public class MemoryFile extends Object
| Constructor and Description |
|---|
MemoryFile(String name,
int length)
Allocates a new ashmem region.
|
| Modifier and Type | Method and Description |
|---|---|
boolean |
allowPurging(boolean allowPurging)
Enables or disables purging of the memory file.
|
void |
close()
Closes the memory file.
|
protected void |
finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
|
FileDescriptor |
getFileDescriptor()
Gets a FileDescriptor for 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.
|
static int |
getSize(FileDescriptor fd)
Returns the size of the memory file that the file descriptor refers to,
or -1 if the file descriptor does not refer to a 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.
|
public MemoryFile(String name, int length) throws IOException
name - optional name for the file (can be null).length - of the memory file in bytes, must be non-negative.IOException - if the memory file could not be created.public void close()
protected void finalize()
ObjectNote 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.
public int length()
public boolean isPurgingAllowed()
public boolean allowPurging(boolean allowPurging)
throws IOException
allowPurging - true if the operating system can purge the contents
of the file in low memory situationsIOExceptionpublic InputStream getInputStream()
public OutputStream getOutputStream()
public int readBytes(byte[] buffer,
int srcOffset,
int destOffset,
int count)
throws IOException
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.IOException - if the memory file has been purged or deactivated.public void writeBytes(byte[] buffer,
int srcOffset,
int destOffset,
int count)
throws IOException
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.IOException - if the memory file has been purged or deactivated.public FileDescriptor getFileDescriptor() throws IOException
IOException - If the memory file has been closed.public static int getSize(FileDescriptor fd) throws IOException
IOException - If fd is not a valid file descriptor.