Address possible data race with loggerApi

WARNING: ThreadSanitizer: data race (pid=16718)

  Write of size 8 at 0x7f6a616aad60 by main thread:
    #0 create_instance /home/abhinav/couchbase/ep-engine/src/ep_engine.cc:1809:9 (ep.so+0x0000000b2c9c)
    couchbase#1 create_engine_instance /home/abhinav/couchbase/memcached/utilities/engine_loader.c:121:31 (libmcd_util.so.1.0.0+0x0000000056fd)
    couchbase#2 create_bucket(bool, char const*) /home/abhinav/couchbase/memcached/programs/engine_testapp/engine_testapp.cc:924:9 (engine_testapp+0x0000000b99ed)
    couchbase#3 create_buckets(char const*, int, std::vector<BucketHolder, std::allocator<BucketHolder> >&) /home/abhinav/couchbase/ep-engine/tests/ep_testsuite_common.cc:316:36 (ep_testsuite.so+0x0000000ab215)
    couchbase#4 test_multi_bucket_set_get(test*) /home/abhinav/couchbase/ep-engine/tests/ep_testsuite.cc:14174:9 (ep_testsuite.so+0x000000093011)
    couchbase#5 execute_test(test, char const*, char const*) /home/abhinav/couchbase/memcached/programs/engine_testapp/engine_testapp.cc:1103:19 (engine_testapp+0x0000000b937d)
    #6 main /home/abhinav/couchbase/memcached/programs/engine_testapp/engine_testapp.cc:1439 (engine_testapp+0x0000000b937d)

  Previous read of size 8 at 0x7f6a616aad60 by thread T2 (mutexes: write M11526, write M11540):
    #0 LOG(EXTENSION_LOG_LEVEL, char const*, ...) /home/abhinav/couchbase/ep-engine/src/ep_engine.cc:1916:9 (ep.so+0x0000000b2eb4)
    couchbase#1 TaskQueue::_schedule(SingleThreadedRCPtr<GlobalTask>&) /home/abhinav/couchbase/ep-engine/src/taskqueue.cc:225:5 (ep.so+0x000000141957)
    couchbase#2 TaskQueue::schedule(SingleThreadedRCPtr<GlobalTask>&) /home/abhinav/couchbase/ep-engine/src/taskqueue.cc:239:5 (ep.so+0x000000141bde)
    couchbase#3 ExecutorPool::_schedule(SingleThreadedRCPtr<GlobalTask>, task_type_t) /home/abhinav/couchbase/ep-engine/src/executorpool.cc:430:5 (ep.so+0x0000000ef2f5)
    couchbase#4 ExecutorPool::schedule(SingleThreadedRCPtr<GlobalTask>, task_type_t) /home/abhinav/couchbase/ep-engine/src/executorpool.cc:437:17 (ep.so+0x0000000ef44f)
    couchbase#5 Warmup::scheduleEstimateDatabaseItemCount() /home/abhinav/couchbase/ep-engine/src/warmup.cc:538:9 (ep.so+0x000000158b7a)
    #6 Warmup::step() /home/abhinav/couchbase/ep-engine/src/warmup.cc:883:13 (ep.so+0x000000155510)
    #7 Warmup::transition(int, bool) /home/abhinav/couchbase/ep-engine/src/warmup.cc:920:9 (ep.so+0x00000015856e)
    #8 Warmup::createVBuckets(unsigned short) /home/abhinav/couchbase/ep-engine/src/warmup.cc:525 (ep.so+0x00000015856e)
    #9 WarmupCreateVBuckets::run() /home/abhinav/couchbase/ep-engine/src/warmup.h:249:9 (ep.so+0x000000165236)
    #10 ExecutorThread::run() /home/abhinav/couchbase/ep-engine/src/executorthread.cc:112:26 (ep.so+0x0000000f8296)
    #11 launch_executor_thread(void*) /home/abhinav/couchbase/ep-engine/src/executorthread.cc:33:9 (ep.so+0x0000000f7e35)
    #12 platform_thread_wrap /home/abhinav/couchbase/platform/src/cb_pthreads.c:23:5 (libplatform.so.0.1.0+0x000000003d31)

  Location is global 'loggerApi' of size 8 at 0x7f6a616aad60 (ep.so+0x00000042ad60)

Change-Id: I3ec917106a9684dfc8ce26664a6926135b6cb299
Reviewed-on: http://review.couchbase.org/55840
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: buildbot <build@couchbase.com>

Author: abhinavdangeti

src/ep_engine.cc

@@ -50,8 +50,8 @@
 #include "dcp/producer.h"
 #include "warmup.h"
 
-static ALLOCATOR_HOOKS_API *hooksApi;
-static SERVER_LOG_API *loggerApi;
+static AtomicValue<ALLOCATOR_HOOKS_API*> hooksApi;
+static AtomicValue<SERVER_LOG_API*> loggerApi;
 
 static size_t percentOf(size_t val, double percent) {
     return static_cast<size_t>(static_cast<double>(val) * percent);
@@ -1805,8 +1805,8 @@ extern "C" {
             return ENGINE_ENOTSUP;
         }
 
-        hooksApi = api->alloc_hooks;
-        loggerApi = api->log;
+        hooksApi.store(api->alloc_hooks, std::memory_order_relaxed);
+        loggerApi.store(api->log, std::memory_order_relaxed);
         MemoryTracker::getInstance();
         ObjectRegistry::initialize(api->alloc_hooks->get_allocation_size);
 
@@ -1913,18 +1913,18 @@ extern "C" {
 void LOG(EXTENSION_LOG_LEVEL severity, const char *fmt, ...) {
     char buffer[2048];
 
-    if (loggerApi != nullptr) {
+    if (loggerApi.load(std::memory_order_relaxed) != nullptr) {
         static EXTENSION_LOGGER_DESCRIPTOR* logger;
         if (logger == nullptr) {
             // This locking isn't really needed because get_logger will
             // always return the same address, but it'll keep thread sanitizer
             // and other tools from complaining ;-)
             static std::mutex mutex;
             std::lock_guard<std::mutex> guard(mutex);
-            logger = loggerApi->get_logger();
+            logger = loggerApi.load(std::memory_order_relaxed)->get_logger();
         }
 
-        if (loggerApi->get_level() <= severity) {
+        if (loggerApi.load(std::memory_order_relaxed)->get_level() <= severity) {
             EventuallyPersistentEngine *engine = ObjectRegistry::onSwitchThread(NULL, true);
             va_list va;
             va_start(va, fmt);
@@ -1942,7 +1942,7 @@ void LOG(EXTENSION_LOG_LEVEL severity, const char *fmt, ...) {
 }
 
 ALLOCATOR_HOOKS_API *getHooksApi(void) {
-    return hooksApi;
+    return hooksApi.load(std::memory_order_relaxed);
 }
 
 EventuallyPersistentEngine::EventuallyPersistentEngine(