mirror of https://github.com/facebook/rocksdb.git
102 lines
3.7 KiB
C++
102 lines
3.7 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <atomic>
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#include <functional>
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#include <memory>
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#include <unordered_map>
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#include <vector>
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#include "util/autovector.h"
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#include "port/port.h"
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namespace ROCKSDB_NAMESPACE {
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// Cleanup function that will be called for a stored thread local
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// pointer (if not NULL) when one of the following happens:
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// (1) a thread terminates
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// (2) a ThreadLocalPtr is destroyed
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//
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// Warning: this function is called while holding a global mutex. The same mutex
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// is used (at least in some cases) by most methods of ThreadLocalPtr, and it's
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// shared across all instances of ThreadLocalPtr. Thereforere extra care
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// is needed to avoid deadlocks. In particular, the handler shouldn't lock any
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// mutexes and shouldn't call any methods of any ThreadLocalPtr instances,
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// unless you know what you're doing.
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using UnrefHandler = void (*)(void* ptr);
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// ThreadLocalPtr stores only values of pointer type. Different from
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// the usual thread-local-storage, ThreadLocalPtr has the ability to
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// distinguish data coming from different threads and different
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// ThreadLocalPtr instances. For example, if a regular thread_local
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// variable A is declared in DBImpl, two DBImpl objects would share
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// the same A. However, a ThreadLocalPtr that is defined under the
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// scope of DBImpl can avoid such confliction. As a result, its memory
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// usage would be O(# of threads * # of ThreadLocalPtr instances).
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class ThreadLocalPtr {
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public:
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explicit ThreadLocalPtr(UnrefHandler handler = nullptr);
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ThreadLocalPtr(const ThreadLocalPtr&) = delete;
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ThreadLocalPtr& operator=(const ThreadLocalPtr&) = delete;
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~ThreadLocalPtr();
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// Return the current pointer stored in thread local
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void* Get() const;
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// Set a new pointer value to the thread local storage.
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void Reset(void* ptr);
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// Atomically swap the supplied ptr and return the previous value
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void* Swap(void* ptr);
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// Atomically compare the stored value with expected. Set the new
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// pointer value to thread local only if the comparison is true.
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// Otherwise, expected returns the stored value.
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// Return true on success, false on failure
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bool CompareAndSwap(void* ptr, void*& expected);
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// Reset all thread local data to replacement, and return non-nullptr
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// data for all existing threads
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void Scrape(autovector<void*>* ptrs, void* const replacement);
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using FoldFunc = std::function<void(void*, void*)>;
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// Update res by applying func on each thread-local value. Holds a lock that
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// prevents unref handler from running during this call, but clients must
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// still provide external synchronization since the owning thread can
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// access the values without internal locking, e.g., via Get() and Reset().
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void Fold(FoldFunc func, void* res);
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// Add here for testing
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// Return the next available Id without claiming it
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static uint32_t TEST_PeekId();
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// Initialize the static singletons of the ThreadLocalPtr.
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//
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// If this function is not called, then the singletons will be
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// automatically initialized when they are used.
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//
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// Calling this function twice or after the singletons have been
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// initialized will be no-op.
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static void InitSingletons();
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class StaticMeta;
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private:
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static StaticMeta* Instance();
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const uint32_t id_;
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};
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} // namespace ROCKSDB_NAMESPACE
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