Remove dead code from class StorageManager (#4665)

* Remove member variables and code to track open groups. The resulting
container was not used for any purpose outside of `Debug` builds, and of
very limited utility within them.
* Remove unreferenced member variable `xlock_cv_`.

This PR supports the goal of shrinking the storage manager.

---
TYPE: NO_HISTORY
DESC: Remove dead code from `class StorageManager`

Author: eric-hughes-tiledb

tiledb/sm/storage_manager/storage_manager.cc

@@ -132,19 +132,12 @@ StorageManagerCanonical::~StorageManagerCanonical() {
 /*               API              */
 /* ****************************** */
 
-Status StorageManagerCanonical::group_close_for_reads(Group* group) {
-  assert(open_groups_.find(group) != open_groups_.end());
-
-  // Remove entry from open groups
-  std::lock_guard<std::mutex> lock{open_groups_mtx_};
-  open_groups_.erase(group);
-
+Status StorageManagerCanonical::group_close_for_reads(Group*) {
+  // Closing a group does nothing at present
   return Status::Ok();
 }
 
 Status StorageManagerCanonical::group_close_for_writes(Group* group) {
-  assert(open_groups_.find(group) != open_groups_.end());
-
   // Flush the group metadata
   RETURN_NOT_OK(store_metadata(
       group->group_uri(), *group->encryption_key(), group->unsafe_metadata()));
@@ -159,11 +152,6 @@ Status StorageManagerCanonical::group_close_for_writes(Group* group) {
         group->group_details(),
         *group->encryption_key()));
   }
-
-  // Remove entry from open groups
-  std::lock_guard<std::mutex> lock{open_groups_mtx_};
-  open_groups_.erase(group);
-
   return Status::Ok();
 }
 
@@ -1738,10 +1726,6 @@ StorageManagerCanonical::group_open_for_reads(Group* group) {
       load_group_details(group->group_directory(), *group->encryption_key());
   RETURN_NOT_OK_TUPLE(st, std::nullopt);
 
-  // Mark the array as now open
-  std::lock_guard<std::mutex> lock{open_groups_mtx_};
-  open_groups_.insert(group);
-
   if (group_deserialized.has_value()) {
     return {Status::Ok(), group_deserialized.value()};
   }
@@ -1760,10 +1744,6 @@ StorageManagerCanonical::group_open_for_writes(Group* group) {
       load_group_details(group->group_directory(), *group->encryption_key());
   RETURN_NOT_OK_TUPLE(st, std::nullopt);
 
-  // Mark the array as now open
-  std::lock_guard<std::mutex> lock{open_groups_mtx_};
-  open_groups_.insert(group);
-
   if (group_deserialized.has_value()) {
     return {Status::Ok(), group_deserialized.value()};
   }

tiledb/sm/storage_manager/storage_manager_canonical.h

@@ -845,25 +845,12 @@ class StorageManagerCanonical {
   /** Mutex protecting cancellation_in_progress_. */
   std::mutex cancellation_in_progress_mtx_;
 
-  /**
-   * The condition variable for exlcusively locking arrays. This is used
-   * to wait for an array to be closed, before being exclusively locked
-   * by `array_xlock`.
-   */
-  std::condition_variable xlock_cv_;
-
   /** Mutex for providing thread-safety upon creating TileDB objects. */
   std::mutex object_create_mtx_;
 
   /** Stores the TileDB configuration parameters. */
   Config config_;
 
-  /** Keeps track of which groups are open. */
-  std::set<Group*> open_groups_;
-
-  /** Mutex for managing open groups. */
-  std::mutex open_groups_mtx_;
-
   /** Count of the number of queries currently in progress. */
   uint64_t queries_in_progress_;