// Copyright 2017 The Chromium 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.
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#ifndef BASE_THREADING_SEQUENCE_LOCAL_STORAGE_MAP_H_
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#define BASE_THREADING_SEQUENCE_LOCAL_STORAGE_MAP_H_
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#include "base/base_export.h"
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#include "base/containers/flat_map.h"
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#include "base/macros.h"
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namespace base {
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namespace internal {
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// A SequenceLocalStorageMap holds (slot_id) -> (value, destructor) items for a
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// sequence. When a task runs, it is expected that a pointer to its sequence's
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// SequenceLocalStorageMap is set in TLS using
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// ScopedSetSequenceMapLocalStorageForCurrentThread. When a
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// SequenceLocalStorageMap is destroyed, it invokes the destructors associated
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// with values stored within it.
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// The Get() and Set() methods should not be accessed directly.
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// Use SequenceLocalStorageSlot to Get() and Set() values in the current
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// sequence's SequenceLocalStorageMap.
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class BASE_EXPORT SequenceLocalStorageMap {
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public:
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SequenceLocalStorageMap();
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~SequenceLocalStorageMap();
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// Returns the SequenceLocalStorage bound to the current thread. It is invalid
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// to call this outside the scope of a
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// ScopedSetSequenceLocalStorageForCurrentThread.
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static SequenceLocalStorageMap& GetForCurrentThread();
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// Holds a pointer to a value alongside a destructor for this pointer.
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// Calls the destructor on the value upon destruction.
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class BASE_EXPORT ValueDestructorPair {
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public:
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using DestructorFunc = void(void*);
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ValueDestructorPair(void* value, DestructorFunc* destructor);
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~ValueDestructorPair();
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ValueDestructorPair(ValueDestructorPair&& value_destructor_pair);
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ValueDestructorPair& operator=(ValueDestructorPair&& value_destructor_pair);
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void* value() const { return value_; }
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private:
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void* value_;
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DestructorFunc* destructor_;
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DISALLOW_COPY_AND_ASSIGN(ValueDestructorPair);
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};
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// Returns the value stored in |slot_id| or nullptr if no value was stored.
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void* Get(int slot_id);
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// Stores |value_destructor_pair| in |slot_id|. Overwrites and destroys any
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// previously stored value.
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void Set(int slot_id, ValueDestructorPair value_destructor_pair);
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private:
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// Map from slot id to ValueDestructorPair.
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// flat_map was chosen because there are expected to be relatively few entries
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// in the map. For low number of entries, flat_map is known to perform better
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// than other map implementations.
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base::flat_map<int, ValueDestructorPair> sls_map_;
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DISALLOW_COPY_AND_ASSIGN(SequenceLocalStorageMap);
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};
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// Within the scope of this object,
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// SequenceLocalStorageMap::GetForCurrentThread() will return a reference to the
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// SequenceLocalStorageMap object passed to the constructor. There can be only
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// one ScopedSetSequenceLocalStorageMapForCurrentThread instance per scope.
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class BASE_EXPORT ScopedSetSequenceLocalStorageMapForCurrentThread {
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public:
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ScopedSetSequenceLocalStorageMapForCurrentThread(
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SequenceLocalStorageMap* sequence_local_storage);
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~ScopedSetSequenceLocalStorageMapForCurrentThread();
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private:
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DISALLOW_COPY_AND_ASSIGN(ScopedSetSequenceLocalStorageMapForCurrentThread);
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};
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} // namespace internal
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} // namespace base
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#endif // BASE_THREADING_SEQUENCE_LOCAL_STORAGE_MAP_H_
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