The ObjectRegistry class replaces the Registrar and NewCustomObjects.… (#5293)

Summary:
The ObjectRegistry class replaces the Registrar and NewCustomObjects.  Objects are registered with the registry by Type (the class must implement the static const char *Type() method).

This change is necessary for a few reasons:
- By having a class (rather than static template instances), the class can be passed between compilation units, meaning that objects could be registered and shared from a dynamic library with an executable.
- By having a class with instances, different units could have different objects registered.  This could be useful if, for example, one Option allowed for a dynamic library and one did not.

When combined with some other PRs (being able to load shared libraries, a Configurable interface to configure objects to/from string), this code will allow objects in external shared libraries to be added to a RocksDB image at run-time, rather than requiring every new extension to be built into the main library and called explicitly by every program.

Test plan (on riversand963's  devserver)
```
$COMPILE_WITH_ASAN=1 make -j32 all && sleep 1 && make check
```
All tests pass.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5293

Differential Revision: D16363396

Pulled By: riversand963

fbshipit-source-id: fbe4acb615bfc11103eef40a0b288845791c0180

CMakeLists.txt

@@ -520,7 +520,7 @@ set(SOURCES
         db/flush_job.cc
         db/flush_scheduler.cc
         db/forward_iterator.cc
-	db/import_column_family_job.cc
+        db/import_column_family_job.cc
         db/internal_stats.cc
         db/logs_with_prep_tracker.cc
         db/log_reader.cc
@@ -681,6 +681,7 @@ set(SOURCES
         utilities/merge_operators/string_append/stringappend.cc
         utilities/merge_operators/string_append/stringappend2.cc
         utilities/merge_operators/uint64add.cc
+        utilities/object_registry.cc
         utilities/option_change_migration/option_change_migration.cc
         utilities/options/options_util.cc
         utilities/persistent_cache/block_cache_tier.cc

HISTORY.md

@@ -20,6 +20,7 @@
 * Overload GetAllKeyVersions() to support non-default column family.
 * Added new APIs ExportColumnFamily() and CreateColumnFamilyWithImport() to support export and import of a Column Family. https://github.com/facebook/rocksdb/issues/3469
 * ldb sometimes uses a string-append merge operator if no merge operator is passed in. This is to allow users to print keys from a DB with a merge operator.
+* Replaces old Registra with ObjectRegistry to allow user to create custom object from string, also add LoadEnv() to Env.
 
 ### New Features
 * Add an option `snap_refresh_nanos` (default to 0) to periodically refresh the snapshot list in compaction jobs. Assign to 0 to disable the feature.

TARGETS

@@ -276,6 +276,7 @@ cpp_library(
         "utilities/merge_operators/string_append/stringappend.cc",
         "utilities/merge_operators/string_append/stringappend2.cc",
         "utilities/merge_operators/uint64add.cc",
+        "utilities/object_registry.cc",
         "utilities/option_change_migration/option_change_migration.cc",
         "utilities/options/options_util.cc",
         "utilities/persistent_cache/block_cache_tier.cc",
@@ -371,11 +372,6 @@ ROCKS_TESTS = [
         "logging/auto_roll_logger_test.cc",
         "serial",
     ],
-    [
-        "env_logger_test",
-        "logging/env_logger_test.cc",
-        "serial",
-    ],
     [
         "autovector_test",
         "util/autovector_test.cc",
@@ -422,13 +418,13 @@ ROCKS_TESTS = [
         "serial",
     ],
     [
-        "cache_test",
+        "cache_simulator_test",
-        "cache/cache_test.cc",
+        "utilities/simulator_cache/cache_simulator_test.cc",
         "serial",
     ],
     [
-        "cache_simulator_test",
+        "cache_test",
-        "utilities/simulator_cache/cache_simulator_test.cc",
+        "cache/cache_test.cc",
         "serial",
     ],
     [
@@ -554,7 +550,7 @@ ROCKS_TESTS = [
     [
         "db_bloom_filter_test",
         "db/db_bloom_filter_test.cc",
-        "parallel",
+        "serial",
     ],
     [
         "db_compaction_filter_test",
@@ -711,6 +707,11 @@ ROCKS_TESTS = [
         "env/env_basic_test.cc",
         "serial",
     ],
+    [
+        "env_logger_test",
+        "logging/env_logger_test.cc",
+        "serial",
+    ],
     [
         "env_test",
         "env/env_test.cc",
@@ -796,6 +797,11 @@ ROCKS_TESTS = [
         "monitoring/histogram_test.cc",
         "serial",
     ],
+    [
+        "import_column_family_test",
+        "db/import_column_family_test.cc",
+        "parallel",
+    ],
     [
         "inlineskiplist_test",
         "memtable/inlineskiplist_test.cc",

env/env.cc

@@ -16,6 +16,7 @@
 #include "port/port.h"
 #include "port/sys_time.h"
 #include "rocksdb/options.h"
+#include "rocksdb/utilities/object_registry.h"
 #include "util/autovector.h"
 
 namespace rocksdb {
@@ -28,6 +29,20 @@ Status Env::NewLogger(const std::string& fname,
   return NewEnvLogger(fname, this, result);
 }
 
+Status Env::LoadEnv(const std::string& value, Env** result) {
+  Env* env = *result;
+  Status s;
+#ifndef ROCKSDB_LITE
+  s = ObjectRegistry::NewInstance()->NewStaticObject<Env>(value, &env);
+#else
+  s = Status::NotSupported("Cannot load environment in LITE mode: ", value);
+#endif
+  if (s.ok()) {
+    *result = env;
+  }
+  return s;
+}
+
 std::string Env::PriorityToString(Env::Priority priority) {
   switch (priority) {
     case Env::Priority::BOTTOM:

env/env_basic_test.cc

@@ -11,7 +11,6 @@
 
 #include "env/mock_env.h"
 #include "rocksdb/env.h"
-#include "rocksdb/utilities/object_registry.h"
 #include "test_util/testharness.h"
 
 namespace rocksdb {
@@ -104,13 +103,12 @@ namespace {
 // ValuesIn() will skip running tests when given an empty collection.
 std::vector<Env*> GetCustomEnvs() {
   static Env* custom_env;
-  static std::unique_ptr<Env> custom_env_guard;
   static bool init = false;
   if (!init) {
     init = true;
     const char* uri = getenv("TEST_ENV_URI");
     if (uri != nullptr) {
-      custom_env = NewCustomObject<Env>(uri, &custom_env_guard);
+      Env::LoadEnv(uri, &custom_env);
     }
   }
 

include/rocksdb/comparator.h

@@ -35,6 +35,7 @@ class Comparator {
 
   virtual ~Comparator() {}
 
+  static const char* Type() { return "Comparator"; }
   // Three-way comparison.  Returns value:
   //   < 0 iff "a" < "b",
   //   == 0 iff "a" == "b",

include/rocksdb/env.h

@@ -144,6 +144,11 @@ class Env {
 
   virtual ~Env();
 
+  static const char* Type() { return "Environment"; }
+
+  // Loads the environment specified by the input value into the result
+  static Status LoadEnv(const std::string& value, Env** result);
+
   // Return a default environment suitable for the current operating
   // system.  Sophisticated users may wish to provide their own Env
   // implementation instead of relying on this default environment.

include/rocksdb/merge_operator.h

@@ -46,6 +46,7 @@ class Logger;
 class MergeOperator {
  public:
   virtual ~MergeOperator() {}
+  static const char* Type() { return "MergeOperator"; }
 
   // Gives the client a way to express the read -> modify -> write semantics
   // key:      (IN)    The key that's associated with this merge operation.

include/rocksdb/statistics.h

@@ -480,7 +480,7 @@ enum StatsLevel : uint8_t {
 class Statistics {
  public:
   virtual ~Statistics() {}
-
+  static const char* Type() { return "Statistics"; }
   virtual uint64_t getTickerCount(uint32_t tickerType) const = 0;
   virtual void histogramData(uint32_t type,
                              HistogramData* const data) const = 0;

include/rocksdb/utilities/object_registry.h

@@ -11,80 +11,195 @@
 #include <memory>
 #include <regex>
 #include <string>
+#include <unordered_map>
 #include <vector>
-
+#include "rocksdb/status.h"
-#include "rocksdb/env.h"
 
 namespace rocksdb {
-
+class Logger;
-// Creates a new T using the factory function that was registered with a pattern
-// that matches the provided "target" string according to std::regex_match.
-//
-// If no registered functions match, returns nullptr. If multiple functions
-// match, the factory function used is unspecified.
-//
-// Populates res_guard with result pointer if caller is granted ownership.
-template <typename T>
-T* NewCustomObject(const std::string& target, std::unique_ptr<T>* res_guard);
-
 // Returns a new T when called with a string. Populates the std::unique_ptr
 // argument if granting ownership to caller.
 template <typename T>
-using FactoryFunc = std::function<T*(const std::string&, std::unique_ptr<T>*)>;
+using FactoryFunc =
+    std::function<T*(const std::string&, std::unique_ptr<T>*, std::string*)>;
 
-// To register a factory function for a type T, initialize a Registrar<T> object
+class ObjectLibrary {
-// with static storage duration. For example:
-//
-//   static Registrar<Env> hdfs_reg("hdfs://.*", &CreateHdfsEnv);
-//
-// Then, calling NewCustomObject<Env>("hdfs://some_path", ...) will match the
-// regex provided above, so it returns the result of invoking CreateHdfsEnv.
-template <typename T>
-class Registrar {
  public:
-  explicit Registrar(std::string pattern, FactoryFunc<T> factory);
+  // Base class for an Entry in the Registry.
-};
+  class Entry {
+   public:
+    virtual ~Entry() {}
+    Entry(const std::string& name) : name_(std::move(name)) {}
 
-// Implementation details follow.
+    // Checks to see if the target matches this entry
+    virtual bool matches(const std::string& target) const {
+      return name_ == target;
+    }
+    const std::string& Name() const { return name_; }
 
-namespace internal {
+   private:
+    const std::string name_;  // The name of the Entry
+  };                          // End class Entry
 
-template <typename T>
+  // An Entry containing a FactoryFunc for creating new Objects
-struct RegistryEntry {
+  template <typename T>
-  std::regex pattern;
+  class FactoryEntry : public Entry {
-  FactoryFunc<T> factory;
+   public:
-};
+    FactoryEntry(const std::string& name, FactoryFunc<T> f)
+        : Entry(name), pattern_(std::move(name)), factory_(std::move(f)) {}
+    ~FactoryEntry() override {}
+    bool matches(const std::string& target) const override {
+      return std::regex_match(target, pattern_);
+    }
+    // Creates a new T object.
+    T* NewFactoryObject(const std::string& target, std::unique_ptr<T>* guard,
+                        std::string* msg) const {
+      return factory_(target, guard, msg);
+    }
 
-template <typename T>
+   private:
-struct Registry {
+    std::regex pattern_;  // The pattern for this entry
-  static Registry* Get() {
+    FactoryFunc<T> factory_;
-    static Registry<T> instance;
+  };  // End class FactoryEntry
-    return &instance;
+ public:
+  // Finds the entry matching the input name and type
+  const Entry* FindEntry(const std::string& type,
+                         const std::string& name) const;
+  void Dump(Logger* logger) const;
+
+  // Registers the factory with the library for the pattern.
+  // If the pattern matches, the factory may be used to create a new object.
+  template <typename T>
+  const FactoryFunc<T>& Register(const std::string& pattern,
+                                 const FactoryFunc<T>& factory) {
+    std::unique_ptr<Entry> entry(new FactoryEntry<T>(pattern, factory));
+    AddEntry(T::Type(), entry);
+    return factory;
   }
-  std::vector<RegistryEntry<T>> entries;
+  // Returns the default ObjectLibrary
+  static std::shared_ptr<ObjectLibrary>& Default();
 
  private:
-  Registry() = default;
+  // Adds the input entry to the list for the given type
+  void AddEntry(const std::string& type, std::unique_ptr<Entry>& entry);
+
+  // ** FactoryFunctions for this loader, organized by type
+  std::unordered_map<std::string, std::vector<std::unique_ptr<Entry>>> entries_;
 };
 
-}  // namespace internal
+// The ObjectRegistry is used to register objects that can be created by a
+// name/pattern at run-time where the specific implementation of the object may
+// not be known in advance.
+class ObjectRegistry {
+ public:
+  static std::shared_ptr<ObjectRegistry> NewInstance();
 
-template <typename T>
+  ObjectRegistry();
-T* NewCustomObject(const std::string& target, std::unique_ptr<T>* res_guard) {
+
-  res_guard->reset();
+  void AddLibrary(const std::shared_ptr<ObjectLibrary>& library) {
-  for (const auto& entry : internal::Registry<T>::Get()->entries) {
+    libraries_.emplace_back(library);
-    if (std::regex_match(target, entry.pattern)) {
+  }
-      return entry.factory(target, res_guard);
+
+  // Creates a new T using the factory function that was registered with a
+  // pattern that matches the provided "target" string according to
+  // std::regex_match.
+  //
+  // If no registered functions match, returns nullptr. If multiple functions
+  // match, the factory function used is unspecified.
+  //
+  // Populates res_guard with result pointer if caller is granted ownership.
+  template <typename T>
+  T* NewObject(const std::string& target, std::unique_ptr<T>* guard,
+               std::string* errmsg) {
+    guard->reset();
+    const auto* basic = FindEntry(T::Type(), target);
+    if (basic != nullptr) {
+      const auto* factory =
+          static_cast<const ObjectLibrary::FactoryEntry<T>*>(basic);
+      return factory->NewFactoryObject(target, guard, errmsg);
+    } else {
+      *errmsg = std::string("Could not load ") + T::Type();
+      return nullptr;
     }
   }
-  return nullptr;
-}
 
-template <typename T>
+  // Creates a new unique T using the input factory functions.
-Registrar<T>::Registrar(std::string pattern, FactoryFunc<T> factory) {
+  // Returns OK if a new unique T was successfully created
-  internal::Registry<T>::Get()->entries.emplace_back(internal::RegistryEntry<T>{
+  // Returns NotFound if the type/target could not be created
-      std::regex(std::move(pattern)), std::move(factory)});
+  // Returns InvalidArgument if the factory return an unguarded object
-}
+  //                      (meaning it cannot be managed by a unique ptr)
+  template <typename T>
+  Status NewUniqueObject(const std::string& target,
+                         std::unique_ptr<T>* result) {
+    std::string errmsg;
+    T* ptr = NewObject(target, result, &errmsg);
+    if (ptr == nullptr) {
+      return Status::NotFound(errmsg, target);
+    } else if (*result) {
+      return Status::OK();
+    } else {
+      return Status::InvalidArgument(std::string("Cannot make a unique ") +
+                                         T::Type() + " from unguarded one ",
+                                     target);
+    }
+  }
 
+  // Creates a new shared T using the input factory functions.
+  // Returns OK if a new shared T was successfully created
+  // Returns NotFound if the type/target could not be created
+  // Returns InvalidArgument if the factory return an unguarded object
+  //                      (meaning it cannot be managed by a shared ptr)
+  template <typename T>
+  Status NewSharedObject(const std::string& target,
+                         std::shared_ptr<T>* result) {
+    std::string errmsg;
+    std::unique_ptr<T> guard;
+    T* ptr = NewObject(target, &guard, &errmsg);
+    if (ptr == nullptr) {
+      return Status::NotFound(errmsg, target);
+    } else if (guard) {
+      result->reset(guard.release());
+      return Status::OK();
+    } else {
+      return Status::InvalidArgument(std::string("Cannot make a shared ") +
+                                         T::Type() + " from unguarded one ",
+                                     target);
+    }
+  }
+
+  // Creates a new static T using the input factory functions.
+  // Returns OK if a new static T was successfully created
+  // Returns NotFound if the type/target could not be created
+  // Returns InvalidArgument if the factory return a guarded object
+  //                      (meaning it is managed by a unique ptr)
+  template <typename T>
+  Status NewStaticObject(const std::string& target, T** result) {
+    std::string errmsg;
+    std::unique_ptr<T> guard;
+    T* ptr = NewObject(target, &guard, &errmsg);
+    if (ptr == nullptr) {
+      return Status::NotFound(errmsg, target);
+    } else if (guard.get()) {
+      return Status::InvalidArgument(std::string("Cannot make a static ") +
+                                         T::Type() + " from a guarded one ",
+                                     target);
+    } else {
+      *result = ptr;
+      return Status::OK();
+    }
+  }
+
+  // Dump the contents of the registry to the logger
+  void Dump(Logger* logger) const;
+
+ private:
+  const ObjectLibrary::Entry* FindEntry(const std::string& type,
+                                        const std::string& name) const;
+
+  // The set of libraries to search for factories for this registry.
+  // The libraries are searched in reverse order (back to front) when
+  // searching for entries.
+  std::vector<std::shared_ptr<ObjectLibrary>> libraries_;
+};
 }  // namespace rocksdb
 #endif  // ROCKSDB_LITE

options/options_helper.cc

@@ -1045,21 +1045,21 @@ Status ParseColumnFamilyOption(const std::string& name,
     } else {
       if (name == kNameComparator) {
         // Try to get comparator from object registry first.
-        std::unique_ptr<const Comparator> comp_guard;
-        const Comparator* comp =
-            NewCustomObject<const Comparator>(value, &comp_guard);
         // Only support static comparator for now.
-        if (comp != nullptr && !comp_guard) {
+        Status status = ObjectRegistry::NewInstance()->NewStaticObject(
-          new_options->comparator = comp;
+            value, &new_options->comparator);
+        if (status.ok()) {
+          return status;
         }
       } else if (name == kNameMergeOperator) {
         // Try to get merge operator from object registry first.
-        std::unique_ptr<std::shared_ptr<MergeOperator>> mo_guard;
+        std::shared_ptr<MergeOperator> mo;
-        std::shared_ptr<MergeOperator>* mo =
+        Status status =
-            NewCustomObject<std::shared_ptr<MergeOperator>>(value, &mo_guard);
+            ObjectRegistry::NewInstance()->NewSharedObject<MergeOperator>(
+                value, &new_options->merge_operator);
         // Only support static comparator for now.
-        if (mo != nullptr) {
+        if (status.ok()) {
-          new_options->merge_operator = *mo;
+          return status;
         }
       }
 
@@ -1191,10 +1191,10 @@ Status ParseDBOption(const std::string& name,
           NewGenericRateLimiter(static_cast<int64_t>(ParseUint64(value))));
     } else if (name == kNameEnv) {
       // Currently `Env` can be deserialized from object registry only.
-      std::unique_ptr<Env> env_guard;
+      Env* env = new_options->env;
-      Env* env = NewCustomObject<Env>(value, &env_guard);
+      Status status = Env::LoadEnv(value, &env);
       // Only support static env for now.
-      if (env != nullptr && !env_guard) {
+      if (status.ok()) {
         new_options->env = env;
       }
     } else {

options/options_test.cc

@@ -341,11 +341,11 @@ TEST_F(OptionsTest, GetColumnFamilyOptionsFromStringTest) {
 
   // Comparator from object registry
   std::string kCompName = "reverse_comp";
-  static Registrar<const Comparator> test_reg_a(
+  ObjectLibrary::Default()->Register<const Comparator>(
-      kCompName, [](const std::string& /*name*/,
+      kCompName,
-                    std::unique_ptr<const Comparator>* /*comparator_guard*/) {
+      [](const std::string& /*name*/,
-        return ReverseBytewiseComparator();
+         std::unique_ptr<const Comparator>* /*guard*/,
-      });
+         std::string* /* errmsg */) { return ReverseBytewiseComparator(); });
 
   ASSERT_OK(GetColumnFamilyOptionsFromString(
       base_cf_opt, "comparator=" + kCompName + ";", &new_cf_opt));
@@ -354,13 +354,12 @@ TEST_F(OptionsTest, GetColumnFamilyOptionsFromStringTest) {
   // MergeOperator from object registry
   std::unique_ptr<BytesXOROperator> bxo(new BytesXOROperator());
   std::string kMoName = bxo->Name();
-  static Registrar<std::shared_ptr<MergeOperator>> test_reg_b(
+  ObjectLibrary::Default()->Register<MergeOperator>(
-      kMoName, [](const std::string& /*name*/,
+      kMoName,
-                  std::unique_ptr<std::shared_ptr<MergeOperator>>*
+      [](const std::string& /*name*/, std::unique_ptr<MergeOperator>* guard,
-                      merge_operator_guard) {
+         std::string* /* errmsg */) {
-        merge_operator_guard->reset(
+        guard->reset(new BytesXOROperator());
-            new std::shared_ptr<MergeOperator>(new BytesXOROperator()));
+        return guard->get();
-        return merge_operator_guard->get();
       });
 
   ASSERT_OK(GetColumnFamilyOptionsFromString(
@@ -770,9 +769,10 @@ TEST_F(OptionsTest, GetOptionsFromStringTest) {
     explicit CustomEnv(Env* _target) : EnvWrapper(_target) {}
   };
 
-  static Registrar<Env> test_reg_env(
+  ObjectLibrary::Default()->Register<Env>(
       kCustomEnvName,
-      [](const std::string& /*name*/, std::unique_ptr<Env>* /*env_guard*/) {
+      [](const std::string& /*name*/, std::unique_ptr<Env>* /*env_guard*/,
+         std::string* /* errmsg */) {
         static CustomEnv env(Env::Default());
         return &env;
       });
@@ -813,8 +813,9 @@ TEST_F(OptionsTest, GetOptionsFromStringTest) {
   ASSERT_EQ(new_options.create_if_missing, true);
   ASSERT_EQ(new_options.max_open_files, 1);
   ASSERT_TRUE(new_options.rate_limiter.get() != nullptr);
-  std::unique_ptr<Env> env_guard;
+  Env* newEnv = new_options.env;
-  ASSERT_EQ(NewCustomObject<Env>(kCustomEnvName, &env_guard), new_options.env);
+  ASSERT_OK(Env::LoadEnv(kCustomEnvName, &newEnv));
+  ASSERT_EQ(newEnv, new_options.env);
 }
 
 TEST_F(OptionsTest, DBOptionsSerialization) {

src.mk

@@ -195,6 +195,7 @@ LIB_SOURCES =                                                   \
   utilities/merge_operators/string_append/stringappend2.cc      \
   utilities/merge_operators/uint64add.cc                        \
   utilities/merge_operators/bytesxor.cc                         \
+  utilities/object_registry.cc                                  \
   utilities/option_change_migration/option_change_migration.cc  \
   utilities/options/options_util.cc                             \
   utilities/persistent_cache/block_cache_tier.cc                \

tools/block_cache_trace_analyzer.cc

@@ -1637,7 +1637,7 @@ void BlockCacheTraceAnalyzer::PrintAccessCountStats(bool user_access_only,
     }
     fprintf(stdout,
             "Bottom %" PRIu32 " access count. Access count=%" PRIu64
-            " nblocks=%" PRIu64 " %s\n",
+            " nblocks=%" ROCKSDB_PRIszt " %s\n",
             bottom_k, naccess_it->first, naccess_it->second.size(),
             statistics.c_str());
   }

tools/db_bench_tool.cc

@@ -3049,8 +3049,9 @@ class Benchmark {
   std::shared_ptr<TimestampEmulator> timestamp_emulator_;
   std::unique_ptr<port::Thread> secondary_update_thread_;
   std::atomic<int> secondary_update_stopped_{0};
+#ifndef ROCKSDB_LITE
   uint64_t secondary_db_updates_ = 0;
-
+#endif  // ROCKSDB_LITE
   struct ThreadArg {
     Benchmark* bm;
     SharedState* shared;
@@ -6366,13 +6367,12 @@ int db_bench_tool(int argc, char** argv) {
     exit(1);
   }
   if (!FLAGS_statistics_string.empty()) {
-    std::unique_ptr<Statistics> custom_stats_guard;
+    Status s = ObjectRegistry::NewInstance()->NewSharedObject<Statistics>(
-    dbstats.reset(NewCustomObject<Statistics>(FLAGS_statistics_string,
+        FLAGS_statistics_string, &dbstats);
-                                              &custom_stats_guard));
-    custom_stats_guard.release();
     if (dbstats == nullptr) {
-      fprintf(stderr, "No Statistics registered matching string: %s\n",
+      fprintf(stderr,
-              FLAGS_statistics_string.c_str());
+              "No Statistics registered matching string: %s status=%s\n",
+              FLAGS_statistics_string.c_str(), s.ToString().c_str());
       exit(1);
     }
   }
@@ -6400,12 +6400,11 @@ int db_bench_tool(int argc, char** argv) {
     StringToCompressionType(FLAGS_compression_type.c_str());
 
 #ifndef ROCKSDB_LITE
-  std::unique_ptr<Env> custom_env_guard;
   if (!FLAGS_hdfs.empty() && !FLAGS_env_uri.empty()) {
     fprintf(stderr, "Cannot provide both --hdfs and --env_uri.\n");
     exit(1);
   } else if (!FLAGS_env_uri.empty()) {
-    FLAGS_env = NewCustomObject<Env>(FLAGS_env_uri, &custom_env_guard);
+    Status s = Env::LoadEnv(FLAGS_env_uri, &FLAGS_env);
     if (FLAGS_env == nullptr) {
       fprintf(stderr, "No Env registered for URI: %s\n", FLAGS_env_uri.c_str());
       exit(1);

tools/ldb_cmd.cc

@@ -20,7 +20,6 @@
 #include "rocksdb/utilities/backupable_db.h"
 #include "rocksdb/utilities/checkpoint.h"
 #include "rocksdb/utilities/debug.h"
-#include "rocksdb/utilities/object_registry.h"
 #include "rocksdb/utilities/options_util.h"
 #include "rocksdb/write_batch.h"
 #include "rocksdb/write_buffer_manager.h"
@@ -2854,8 +2853,9 @@ void BackupCommand::DoCommand() {
     return;
   }
   printf("open db OK\n");
-  std::unique_ptr<Env> custom_env_guard;
+  Env* custom_env = nullptr;
-  Env* custom_env = NewCustomObject<Env>(backup_env_uri_, &custom_env_guard);
+  Env::LoadEnv(backup_env_uri_, &custom_env);
+
   BackupableDBOptions backup_options =
       BackupableDBOptions(backup_dir_, custom_env);
   backup_options.info_log = logger_.get();
@@ -2889,8 +2889,9 @@ void RestoreCommand::Help(std::string& ret) {
 }
 
 void RestoreCommand::DoCommand() {
-  std::unique_ptr<Env> custom_env_guard;
+  Env* custom_env = nullptr;
-  Env* custom_env = NewCustomObject<Env>(backup_env_uri_, &custom_env_guard);
+  Env::LoadEnv(backup_env_uri_, &custom_env);
+
   std::unique_ptr<BackupEngineReadOnly> restore_engine;
   Status status;
   {

utilities/object_registry.cc

@@ -0,0 +1,87 @@
+// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+
+#include "rocksdb/utilities/object_registry.h"
+
+#include "logging/logging.h"
+#include "rocksdb/env.h"
+
+namespace rocksdb {
+#ifndef ROCKSDB_LITE
+// Looks through the "type" factories for one that matches "name".
+// If found, returns the pointer to the Entry matching this name.
+// Otherwise, nullptr is returned
+const ObjectLibrary::Entry *ObjectLibrary::FindEntry(
+    const std::string &type, const std::string &name) const {
+  auto entries = entries_.find(type);
+  if (entries != entries_.end()) {
+    for (const auto &entry : entries->second) {
+      if (entry->matches(name)) {
+        return entry.get();
+      }
+    }
+  }
+  return nullptr;
+}
+
+void ObjectLibrary::AddEntry(const std::string &type,
+                             std::unique_ptr<Entry> &entry) {
+  auto &entries = entries_[type];
+  entries.emplace_back(std::move(entry));
+}
+
+void ObjectLibrary::Dump(Logger *logger) const {
+  for (const auto &iter : entries_) {
+    ROCKS_LOG_HEADER(logger, "    Registered factories for type[%s] ",
+                     iter.first.c_str());
+    bool printed_one = false;
+    for (const auto &e : iter.second) {
+      ROCKS_LOG_HEADER(logger, "%c %s", (printed_one) ? ',' : ':',
+                       e->Name().c_str());
+      printed_one = true;
+    }
+  }
+  ROCKS_LOG_HEADER(logger, "\n");
+}
+
+// Returns the Default singleton instance of the ObjectLibrary
+// This instance will contain most of the "standard" registered objects
+std::shared_ptr<ObjectLibrary> &ObjectLibrary::Default() {
+  static std::shared_ptr<ObjectLibrary> instance =
+      std::make_shared<ObjectLibrary>();
+  return instance;
+}
+
+std::shared_ptr<ObjectRegistry> ObjectRegistry::NewInstance() {
+  std::shared_ptr<ObjectRegistry> instance = std::make_shared<ObjectRegistry>();
+  return instance;
+}
+
+ObjectRegistry::ObjectRegistry() {
+  libraries_.push_back(ObjectLibrary::Default());
+}
+
+// Searches (from back to front) the libraries looking for the
+// an entry that matches this pattern.
+// Returns the entry if it is found, and nullptr otherwise
+const ObjectLibrary::Entry *ObjectRegistry::FindEntry(
+    const std::string &type, const std::string &name) const {
+  for (auto iter = libraries_.crbegin(); iter != libraries_.crend(); ++iter) {
+    const auto *entry = iter->get()->FindEntry(type, name);
+    if (entry != nullptr) {
+      return entry;
+    }
+  }
+  return nullptr;
+}
+
+void ObjectRegistry::Dump(Logger *logger) const {
+  for (auto iter = libraries_.crbegin(); iter != libraries_.crend(); ++iter) {
+    iter->get()->Dump(logger);
+  }
+}
+
+#endif  // ROCKSDB_LITE
+}  // namespace rocksdb

utilities/object_registry_test.cc

@@ -17,44 +17,145 @@ class EnvRegistryTest : public testing::Test {
 
 int EnvRegistryTest::num_a = 0;
 int EnvRegistryTest::num_b = 0;
+static FactoryFunc<Env> test_reg_a = ObjectLibrary::Default()->Register<Env>(
+    "a://.*",
+    [](const std::string& /*uri*/, std::unique_ptr<Env>* /*env_guard*/,
+       std::string* /* errmsg */) {
+      ++EnvRegistryTest::num_a;
+      return Env::Default();
+    });
 
-static Registrar<Env> test_reg_a("a://.*",
+static FactoryFunc<Env> test_reg_b = ObjectLibrary::Default()->Register<Env>(
-                                 [](const std::string& /*uri*/,
+    "b://.*", [](const std::string& /*uri*/, std::unique_ptr<Env>* env_guard,
-                                    std::unique_ptr<Env>* /*env_guard*/) {
+                 std::string* /* errmsg */) {
-                                   ++EnvRegistryTest::num_a;
+      ++EnvRegistryTest::num_b;
-                                   return Env::Default();
+      // Env::Default() is a singleton so we can't grant ownership directly to
-                                 });
+      // the caller - we must wrap it first.
-
+      env_guard->reset(new EnvWrapper(Env::Default()));
-static Registrar<Env> test_reg_b("b://.*", [](const std::string& /*uri*/,
+      return env_guard->get();
-                                              std::unique_ptr<Env>* env_guard) {
+    });
-  ++EnvRegistryTest::num_b;
-  // Env::Default() is a singleton so we can't grant ownership directly to the
-  // caller - we must wrap it first.
-  env_guard->reset(new EnvWrapper(Env::Default()));
-  return env_guard->get();
-});
 
 TEST_F(EnvRegistryTest, Basics) {
+  std::string msg;
   std::unique_ptr<Env> env_guard;
-  auto res = NewCustomObject<Env>("a://test", &env_guard);
+  auto registry = ObjectRegistry::NewInstance();
+  auto res = registry->NewObject<Env>("a://test", &env_guard, &msg);
   ASSERT_NE(res, nullptr);
   ASSERT_EQ(env_guard, nullptr);
   ASSERT_EQ(1, num_a);
   ASSERT_EQ(0, num_b);
 
-  res = NewCustomObject<Env>("b://test", &env_guard);
+  res = registry->NewObject<Env>("b://test", &env_guard, &msg);
   ASSERT_NE(res, nullptr);
   ASSERT_NE(env_guard, nullptr);
   ASSERT_EQ(1, num_a);
   ASSERT_EQ(1, num_b);
 
-  res = NewCustomObject<Env>("c://test", &env_guard);
+  res = registry->NewObject<Env>("c://test", &env_guard, &msg);
   ASSERT_EQ(res, nullptr);
   ASSERT_EQ(env_guard, nullptr);
   ASSERT_EQ(1, num_a);
   ASSERT_EQ(1, num_b);
 }
 
+TEST_F(EnvRegistryTest, LocalRegistry) {
+  std::string msg;
+  std::unique_ptr<Env> guard;
+  auto registry = ObjectRegistry::NewInstance();
+  std::shared_ptr<ObjectLibrary> library = std::make_shared<ObjectLibrary>();
+  registry->AddLibrary(library);
+  library->Register<Env>(
+      "test-local",
+      [](const std::string& /*uri*/, std::unique_ptr<Env>* /*guard */,
+         std::string* /* errmsg */) { return Env::Default(); });
+
+  ObjectLibrary::Default()->Register<Env>(
+      "test-global",
+      [](const std::string& /*uri*/, std::unique_ptr<Env>* /*guard */,
+         std::string* /* errmsg */) { return Env::Default(); });
+
+  ASSERT_EQ(
+      ObjectRegistry::NewInstance()->NewObject<Env>("test-local", &guard, &msg),
+      nullptr);
+  ASSERT_NE(
+      ObjectRegistry::NewInstance()->NewObject("test-global", &guard, &msg),
+      nullptr);
+  ASSERT_NE(registry->NewObject<Env>("test-local", &guard, &msg), nullptr);
+  ASSERT_NE(registry->NewObject<Env>("test-global", &guard, &msg), nullptr);
+}
+
+TEST_F(EnvRegistryTest, CheckShared) {
+  std::shared_ptr<Env> shared;
+  std::shared_ptr<ObjectRegistry> registry = ObjectRegistry::NewInstance();
+  std::shared_ptr<ObjectLibrary> library = std::make_shared<ObjectLibrary>();
+  registry->AddLibrary(library);
+  library->Register<Env>(
+      "unguarded",
+      [](const std::string& /*uri*/, std::unique_ptr<Env>* /*guard */,
+         std::string* /* errmsg */) { return Env::Default(); });
+
+  library->Register<Env>(
+      "guarded", [](const std::string& /*uri*/, std::unique_ptr<Env>* guard,
+                    std::string* /* errmsg */) {
+        guard->reset(new EnvWrapper(Env::Default()));
+        return guard->get();
+      });
+
+  ASSERT_OK(registry->NewSharedObject<Env>("guarded", &shared));
+  ASSERT_NE(shared, nullptr);
+  shared.reset();
+  ASSERT_NOK(registry->NewSharedObject<Env>("unguarded", &shared));
+  ASSERT_EQ(shared, nullptr);
+}
+
+TEST_F(EnvRegistryTest, CheckStatic) {
+  Env* env = nullptr;
+  std::shared_ptr<ObjectRegistry> registry = ObjectRegistry::NewInstance();
+  std::shared_ptr<ObjectLibrary> library = std::make_shared<ObjectLibrary>();
+  registry->AddLibrary(library);
+  library->Register<Env>(
+      "unguarded",
+      [](const std::string& /*uri*/, std::unique_ptr<Env>* /*guard */,
+         std::string* /* errmsg */) { return Env::Default(); });
+
+  library->Register<Env>(
+      "guarded", [](const std::string& /*uri*/, std::unique_ptr<Env>* guard,
+                    std::string* /* errmsg */) {
+        guard->reset(new EnvWrapper(Env::Default()));
+        return guard->get();
+      });
+
+  ASSERT_NOK(registry->NewStaticObject<Env>("guarded", &env));
+  ASSERT_EQ(env, nullptr);
+  env = nullptr;
+  ASSERT_OK(registry->NewStaticObject<Env>("unguarded", &env));
+  ASSERT_NE(env, nullptr);
+}
+
+TEST_F(EnvRegistryTest, CheckUnique) {
+  std::unique_ptr<Env> unique;
+  std::shared_ptr<ObjectRegistry> registry = ObjectRegistry::NewInstance();
+  std::shared_ptr<ObjectLibrary> library = std::make_shared<ObjectLibrary>();
+  registry->AddLibrary(library);
+  library->Register<Env>(
+      "unguarded",
+      [](const std::string& /*uri*/, std::unique_ptr<Env>* /*guard */,
+         std::string* /* errmsg */) { return Env::Default(); });
+
+  library->Register<Env>(
+      "guarded", [](const std::string& /*uri*/, std::unique_ptr<Env>* guard,
+                    std::string* /* errmsg */) {
+        guard->reset(new EnvWrapper(Env::Default()));
+        return guard->get();
+      });
+
+  ASSERT_OK(registry->NewUniqueObject<Env>("guarded", &unique));
+  ASSERT_NE(unique, nullptr);
+  unique.reset();
+  ASSERT_NOK(registry->NewUniqueObject<Env>("unguarded", &unique));
+  ASSERT_EQ(unique, nullptr);
+}
+
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {