diff --git a/.bazelrc b/.bazelrc
index 2fc26dd44..8ef0453f3 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -29,3 +29,11 @@ build --http_timeout_scaling=5.0
 # This workaround is due to an incompatibility of
 # bazel_common/tools/maven/pom_file.bzl with Bazel 1.0
 build --incompatible_depset_is_not_iterable=false
+
+# Thread sanitizer configuration:
+build:tsan --strip=never
+build:tsan --copt -fsanitize=thread
+build:tsan --copt -DTHREAD_SANITIZER
+build:tsan --copt -g
+build:tsan --copt -fno-omit-frame-pointer
+build:tsan --linkopt -fsanitize=thread
diff --git a/.travis.yml b/.travis.yml
index 6702f3fda..92eba64c2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -80,6 +80,22 @@ matrix:
         - go get github.com/bazelbuild/buildtools/buildifier
         - ./ci/travis/bazel-format.sh
 
+    - os: linux
+      env: SANITIZER=1 CC=clang PYTHON=3.5 PYTHONWARNINGS=ignore
+
+      install:
+        - eval `python $TRAVIS_BUILD_DIR/ci/travis/determine_tests_to_run.py`
+        - if [ $RAY_CI_PYTHON_AFFECTED != "1" ]; then exit; fi
+
+        - ./ci/suppress_output ./ci/travis/install-bazel.sh
+        - ./ci/suppress_output ./ci/travis/install-dependencies.sh
+        - export PATH="$HOME/miniconda/bin:$PATH"
+        - ./ci/suppress_output ./ci/travis/install-ray.sh
+
+      script:
+        # Run core worker tests with thread sanitizer
+        - RAY_BAZEL_CONFIG="--config=tsan" TSAN_OPTIONS="report_atomic_races=0" ./ci/suppress_output bash src/ray/test/run_core_worker_tests.sh
+
     # Build Linux wheels.
     - os: linux
       env: LINUX_WHEELS=1 PYTHONWARNINGS=ignore
diff --git a/src/ray/core_worker/actor_handle.cc b/src/ray/core_worker/actor_handle.cc
index 4123f865d..461a0ab14 100644
--- a/src/ray/core_worker/actor_handle.cc
+++ b/src/ray/core_worker/actor_handle.cc
@@ -44,7 +44,7 @@ ActorHandle::ActorHandle(const std::string &serialized)
 void ActorHandle::SetActorTaskSpec(TaskSpecBuilder &builder,
                                    const TaskTransportType transport_type,
                                    const ObjectID new_cursor) {
-  std::unique_lock<std::mutex> guard(mutex_);
+  absl::MutexLock guard(&mutex_);
   // Build actor task spec.
   const TaskID actor_creation_task_id = TaskID::ForActorCreationTask(GetActorID());
   const ObjectID actor_creation_dummy_object_id =
@@ -59,7 +59,7 @@ void ActorHandle::SetActorTaskSpec(TaskSpecBuilder &builder,
 void ActorHandle::Serialize(std::string *output) { inner_.SerializeToString(output); }
 
 void ActorHandle::Reset() {
-  std::unique_lock<std::mutex> guard(mutex_);
+  absl::MutexLock guard(&mutex_);
   task_counter_ = 0;
   actor_cursor_ = ObjectID::FromBinary(inner_.actor_cursor());
 }
diff --git a/src/ray/core_worker/actor_handle.h b/src/ray/core_worker/actor_handle.h
index f2b6bd92c..68554de0b 100644
--- a/src/ray/core_worker/actor_handle.h
+++ b/src/ray/core_worker/actor_handle.h
@@ -54,10 +54,16 @@ class ActorHandle {
   void Reset();
 
   // Mark the actor handle as dead.
-  void MarkDead() { state_ = rpc::ActorTableData::DEAD; }
+  void MarkDead() {
+    absl::MutexLock lock(&mutex_);
+    state_ = rpc::ActorTableData::DEAD;
+  }
 
   // Returns whether the actor is known to be dead.
-  bool IsDead() const { return state_ == rpc::ActorTableData::DEAD; }
+  bool IsDead() const {
+    absl::MutexLock lock(&mutex_);
+    return state_ == rpc::ActorTableData::DEAD;
+  }
 
  private:
   // Protobuf-defined persistent state of the actor handle.
@@ -65,18 +71,18 @@ class ActorHandle {
 
   /// The actor's state (alive or dead). This defaults to ALIVE. Once marked
   /// DEAD, the actor handle can never go back to being ALIVE.
-  rpc::ActorTableData::ActorState state_ = rpc::ActorTableData::ALIVE;
+  rpc::ActorTableData::ActorState state_ GUARDED_BY(mutex_) = rpc::ActorTableData::ALIVE;
 
   /// The unique id of the dummy object returned by the previous task.
   /// TODO: This can be removed once we schedule actor tasks by task counter
   /// only.
   // TODO: Save this state in the core worker.
-  ObjectID actor_cursor_;
+  ObjectID actor_cursor_ GUARDED_BY(mutex_);
   // Number of tasks that have been submitted on this handle.
-  uint64_t task_counter_ = 0;
+  uint64_t task_counter_ GUARDED_BY(mutex_) = 0;
 
-  /// Guards actor_cursor_ and task_counter_.
-  std::mutex mutex_;
+  /// Mutex to protect fields in the actor handle.
+  mutable absl::Mutex mutex_;
 
   FRIEND_TEST(ZeroNodeTest, TestActorHandle);
 };
diff --git a/src/ray/rpc/client_call.h b/src/ray/rpc/client_call.h
index a62f5147f..3a053ff0b 100644
--- a/src/ray/rpc/client_call.h
+++ b/src/ray/rpc/client_call.h
@@ -3,6 +3,7 @@
 
 #include <grpcpp/grpcpp.h>
 #include <boost/asio.hpp>
+#include "absl/synchronization/mutex.h"
 
 #include "ray/common/grpc_util.h"
 #include "ray/common/status.h"
@@ -22,6 +23,8 @@ class ClientCall {
   virtual void OnReplyReceived() = 0;
   /// Return status.
   virtual ray::Status GetStatus() = 0;
+  /// Set return status.
+  virtual void SetReturnStatus() = 0;
 
   virtual ~ClientCall() = default;
 };
@@ -46,11 +49,24 @@ class ClientCallImpl : public ClientCall {
   /// \param[in] callback The callback function to handle the reply.
   explicit ClientCallImpl(const ClientCallback<Reply> &callback) : callback_(callback) {}
 
-  Status GetStatus() override { return GrpcStatusToRayStatus(status_); }
+  Status GetStatus() override {
+    absl::MutexLock lock(&mutex_);
+    return return_status_;
+  }
+
+  void SetReturnStatus() override {
+    absl::MutexLock lock(&mutex_);
+    return_status_ = GrpcStatusToRayStatus(status_);
+  }
 
   void OnReplyReceived() override {
+    ray::Status status;
+    {
+      absl::MutexLock lock(&mutex_);
+      status = return_status_;
+    }
     if (callback_ != nullptr) {
-      callback_(GrpcStatusToRayStatus(status_), reply_);
+      callback_(status, reply_);
     }
   }
 
@@ -67,6 +83,16 @@ class ClientCallImpl : public ClientCall {
   /// gRPC status of this request.
   grpc::Status status_;
 
+  /// Mutex to protect the return_status_ field.
+  absl::Mutex mutex_;
+
+  /// This is the status to be returned from GetStatus(). It is safe
+  /// to read from other threads while they hold mutex_. We have
+  /// return_status_ = GrpcStatusToRayStatus(status_) but need
+  /// a separate variable because status_ is set internally by
+  /// GRPC and we cannot control it holding the lock.
+  ray::Status return_status_ GUARDED_BY(mutex_);
+
   /// Context for the client. It could be used to convey extra information to
   /// the server and/or tweak certain RPC behaviors.
   grpc::ClientContext context_;
@@ -205,6 +231,7 @@ class ClientCallManager {
         break;
       } else if (status != grpc::CompletionQueue::TIMEOUT) {
         auto tag = reinterpret_cast<ClientCallTag *>(got_tag);
+        tag->GetCall()->SetReturnStatus();
         if (ok && !main_service_.stopped() && !shutdown_) {
           // Post the callback to the main event loop.
           main_service_.post([tag]() {
diff --git a/src/ray/test/run_core_worker_tests.sh b/src/ray/test/run_core_worker_tests.sh
index 709d30daa..4a602d2cd 100644
--- a/src/ray/test/run_core_worker_tests.sh
+++ b/src/ray/test/run_core_worker_tests.sh
@@ -22,7 +22,7 @@ fi
 set -e
 set -x
 
-bazel build "//:core_worker_test" "//:mock_worker"  "//:raylet" "//:raylet_monitor" "//:libray_redis_module.so" "@plasma//:plasma_store_server"
+bazel build -c dbg $RAY_BAZEL_CONFIG "//:core_worker_test" "//:mock_worker"  "//:raylet" "//:raylet_monitor" "//:libray_redis_module.so" "@plasma//:plasma_store_server"
 
 # Get the directory in which this script is executing.
 SCRIPT_DIR="`dirname \"$0\"`"
@@ -39,24 +39,25 @@ if [ ! -d "$RAY_ROOT/python" ]; then
 fi
 
 REDIS_MODULE="./bazel-bin/libray_redis_module.so"
+BAZEL_BIN_PREFIX="$(bazel info -c dbg $RAY_BAZEL_CONFIG bazel-bin)"
 LOAD_MODULE_ARGS="--loadmodule ${REDIS_MODULE}"
-STORE_EXEC="./bazel-bin/external/plasma/plasma_store_server"
-RAYLET_EXEC="./bazel-bin/raylet"
-RAYLET_MONITOR_EXEC="./bazel-bin/raylet_monitor"
-MOCK_WORKER_EXEC="./bazel-bin/mock_worker"
+STORE_EXEC="$BAZEL_BIN_PREFIX/external/plasma/plasma_store_server"
+RAYLET_EXEC="$BAZEL_BIN_PREFIX/raylet"
+RAYLET_MONITOR_EXEC="$BAZEL_BIN_PREFIX/raylet_monitor"
+MOCK_WORKER_EXEC="$BAZEL_BIN_PREFIX/mock_worker"
 
 # Allow cleanup commands to fail.
-bazel run //:redis-cli -- -p 6379 shutdown || true
+bazel run "//:redis-cli" -- -p 6379 shutdown || true
 sleep 1s
-bazel run //:redis-cli -- -p 6380 shutdown || true
+bazel run "//:redis-cli" -- -p 6380 shutdown || true
 sleep 1s
-bazel run //:redis-server -- --loglevel warning ${LOAD_MODULE_ARGS} --port 6379 &
+bazel run "//:redis-server" -- --loglevel warning ${LOAD_MODULE_ARGS} --port 6379 &
 sleep 2s
-bazel run //:redis-server -- --loglevel warning ${LOAD_MODULE_ARGS} --port 6380 &
+bazel run "//:redis-server" -- --loglevel warning ${LOAD_MODULE_ARGS} --port 6380 &
 sleep 2s
 # Run tests.
-./bazel-bin/core_worker_test $STORE_EXEC $RAYLET_EXEC $RAYLET_PORT $RAYLET_MONITOR_EXEC $MOCK_WORKER_EXEC
+bazel run -c dbg $RAY_BAZEL_CONFIG "//:core_worker_test" $STORE_EXEC $RAYLET_EXEC $RAYLET_PORT $RAYLET_MONITOR_EXEC $MOCK_WORKER_EXEC
 sleep 1s
-bazel run //:redis-cli -- -p 6379 shutdown
-bazel run //:redis-cli -- -p 6380 shutdown
+bazel run "//:redis-cli" -- -p 6379 shutdown
+bazel run "//:redis-cli" -- -p 6380 shutdown
 sleep 1s