TSan Intermittent error in 'mem stats' test, comp_active variant.

WARNING: ThreadSanitizer: heap-use-after-free (pid=5347)

  Read of size 1 at 0x7b7400040609 by main thread:

    #0 memcmp <null> (libtsan.so.0+0x000000043643)

    #1 check_key_value(engine_interface*, engine_interface_v1*, char const*, char const*, unsigned long, unsigned short) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/tests/ep_testsuite_common.cc:468 (ep_testsuite.so+0x0000000975ad)

    #2 test_mem_stats /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/tests/ep_testsuite.cc:2036 (ep_testsuite.so+0x00000002c5c6)

    #3 execute_test /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/programs/engine_testapp/engine_testapp.cc:1102 (engine_testapp+0x00000041b0ba)

    #4 main /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/programs/engine_testapp/engine_testapp.cc:1499 (engine_testapp+0x00000041c5b2)

  Previous write of size 8 at 0x7b7400040608 by thread T11 (mutexes: write M3231945710371016):

    #0 operator delete(void*) <null> (libtsan.so.0+0x00000006a7b4)

    #1 Blob::operator delete(void*) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/blob.h:124 (ep.so+0x0000001959c2)

    #2 Blob::Deleter::operator()(TaggedPtr<Blob>) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/blob.h:137 (ep.so+0x0000001959c2)

    #3 SingleThreadedRCPtr<Blob, TaggedPtr<Blob>, Blob::Deleter>::swap(TaggedPtr<Blob>) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/atomic.h:362 (ep.so+0x0000001959c2)

    #4 SingleThreadedRCPtr<Blob, TaggedPtr<Blob>, Blob::Deleter>::reset(TaggedPtr<Blob>) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/atomic.h:298 (ep.so+0x0000001959c2)

    #5 StoredValue::replaceValue(TaggedPtr<Blob>) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/stored-value.h:540 (ep.so+0x0000001959c2)

    #6 StoredValue::storeCompressedBuffer(cb::const_char_buffer) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/stored-value.cc:362 (ep.so+0x0000001959c2)

    #7 HashTable::storeCompressedBuffer(cb::const_char_buffer, StoredValue&) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/hash_table.cc:620 (ep.so+0x00000012be5c)

    #8 ItemCompressorVisitor::visit(HashTable::HashBucketLock const&, StoredValue&) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/item_compressor_visitor.cc:52 (ep.so+0x000000139780)

    #9 HashTable::pauseResumeVisit(HashTableVisitor&, HashTable::Position&) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/hash_table.cc:753 (ep.so+0x000000127b6c)

    #10 PauseResumeVBAdapter::visit(VBucket&) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/vb_visitors.cc:36 (ep.so+0x0000001a81b1)

    #11 KVBucket::pauseResumeVisit(PauseResumeVBVisitor&, KVBucketIface::Position&) /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/kv_bucket.cc:2177 (ep.so+0x000000158ec9)

    #12 ItemCompressorTask::run() /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/item_compressor.cc:70 (ep.so+0x000000138204)

    #13 ExecutorThread::run() /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/executorthread.cc:146 (ep.so+0x00000011da74)

    #14 launch_executor_thread /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/kv_engine/engines/ep/src/executorthread.cc:34 (ep.so+0x00000011e0ae)

    #15 CouchbaseThread::run() /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/platform/src/cb_pthreads.cc:59 (libplatform_so.so.0.1.0+0x000000009cc9)

    #16 platform_thread_wrap /home/couchbase/jenkins/workspace/kv_engine-threadsanitizer-master/platform/src/cb_pthreads.cc:72 (libplatform_so.so.0.1.0+0x000000009cc9)

    #17 <null> <null> (libtsan.so.0+0x000000024feb)

  Mutex M3231945710371016 is already destroyed.

bool get_item_info(ENGINE_HANDLE *h, ENGINE_HANDLE_V1 *h1, item_info *info,

                   const char* key, uint16_t vb) {

    auto ret = get(h, h1, NULL, key, vb);

    if (ret.first != cb::engine_errc::success) {

        return false;

    }

    if (!h1->get_item_info(h, ret.second.get(), info)) {

        fprintf(stderr, "get_item_info failed\n");

        return false;

    }

    return true;

}