6 // The config module maintains views. As a node joins or leaves a
7 // view, the next view will be the same as previous view, except with
8 // the new node added or removed. The first view contains only node
9 // 1. If node 2 joins after the first node (it will download the views
10 // from node 1), it will learn about view 1 with the first node as the
11 // only member. It will then invoke Paxos to create the next view.
12 // It will tell Paxos to ask the nodes in view 1 to agree on the value
13 // {1, 2}. If Paxos returns success, then it moves to view 2 with
14 // {1,2} as the members. When node 3 joins, the config module runs
15 // Paxos with the nodes in view 2 and the proposed value to be
16 // {1,2,3}. And so on. When a node discovers that some node of the
17 // current view is not responding, it kicks off Paxos to propose a new
18 // value (the current view minus the node that isn't responding). The
19 // config module uses Paxos to create a total order of views, and it
20 // is ensured that the majority of the previous view agrees to the
21 // next view. The Paxos log contains all the values (i.e., views)
24 // The RSM module informs config to add nodes. The config module
25 // runs a heartbeater thread that checks in with nodes. If a node
26 // doesn't respond, the config module will invoke Paxos's proposer to
27 // remove the node. Higher layers will learn about this change when a
28 // Paxos acceptor accepts the new proposed value through
31 // To be able to bring other nodes up to date to the latest formed
32 // view, each node will have a complete history of all view numbers
33 // and their values that it knows about. At any time a node can reboot
34 // and when it re-joins, it may be many views behind; by remembering
35 // all views, the other nodes can bring this re-joined node up to
38 config_view_change::~config_view_change() {}
40 config::config(const string & _first, const string & _me, config_view_change *_vc)
41 : my_view_id(0), first(_first), me(_me), vc(_vc),
42 paxos(this, me == _first, me, me)
44 get_rpcs()->reg(paxos_protocol::heartbeat, &config::heartbeat, this);
45 lock cfg_mutex_lock(cfg_mutex);
46 reconstruct(cfg_mutex_lock);
47 thread(&config::heartbeater, this).detach();
50 void config::restore(const string & s) {
51 lock cfg_mutex_lock(cfg_mutex);
53 reconstruct(cfg_mutex_lock);
56 void config::get_view(unsigned instance, vector<string> & m) {
57 lock cfg_mutex_lock(cfg_mutex);
58 get_view(instance, m, cfg_mutex_lock);
61 void config::get_view(unsigned instance, vector<string> & m, lock & cfg_mutex_lock) {
62 VERIFY(cfg_mutex_lock);
63 string value = paxos.value(instance);
64 LOG << "get_view(" << instance << "): returns " << value;
68 void config::reconstruct(lock & cfg_mutex_lock) {
69 VERIFY(cfg_mutex_lock);
70 my_view_id = paxos.instance();
72 get_view(my_view_id, mems, cfg_mutex_lock);
73 LOG << "view " << my_view_id << " " << mems;
77 // Called by Paxos's acceptor.
78 void config::paxos_commit(unsigned instance, const string & value) {
79 lock cfg_mutex_lock(cfg_mutex);
81 vector<string> newmem = explode(value);
82 LOG << "instance " << instance << ": " << newmem;
84 for (auto mem : mems) {
85 LOG << "is " << mem << " still a member?";
86 if (!isamember(mem, newmem) && me != mem) {
87 LOG << "delete " << mem;
88 handle(mem).invalidate();
93 my_view_id = instance;
95 cfg_mutex_lock.unlock();
96 vc->commit_change(instance);
97 cfg_mutex_lock.lock();
101 bool config::ismember(const string & m, unsigned vid) {
102 lock cfg_mutex_lock(cfg_mutex);
104 get_view(vid, v, cfg_mutex_lock);
105 return isamember(m, v);
108 bool config::add(const string & new_m, unsigned vid) {
109 lock cfg_mutex_lock(cfg_mutex);
110 LOG << "adding " << new_m << " to " << vid;
111 if (vid != my_view_id) {
112 LOG << "that's not my view id, " << my_view_id << "!";
115 LOG << "calling down to paxos layer";
116 vector<string> m(mems), cmems(mems);
118 LOG << "old mems " << cmems << " " << implode(cmems);
119 LOG << "new mems " << m << " " << implode(m);
120 unsigned nextvid = my_view_id + 1;
121 cfg_mutex_lock.unlock();
122 bool r = paxos.run(nextvid, cmems, implode(m));
123 cfg_mutex_lock.lock();
124 LOG << "paxos proposer returned " << (r ? "success" : "failure");
128 // caller should hold cfg_mutex
129 bool config::remove(const string & m, lock & cfg_mutex_lock) {
130 VERIFY(cfg_mutex_lock);
131 LOG << "my_view_id " << my_view_id << " remove? " << m;
133 for (auto mem : mems) {
137 vector<string> cmems = mems;
138 unsigned nextvid = my_view_id + 1;
139 cfg_mutex_lock.unlock();
140 bool r = paxos.run(nextvid, cmems, implode(n));
141 cfg_mutex_lock.lock();
142 LOG << "proposer returned " << (r ? "success" : "failure");
146 void config::heartbeater() {
147 lock cfg_mutex_lock(cfg_mutex);
150 auto next_timeout = steady_clock::now() + milliseconds(300);
151 LOG << "go to sleep";
152 config_cond.wait_until(cfg_mutex_lock, next_timeout);
154 unsigned vid = my_view_id;
155 vector<string> cmems;
156 get_view(vid, cmems, cfg_mutex_lock);
157 LOG << "current membership " << cmems;
159 if (!isamember(me, cmems)) {
160 LOG << "not member yet; skip hearbeat";
164 // who has the smallest ID?
165 string m = std::min(me, *std::min_element(cmems.begin(), cmems.end()));
168 // ping the other nodes
169 for (string mem : cmems) {
170 if (mem == me || doheartbeat(mem, cfg_mutex_lock) == OK)
172 if (vid == my_view_id)
173 remove(mem, cfg_mutex_lock);
177 // ping the node with the smallest ID
178 if (doheartbeat(m, cfg_mutex_lock) != OK && vid == my_view_id)
179 remove(m, cfg_mutex_lock);
184 paxos_protocol::status config::heartbeat(int & r, string m, unsigned vid) {
185 lock cfg_mutex_lock(cfg_mutex);
186 r = (int) my_view_id;
187 LOG<< "heartbeat from " << m << "(" << vid << ") my_view_id " << my_view_id;
188 if (vid == my_view_id)
189 return paxos_protocol::OK;
190 else if (paxos.isrunning()) {
191 VERIFY (vid == my_view_id + 1 || vid + 1 == my_view_id);
192 return paxos_protocol::OK;
194 return paxos_protocol::ERR;
197 config::heartbeat_t config::doheartbeat(const string & m, lock & cfg_mutex_lock) {
198 VERIFY(cfg_mutex_lock);
199 unsigned vid = my_view_id;
200 LOG << "heartbeat to " << m << " (" << vid << ")";
203 cfg_mutex_lock.unlock();
204 int r = 0, ret = rpc_protocol::bind_failure;
205 if (rpcc *cl = h.safebind())
206 ret = cl->call_timeout(paxos_protocol::heartbeat, milliseconds(100), r, me, vid);
207 cfg_mutex_lock.lock();
209 heartbeat_t res = OK;
211 case paxos_protocol::OK:
213 case rpc_protocol::atmostonce_failure:
214 case rpc_protocol::oldsrv_failure:
218 LOG << "problem with " << m << " (" << ret << ") my vid " << vid << " his vid " << r;
219 res = (ret < 0) ? FAILURE : VIEWERR;
221 LOG << "done " << res;