#include "paxos.h"
#include "handle.h"
-#include "threaded_log.h"
-#include "lang/verify.h"
-#include "lock.h"
-using std::stoi;
+bool isamember(const node_t & m, const nodes_t & nodes) {
+ return find(nodes.begin(), nodes.end(), m) != nodes.end();
+}
+
+// check if l2 contains a majority of the elements of l1
+bool majority(const nodes_t & l1, const nodes_t & l2) {
+ auto overlap = (size_t)count_if(l1.begin(), l1.end(), std::bind(isamember, _1, l2));
+ return overlap >= (l1.size() >> 1) + 1;
+}
// This module implements the proposer and acceptor of the Paxos
// distributed algorithm as described by Lamport's "Paxos Made
// paxos_commit to inform higher layers of the agreed value for this
// instance.
-bool operator> (const prop_t &a, const prop_t &b) {
- return (a.n > b.n || (a.n == b.n && a.m > b.m));
-}
-
-bool operator>= (const prop_t &a, const prop_t &b) {
- return (a.n > b.n || (a.n == b.n && a.m >= b.m));
-}
-
-string
-print_members(const vector<string> &nodes) {
- string s;
- s.clear();
- for (unsigned i = 0; i < nodes.size(); i++) {
- s += nodes[i];
- if (i < (nodes.size()-1))
- s += ",";
- }
- return s;
-}
-
-
-bool isamember(const string & m, const vector<string> & nodes) {
- for (auto n : nodes) {
- if (n == m)
- return 1;
- }
- return 0;
-}
-
-bool proposer::isrunning() {
- bool r;
- lock ml(pxs_mutex);
- r = !stable;
- return r;
-}
-
-// check if the servers in l2 contains a majority of servers in l1
-bool proposer::majority(const vector<string> &l1, const vector<string> &l2) {
- unsigned n = 0;
-
- for (unsigned i = 0; i < l1.size(); i++) {
- if (isamember(l1[i], l2))
- n++;
- }
- return n >= (l1.size() >> 1) + 1;
-}
-
-proposer::proposer(class paxos_change *_cfg, class acceptor *_acceptor, const string &_me)
- : cfg(_cfg), acc (_acceptor), me (_me), break1 (false), break2 (false),
- stable (true)
+proposer_acceptor::proposer_acceptor(paxos_change *_delegate,
+ bool _first, const node_t & _me, const value_t & _value)
+ : delegate(_delegate), me (_me)
{
- my_n.n = 0;
- my_n.m = me;
-}
+ // at this point, the log has already been replayed
+ if (instance_h == 0 && _first) {
+ values[1] = _value;
+ l.loginstance(1, _value);
+ instance_h = 1;
+ }
-void proposer::setn()
-{
- my_n.n = acc->get_n_h().n + 1 > my_n.n + 1 ? acc->get_n_h().n + 1 : my_n.n + 1;
+ pxs.reg(paxos_protocol::preparereq, &proposer_acceptor::preparereq, this);
+ pxs.reg(paxos_protocol::acceptreq, &proposer_acceptor::acceptreq, this);
+ pxs.reg(paxos_protocol::decidereq, &proposer_acceptor::decidereq, this);
}
-bool proposer::run(unsigned instance, const vector<string> & cur_nodes, const string & newv)
+bool proposer_acceptor::run(unsigned instance, const nodes_t & cur_nodes, const value_t & newv)
{
- vector<string> accepts;
- vector<string> nodes;
- string v;
- bool r = false;
-
- lock ml(pxs_mutex);
- LOG("start: initiate paxos for " << print_members(cur_nodes) << " w. i=" << instance << " v=" << newv << " stable=" << stable);
+ lock ml(proposer_mutex);
+ LOG("initiate paxos for " << cur_nodes << " w. i=" << instance << " v=\"" << newv << "\" stable=" << stable);
if (!stable) { // already running proposer?
- LOG("proposer::run: already running");
+ LOG("paxos proposer already running");
return false;
}
stable = false;
- setn();
- accepts.clear();
- v.clear();
+ bool r = false;
+ proposal.n = max(promise.n, proposal.n) + 1;
+ nodes_t accepts;
+ value_t v;
if (prepare(instance, accepts, cur_nodes, v)) {
if (majority(cur_nodes, accepts)) {
- LOG("paxos::manager: received a majority of prepare responses");
+ LOG("received a majority of prepare responses");
- if (v.size() == 0)
+ if (!v.size())
v = newv;
breakpoint1();
- nodes = accepts;
- accepts.clear();
+ nodes_t nodes;
+ nodes.swap(accepts);
accept(instance, accepts, nodes, v);
if (majority(cur_nodes, accepts)) {
- LOG("paxos::manager: received a majority of accept responses");
+ LOG("received a majority of accept responses");
breakpoint2();
decide(instance, accepts, v);
r = true;
} else {
- LOG("paxos::manager: no majority of accept responses");
+ LOG("no majority of accept responses");
}
} else {
- LOG("paxos::manager: no majority of prepare responses");
+ LOG("no majority of prepare responses");
}
} else {
- LOG("paxos::manager: prepare is rejected " << stable);
+ LOG("prepare is rejected " << stable);
}
stable = true;
return r;
}
-// proposer::run() calls prepare to send prepare RPCs to nodes
-// and collect responses. if one of those nodes
-// replies with an oldinstance, return false.
-// otherwise fill in accepts with set of nodes that accepted,
-// set v to the v_a with the highest n_a, and return true.
-bool
-proposer::prepare(unsigned instance, vector<string> & accepts,
- const vector<string> & nodes,
- string & v)
-{
- struct paxos_protocol::preparearg arg = { instance, my_n };
- struct paxos_protocol::prepareres res;
- prop_t n_a = { 0, "" };
- rpcc *r;
+bool proposer_acceptor::prepare(unsigned instance, nodes_t & accepts,
+ const nodes_t & nodes, value_t & v) {
+ LOG("sending prepare messages (" << proposal.n << ", " << proposal.m << ", \"" << v << "\")");
+ prepareres res;
+ prop_t highest_n_a{0, ""};
for (auto i : nodes) {
handle h(i);
- if (!(r = h.safebind()))
+ rpcc *r = h.safebind();
+ if (!r)
continue;
- int status = r->call_timeout(paxos_protocol::preparereq, rpcc::to(1000), res, me, arg);
+ auto status = (paxos_protocol::status)r->call_timeout(
+ paxos_protocol::preparereq, milliseconds(100), res, me, instance, proposal);
if (status == paxos_protocol::OK) {
if (res.oldinstance) {
LOG("commiting old instance!");
- acc->commit(instance, res.v_a);
+ commit(instance, res.v_a);
return false;
}
+ LOG("preparereq responded with oldinstance=" << res.oldinstance << " accept=" << res.accept << " n_a=(" << res.n_a.n << ", " << res.n_a.m << ") " <<
+ "v_a=\"" << res.v_a << "\"");
if (res.accept) {
accepts.push_back(i);
- if (res.n_a >= n_a) {
- LOG("found a newer accepted proposal");
+ if (res.n_a >= highest_n_a) {
+ LOG("found a newer accepted proposal, \"" << res.v_a << "\", with number (" << res.n_a.n << ", " << res.n_a.m << ")");
v = res.v_a;
- n_a = res.n_a;
+ highest_n_a = res.n_a;
}
}
}
return true;
}
-// run() calls this to send out accept RPCs to accepts.
-// fill in accepts with list of nodes that accepted.
-void
-proposer::accept(unsigned instance, vector<string> & accepts,
- const vector<string> & nodes, const string & v)
-{
- struct paxos_protocol::acceptarg arg = { instance, my_n, v };
- rpcc *r;
+void proposer_acceptor::accept(unsigned instance, nodes_t & accepts,
+ const nodes_t & nodes, const value_t & v) {
for (auto i : nodes) {
handle h(i);
- if (!(r = h.safebind()))
+ rpcc *r = h.safebind();
+ if (!r)
continue;
bool accept = false;
- int status = r->call_timeout(paxos_protocol::acceptreq, rpcc::to(1000), accept, me, arg);
+ int status = r->call_timeout(
+ paxos_protocol::acceptreq, milliseconds(100), accept, me, instance, proposal, v);
if (status == paxos_protocol::OK && accept)
accepts.push_back(i);
}
}
-void
-proposer::decide(unsigned instance, const vector<string> & accepts,
- const string & v)
-{
- struct paxos_protocol::decidearg arg = { instance, v };
- rpcc *r;
+void proposer_acceptor::decide(unsigned instance, const nodes_t & accepts, const value_t & v) {
for (auto i : accepts) {
handle h(i);
- if (!(r = h.safebind()))
+ rpcc *r = h.safebind();
+ if (!r)
continue;
int res = 0;
- r->call_timeout(paxos_protocol::decidereq, rpcc::to(1000), res, me, arg);
+ r->call_timeout(paxos_protocol::decidereq, milliseconds(100), res, me, instance, v);
}
}
-acceptor::acceptor(class paxos_change *_cfg, bool _first, const string & _me,
- const string & _value)
- : cfg(_cfg), me (_me), instance_h(0)
-{
- n_h.n = 0;
- n_h.m = me;
- n_a.n = 0;
- n_a.m = me;
- v_a.clear();
-
- l = new log (this, me);
-
- if (instance_h == 0 && _first) {
- values[1] = _value;
- l->loginstance(1, _value);
- instance_h = 1;
- }
-
- pxs = new rpcs((uint32_t)stoi(_me));
- pxs->reg(paxos_protocol::preparereq, &acceptor::preparereq, this);
- pxs->reg(paxos_protocol::acceptreq, &acceptor::acceptreq, this);
- pxs->reg(paxos_protocol::decidereq, &acceptor::decidereq, this);
-}
-
paxos_protocol::status
-acceptor::preparereq(paxos_protocol::prepareres & r, const string &,
- paxos_protocol::preparearg a)
-{
- lock ml(pxs_mutex);
+proposer_acceptor::preparereq(prepareres & r, const node_t &, unsigned instance, prop_t n) {
+ LOG("instance " << instance << " proposal (" << n.n << ", " << n.m << ")");
+ lock ml(acceptor_mutex);
r.oldinstance = false;
r.accept = false;
- r.n_a = n_a;
- r.v_a = v_a;
- if (a.instance <= instance_h) {
+ r.n_a = accepted;
+ r.v_a = accepted_value;
+ if (instance <= instance_h) {
+ LOG("old instance " << instance << " has value " << values[instance]);
r.oldinstance = true;
- r.v_a = values[a.instance];
- } else if (a.n > n_h) {
- n_h = a.n;
- l->logprop(n_h);
+ r.v_a = values[instance];
+ } else if (n > promise) {
+ LOG("looks good to me");
+ promise = n;
+ l.logprop(promise);
r.accept = true;
} else {
LOG("I totally rejected this request. Ha.");
}
+ LOG("preparereq is responding with oldinstance=" << r.oldinstance << " accept=" << r.accept << " n_a=(" << r.n_a.n << ", " << r.n_a.m << ") " <<
+ "v_a=\"" << r.v_a << "\"");
return paxos_protocol::OK;
}
paxos_protocol::status
-acceptor::acceptreq(bool & r, const string &, paxos_protocol::acceptarg a)
-{
- lock ml(pxs_mutex);
+proposer_acceptor::acceptreq(bool & r, const node_t &, unsigned instance, prop_t n, const value_t & v) {
+ lock ml(acceptor_mutex);
r = false;
- if (a.n >= n_h) {
- n_a = a.n;
- v_a = a.v;
- l->logaccept(n_a, v_a);
- r = true;
+ if (instance == instance_h + 1) {
+ if (n >= promise) {
+ accepted = n;
+ accepted_value = v;
+ l.logaccept(accepted, accepted_value);
+ r = true;
+ }
+ return paxos_protocol::OK;
+ } else {
+ return paxos_protocol::ERR;
}
- return paxos_protocol::OK;
}
-// the src argument is only for debugging
paxos_protocol::status
-acceptor::decidereq(int &, const string &, paxos_protocol::decidearg a)
-{
- lock ml(pxs_mutex);
- LOG("decidereq for accepted instance " << a.instance << " (my instance " << instance_h << ") v=" << v_a);
- if (a.instance == instance_h + 1) {
- VERIFY(v_a == a.v);
- commit(a.instance, v_a, ml);
- } else if (a.instance <= instance_h) {
- // we are ahead ignore.
+proposer_acceptor::decidereq(int &, const node_t &, unsigned instance, const value_t & v) {
+ lock ml(acceptor_mutex);
+ LOG("decidereq for accepted instance " << instance << " (my instance " << instance_h << ") v=" << accepted_value);
+ if (instance == instance_h + 1) {
+ VERIFY(accepted_value == v);
+ commit(instance, accepted_value, ml);
+ } else if (instance <= instance_h) {
+ // we are ahead; ignore.
} else {
- // we are behind
+ // we are behind.
VERIFY(0);
}
return paxos_protocol::OK;
}
-void
-acceptor::commit(unsigned instance, const string & value, lock & pxs_mutex_lock)
-{
- LOG("acceptor::commit: instance=" << instance << " has v=" << value);
+void proposer_acceptor::commit(unsigned instance, const value_t & value) {
+ lock ml(acceptor_mutex);
+ commit(instance, value, ml);
+}
+
+void proposer_acceptor::commit(unsigned instance, const value_t & value, lock & pxs_mutex_lock) {
+ LOG("instance=" << instance << " has v=" << value);
if (instance > instance_h) {
- LOG("commit: highestaccepteinstance = " << instance);
+ LOG("highestacceptedinstance = " << instance);
values[instance] = value;
- l->loginstance(instance, value);
+ l.loginstance(instance, value);
instance_h = instance;
- n_h.n = 0;
- n_h.m = me;
- n_a.n = 0;
- n_a.m = me;
- v_a.clear();
- if (cfg) {
+ accepted = promise = {0, me};
+ string v = value; // gaaahhh aliasing of value and accepted_value
+ accepted_value.clear(); // this wipes out "value", too
+ if (delegate) {
pxs_mutex_lock.unlock();
- cfg->paxos_commit(instance, value);
+ delegate->paxos_commit(instance, v);
pxs_mutex_lock.lock();
}
}
}
-void
-acceptor::commit(unsigned instance, const string & value)
-{
- lock ml(pxs_mutex);
- commit(instance, value, ml);
-}
-
-string
-acceptor::dump()
-{
- return l->dump();
-}
-
-void
-acceptor::restore(const string & s)
-{
- l->restore(s);
- l->logread();
-}
-
-
-
// For testing purposes
-
-// Call this from your code between phases prepare and accept of proposer
-void
-proposer::breakpoint1()
-{
+void proposer_acceptor::breakpoint1() {
if (break1) {
LOG("Dying at breakpoint 1!");
exit(1);
}
}
-// Call this from your code between phases accept and decide of proposer
-void
-proposer::breakpoint2()
-{
+void proposer_acceptor::breakpoint2() {
if (break2) {
LOG("Dying at breakpoint 2!");
exit(1);
}
}
-void
-proposer::breakpoint(int b)
-{
+void proposer_acceptor::breakpoint(int b) {
if (b == 3) {
- LOG("Proposer: breakpoint 1");
+ LOG("breakpoint 1");
break1 = true;
} else if (b == 4) {
- LOG("Proposer: breakpoint 2");
+ LOG("breakpoint 2");
break2 = true;
}
}
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