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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()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

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 ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the JavaTM virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

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