Class SimpleCache

  • All Implemented Interfaces:
    Cache

    public final class SimpleCache
    extends Object
    implements Cache
    A Cache implementation that maintains an in-memory representation.

    Only one instance of SimpleCache is allowed for a given directory at a given time.

    To delete a SimpleCache, use delete(File, DatabaseProvider) rather than deleting the directory and its contents directly. This is necessary to ensure that associated index data is also removed.

    • Constructor Detail

      • SimpleCache

        @Deprecated
        public SimpleCache​(File cacheDir,
                           CacheEvictor evictor)
        Deprecated.
        Use a constructor that takes a DatabaseProvider for improved performance.
        Constructs the cache. The cache will delete any unrecognized files from the directory. Hence the directory cannot be used to store other files.
        Parameters:
        cacheDir - A dedicated cache directory.
        evictor - The evictor to be used. For download use cases where cache eviction should not occur, use NoOpCacheEvictor.
      • SimpleCache

        @Deprecated
        public SimpleCache​(File cacheDir,
                           CacheEvictor evictor,
                           @Nullable
                           byte[] secretKey)
        Deprecated.
        Use a constructor that takes a DatabaseProvider for improved performance.
        Constructs the cache. The cache will delete any unrecognized files from the directory. Hence the directory cannot be used to store other files.
        Parameters:
        cacheDir - A dedicated cache directory.
        evictor - The evictor to be used. For download use cases where cache eviction should not occur, use NoOpCacheEvictor.
        secretKey - If not null, cache keys will be stored encrypted on filesystem using AES/CBC. The key must be 16 bytes long.
      • SimpleCache

        @Deprecated
        public SimpleCache​(File cacheDir,
                           CacheEvictor evictor,
                           @Nullable
                           byte[] secretKey,
                           boolean encrypt)
        Deprecated.
        Use a constructor that takes a DatabaseProvider for improved performance.
        Constructs the cache. The cache will delete any unrecognized files from the directory. Hence the directory cannot be used to store other files.
        Parameters:
        cacheDir - A dedicated cache directory.
        evictor - The evictor to be used. For download use cases where cache eviction should not occur, use NoOpCacheEvictor.
        secretKey - If not null, cache keys will be stored encrypted on filesystem using AES/CBC. The key must be 16 bytes long.
        encrypt - Whether the index will be encrypted when written. Must be false if secretKey is null.
      • SimpleCache

        public SimpleCache​(File cacheDir,
                           CacheEvictor evictor,
                           DatabaseProvider databaseProvider)
        Constructs the cache. The cache will delete any unrecognized files from the directory. Hence the directory cannot be used to store other files.
        Parameters:
        cacheDir - A dedicated cache directory.
        evictor - The evictor to be used. For download use cases where cache eviction should not occur, use NoOpCacheEvictor.
        databaseProvider - Provides the database in which the cache index is stored.
      • SimpleCache

        public SimpleCache​(File cacheDir,
                           CacheEvictor evictor,
                           @Nullable
                           DatabaseProvider databaseProvider,
                           @Nullable
                           byte[] legacyIndexSecretKey,
                           boolean legacyIndexEncrypt,
                           boolean preferLegacyIndex)
        Constructs the cache. The cache will delete any unrecognized files from the cache directory. Hence the directory cannot be used to store other files.
        Parameters:
        cacheDir - A dedicated cache directory.
        evictor - The evictor to be used. For download use cases where cache eviction should not occur, use NoOpCacheEvictor.
        databaseProvider - Provides the database in which the cache index is stored, or null to use a legacy index. Using a database index is highly recommended for performance reasons.
        legacyIndexSecretKey - A 16 byte AES key for reading, and optionally writing, the legacy index. Not used by the database index, however should still be provided when using the database index in cases where upgrading from the legacy index may be necessary.
        legacyIndexEncrypt - Whether to encrypt when writing to the legacy index. Must be false if legacyIndexSecretKey is null. Not used by the database index.
        preferLegacyIndex - Whether to use the legacy index even if a databaseProvider is provided. Should be false in nearly all cases. Setting this to true is only useful for downgrading from the database index back to the legacy index.
    • Method Detail

      • isCacheFolderLocked

        public static boolean isCacheFolderLocked​(File cacheFolder)
        Returns whether cacheFolder is locked by a SimpleCache instance. To unlock the folder the SimpleCache instance should be released.
      • delete

        @WorkerThread
        public static void delete​(File cacheDir,
                                  @Nullable
                                  DatabaseProvider databaseProvider)
        Deletes all content belonging to a cache instance.

        This method may be slow and shouldn't normally be called on the main thread.

        Parameters:
        cacheDir - The cache directory.
        databaseProvider - The database in which index data is stored, or null if the cache used a legacy index.
      • checkInitialization

        public void checkInitialization()
                                 throws Cache.CacheException
        Checks whether the cache was initialized successfully.
        Throws:
        Cache.CacheException - If an error occurred during initialization.
      • getUid

        public long getUid()
        Description copied from interface: Cache
        Returns a non-negative unique identifier for the cache, or Cache.UID_UNSET if initialization failed before the unique identifier was determined.

        Implementations are expected to generate and store the unique identifier alongside the cached content. If the location of the cache is deleted or swapped, it is expected that a new unique identifier will be generated when the cache is recreated.

        Specified by:
        getUid in interface Cache
      • release

        public void release()
        Description copied from interface: Cache
        Releases the cache. This method must be called when the cache is no longer required. The cache must not be used after calling this method.

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        release in interface Cache
      • addListener

        public NavigableSet<CacheSpan> addListener​(String key,
                                                   Cache.Listener listener)
        Description copied from interface: Cache
        Registers a listener to listen for changes to a given resource.

        No guarantees are made about the thread or threads on which the listener is called, but it is guaranteed that listener methods will be called in a serial fashion (i.e. one at a time) and in the same order as events occurred.

        Specified by:
        addListener in interface Cache
        Parameters:
        key - The cache key of the resource.
        listener - The listener to add.
        Returns:
        The current spans for the resource.
      • removeListener

        public void removeListener​(String key,
                                   Cache.Listener listener)
        Description copied from interface: Cache
        Unregisters a listener.
        Specified by:
        removeListener in interface Cache
        Parameters:
        key - The cache key of the resource.
        listener - The listener to remove.
      • getCachedSpans

        public NavigableSet<CacheSpan> getCachedSpans​(String key)
        Description copied from interface: Cache
        Returns the cached spans for a given resource.
        Specified by:
        getCachedSpans in interface Cache
        Parameters:
        key - The cache key of the resource.
        Returns:
        The spans for the key.
      • getKeys

        public Set<String> getKeys()
        Description copied from interface: Cache
        Returns the cache keys of all of the resources that are at least partially cached.
        Specified by:
        getKeys in interface Cache
      • getCacheSpace

        public long getCacheSpace()
        Description copied from interface: Cache
        Returns the total disk space in bytes used by the cache.
        Specified by:
        getCacheSpace in interface Cache
      • startReadWrite

        public CacheSpan startReadWrite​(String key,
                                        long position,
                                        long length)
                                 throws InterruptedException,
                                        Cache.CacheException
        Description copied from interface: Cache
        A caller should invoke this method when they require data starting from a given position in a given resource.

        If there is a cache entry that overlaps the position, then the returned CacheSpan defines the file in which the data is stored. CacheSpan.isCached is true. The caller may read from the cache file, but does not acquire any locks.

        If there is no cache entry overlapping position, then the returned CacheSpan defines a hole in the cache starting at position into which the caller may write as it obtains the data from some other source. The returned CacheSpan serves as a lock. Whilst the caller holds the lock it may write data into the hole. It may split data into multiple files. When the caller has finished writing a file it should commit it to the cache by calling Cache.commitFile(File, long). When the caller has finished writing, it must release the lock by calling Cache.releaseHoleSpan(com.google.android.exoplayer2.upstream.cache.CacheSpan).

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        startReadWrite in interface Cache
        Parameters:
        key - The cache key of the resource.
        position - The starting position in the resource from which data is required.
        length - The length of the data being requested, or C.LENGTH_UNSET if unbounded. The length is ignored if there is a cache entry that overlaps the position. Else, it defines the maximum length of the hole CacheSpan that's returned. Cache implementations may support parallel writes into non-overlapping holes, and so passing the actual required length should be preferred to passing C.LENGTH_UNSET when possible.
        Returns:
        The CacheSpan.
        Throws:
        InterruptedException - If the thread was interrupted.
        Cache.CacheException - If an error is encountered.
      • startReadWriteNonBlocking

        @Nullable
        public CacheSpan startReadWriteNonBlocking​(String key,
                                                   long position,
                                                   long length)
                                            throws Cache.CacheException
        Description copied from interface: Cache
        Same as Cache.startReadWrite(String, long, long). However, if the cache entry is locked, then instead of blocking, this method will return null as the CacheSpan.

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        startReadWriteNonBlocking in interface Cache
        Parameters:
        key - The cache key of the resource.
        position - The starting position in the resource from which data is required.
        length - The length of the data being requested, or C.LENGTH_UNSET if unbounded. The length is ignored if there is a cache entry that overlaps the position. Else, it defines the range of data locked by the returned CacheSpan.
        Returns:
        The CacheSpan. Or null if the cache entry is locked.
        Throws:
        Cache.CacheException - If an error is encountered.
      • startFile

        public File startFile​(String key,
                              long position,
                              long length)
                       throws Cache.CacheException
        Description copied from interface: Cache
        Obtains a cache file into which data can be written. Must only be called when holding a corresponding hole CacheSpan obtained from Cache.startReadWrite(String, long, long).

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        startFile in interface Cache
        Parameters:
        key - The cache key of the resource being written.
        position - The starting position in the resource from which data will be written.
        length - The length of the data being written, or C.LENGTH_UNSET if unknown. Used only to ensure that there is enough space in the cache.
        Returns:
        The file into which data should be written.
        Throws:
        Cache.CacheException - If an error is encountered.
      • commitFile

        public void commitFile​(File file,
                               long length)
                        throws Cache.CacheException
        Description copied from interface: Cache
        Commits a file into the cache. Must only be called when holding a corresponding hole CacheSpan obtained from Cache.startReadWrite(String, long, long).

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        commitFile in interface Cache
        Parameters:
        file - A newly written cache file.
        length - The length of the newly written cache file in bytes.
        Throws:
        Cache.CacheException - If an error is encountered.
      • removeResource

        public void removeResource​(String key)
        Description copied from interface: Cache
        Removes all CacheSpans for a resource, deleting the underlying files.
        Specified by:
        removeResource in interface Cache
        Parameters:
        key - The cache key of the resource being removed.
      • removeSpan

        public void removeSpan​(CacheSpan span)
        Description copied from interface: Cache
        Removes a cached CacheSpan from the cache, deleting the underlying file.

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        removeSpan in interface Cache
        Parameters:
        span - The CacheSpan to remove.
      • isCached

        public boolean isCached​(String key,
                                long position,
                                long length)
        Description copied from interface: Cache
        Returns whether the specified range of data in a resource is fully cached.
        Specified by:
        isCached in interface Cache
        Parameters:
        key - The cache key of the resource.
        position - The starting position of the data in the resource.
        length - The length of the data.
        Returns:
        true if the data is available in the Cache otherwise false;
      • getCachedLength

        public long getCachedLength​(String key,
                                    long position,
                                    long length)
        Description copied from interface: Cache
        Returns the length of continuously cached data starting from position, up to a maximum of maxLength, of a resource. If position isn't cached then -holeLength is returned, where holeLength is the length of continuously uncached data starting from position, up to a maximum of maxLength.
        Specified by:
        getCachedLength in interface Cache
        Parameters:
        key - The cache key of the resource.
        position - The starting position of the data in the resource.
        length - The maximum length of the data or hole to be returned. C.LENGTH_UNSET is permitted, and is equivalent to passing Long.MAX_VALUE.
        Returns:
        The length of the continuously cached data, or -holeLength if position isn't cached.
      • getCachedBytes

        public long getCachedBytes​(String key,
                                   long position,
                                   long length)
        Description copied from interface: Cache
        Returns the total number of cached bytes between position (inclusive) and (position + length) (exclusive) of a resource.
        Specified by:
        getCachedBytes in interface Cache
        Parameters:
        key - The cache key of the resource.
        position - The starting position of the data in the resource.
        length - The length of the data to check. C.LENGTH_UNSET is permitted, and is equivalent to passing Long.MAX_VALUE.
        Returns:
        The total number of cached bytes.
      • applyContentMetadataMutations

        public void applyContentMetadataMutations​(String key,
                                                  ContentMetadataMutations mutations)
                                           throws Cache.CacheException
        Description copied from interface: Cache
        Applies mutations to the ContentMetadata for the given resource. A new CachedContent is added if there isn't one already for the resource.

        This method may be slow and shouldn't normally be called on the main thread.

        Specified by:
        applyContentMetadataMutations in interface Cache
        Parameters:
        key - The cache key of the resource.
        mutations - Contains mutations to be applied to the metadata.
        Throws:
        Cache.CacheException - If an error is encountered.