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// Copyright (c) 2011-present, Facebook, Inc. 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).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <atomic>
#include <functional>
#include <memory>
#include <unordered_map>
#include <vector>
#include "port/port.h"
#include "util/autovector.h"
namespace ROCKSDB_NAMESPACE {
// Cleanup function that will be called for a stored thread local
// pointer (if not NULL) when one of the following happens:
// (1) a thread terminates
// (2) a ThreadLocalPtr is destroyed
//
// Warning: this function is called while holding a global mutex. The same mutex
// is used (at least in some cases) by most methods of ThreadLocalPtr, and it's
// shared across all instances of ThreadLocalPtr. Thereforere extra care
// is needed to avoid deadlocks. In particular, the handler shouldn't lock any
// mutexes and shouldn't call any methods of any ThreadLocalPtr instances,
// unless you know what you're doing.
using UnrefHandler = void (*)(void* ptr);
// ThreadLocalPtr stores only values of pointer type. Different from
// the usual thread-local-storage, ThreadLocalPtr has the ability to
// distinguish data coming from different threads and different
// ThreadLocalPtr instances. For example, if a regular thread_local
// variable A is declared in DBImpl, two DBImpl objects would share
// the same A. However, a ThreadLocalPtr that is defined under the
// scope of DBImpl can avoid such confliction. As a result, its memory
// usage would be O(# of threads * # of ThreadLocalPtr instances).
class ThreadLocalPtr {
public:
explicit ThreadLocalPtr(UnrefHandler handler = nullptr);
ThreadLocalPtr(const ThreadLocalPtr&) = delete;
ThreadLocalPtr& operator=(const ThreadLocalPtr&) = delete;
~ThreadLocalPtr();
// Return the current pointer stored in thread local
void* Get() const;
// Set a new pointer value to the thread local storage.
void Reset(void* ptr);
// Atomically swap the supplied ptr and return the previous value
void* Swap(void* ptr);
// Atomically compare the stored value with expected. Set the new
// pointer value to thread local only if the comparison is true.
// Otherwise, expected returns the stored value.
// Return true on success, false on failure
bool CompareAndSwap(void* ptr, void*& expected);
// Reset all thread local data to replacement, and return non-nullptr
// data for all existing threads
void Scrape(autovector<void*>* ptrs, void* const replacement);
using FoldFunc = std::function<void(void*, void*)>;
// Update res by applying func on each thread-local value. Holds a lock that
// prevents unref handler from running during this call, but clients must
// still provide external synchronization since the owning thread can
// access the values without internal locking, e.g., via Get() and Reset().
void Fold(FoldFunc func, void* res);
// Add here for testing
// Return the next available Id without claiming it
static uint32_t TEST_PeekId();
// Initialize the static singletons of the ThreadLocalPtr.
//
// If this function is not called, then the singletons will be
// automatically initialized when they are used.
//
// Calling this function twice or after the singletons have been
// initialized will be no-op.
static void InitSingletons();
class StaticMeta;
private:
static StaticMeta* Instance();
const uint32_t id_;
};
} // namespace ROCKSDB_NAMESPACE
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