Fixed memory leaks

Summary:
MyRocks valgrind run was showing memory leaks. The fixes are mostly self-explaining.
There is only a single usage of ThreadLocalPtr. Potentially, we may think about replacing this use with thread_local, but it will be a bigger change. Another option to consider is using thread_local instead of __thread in ThreadLocalPtr implementation. This way, tls_ can be stored using std::unique_ptr and no destructor would be required.

Test Plan:
 - make check
 - MyRocks valgrind run doesn't report leaks

Reviewers: rven, sdong

Reviewed By: sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D43677

util/comparator.cc

@@ -8,6 +8,7 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include <algorithm>
+#include <memory>
 #include <stdint.h>
 #include "rocksdb/comparator.h"
 #include "rocksdb/slice.h"
@@ -85,22 +86,22 @@ class ReverseBytewiseComparatorImpl : public BytewiseComparatorImpl {
 }// namespace
 
 static port::OnceType once = LEVELDB_ONCE_INIT;
-static const Comparator* bytewise;
-static const Comparator* rbytewise;
+static std::unique_ptr<const Comparator> bytewise;
+static std::unique_ptr<const Comparator> rbytewise;
 
 static void InitModule() {
-  bytewise = new BytewiseComparatorImpl;
-  rbytewise= new ReverseBytewiseComparatorImpl;
+  bytewise.reset(new BytewiseComparatorImpl);
+  rbytewise.reset(new ReverseBytewiseComparatorImpl);
 }
 
 const Comparator* BytewiseComparator() {
   port::InitOnce(&once, InitModule);
-  return bytewise;
+  return bytewise.get();
 }
 
 const Comparator* ReverseBytewiseComparator() {
   port::InitOnce(&once, InitModule);
-  return rbytewise;
+  return rbytewise.get();
 }
 
 }  // namespace rocksdb

util/thread_local.cc

@@ -137,6 +137,17 @@ ThreadLocalPtr::StaticMeta::StaticMeta() : next_instance_id_(0) {
   if (pthread_key_create(&pthread_key_, &OnThreadExit) != 0) {
     abort();
   }
+
+  // OnThreadExit is not getting called on the main thread.
+  // Call through the static destructor mechanism to avoid memory leak.
+  static struct A {
+    ~A() {
+      if (tls_) {
+        OnThreadExit(tls_);
+      }
+    }
+  } a;
+
   head_.next = &head_;
   head_.prev = &head_;