Fix deadlock in RibOutUpdates::TailDequeue/PeerDequeue

RibOutUpdates::TailDequeue/PeerDequeue can deadlock if 2 RouteUpdates
have the same timestamp.  Calling clock_gettime with CLOCK_MONOTONIC
does not guarantee monotonically increasing timestamps.

Use atomic uint64_t to implement relative timestamp for RouteUpdate.

Change-Id: I328fc96405c51dace5b5e8a79b80026631a0bb4b
Partial-Bug: 1411855

src/bgp/bgp_update.cc

@@ -4,14 +4,13 @@
 
 #include "bgp/bgp_update.h"
 
-#include <time.h>
-#ifdef __APPLE__
-#include <mach/mach_time.h>
-#endif
 #include "base/logging.h"
 #include "bgp/bgp_route.h"
 #include "bgp/bgp_table.h"
 
+// Automatically initialized to 0 in C++03 mode.
+tbb::atomic<uint64_t> RouteUpdate::global_tstamp_;
+
 //
 // Find the UpdateInfo element with matching RibOutAttr.
 //
@@ -421,18 +420,9 @@ UpdateList *RouteUpdate::GetUpdateList(RibOut *ribout) {
 
 //
 // Update the timestamp in this RouteUpdate.
-
-// The code expects that the APIs use the underlying CPU performance counters
-// in order to provide high resolution timestamps.
 //
 void RouteUpdate::set_tstamp_now() {
-#ifdef __APPLE__
-    tstamp_ = mach_absolute_time();
-#else
-    struct timespec ts;
-    clock_gettime(CLOCK_MONOTONIC, &ts);
-    tstamp_ = ts.tv_sec * 1000000000 + ts.tv_nsec;
-#endif
+    tstamp_ = global_tstamp_.fetch_and_increment();
 }
 
 //

src/bgp/bgp_update.h

@@ -10,7 +10,7 @@
 #include <boost/intrusive/list.hpp>
 #include <boost/intrusive/slist.hpp>
 #include <boost/intrusive/set.hpp>
-
+#include <tbb/atomic.h>
 #include <tbb/mutex.h>
 
 #include "bgp/bgp_ribout.h"
@@ -243,6 +243,7 @@ class RouteUpdate : public DBState, public UpdateEntry {
     void FlagSet(Flag flag) { flags_ |= (1 << flag); }
     void FlagReset(Flag flag) { flags_ &= ~(1 << flag); }
 
+    static tbb::atomic<uint64_t> global_tstamp_;
     tbb::mutex mutex_;
     BgpRoute *route_;
     int8_t queue_id_;