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// Copyright 2022 The Dawn & Tint Authors
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#ifndef SRC_TINT_UTILS_CONTAINERS_UNIQUE_ALLOCATOR_H_
#define SRC_TINT_UTILS_CONTAINERS_UNIQUE_ALLOCATOR_H_
#include <functional>
#include <utility>
#include "src/tint/utils/containers/hashmap_base.h"
#include "src/tint/utils/memory/block_allocator.h"
namespace tint {
/// UniqueAllocator is used to allocate unique instances of the template type `T`.
template <typename T, typename HASH = std::hash<T>, typename EQUAL = std::equal_to<T>>
class UniqueAllocator {
public:
/// Iterator is the type returned by begin() and end()
using Iterator = typename BlockAllocator<T>::ConstIterator;
/// @param args the arguments used to construct the object.
/// @return a pointer to an instance of `T` with the provided arguments.
/// If an existing instance of `T` has been constructed, then the same
/// pointer is returned.
template <typename TYPE = T, typename... ARGS>
TYPE* Get(ARGS&&... args) {
// Create a temporary T instance on the stack so that we can hash it, and use it for
// equality lookup for the Set. If the item is not found in the set, then we create the
// persisted instance with the allocator.
TYPE prototype{args...};
Key& key = items.Add(&prototype);
if (key.Value() == &prototype) {
key = allocator.template Create<TYPE>(std::forward<ARGS>(args)...);
}
return static_cast<TYPE*>(key.Value());
}
/// @param args the arguments used to create the temporary used for the search.
/// @return a pointer to an instance of `T` with the provided arguments, or nullptr if the item
/// was not found.
template <typename TYPE = T, typename... ARGS>
TYPE* Find(ARGS&&... args) const {
// Create a temporary T instance on the stack so that we can hash it, and use it for
// equality lookup for the Set.
TYPE prototype{std::forward<ARGS>(args)...};
return static_cast<TYPE*>(items.Get(&prototype));
}
/// Wrap sets this allocator to the objects created with the content of `inner`.
/// The allocator after Wrap is intended to temporarily extend the objects
/// of an existing immutable UniqueAllocator.
/// As the copied objects are owned by `inner`, `inner` must not be destructed
/// or assigned while using this allocator.
/// @param o the immutable UniqueAlllocator to extend
void Wrap(const UniqueAllocator<T, HASH, EQUAL>& o) { items = o.items; }
/// @returns an iterator to the beginning of the types
Iterator begin() const { return allocator.Objects().begin(); }
/// @returns an iterator to the end of the types
Iterator end() const { return allocator.Objects().end(); }
private:
/// Comparator is the hashing function used by the Hashset
struct Hasher {
/// Hashing function
/// @param e the entry
/// @returns the hash of the entry
size_t operator()(T* e) const { return HASH{}(*e); }
};
/// Equality is the equality function used by the Hashset
struct Equality {
/// Equality function
/// @param a the first entry to compare
/// @param b the second entry to compare
/// @returns true if the two entries are equal
bool operator()(T* a, T* b) const { return EQUAL{}(*a, *b); }
};
/// The maximum capacity of Set before it performs heap allocations.
static constexpr size_t kFixedSize = 32;
/// The key type of Set.
using Key = HashmapKey<T*, Hasher, Equality>;
/// A custom Hashset implementation that allows keys to be modified.
class Set : public HashmapBase<Key, kFixedSize> {
public:
Key& Add(T* key) {
auto idx = this->EditAt(key);
if (!idx.entry) {
idx.Insert(std::forward<T*>(key));
}
return *idx.entry;
}
T* Get(T* key) const {
if (auto* entry = this->GetEntry(key)) {
return *entry;
}
return nullptr;
}
};
/// The block allocator used to allocate the unique objects
BlockAllocator<T> allocator;
/// The set of unique item entries
Set items;
};
} // namespace tint
#endif // SRC_TINT_UTILS_CONTAINERS_UNIQUE_ALLOCATOR_H_