Android APIs
public class

MemoryFile

extends Object
java.lang.Object
   ↳ android.os.MemoryFile

Class Overview

MemoryFile is a wrapper for the Linux ashmem driver. MemoryFiles are backed by shared memory, which can be optionally set to be purgeable. Purgeable files may have their contents reclaimed by the kernel in low memory conditions (only if allowPurging is set to true). After a file is purged, attempts to read or write the file will cause an IOException to be thrown.

Summary

Public Constructors
MemoryFile(String name, int length)
Allocates a new ashmem region.
Public Methods
boolean allowPurging(boolean allowPurging)
Enables or disables purging of the memory file.
void close()
Closes the memory file.
InputStream getInputStream()
Creates a new InputStream for reading from the memory file.
OutputStream getOutputStream()
Creates a new OutputStream for writing to the memory file.
boolean isPurgingAllowed()
Is memory file purging enabled?
int length()
Returns the length of the memory file.
int readBytes(byte[] buffer, int srcOffset, int destOffset, int count)
Reads bytes from the memory file.
void writeBytes(byte[] buffer, int srcOffset, int destOffset, int count)
Write bytes to the memory file.
Protected Methods
void finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public MemoryFile (String name, int length)

Added in API level 1

Allocates a new ashmem region. The region is initially not purgable.

Parameters
name optional name for the file (can be null).
length of the memory file in bytes, must be non-negative.
Throws
IOException if the memory file could not be created.

Public Methods

public boolean allowPurging (boolean allowPurging)

Added in API level 1

Enables or disables purging of the memory file.

Parameters
allowPurging true if the operating system can purge the contents of the file in low memory situations
Returns
boolean previous value of allowPurging
Throws
IOException

public void close ()

Added in API level 1

Closes the memory file. If there are no other open references to the memory file, it will be deleted.

public InputStream getInputStream ()

Added in API level 1

Creates a new InputStream for reading from the memory file.

Returns
InputStream InputStream

public OutputStream getOutputStream ()

Added in API level 1

Creates a new OutputStream for writing to the memory file.

Returns
OutputStream OutputStream

public boolean isPurgingAllowed ()

Added in API level 1

Is memory file purging enabled?

Returns
boolean true if the file may be purged.

public int length ()

Added in API level 1

Returns the length of the memory file.

Returns
int file length.

public int readBytes (byte[] buffer, int srcOffset, int destOffset, int count)

Added in API level 1

Reads bytes from the memory file. Will throw an IOException if the file has been purged.

Parameters
buffer byte array to read bytes into.
srcOffset offset into the memory file to read from.
destOffset offset into the byte array buffer to read into.
count number of bytes to read.
Returns
int number of bytes read.
Throws
IOException if the memory file has been purged or deactivated.

public void writeBytes (byte[] buffer, int srcOffset, int destOffset, int count)

Added in API level 1

Write bytes to the memory file. Will throw an IOException if the file has been purged.

Parameters
buffer byte array to write bytes from.
srcOffset offset into the byte array buffer to write from.
destOffset offset into the memory file to write to.
count number of bytes to write.
Throws
IOException if the memory file has been purged or deactivated.

Protected Methods

protected void finalize ()

Added in API level 1

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.