private:

struct Item {

// Global reference to the class file represented by this instance. The

// reference is owned by "JobjectMap".

jobject cls = nullptr;

// Loaded Java class file. "ClassFile" is thread safe, so "class_file" is

// shared between all the threads that referenced it.

std::unique_ptr<ClassFile> class_file;

// Reference count of this class file. When this count is zero, the class

// file is not referenced by anyone and "it_lru" points to the location of

// this class in LRU list.

int ref_count = 0;

// Ignored if "ref_count" is non-zero. Otherwise points to the location

// of this class in LRU list. We use linked list, since its iterators

// stay valid when the list is changed.

std::list<jobject>::iterator it_lru;

};

public:

// Automatically returns the referenced class file when goes out of scope.

class AutoClassFile {

public:

AutoClassFile(ClassFilesCache* owner, Item* item)

: owner_(owner), item_(item) {

}

~AutoClassFile() { owner_->Unref(item_); }

ClassFile* get() { return item_->class_file.get(); }

private:

ClassFilesCache* const owner_;

Item* const item_;

DISALLOW_COPY_AND_ASSIGN(AutoClassFile);

};

// Class constructor. "class_indexer" is not owned by this class and must

// outlive it. It is used to load new class files when not in cache.

// The actual spaced used by "ClassFilesCache" may exceed this threshold

// if too many class files are referenced at the same time.

ClassFilesCache(ClassIndexer* class_indexer, int max_size);

// Gets the class file for the specified class from cache. Returns nullptr

// if the class file is not in cache.

std::unique_ptr<AutoClassFile> Get(jobject cls);

// Gets the class file for the specified class from cache. Loads the class

// file if not found. If the class file was actually loaded (rather than

// retrieved from cache), "loaded" is set to true on return.

std::unique_ptr<AutoClassFile> GetOrLoad(jobject cls, bool* loaded);

// Returns the total size in bytes of all the class files in cache. This

// number can exceed the maximum size if too many class files are referenced

// at the same time.

int total_size() const { return total_size_; }

private:

// Increases the "ref_count" if the class file is already referenced.

// Otherwise removes it from LRU list and sets "ref_count" to 1.

// Must be called with "mu_" locked.

std::unique_ptr<ClassFilesCache::AutoClassFile> Reference(Item* item);

// Returns the class file to the cache. If the class file is not referenced

// any more, adds the class file to LRU cache. Must be called with "mu_"

// unlocked.

void Unref(Item* item);

// Releases class files from LRU list as long as the total space used by

// the cache exceeds the threshold. Must be called with "mu_" locked.

void GarbageCollect();

private:

// Used to load Java classes. See "ClassFile" for more details.

ClassIndexer* const class_indexer_;

// Maximum total size of the class files before the garbage collection kicks

// in and starts releasing unreferenced class files.

const int max_size_;

// Locks changes to "classes_, "lru_" and "total_size_".

absl::Mutex mu_;

// All cached class files. We keep "Item" by value because "JobjectMap"

// guarantees that it will not move when the entries are added or removed

// from it.

JobjectMap<JObject_GlobalRef, Item> classes_;

// Class files that are not referenced and can be released if the cache

// needs more space. The most recently used classes are at the end. Class

// files are garbage collected starting from the front.

std::list<jobject> lru_;

// Total number of bytes used by "ClassFile" instances of "classes_".

int total_size_ = 0;

DISALLOW_COPY_AND_ASSIGN(ClassFilesCache);