which can cause
subsequent incremental topology gossips to be rejected due to them
containing references to peers that have been removed by the gc.
Including unestablished connections in topology gossip requires:
- removing the check for 'established' connections in the encoding of
peers for topology gossip,
- adding the 'established' flag to the internal representation of
remote connections,
- adding the 'established' flag to to encoding of connections in
topology gossip,
- treating the *addition* of a connection as an update to the local
peer.
The latter entails
- bumping the peer version on connection addition (as well as on
marking 'established' as previously),
- bumping the peer version *unconditionally* on connection deletion
(rather than only when the connection was 'established', as
previously),
- moving the initial sending of complete topology on the connection,
and the broadcasting of a topology update containing the two peers
at the ends of the connection, from the connection 'established'
logic to the connection addition logic,
- broadcasting just an topology update for the local peer when a
connection gets marked as 'established',
- broadcasting a topology update for the local peer *unconditionally*
when a connection is removed (rather than only doing this when the
connection was 'established', as previously).
Instead of separately calculating routes to every individual peer,
carry out one calculation for routes to all peers. Same as unicast
routes except taking into account asymmetric connections.
When an update contains an older version of a peer we know about,
there is no point in including our better version in the "improved"
update, since we will have told our neighbours about that already and
any race conditions are taken care off by the periodic sending of the
complete topology.
Matthias Radestock