[jira] [Commented] (MESOS-3046) Stout's UUID re-seeds a new random generator during each call to UUID::random.

[Nikita Vetoshkin (JIRA)]

    [ 
https://issues.apache.org/jira/browse/MESOS-3046?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14647282#comment-14647282
 ] 

Nikita Vetoshkin commented on MESOS-3046:
-----------------------------------------

Out of curiosity took a look at this one.
In MESOS-2940 it was suggested to put generator in {{thread_local}} like this
{noformat}
diff --git a/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp 
b/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp
index e8ebe0b..b0facb2 100644
--- a/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp
+++ b/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp
@@ -28,7 +28,7 @@ struct UUID : boost::uuids::uuid
 public:
   static UUID random()
   {
-    return UUID(boost::uuids::random_generator()());
+    return UUID(random_generator());
   }
 
   static UUID fromBytes(const std::string& s)
@@ -62,6 +62,7 @@ public:
 private:
   explicit UUID(const boost::uuids::uuid& uuid)
     : boost::uuids::uuid(uuid) {}
+  static thread_local boost::uuids::random_generator random_generator;
 };
 
 #endif // __STOUT_UUID_HPP__
{noformat}
fails with GCC 5.1.1 on Fedora x64:
{noformat}
./.libs/libmesos.so: error: undefined reference to 'TLS init function for 
UUID::random_generator'
./.libs/libmesos.so: error: undefined reference to 'UUID::random_generator'
{noformat}
However, putting static in function does work
{noformat}
--- a/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp
+++ b/3rdparty/libprocess/3rdparty/stout/include/stout/uuid.hpp
@@ -28,7 +28,8 @@ struct UUID : boost::uuids::uuid
 public:
   static UUID random()
   {
-    return UUID(boost::uuids::random_generator()());
+    static thread_local boost::uuids::random_generator random_generator;
+    return UUID(random_generator());
   }
 
   static UUID fromBytes(const std::string& s)

{noformat}
But I wonder whether it contradicts with "no static objects with non-trivial 
constructors" policy, because lifetime of this object is event more 
sophisticated that ordinary {{static}} with per thread list of destructors to 
call upon thread exit and so on.

> Stout's UUID re-seeds a new random generator during each call to UUID::random.
> ------------------------------------------------------------------------------
>
>                 Key: MESOS-3046
>                 URL: https://issues.apache.org/jira/browse/MESOS-3046
>             Project: Mesos
>          Issue Type: Bug
>          Components: stout
>            Reporter: Benjamin Mahler
>              Labels: newbie, twitter
>
> Per [~StephanErb] and [~kevints]'s observations on MESOS-2940, stout's UUID 
> abstraction is re-seeding the random generator during each call to 
> {{UUID::random()}}, which is really expensive.
> This is confirmed in the perf graph from MESOS-2940.



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