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Made an attempt to explain the requirements placed upon Disk subclasses that wish to support writing.

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This commit is contained in:
Thomas Harte 2016-12-31 15:30:48 -05:00
parent 8eb21c6702
commit b3c33d993a
1 changed files with 18 additions and 1 deletions
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19
Storage/Disk/Disk.hpp
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@ -115,13 +115,30 @@ class Disk {
*/ */
virtual std::shared_ptr<Track> get_uncached_track_at_position(unsigned int head, unsigned int position) = 0; virtual std::shared_ptr<Track> get_uncached_track_at_position(unsigned int head, unsigned int position) = 0;
/*!
Subclasses that support writing should implement @c store_updated_track_at_position to determine which bytes
have to be written from @c track, then obtain @c file_access_mutex and write new data to their file to represent
the track underneath @c head at @c position.
The base class will ensure that calls are made to @c get_uncached_track_at_position only while it holds @c file_access_mutex;
that mutex therefore provides serialisation of file access.
This method will be called asynchronously. Subclasses are responsible for any synchronisation other than that
provided automatically via @c file_access_mutex.
*/
virtual void store_updated_track_at_position(unsigned int head, unsigned int position, const std::shared_ptr<Track> &track, std::mutex &file_access_mutex); virtual void store_updated_track_at_position(unsigned int head, unsigned int position, const std::shared_ptr<Track> &track, std::mutex &file_access_mutex);
/*!
Subclasses that support writing should call @c flush_updates during their destructor if there is anything they
do in @c store_updated_track_at_position that would not be valid after their destructor has completed but prior
to Disk's constructor running.
*/
void flush_updates(); void flush_updates();
private: private:
std::map<int, std::shared_ptr<Track>> cached_tracks_;
int get_id_for_track_at_position(unsigned int head, unsigned int position); int get_id_for_track_at_position(unsigned int head, unsigned int position);
std::map<int, std::shared_ptr<Track>> cached_tracks_;
std::mutex file_access_mutex_; std::mutex file_access_mutex_;
std::unique_ptr<Concurrency::AsyncTaskQueue> update_queue_; std::unique_ptr<Concurrency::AsyncTaskQueue> update_queue_;
}; };