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Added in API level 1

MemoryFile

public class MemoryFile
extends Object

java.lang.Object
   ↳ android.os.MemoryFile


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.

Inherited methods

From class java.lang.Object

Public constructors

MemoryFile

Added in API level 1
MemoryFile (String name, 
                int length)

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

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

Public methods

allowPurging

Added in API level 1
boolean allowPurging (boolean allowPurging)

Enables or disables purging of the memory file.

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

close

Added in API level 1
void close ()

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

getInputStream

Added in API level 1
InputStream getInputStream ()

Creates a new InputStream for reading from the memory file.

Returns
InputStream InputStream

getOutputStream

Added in API level 1
OutputStream getOutputStream ()

Creates a new OutputStream for writing to the memory file.

Returns
OutputStream OutputStream

isPurgingAllowed

Added in API level 1
boolean isPurgingAllowed ()

Is memory file purging enabled?

Returns
boolean true if the file may be purged.

length

Added in API level 1
int length ()

Returns the length of the memory file.

Returns
int file length.

readBytes

Added in API level 1
int readBytes (byte[] buffer, 
                int srcOffset, 
                int destOffset, 
                int count)

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

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

writeBytes

Added in API level 1
void writeBytes (byte[] buffer, 
                int srcOffset, 
                int destOffset, 
                int count)

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

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

Protected methods

finalize

Added in API level 1
void finalize ()

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.

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