[BP] Update FileMgr's KvHeader only within FileMgr's spin lock context

This is to avoid racing in setting KvHeader which could potentially
cause leaks.

11:58:40 Direct leak of 56 byte(s) in 1 object(s) allocated from:
11:58:40     #0 0x4eead2 in operator new(unsigned long) (/home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/build/forestdb/tests/usecase/usecase_test+0x4eead2)
11:58:40     #1 0x5db423 in _fdb_kvs_header_create /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/src/kv_instance.cc:282:28
11:58:40     #2 0x599fb4 in FdbEngine::openFdb(FdbKvsHandle*, char const*, fdb_filename_mode_t, fdb_config const*) /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/src/forestdb.cc:2302:25
11:58:40     #3 0x5a582b in fdb_check_file_reopen /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/src/forestdb.cc:1175:18
11:58:40     #4 0x5aa1dc in FdbEngine::set(FdbKvsHandle*, fdb_doc_struct*) /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/src/forestdb.cc:3341:10
11:58:40     #5 0x506741 in FdbEngine::setKeyValue(FdbKvsHandle*, void const*, unsigned long, void const*, unsigned long) /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/src/api_wrapper.cc:165:10
11:58:40     #6 0x4f6acd in test_writes_on_kv_stores_with_compaction(unsigned short, int) /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/tests/usecase/usecase_test.cc:988:22
11:58:40     #7 0x4fc60a in main /home/couchbase/jenkins/workspace/forestdb-address_sanitizer-unstable/forestdb/tests/usecase/usecase_test.cc:1262:5
11:58:40     #8 0x2b3f217b376c in __libc_start_main /build/buildd/eglibc-2.15/csu/libc-start.c:226

(Reviewed-on: http://review.couchbase.org/67078)

Change-Id: Ic23d15d8e95bfea5945fe3c4a3051bc491f21820
Reviewed-on: http://review.couchbase.org/67173
Reviewed-by: Chiyoung Seo <[email protected]>
Tested-by: buildbot <[email protected]>

Author: abhinavdangeti

src/kv_instance.cc

@@ -287,14 +287,17 @@ void _fdb_kvs_header_create(KvsHeader **kv_header_ptr)
 
 void fdb_kvs_header_create(FileMgr *file)
 {
+    file->acquireSpinLock();
     KvsHeader *kv_header = file->getKVHeader_UNLOCKED();
     if (kv_header) {
-        return; // already exist
+        file->releaseSpinLock();
+        return; // already exists
     }
 
     _fdb_kvs_header_create(&kv_header);
     file->setKVHeader_UNLOCKED(kv_header);
     file->setFreeKVHeaderCB(fdb_kvs_header_free);
+    file->releaseSpinLock();
 }
 
 void fdb_kvs_header_reset_all_stats(FileMgr *file)
@@ -956,12 +959,15 @@ void _fdb_kvs_header_free(KvsHeader *kv_header)
 
 void fdb_kvs_header_free(FileMgr *file)
 {
+    file->acquireSpinLock();
     if (file->getKVHeader_UNLOCKED() == NULL) {
+        file->releaseSpinLock();
         return;
     }
 
     _fdb_kvs_header_free(file->getKVHeader_UNLOCKED());
     file->setKVHeader_UNLOCKED(NULL);
+    file->releaseSpinLock();
 }
 
 // this function just returns pointer