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.
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
| |
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. |
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 |
|
void close ()
Closes the memory file. If there are no other open references to the memory file, it will be deleted.
InputStream getInputStream ()
Creates a new InputStream for reading from the memory file.
| Returns | |
|---|---|
InputStream |
InputStream |
OutputStream getOutputStream ()
Creates a new OutputStream for writing to the memory file.
| Returns | |
|---|---|
OutputStream |
OutputStream |
boolean isPurgingAllowed ()
Is memory file purging enabled?
| Returns | |
|---|---|
boolean |
true if the file may be purged. |
int length ()
Returns the length of the memory file.
| Returns | |
|---|---|
int |
file length. |
Developers
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. |
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. |
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.