// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_ID_MAP_H_
#define BASE_ID_MAP_H_
#include <set>
#include "base/basictypes.h"
#include "base/containers/hash_tables.h"
#include "base/logging.h"
#include "base/threading/non_thread_safe.h"
// Ownership semantics - own pointer means the pointer is deleted in Remove()
// & during destruction
enum IDMapOwnershipSemantics {
IDMapExternalPointer,
IDMapOwnPointer
};
// This object maintains a list of IDs that can be quickly converted to
// pointers to objects. It is implemented as a hash table, optimized for
// relatively small data sets (in the common case, there will be exactly one
// item in the list).
//
// Items can be inserted into the container with arbitrary ID, but the caller
// must ensure they are unique. Inserting IDs and relying on automatically
// generated ones is not allowed because they can collide.
//
// This class does not have a virtual destructor, do not inherit from it when
// ownership semantics are set to own because pointers will leak.
template<typename T, IDMapOwnershipSemantics OS = IDMapExternalPointer>
class IDMap : public base::NonThreadSafe {
private:
typedef int32 KeyType;
typedef base::hash_map<KeyType, T*> HashTable;
public:
IDMap() : iteration_depth_(0), next_id_(1), check_on_null_data_(false) {
// A number of consumers of IDMap create it on one thread but always access
// it from a different, but consitent, thread post-construction.
DetachFromThread();
}
~IDMap() {
// Many IDMap's are static, and hence will be destroyed on the main thread.
// However, all the accesses may take place on another thread, such as the
// IO thread. Detaching again to clean this up.
DetachFromThread();
Releaser<OS, 0>::release_all(&data_);
}
// Sets whether Add should CHECK if passed in NULL data. Default is false.
void set_check_on_null_data(bool value) { check_on_null_data_ = value; }
// Adds a view with an automatically generated unique ID. See AddWithID.
KeyType Add(T* data) {
DCHECK(CalledOnValidThread());
CHECK(!check_on_null_data_ || data);
KeyType this_id = next_id_;
DCHECK(data_.find(this_id) == data_.end()) << "Inserting duplicate item";
data_[this_id] = data;
next_id_++;
return this_id;
}
// Adds a new data member with the specified ID. The ID must not be in
// the list. The caller either must generate all unique IDs itself and use
// this function, or allow this object to generate IDs and call Add. These
// two methods may not be mixed, or duplicate IDs may be generated
void AddWithID(T* data, KeyType id) {
DCHECK(CalledOnValidThread());
CHECK(!check_on_null_data_ || data);
DCHECK(data_.find(id) == data_.end()) << "Inserting duplicate item";
data_[id] = data;
}
void Remove(KeyType id) {
DCHECK(CalledOnValidThread());
typename HashTable::iterator i = data_.find(id);
if (i == data_.end()) {
NOTREACHED() << "Attempting to remove an item not in the list";
return;
}
if (iteration_depth_ == 0) {
Releaser<OS, 0>::release(i->second);
data_.erase(i);
} else {
removed_ids_.insert(id);
}
}
void Clear() {
DCHECK(CalledOnValidThread());
if (iteration_depth_ == 0) {
Releaser<OS, 0>::release_all(&data_);
} else {
for (typename HashTable::iterator i = data_.begin();
i != data_.end(); ++i)
removed_ids_.insert(i->first);
}
}
bool IsEmpty() const {
DCHECK(CalledOnValidThread());
return size() == 0u;
}
T* Lookup(KeyType id) const {
DCHECK(CalledOnValidThread());
typename HashTable::const_iterator i = data_.find(id);
if (i == data_.end())
return NULL;
return i->second;
}
size_t size() const {
DCHECK(CalledOnValidThread());
return data_.size() - removed_ids_.size();
}
#if defined(UNIT_TEST)
int iteration_depth() const {
return iteration_depth_;
}
#endif // defined(UNIT_TEST)
// It is safe to remove elements from the map during iteration. All iterators
// will remain valid.
template<class ReturnType>
class Iterator {
public:
Iterator(IDMap<T, OS>* map)
: map_(map),
iter_(map_->data_.begin()) {
Init();
}
Iterator(const Iterator& iter)
: map_(iter.map_),
iter_(iter.iter_) {
Init();
}
const Iterator& operator=(const Iterator& iter) {
map_ = iter.map;
iter_ = iter.iter;
Init();
return *this;
}
~Iterator() {
DCHECK(map_->CalledOnValidThread());
// We're going to decrement iteration depth. Make sure it's greater than
// zero so that it doesn't become negative.
DCHECK_LT(0, map_->iteration_depth_);
if (--map_->iteration_depth_ == 0)
map_->Compact();
}
bool IsAtEnd() const {
DCHECK(map_->CalledOnValidThread());
return iter_ == map_->data_.end();
}
KeyType GetCurrentKey() const {
DCHECK(map_->CalledOnValidThread());
return iter_->first;
}
ReturnType* GetCurrentValue() const {
DCHECK(map_->CalledOnValidThread());
return iter_->second;
}
void Advance() {
DCHECK(map_->CalledOnValidThread());
++iter_;
SkipRemovedEntries();
}
private:
void Init() {
DCHECK(map_->CalledOnValidThread());
++map_->iteration_depth_;
SkipRemovedEntries();
}
void SkipRemovedEntries() {
while (iter_ != map_->data_.end() &&
map_->removed_ids_.find(iter_->first) !=
map_->removed_ids_.end()) {
++iter_;
}
}
IDMap<T, OS>* map_;
typename HashTable::const_iterator iter_;
};
typedef Iterator<T> iterator;
typedef Iterator<const T> const_iterator;
private:
// The dummy parameter is there because C++ standard does not allow
// explicitly specialized templates inside classes
template<IDMapOwnershipSemantics OI, int dummy> struct Releaser {
static inline void release(T* ptr) {}
static inline void release_all(HashTable* table) {}
};
template<int dummy> struct Releaser<IDMapOwnPointer, dummy> {
static inline void release(T* ptr) { delete ptr;}
static inline void release_all(HashTable* table) {
for (typename HashTable::iterator i = table->begin();
i != table->end(); ++i) {
delete i->second;
}
table->clear();
}
};
void Compact() {
DCHECK_EQ(0, iteration_depth_);
for (std::set<KeyType>::const_iterator i = removed_ids_.begin();
i != removed_ids_.end(); ++i) {
Remove(*i);
}
removed_ids_.clear();
}
// Keep track of how many iterators are currently iterating on us to safely
// handle removing items during iteration.
int iteration_depth_;
// Keep set of IDs that should be removed after the outermost iteration has
// finished. This way we manage to not invalidate the iterator when an element
// is removed.
std::set<KeyType> removed_ids_;
// The next ID that we will return from Add()
KeyType next_id_;
HashTable data_;
// See description above setter.
bool check_on_null_data_;
DISALLOW_COPY_AND_ASSIGN(IDMap);
};
#endif // BASE_ID_MAP_H_