| 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 | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Allocates a new ashmem region.
| |||||||||||
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Enables or disables purging of the memory file.
| |||||||||||
Closes the memory file.
| |||||||||||
Creates a new InputStream for reading from the memory file.
| |||||||||||
Creates a new OutputStream for writing to the memory file.
| |||||||||||
Is memory file purging enabled?
| |||||||||||
Returns the length of the memory file.
| |||||||||||
Reads bytes from the memory file.
| |||||||||||
Write bytes to the memory file.
| |||||||||||
| Protected Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Invoked when the garbage collector has detected that this instance is no longer reachable.
| |||||||||||
|
[Expand]
Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
Allocates a new ashmem region. The region is initially not purgable.
| name | optional name for the file (can be null). |
|---|---|
| length | of the memory file in bytes. |
| IOException | if the memory file could not be created. |
|---|
Enables or disables purging of the memory file.
| allowPurging | true if the operating system can purge the contents of the file in low memory situations |
|---|
| IOException |
|---|
Closes the memory file. If there are no other open references to the memory file, it will be deleted.
Creates a new InputStream for reading from the memory file.
Creates a new OutputStream for writing to the memory file.
Is memory file purging enabled?
Returns the length of the memory file.
Reads bytes from the memory file. Will throw an IOException if the file has been purged.
| 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. |
|---|
Write bytes to the memory file. Will throw an IOException if the file has been purged.
| 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. |
|---|
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.