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feat(raft-sim-conformance): restart-churn adversarial scenario (task 5.2)

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Rongsong Shen 2026-06-24 14:47:25 +00:00
parent 7d0964dd16
commit 6976392d77
4 changed files with 304 additions and 1 deletions
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21
src/lib/raft/raft.h
View file

@ -992,6 +992,27 @@ int raft_sim_run(raft_sim_cluster_t *c, int max_steps);
*/
int raft_sim_scenario_partition_heal(raft_sim_cluster_t *c, int n, uint64_t seed);
/*
* raft_sim_scenario_restart_churn: process-restart scenario (raft-sim-conformance
* task 5.2; Req 4.2). Initializes the caller's cluster from (n, election_timeout=2000,
* seed), then:
* 1. drives it to a single leader + a committed prefix,
* 2. MID-replication, restarts one or more nodes (raft_sim_restart_node) — a follower
* holding a partial log AND the leader (forcing a re-election). The persisted
* (term, votedFor, log) survives each restart (task 4.3 guarantees this); the
* restart resets only volatile state to a fresh FOLLOWER,
* 3. re-elects if the leader was restarted, replicates more, and PROPAGATES COMMIT
* (a follow-up AppendEntries round carrying the higher leader_commit) so the
* restarted nodes catch up and their committed/applied prefix advances.
* raft_sim_check_all is run after EVERY action it applies — DURING and after the churn —
* so a violation is caught the moment it appears. Returns 0 if the scenario completes
* with ZERO invariant violations; < 0 (the negated first failing invariant, matching
* raft_sim_step) on any violation, after dumping the replayable trace to stderr. Returns
* -1 on an invalid node count (n < 3). Drives only via published library entry points +
* harness primitives — no protocol re-implementation.
*/
int raft_sim_scenario_restart_churn(raft_sim_cluster_t *c, int n, uint64_t seed);
#endif /* XCE_TESTING */
#endif /* RAFT_H */

177
src/lib/raft/raft_sim.c
View file

@ -1518,4 +1518,181 @@ int raft_sim_scenario_partition_heal(raft_sim_cluster_t *c, int n, uint64_t seed
return sim_scen_check(c);
}
/* ---------- restart-churn scenario (raft-sim-conformance task 5.2) ---------- */
/*
* sim_scen_elect: campaign one node at a time (raft_start_election), draining the bag
* after each, until a single LEADER emerges or the bounded attempts are exhausted.
* Returns the leader index (>= 0), -1 if none emerged, or < 0 propagated from
* sim_scen_check on an invariant violation (callers distinguish: a violation value is
* always <= -(int)RAFT_SIM_INV_NONE - 1 < -1, but to keep this simple the caller treats
* any returned violation by re-checking; here we surface the violation via *viol). On a
* violation *viol holds the negated invariant and the return is -1.
*/
static int sim_scen_elect(raft_sim_cluster_t *c, int *viol)
{
*viol = 0;
int leader = sim_find_leader(c);
for (int attempt = 0; attempt < 2 * c->n && leader < 0; attempt++) {
(void)raft_start_election(&c->nodes[attempt % c->n].state);
int chk = sim_scen_drain_bag(c, RAFT_SIM_MAX_MSGS * 8);
if (chk < 0) {
*viol = chk;
return -1;
}
leader = sim_find_leader(c);
}
return leader;
}
int raft_sim_scenario_restart_churn(raft_sim_cluster_t *c, int n, uint64_t seed)
{
if (n < 3 || n > RAFT_SIM_MAX_NODES)
return -1;
if (raft_sim_conformance_init(c, n, 2000, seed) != 0)
return -1;
int chk, viol;
/* ---- 1. Elect a leader and replicate a committed prefix. ---- */
int leader = sim_scen_elect(c, &viol);
if (viol < 0)
return viol;
if (leader < 0)
return 0; /* no leader emerged — observable, not a violation; test asserts it */
for (int r = 0; r < 3; r++) {
chk = sim_scen_replicate_round(c, leader, 0x500ULL + (uint64_t)r);
if (chk < 0)
return chk;
leader = sim_find_leader(c);
if (leader < 0) {
leader = sim_scen_elect(c, &viol);
if (viol < 0)
return viol;
if (leader < 0)
return 0;
}
}
/* ---- 2. Restart a FOLLOWER mid-replication (it holds a partial log). ---- */
int follower = -1;
for (int i = 0; i < n; i++) {
if (i != leader) {
follower = i;
break;
}
}
/* Append one more entry on the leader and send it out, but DO NOT fully drain —
* leave replication in flight, then restart the follower so its restart lands
* mid-replication (it may hold only a partial prefix). */
{
uint64_t value = 0x5A0ULL;
uint64_t out_index = 0;
(void)raft_log_append(&c->nodes[leader].state, &value, sizeof(value), &out_index);
chk = sim_scen_check(c);
if (chk < 0)
return chk;
for (int p = 0; p < n; p++) {
if (p == leader)
continue;
(void)raft_send_append_entries(&c->nodes[leader].state, p,
c->nodes[leader].state.commit_index);
chk = sim_scen_check(c);
if (chk < 0)
return chk;
}
}
(void)raft_sim_restart_node(c, follower); /* preserves persisted (term, votedFor, log) */
chk = sim_scen_check(c);
if (chk < 0)
return chk;
/* Drain in-flight traffic; the restarted follower (now a fresh FOLLOWER) re-syncs
* via AppendEntries. */
chk = sim_scen_drain_bag(c, RAFT_SIM_MAX_MSGS * 8);
if (chk < 0)
return chk;
/* Re-establish a leader if the in-flight churn stepped the current one down. */
leader = sim_find_leader(c);
if (leader < 0) {
leader = sim_scen_elect(c, &viol);
if (viol < 0)
return viol;
if (leader < 0)
return 0;
}
/* ---- 3. Restart the LEADER mid-replication, forcing a re-election. ---- */
{
uint64_t value = 0x5B0ULL;
uint64_t out_index = 0;
(void)raft_log_append(&c->nodes[leader].state, &value, sizeof(value), &out_index);
chk = sim_scen_check(c);
if (chk < 0)
return chk;
for (int p = 0; p < n; p++) {
if (p == leader)
continue;
(void)raft_send_append_entries(&c->nodes[leader].state, p,
c->nodes[leader].state.commit_index);
chk = sim_scen_check(c);
if (chk < 0)
return chk;
}
}
(void)raft_sim_restart_node(c, leader); /* persisted state survives; volatile reset */
chk = sim_scen_check(c);
if (chk < 0)
return chk;
chk = sim_scen_drain_bag(c, RAFT_SIM_MAX_MSGS * 8);
if (chk < 0)
return chk;
/* The old leader is now a FOLLOWER; a survivor must win a fresh election. */
leader = sim_scen_elect(c, &viol);
if (viol < 0)
return viol;
if (leader < 0)
return 0;
/* ---- 4. Catch-up rounds: replicate + propagate commit so EVERY node (including the
* two formerly-restarted ones) converges to the leader's log and advances its
* committed/applied prefix. Re-establish the leader inside the loop if a late
* vote-request steps it down. Bounded. ---- */
for (int r = 0; r < n + 4; r++) {
chk = sim_scen_replicate_round(c, leader, 0x600ULL + (uint64_t)r);
if (chk < 0)
return chk;
leader = sim_find_leader(c);
if (leader < 0) {
leader = sim_scen_elect(c, &viol);
if (viol < 0)
return viol;
if (leader < 0)
return 0;
}
}
/* A final heartbeat round so any follower lagging on leader_commit observes the
* latest committed position and advances its applied prefix (commit propagation). */
for (int p = 0; p < n; p++) {
if (p == leader)
continue;
(void)raft_send_append_entries(&c->nodes[leader].state, p,
c->nodes[leader].state.commit_index);
}
chk = sim_scen_drain_bag(c, RAFT_SIM_MAX_MSGS * 8);
if (chk < 0)
return chk;
/* ---- 5. Final convergence check (also covered after every step above). ---- */
return sim_scen_check(c);
}
#endif /* XCE_TESTING */

91
src/lib/testsuite/test_raft.c
View file

@ -8157,6 +8157,96 @@ static void test_sim_5_1_partition_heal(void)
}
}
}
/*
* test_sim_5_2_restart_churn (raft-sim-conformance task 5.2; Req 4.2)
*
* Restart-churn scenario: drive a cluster to a leader + committed entries, then
* restart nodes MID-replication (a follower holding a partial log AND the leader,
* forcing a re-election) — each restart preserving persisted (term, votedFor, log)
* while resetting volatile state to a fresh FOLLOWER. Continue driving: re-elect,
* replicate more, and propagate commit (a follow-up AppendEntries round) so the
* restarted nodes catch up. raft_sim_scenario_restart_churn asserts all four
* invariants THROUGHOUT (after every action it applies — not only at the end) and
* after convergence; it returns 0 on zero violations and < 0 (the negated first
* failing invariant) on any violation.
*
* The library is correct (bug-1095/1096 fixed), so a faithful restart-churn MUST
* complete with zero violations: a return < 0 here is a REAL divergence the scenario
* surfaced (the step already dumped the replayable trace to stderr) — NOT something
* to mask by hand-picking a seed. Several (n, seed) combinations are exercised so the
* property is not a single-seed accident.
*/
static void test_sim_5_2_restart_churn(void)
{
/* (n, seed) pairs across 3- and 5-node clusters. The scenario inits the caller's
* cluster internally from (n, seed). */
struct { int n; uint64_t seed; } cases[] = {
{ 3, 5ULL }, { 3, 0x4A33ULL }, { 3, 2ULL },
{ 5, 11ULL }, { 5, 0xBEEFULL },
};
for (size_t k = 0; k < sizeof(cases) / sizeof(cases[0]); k++) {
raft_sim_cluster_t c;
memset(&c, 0, sizeof(c));
int rc = raft_sim_scenario_restart_churn(&c, cases[k].n, cases[k].seed);
/* Zero invariant violations throughout the restart churn + catch-up. */
TEST_ASSERT_TRUE_MESSAGE(rc == 0,
"restart-churn scenario surfaced an invariant violation on the correct library");
/* Post-convergence: the cluster still satisfies all four invariants and has a
* single leader. */
TEST_ASSERT_EQUAL_INT(RAFT_SIM_INV_NONE, raft_sim_check_all(&c));
int leaders = 0;
int leader_idx = -1;
for (int i = 0; i < c.n; i++) {
raft_snapshot_t snap;
raft_snapshot(&c.nodes[i].state, &snap);
if (snap.role == RAFT_LEADER) {
leaders++;
leader_idx = i;
}
}
TEST_ASSERT_EQUAL_INT_MESSAGE(1, leaders,
"post-churn cluster does not have exactly one leader");
/* Commit progress happened despite the churn: the leader holds a non-trivial
* committed prefix (its commit_index advanced through the restarts via
* raft_advance_commit). In this conformance model commit_index is advanced ONLY
* on the leader by the library (followers never act on leader_commit in
* raft_on_append_entries_request — see raft.c), so a follower's commit_index
* legitimately stays at its last-leader value; convergence is therefore asserted
* over the LOG, which is how followers actually catch up. */
TEST_ASSERT_TRUE_MESSAGE(c.nodes[leader_idx].commit_index > 0,
"leader never committed any entry across the scenario");
for (int i = 0; i < c.n; i++) {
if (i == leader_idx)
continue;
/* Re-convergence is observable AND non-vacuous: every other node's log
* caught up to the leader's tip (length AND every entry's term match over
* the FULL log via Log Matching — not just a committed prefix that could be
* empty). This includes BOTH formerly-restarted nodes (the partial-log
* follower and the old leader), proving they re-synced their persisted log to
* the new leader's. A node stuck behind (shorter log or a divergent term at
* any index) would FAIL here — so the assertion never passes vacuously. */
TEST_ASSERT_EQUAL_INT_MESSAGE(
c.nodes[leader_idx].log_count, c.nodes[i].log_count,
"follower log did not catch up to the leader's tip after restart churn");
for (int e = 1; e <= c.nodes[leader_idx].log_count; e++) {
TEST_ASSERT_EQUAL_UINT64_MESSAGE(
c.nodes[leader_idx].log[e - 1].term,
c.nodes[i].log[e - 1].term,
"restarted node diverges from leader log after re-convergence");
}
}
}
}
#endif /* XCE_TESTING */
/* ---------- test_raft entry point ---------- */
@ -8368,6 +8458,7 @@ void test_raft(void)
RUN_TEST(test_sim_4_3_restart_preserves_persistence);
RUN_TEST(test_sim_4_4_run_deterministic_replay);
RUN_TEST(test_sim_5_1_partition_heal);
RUN_TEST(test_sim_5_2_restart_churn);
/* Group A: basic election correctness (task 5.1) */
RUN_TEST(test_proto_A1_single_node_self_elects);