- Address seg fault in "storageRecruiter" actor

fdbserver/DDTeamCollection.actor.cpp

@@ -2631,7 +2631,11 @@ public:
 										    .detail("TSSID", tssId)
 										    .detail("Reason",
 										            self->zeroHealthyTeams->get() ? "ZeroHealthyTeams" : "TooMany");
+										Promise<Void> shutdown = self->shutdown;
 										killPromise.send(Void());
+										if (!shutdown.canBeSet()) {
+											return Void(); // "self" got destroyed, so return.
+										}
 									}
 								}
 							}
@@ -3582,6 +3586,8 @@ DDTeamCollection::DDTeamCollection(Database const& cx,
 
 DDTeamCollection::~DDTeamCollection() {
 	TraceEvent("DDTeamCollectionDestructed", distributorId).detail("Primary", primary);
+	// Signal that the object is being destroyed.
+	shutdown.send(Void());
 
 	// Cancel the teamBuilder to avoid creating new teams after teams are cancelled.
 	teamBuilder.cancel();

fdbserver/DDTeamCollection.h

@@ -272,6 +272,12 @@ class DDTeamCollection : public ReferenceCounted<DDTeamCollection> {
 
 	LocalityMap<UID> machineLocalityMap; // locality info of machines
 
+	// A mechanism to tell actors that reference a DDTeamCollection object through a direct
+	// pointer (without doing reference counting) that the object is being destroyed.
+	// (Introduced to solve the problem of "self" getting destroyed from underneath the
+	// "storageRecruiter" actor).
+	Promise<Void> shutdown;
+
 	// Randomly choose one machine team that has chosenServer and has the correct size
 	// When configuration is changed, we may have machine teams with old storageTeamSize
 	Reference<TCMachineTeamInfo> findOneRandomMachineTeam(TCServerInfo const& chosenServer) const;