rocksdb/util/thread_status_util.h

// Copyright (c) 2013, Facebook, Inc.  All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.

#pragma once

#include "db/column_family.h"
#include "rocksdb/env.h"
#include "rocksdb/thread_status.h"
#include "util/thread_status_updater.h"

namespace rocksdb {

// The static utility class for updating thread-local status.
//
// The thread-local status is updated via the thread-local cached
// pointer thread_updater_local_cache_.  During each function call,
// when ThreadStatusUtil finds thread_updater_local_cache_ is
// left uninitialized (determined by thread_updater_initialized_),
// it will tries to initialize it using the return value of
// Env::GetThreadStatusUpdater().  When thread_updater_local_cache_
// is initialized by a non-null pointer, each function call will
// then update the status of the current thread.  Otherwise,
// all function calls to ThreadStatusUtil will be no-op.
class ThreadStatusUtil {
 public:
  // Set the thread type of the current thread.
  static void SetThreadType(
      const Env* env, ThreadStatus::ThreadType thread_type);

  // Unregister the current thread.
  static void UnregisterThread();

  // Create an entry in the global ColumnFamilyInfo table for the
  // specified column family.  This function should be called only
  // when the current thread does not hold db_mutex.
  static void NewColumnFamilyInfo(
      const DB* db, const ColumnFamilyData* cfd);

  // Erase the ConstantColumnFamilyInfo that is associated with the
  // specified ColumnFamilyData.  This function should be called only
  // when the current thread does not hold db_mutex.
  static void EraseColumnFamilyInfo(const ColumnFamilyData* cfd);

  // Erase all ConstantColumnFamilyInfo that is associated with the
  // specified db instance.  This function should be called only when
  // the current thread does not hold db_mutex.
  static void EraseDatabaseInfo(const DB* db);

  // Update the thread status to indicate the current thread is doing
  // something related to the specified column family.
  static void SetColumnFamily(const ColumnFamilyData* cfd);

 protected:
  // Initialize the thread-local ThreadStatusUpdater when it finds
  // the cached value is nullptr.  Returns true if it has cached
  // a non-null pointer.
  static bool MaybeInitThreadLocalUpdater(const Env* env);

#if ROCKSDB_USING_THREAD_STATUS
  // A boolean flag indicating whether thread_updater_local_cache_
  // is initialized.  It is set to true when an Env uses any
  // ThreadStatusUtil functions using the current thread other
  // than UnregisterThread().  It will be set to false when
  // UnregisterThread() is called.
  //
  // When this variable is set to true, thread_updater_local_cache_
  // will not be updated until this variable is again set to false
  // in UnregisterThread().
  static  __thread bool thread_updater_initialized_;

  // The thread-local cached ThreadStatusUpdater that caches the
  // thread_status_updater_ of the first Env that uses any ThreadStatusUtil
  // function other than UnregisterThread().  This variable will
  // be cleared when UnregisterThread() is called.
  //
  // When this variable is set to a non-null pointer, then the status
  // of the current thread will be updated when a function of
  // ThreadStatusUtil is called.  Otherwise, all functions of
  // ThreadStatusUtil will be no-op.
  //
  // When thread_updater_initialized_ is set to true, this variable
  // will not be updated until this thread_updater_initialized_ is
  // again set to false in UnregisterThread().
  static __thread ThreadStatusUpdater* thread_updater_local_cache_;
#else
  static bool thread_updater_initialized_;
  static ThreadStatusUpdater* thread_updater_local_cache_;
#endif
};

}  // namespace rocksdb