BIND 10 trac495, updated. 87308eeddf767dea581b817d1d2ab2aaa4a99dd3 [trac495] update internal documentation of RunningQuery
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Thu Mar 3 10:24:32 UTC 2011
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- Log -----------------------------------------------------------------
commit 87308eeddf767dea581b817d1d2ab2aaa4a99dd3
Author: Jelte Jansen <jelte at isc.org>
Date: Thu Mar 3 11:24:17 2011 +0100
[trac495] update internal documentation of RunningQuery
-----------------------------------------------------------------------
Summary of changes:
src/lib/resolve/recursive_query.cc | 81 +++++++++++++++------
src/lib/resolve/tests/recursive_query_unittest.cc | 1 -
2 files changed, 60 insertions(+), 22 deletions(-)
-----------------------------------------------------------------------
diff --git a/src/lib/resolve/recursive_query.cc b/src/lib/resolve/recursive_query.cc
index e0474d7..1fd9f9a 100644
--- a/src/lib/resolve/recursive_query.cc
+++ b/src/lib/resolve/recursive_query.cc
@@ -117,11 +117,11 @@ private:
// we should differentiate between forwarding and resolving
boost::shared_ptr<AddressVector> upstream_;
- // Buffer to store the result.
+ // Buffer to store the intermediate results.
OutputBufferPtr buffer_;
- // Server to notify when we succeed or fail
- //shared_ptr<DNSServer> server_;
+ // The callback will be called when we have either decided we
+ // are done, or when we give up
isc::resolve::ResolverInterface::CallbackPtr resolvercallback_;
// To prevent both unreasonably long cname chains and cname loops,
@@ -134,7 +134,7 @@ private:
* TODO Do something more clever with timeouts. In the long term, some
* computation of average RTT, increase with each retry, etc.
*/
- // Timeout information
+ // Timeout information for outgoing queries
int query_timeout_;
unsigned retries_;
@@ -152,9 +152,9 @@ private:
// If we timed out ourselves (lookup timeout), stop issuing queries
bool done_;
- // If we have a client timeout, we send back an answer, but don't
- // stop. We use this variable to make sure we don't send another
- // answer if we do find one later (or if we have a lookup_timeout)
+ // If we have a client timeout, we call back with a failure message,
+ // but we do not stop yet. We use this variable to make sure we
+ // don't call back a second time later
bool callback_called_;
// Reference to our NSAS
@@ -163,15 +163,38 @@ private:
// Reference to our cache
isc::cache::ResolverCache& cache_;
- // the 'current' nameserver we have a query out to
+ // the 'current' zone we are in (i.e.) we start out at the root,
+ // and for each delegation this gets updated with the zone the
+ // delegation points to
std::string cur_zone_;
+
+ // This is the handler we pass on to the NSAS; it is called when
+ // the NSAS has an address for us to query
boost::shared_ptr<ResolverNSASCallback> nsas_callback_;
+
// this is set to true if we have asked the nsas to give us
- // an address and we are waiting for it to call us back
+ // an address and we are waiting for it to call us back.
+ // We use is to cancel the outstanding callback in case we
+ // have a lookup timeout and decide to give up
bool nsas_callback_out_;
+
+ // This is the nameserver we have an outstanding query to.
+ // It is used to update the RTT once the query returns
isc::nsas::NameserverAddress current_ns_address;
+
+ // The moment in time we sent a query to the nameserver above.
struct timeval current_ns_qsent_time;
+ // RunningQuery deletes itself when it is done. In order for us
+ // to do this safely, we must make sure that there are no events
+ // that might call back to it. There are two types of events in
+ // this sense; the timers we set ourselves (lookup and client),
+ // and outstanding queries to nameservers. When each of these is
+ // started, we increase this value. When they fire, it is decreased
+ // again. We cannot delete ourselves until this value is back to 0.
+ //
+ // Note that the NSAS callback is *not* seen as an outstanding
+ // event; we can cancel the NSAS callback safely.
size_t outstanding_events_;
// perform a single lookup; first we check the cache to see
@@ -199,6 +222,7 @@ private:
}
+ // Send the current question to the given nameserver address
void sendTo(const isc::nsas::NameserverAddress& address) {
// We need to keep track of the Address, so that we can update
// the RTT
@@ -212,6 +236,9 @@ private:
io_.get_io_service().post(query);
}
+ // 'general' send; if we are in forwarder mode, send a query to
+ // a random nameserver in our forwarders list. If we are in
+ // recursive mode, ask the NSAS to give us an address.
void send() {
// If are in forwarder mode, send it to a random
// forwarder. If not, ask the NSAS for an address
@@ -238,16 +265,20 @@ private:
}
}
+ // Called by our NSAS callback handler so we know we do not have
+ // an outstanding NSAS call anymore.
void nsasCallbackCalled() {
nsas_callback_out_ = false;
}
- // This function is called by operator() if there is an actual
- // answer from a server and we are in recursive mode
- // depending on the contents, we go on recursing or return
+ // This function is called by operator() and lookup();
+ // We have an answer either from a nameserver or the cache, and
+ // we do not know yet if this is a final answer we can send back or
+ // that more recursive processing needs to be done.
+ // Depending on the content, we go on recursing or return
//
- // Note that the footprint may change as this function may
- // need to append data to the answer we are building later.
+ // This method also updates the cache, depending on the content
+ // of the message
//
// returns true if we are done (either we have an answer or an
// error message)
@@ -361,10 +392,10 @@ private:
return true;
break;
}
- // should not be reached. assert here?
- // (since we do not have a default in the switch above,
+
+ // Since we do not have a default in the switch above,
// the compiler should have errored on any missing case
- // statements
+ // statements.
assert(false);
return true;
}
@@ -426,6 +457,7 @@ public:
makeSERVFAIL();
callCallback(true);
}
+ assert(outstanding_events_ > 0);
--outstanding_events_;
stop();
}
@@ -437,7 +469,11 @@ public:
makeSERVFAIL();
callCallback(true);
}
+ assert(outstanding_events_ > 0);
--outstanding_events_;
+ if (outstanding_events_ == 0) {
+ stop();
+ }
}
// If the callback has not been called yet, call it now
@@ -472,6 +508,8 @@ public:
}
}
+ // We are done. If there are no more outstanding events, we delete
+ // ourselves. If there are any, we do not.
void stop() {
done_ = true;
if (nsas_callback_out_) {
@@ -490,6 +528,7 @@ public:
// This function is used as callback from DNSQuery.
virtual void operator()(IOFetch::Result result) {
// XXX is this the place for TCP retry?
+ assert(outstanding_events_ > 0);
--outstanding_events_;
if (!done_ && result != IOFetch::TIME_OUT) {
@@ -528,16 +567,16 @@ public:
stop();
}
} else if (!done_ && retries_--) {
- // We timed out, but we have some retries, so send again
+ // Query timed out, but we have some retries, so send again
dlog("Timeout for " + question_.toText() + " to " + current_ns_address.getAddress().toText() + ", resending query");
if (recursive_mode()) {
current_ns_address.updateRTT(isc::nsas::AddressEntry::UNREACHABLE);
}
send();
} else {
- // out of retries, give up for now
- dlog("Timeout for " + question_.toText() + " to " + current_ns_address.getAddress().toText() + ", giving up");
- if (recursive_mode()) {
+ // We are either already done, or out of retries
+ if (recursive_mode() && result == IOFetch::TIME_OUT) {
+ dlog("Timeout for " + question_.toText() + " to " + current_ns_address.getAddress().toText() + ", giving up");
current_ns_address.updateRTT(isc::nsas::AddressEntry::UNREACHABLE);
}
if (!callback_called_) {
diff --git a/src/lib/resolve/tests/recursive_query_unittest.cc b/src/lib/resolve/tests/recursive_query_unittest.cc
index 2cf5963..b005d5b 100644
--- a/src/lib/resolve/tests/recursive_query_unittest.cc
+++ b/src/lib/resolve/tests/recursive_query_unittest.cc
@@ -335,7 +335,6 @@ protected:
{}
void resume(const bool done) {
- std::cout << "[XX] RESUME!" << std::endl;
*done_ = done;
io_.stop();
}
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