Track c-ares socket opens and closes

Summary: Add dedicated c-ares socket open and close counters alongside the existing `cares_open_sockets` gauge, and track socket state in `CAresResolver` so fwdproxy can distinguish steady-state socket occupancy from churn during DNS outages.

Differential Revision: D106704403

fbshipit-source-id: 3ac9b71221fe87b3abcab465f15739b5a5facf9c

Author: Jorge Lopez Silva

proxygen/lib/dns/CAresResolver.cpp

@@ -697,6 +697,19 @@ void CAresResolver::sampleOpenSockets() {
   getStatsCollector()->recordCAresOpenSockets(socketHandlers_.size());
 }
 
+void CAresResolver::recordSocketOpened() {
+  if (!caresStateSamplingEnabled_) {
+    return;
+  }
+  getStatsCollector()->recordCAresSocketOpen();
+}
+
+void CAresResolver::recordSocketClosed() {
+  if (!caresStateSamplingEnabled_) {
+    return;
+  }
+  getStatsCollector()->recordCAresSocketClose();
+}
 void CAresResolver::init() {
   CHECK(base_ != nullptr);
 
@@ -1057,6 +1070,7 @@ void CAresResolver::dnsSocketReady(void* data,
         << "dnsSocketReady() asked to close a socket that we don't kow about";
     if (it != self->socketHandlers_.end()) {
       self->socketHandlers_.erase(it);
+      self->recordSocketClosed();
       self->sampleOpenSockets();
     }
 
@@ -1066,10 +1080,12 @@ void CAresResolver::dnsSocketReady(void* data,
   // Find the EventHandler that's managing our socket, creating one if it does
   // not already exist
   SocketHandler* shp = nullptr;
+  bool inserted = false;
   if (it == self->socketHandlers_.end()) {
     shp = new SocketHandler(
         self, self->base_, folly::NetworkSocket(sock), self->channel_);
     self->socketHandlers_[sock].reset(shp);
+    inserted = true;
   } else {
     shp = it->second.get();
   }
@@ -1081,7 +1097,8 @@ void CAresResolver::dnsSocketReady(void* data,
   if (!shp->registerHandler(events)) {
     LOG(DFATAL) << "Failed to register SocketHandler";
   }
-  if (it == self->socketHandlers_.end()) {
+  if (inserted) {
+    self->recordSocketOpened();
     self->sampleOpenSockets();
   }
 }

proxygen/lib/dns/CAresResolver.h

@@ -248,6 +248,8 @@ class CAresResolver : public DNSResolver {
   // state callback.
   void sampleActiveQueries();
   void sampleOpenSockets();
+  void recordSocketOpened();
+  void recordSocketClosed();
 
   // Attempt to resolve literal IPs, invoking the callback and returning
   // true if we succeeded.

proxygen/lib/dns/DNSResolver.h

@@ -361,6 +361,16 @@ class DNSResolver : public folly::DelayedDestruction {
       * Optional: record the current number of open c-ares sockets.
       */
      virtual void recordCAresOpenSockets(size_t /*count*/) noexcept {}
+
+     /**
+      * Optional: record that c-ares opened a socket.
+      */
+     virtual void recordCAresSocketOpen() noexcept {}
+
+     /**
+      * Optional: record that c-ares closed a socket.
+      */
+     virtual void recordCAresSocketClose() noexcept {}
 };