MB-15292: Make CouchbaseAtomic::load() atomic

Identified by ThreadSanitizer running ep_perfsuite.so:

WARNING: ThreadSanitizer: data race (pid=51118)
  Atomic write of size 1 at 0x7d4400009d58 by main thread (mutexes: write M5599):
    #0 __tsan_atomic8_compare_exchange_val <null>:0 (engine_testapp+0x000000093f50)
    couchbase#1 CouchbaseAtomic<bool>::compare_exchange_strong(bool&, bool, memory_order) /root/couchbase-3.0/ep-engine/src/atomic.h:92 (ep.so+0x00000005575d)
    couchbase#2 Flusher::notifyFlushEvent() /root/couchbase-3.0/ep-engine/src/flusher.h:88 (ep.so+0x0000000c6fec)
    couchbase#3 EventuallyPersistentStore::queueDirty(RCPtr<VBucket>&, StoredValue*, LockHolder*, bool, bool, bool) /root/couchbase-3.0/ep-engine/src/ep.cc:2826 (ep.so+0x00000009c796)
    couchbase#4 EventuallyPersistentStore::add(Item const&, void const*) /root/couchbase-3.0/ep-engine/src/ep.cc:728 (ep.so+0x00000009f673)
    couchbase#5 EventuallyPersistentEngine::store(void const*, void*, unsigned long*, ENGINE_STORE_OPERATION, unsigned short) /root/couchbase-3.0/ep-engine/src/ep_engine.cc:2135 (ep.so+0x000000100980)
    #6 EvpStore(engine_interface*, void const*, void*, unsigned long*, ENGINE_STORE_OPERATION, unsigned short) /root/couchbase-3.0/ep-engine/src/ep_engine.cc:229 (ep.so+0x0000000fa21d)
    #7 mock_store /root/couchbase-3.0/memcached/programs/engine_testapp/engine_testapp.c:227 (engine_testapp+0x0000000ade2e)
    #8 storeCasVb11(engine_interface*, engine_interface_v1*, void const*, ENGINE_STORE_OPERATION, char const*, char const*, unsigned long, unsigned int, void**, unsigned long, unsigned short, unsigned int, unsigned char) /root/couchbase-3.0/ep-engine/tests/ep_test_apis.cc:654 (ep_perfsuite.so+0x000000018ec3)
    #9 perf_latency(engine_interface*, engine_interface_v1*, char const*) /root/couchbase-3.0/ep-engine/tests/ep_perfsuite.cc:104 (ep_perfsuite.so+0x0000000097e2)
    #10 perf_latency_baseline(engine_interface*, engine_interface_v1*) /root/couchbase-3.0/ep-engine/tests/ep_perfsuite.cc:169 (ep_perfsuite.so+0x0000000090b7)
    #11 execute_test /root/couchbase-3.0/memcached/programs/engine_testapp/engine_testapp.c:1042 (engine_testapp+0x0000000ab933)
    #12 main /root/couchbase-3.0/memcached/programs/engine_testapp/engine_testapp.c:1296 (engine_testapp+0x0000000a9a19)

  Previous read of size 1 at 0x7d4400009d58 by thread T20:
    #0 CouchbaseAtomic<bool>::load(memory_order) const /root/couchbase-3.0/ep-engine/src/atomic.h:79 (ep.so+0x00000005288c)
    couchbase#1 Flusher::canSnooze() /root/couchbase-3.0/ep-engine/src/flusher.h:104 (ep.so+0x00000018e92b)
    couchbase#2 Flusher::computeMinSleepTime() /root/couchbase-3.0/ep-engine/src/flusher.cc:239 (ep.so+0x00000018dc87)
    couchbase#3 Flusher::step(GlobalTask*) /root/couchbase-3.0/ep-engine/src/flusher.cc:187 (ep.so+0x00000018cb35)

Change-Id: Ie32ca8fa4e662e1244362cbdb0cb2573f80665e2
Reviewed-on: http://review.couchbase.org/51968
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Jim Walker <jim@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>

Author: daverigby

src/atomic.h

@@ -76,7 +76,7 @@ class CouchbaseAtomic {
 
     T load(memory_order sync = memory_order_acq_rel) const {
         (void) sync;
-        return value;
+        return ep_sync_fetch_and_add(const_cast<T*>(&value), T(0));
     }
 
     void store(const T &newValue, memory_order sync = memory_order_acq_rel) {
@@ -163,6 +163,40 @@ class CouchbaseAtomic {
     volatile T value;
 };
 
+template <>
+class CouchbaseAtomic<double> {
+    typedef union doubleIntStore {
+        double d;
+        uint64_t i;
+    } DoubleIntStore;
+
+public:
+    CouchbaseAtomic(const double& initial = 0) {
+        store(initial);
+    }
+
+    double load(memory_order sync = memory_order_acq_rel) const {
+        (void) sync;
+        DoubleIntStore rv;
+        rv.i = ep_sync_fetch_and_add((uint64_t*)&value.i, 0);
+        return rv.d;
+    }
+
+    void store(const double& newValue, memory_order sync = memory_order_acq_rel) {
+        (void) sync;
+        DoubleIntStore input;
+        input.d = newValue;
+        (void)ep_sync_lock_test_and_set(&value.i, input.i);
+    }
+
+    operator double() const {
+        return load();
+    }
+
+private:
+    volatile DoubleIntStore value;
+};
+
 #endif
 
 template <typename T>

tests/module_tests/atomic_test.cc

@@ -82,6 +82,10 @@ static void testSetIfBigger() {
     cb_assert(x.load() == 924);
 }
 
+static void testAtomicDouble(void) {
+    AtomicValue<double> d = 991.5;
+    cb_assert(d == 991.5);
+}
 
 int testAtomicCompareExchangeStrong(void) {
     AtomicValue<bool> x(true);
@@ -125,5 +129,6 @@ int main() {
     testAtomicInt();
     testSetIfLess();
     testSetIfBigger();
+    testAtomicDouble();
     return testAtomicCompareExchangeStrong();
 }