Cache

Artifact: androidx.media3:media3-datasource

Kotlin |Java

@UnstableApi
interface Cache

Known direct subclasses

SimpleCache

SimpleCache

A Cache implementation that maintains an in-memory representation.

A cache that supports partial caching of resources.

Terminology

A resource is a complete piece of logical data, for example a complete media file.
A cache key uniquely identifies a resource. URIs are often suitable for use as cache keys, however this is not always the case. URIs are not suitable when caching resources obtained from a service that generates multiple URIs for the same underlying resource, for example because the service uses expiring URIs as a form of access control.
A cache span is a byte range within a resource, which may or may not be cached. A cache span that's not cached is called a hole span. A cache span that is cached corresponds to a single underlying file in the cache.

Summary

Nested types
`class Cache.CacheException : IOException` Thrown when an error is encountered when writing data.
`interface Cache.Listener` Listener of `Cache` events.

Constants
`const Long`	`UID_UNSET = -1` Returned by `getUid` if initialization failed before the unique identifier was read or generated.

Public functions
`NavigableSet<CacheSpan!>!`	`addListener(key: String!, listener: Cache.Listener!)` Registers a listener to listen for changes to a given resource.
`Unit`	`@WorkerThread applyContentMetadataMutations( key: String!, mutations: ContentMetadataMutations! )` Applies `mutations` to the `ContentMetadata` for the given resource.
`Unit`	`@WorkerThread commitFile(file: File!, length: Long)` Commits a file into the cache.
`Long`	`getCacheSpace()` Returns the total disk space in bytes used by the cache.
`Long`	`getCachedBytes(key: String!, position: Long, length: Long)` Returns the total number of cached bytes between `position` (inclusive) and `(position + length)` (exclusive) of a resource.
`Long`	`getCachedLength(key: String!, position: Long, length: Long)` Returns the length of continuously cached data starting from `position`, up to a maximum of `maxLength`, of a resource.
`NavigableSet<CacheSpan!>!`	`getCachedSpans(key: String!)` Returns the cached spans for a given resource.
`ContentMetadata!`	`getContentMetadata(key: String!)` Returns a `ContentMetadata` for the given resource.
`(Mutable)Set<String!>!`	`getKeys()` Returns the cache keys of all of the resources that are at least partially cached.
`Long`	`getUid()` Returns a non-negative unique identifier for the cache, or `UID_UNSET` if initialization failed before the unique identifier was determined.
`Boolean`	`isCached(key: String!, position: Long, length: Long)` Returns whether the specified range of data in a resource is fully cached.
`Unit`	`@WorkerThread release()` Releases the cache.
`Unit`	`releaseHoleSpan(holeSpan: CacheSpan!)` Releases a `CacheSpan` obtained from `startReadWrite` which corresponded to a hole in the cache.
`Unit`	`removeListener(key: String!, listener: Cache.Listener!)` Unregisters a listener.
`Unit`	`@WorkerThread removeResource(key: String!)` Removes all `CacheSpans` for a resource, deleting the underlying files.
`Unit`	`@WorkerThread removeSpan(span: CacheSpan!)` Removes a cached `CacheSpan` from the cache, deleting the underlying file.
`File!`	`@WorkerThread startFile(key: String!, position: Long, length: Long)` Obtains a cache file into which data can be written.
`CacheSpan!`	`@WorkerThread startReadWrite(key: String!, position: Long, length: Long)` A caller should invoke this method when they require data starting from a given position in a given resource.
`CacheSpan?`	`@WorkerThread startReadWriteNonBlocking(key: String!, position: Long, length: Long)` Same as `startReadWrite`.

Constants

UID_UNSET

const val UID_UNSET = -1: Long

Returned by getUid if initialization failed before the unique identifier was read or generated.

Public functions

addListener

fun addListener(key: String!, listener: Cache.Listener!): NavigableSet<CacheSpan!>!

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.

Parameters
`key: String!`	The cache key of the resource.
`listener: Cache.Listener!`	The listener to add.

Returns
`NavigableSet<CacheSpan!>!`	The current spans for the resource.

applyContentMetadataMutations

@WorkerThread
fun applyContentMetadataMutations(
    key: String!,
    mutations: ContentMetadataMutations!
): Unit

Applies mutations to the ContentMetadata for the given resource. A new 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.

Parameters
`key: String!`	The cache key of the resource.
`mutations: ContentMetadataMutations!`	Contains mutations to be applied to the metadata.

Throws
`androidx.media3.datasource.cache.Cache.CacheException`	If an error is encountered.

commitFile

@WorkerThread
fun commitFile(file: File!, length: Long): Unit

Commits a file into the cache. Must only be called when holding a corresponding hole obtained from startReadWrite.

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

Parameters
`file: File!`	A newly written cache file.
`length: Long`	The length of the newly written cache file in bytes.

Throws
`androidx.media3.datasource.cache.Cache.CacheException`	If an error is encountered.

getCacheSpace

fun getCacheSpace(): Long

Returns the total disk space in bytes used by the cache.

getCachedBytes

fun getCachedBytes(key: String!, position: Long, length: Long): Long

Returns the total number of cached bytes between position (inclusive) and (position + length) (exclusive) of a resource.

Parameters
`key: String!`	The cache key of the resource.
`position: Long`	The starting position of the data in the resource.
`length: Long`	The length of the data to check. `LENGTH_UNSET` is permitted, and is equivalent to passing `MAX_VALUE`.

Returns
`Long`	The total number of cached bytes.

getCachedLength

fun getCachedLength(key: String!, position: Long, length: Long): Long

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.

Parameters
`key: String!`	The cache key of the resource.
`position: Long`	The starting position of the data in the resource.
`length: Long`	The maximum length of the data or hole to be returned. `LENGTH_UNSET` is permitted, and is equivalent to passing `MAX_VALUE`.

Returns
`Long`	The length of the continuously cached data, or `-holeLength` if `position` isn't cached.

getCachedSpans

fun getCachedSpans(key: String!): NavigableSet<CacheSpan!>!

Returns the cached spans for a given resource.

Parameters
`key: String!`	The cache key of the resource.

Returns
`NavigableSet<CacheSpan!>!`	The spans for the key.

getContentMetadata

fun getContentMetadata(key: String!): ContentMetadata!

Returns a ContentMetadata for the given resource.

Parameters
`key: String!`	The cache key of the resource.

Returns
`ContentMetadata!`	The `ContentMetadata` for the resource.

getKeys

fun getKeys(): (Mutable)Set<String!>!

Returns the cache keys of all of the resources that are at least partially cached.

getUid

fun getUid(): Long

Returns a non-negative unique identifier for the cache, or 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.

isCached

fun isCached(key: String!, position: Long, length: Long): Boolean

Returns whether the specified range of data in a resource is fully cached.

Parameters
`key: String!`	The cache key of the resource.
`position: Long`	The starting position of the data in the resource.
`length: Long`	The length of the data.

Returns
`Boolean`	true if the data is available in the Cache otherwise false;

release

@WorkerThread
fun release(): Unit

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.

releaseHoleSpan

fun releaseHoleSpan(holeSpan: CacheSpan!): Unit

Releases a CacheSpan obtained from startReadWrite which corresponded to a hole in the cache.

Parameters
`holeSpan: CacheSpan!`	The `CacheSpan` being released.

removeListener

fun removeListener(key: String!, listener: Cache.Listener!): Unit

Unregisters a listener.

Parameters
`key: String!`	The cache key of the resource.
`listener: Cache.Listener!`	The listener to remove.

removeResource

@WorkerThread
fun removeResource(key: String!): Unit

Removes all CacheSpans for a resource, deleting the underlying files.

Parameters
`key: String!`	The cache key of the resource being removed.

removeSpan

@WorkerThread
fun removeSpan(span: CacheSpan!): Unit

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.

Parameters
`span: CacheSpan!`	The `CacheSpan` to remove.

startFile

@WorkerThread
fun startFile(key: String!, position: Long, length: Long): File!

Obtains a cache file into which data can be written. Must only be called when holding a corresponding hole CacheSpan obtained from startReadWrite.

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

Parameters
`key: String!`	The cache key of the resource being written.
`position: Long`	The starting position in the resource from which data will be written.
`length: Long`	The length of the data being written, or `LENGTH_UNSET` if unknown. Used only to ensure that there is enough space in the cache.

Returns
`File!`	The file into which data should be written.

Throws
`androidx.media3.datasource.cache.Cache.CacheException`	If an error is encountered.

startReadWrite

@WorkerThread
fun startReadWrite(key: String!, position: Long, length: Long): CacheSpan!

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. 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 commitFile. When the caller has finished writing, it must release the lock by calling releaseHoleSpan.

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

Parameters
`key: String!`	The cache key of the resource.
`position: Long`	The starting position in the resource from which data is required.
`length: Long`	The length of the data being requested, or `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 `LENGTH_UNSET` when possible.

Returns
`CacheSpan!`	The `CacheSpan`.

Throws
`java.lang.InterruptedException`	If the thread was interrupted.
`androidx.media3.datasource.cache.Cache.CacheException`	If an error is encountered.

startReadWriteNonBlocking

@WorkerThread
fun startReadWriteNonBlocking(key: String!, position: Long, length: Long): CacheSpan?

Same as startReadWrite. 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.

Parameters
`key: String!`	The cache key of the resource.
`position: Long`	The starting position in the resource from which data is required.
`length: Long`	The length of the data being requested, or `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
`CacheSpan?`	The `CacheSpan`. Or null if the cache entry is locked.

Throws
`androidx.media3.datasource.cache.Cache.CacheException`	If an error is encountered.

Cache

Terminology

Summary

Nested types

Constants

Public functions

Constants

UID_UNSET

Public functions

addListener

applyContentMetadataMutations

commitFile

getCacheSpace

getCachedBytes

getCachedLength

getCachedSpans

getContentMetadata

getKeys

getUid

isCached

release

releaseHoleSpan

removeListener

removeResource

removeSpan

startFile

startReadWrite

startReadWriteNonBlocking