Remove num_threads as a parameter. (#1891)

* remove num_threads as a parameter.

* linting.

* add additional checks.

* Invoke TransferCompleted on failures.

* Fix issue with failed Gets on store.

* ray check status of writing object headers.

* fix mac issues.

src/ray/object_manager/object_manager.h

@@ -33,13 +33,11 @@ namespace ray {
 struct ObjectManagerConfig {
   /// The time in milliseconds to wait before retrying a pull
   /// that failed due to client id lookup.
-  int pull_timeout_ms = 100;
-  /// Size of thread pool.
-  int num_threads = 2;
+  uint pull_timeout_ms = 100;
   /// Maximum number of sends allowed.
-  int max_sends = 20;
+  int max_sends = 2;
   /// Maximum number of receives allowed.
-  int max_receives = 20;
+  int max_receives = 2;
   // TODO(hme): Implement num retries (to avoid infinite retries).
   std::string store_socket_name;
 };
@@ -190,6 +188,10 @@ class ObjectManager {
   std::atomic<int> num_transfers_send_;
   std::atomic<int> num_transfers_receive_;
 
+  /// Size of thread pool. This is the sum of
+  /// config_.max_sends and config_.max_receives
+  const int num_threads_;
+
   /// Cache of locally available objects.
   std::unordered_map<ObjectID, ObjectInfoT, UniqueIDHasher> local_objects_;