From 5300caadf686eca66dc96228d100de9e76d14728 Mon Sep 17 00:00:00 2001
From: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Date: Fri, 3 Apr 2015 17:49:02 +0200
Subject: [PATCH] utils: Fix UUID::get_time_UUID() creating conflicting UUIDs
 in SMP

UUID_gen::create_time_safe() does not synchronize across cores. The
comment says that it assumes it runs on a single core. This is no
longer true, we can run urchin on many cores. This easily leads to
UUID conflicts with more than one core. Fix by adding a per-core
unique number to the node part of the UUID.
---
 utils/UUID_gen.cc | 12 +++++++++---
 utils/UUID_gen.hh |  2 +-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/utils/UUID_gen.cc b/utils/UUID_gen.cc
index 00c92b07b2..c9fa9af212 100644
--- a/utils/UUID_gen.cc
+++ b/utils/UUID_gen.cc
@@ -22,6 +22,7 @@
 #include "UUID_gen.hh"
 
 #include <stdlib.h>
+#include <atomic>
 
 namespace utils {
 
@@ -76,9 +77,14 @@ static int64_t make_node()
 
 static int64_t make_node()
 {
-    // FIXME: don't leave this constant zero! See the above commented-out code
+    // FIXME: Mix-in node's address. See the above commented-out code
     // which is what Cassandra's UUIDGen.java did. We can also get the MAC address.
-    return 0;
+
+    // We should take current core number under consideration
+    // because create_time_safe() doesn't synchronize across cores and
+    // it's easy to get duplicates.
+    static std::atomic<unsigned> core_counter;
+    return core_counter.fetch_add(1);
 }
 
 
@@ -98,7 +104,7 @@ static int64_t make_clock_seq_and_node()
     return lsb;
 }
 
-const int64_t UUID_gen::clock_seq_and_node = make_clock_seq_and_node();
+const thread_local int64_t UUID_gen::clock_seq_and_node = make_clock_seq_and_node();
 thread_local const std::unique_ptr<UUID_gen> UUID_gen::instance (new UUID_gen());
 
 
diff --git a/utils/UUID_gen.hh b/utils/UUID_gen.hh
index d8506e80a0..141247f232 100644
--- a/utils/UUID_gen.hh
+++ b/utils/UUID_gen.hh
@@ -39,7 +39,7 @@ class UUID_gen
 private:
     // A grand day! millis at 00:00:00.000 15 Oct 1582.
     static constexpr int64_t START_EPOCH = -12219292800000L;
-    static const int64_t clock_seq_and_node;
+    static thread_local const int64_t clock_seq_and_node;
 
     /*
      * The min and max possible lsb for a UUID.