/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import android.util.Log;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
/**
* 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 class MemoryFile
{
private static String TAG = "MemoryFile";
// returns fd
private native int native_open(String name, int length);
// returns memory address for ashmem region
private native int native_mmap(int fd, int length);
private native void native_close(int fd);
private native int native_read(int fd, int address, byte[] buffer,
int srcOffset, int destOffset, int count, boolean isUnpinned);
private native void native_write(int fd, int address, byte[] buffer,
int srcOffset, int destOffset, int count, boolean isUnpinned);
private native void native_pin(int fd, boolean pin);
private int mFD; // ashmem file descriptor
private int mAddress; // address of ashmem memory
private int mLength; // total length of our ashmem region
private boolean mAllowPurging = false; // true if our ashmem region is unpinned
/**
* MemoryFile constructor.
*
* @param name optional name for the file (can be null).
* @param length of the memory file in bytes.
*/
public MemoryFile(String name, int length) {
mLength = length;
mFD = native_open(name, length);
mAddress = native_mmap(mFD, length);
}
/**
* Closes and releases all resources for the memory file.
*/
public void close() {
if (mFD > 0) {
native_close(mFD);
mFD = 0;
}
}
@Override
protected void finalize() {
if (mFD > 0) {
Log.e(TAG, "MemoryFile.finalize() called while ashmem still open");
close();
}
}
/**
* Returns the length of the memory file.
*
* @return file length.
*/
public int length() {
return mLength;
}
/**
* Is memory file purging enabled?
*
* @return true if the file may be purged.
*/
public boolean isPurgingAllowed() {
return mAllowPurging;
}
/**
* Enables or disables purging of the memory file.
*
* @param allowPurging true if the operating system can purge the contents
* of the file in low memory situations
* @return previous value of allowPurging
*/
synchronized public boolean allowPurging(boolean allowPurging) throws IOException {
boolean oldValue = mAllowPurging;
if (oldValue != allowPurging) {
native_pin(mFD, !allowPurging);
mAllowPurging = allowPurging;
}
return oldValue;
}
/**
* Creates a new InputStream for reading from the memory file.
*
@return InputStream
*/
public InputStream getInputStream() {
return new MemoryInputStream();
}
/**
* Creates a new OutputStream for writing to the memory file.
*
@return OutputStream
*/
public OutputStream getOutputStream() {
return new MemoryOutputStream();
}
/**
* Reads bytes from the memory file.
* Will throw an IOException if the file has been purged.
*
* @param buffer byte array to read bytes into.
* @param srcOffset offset into the memory file to read from.
* @param destOffset offset into the byte array buffer to read into.
* @param count number of bytes to read.
* @return number of bytes read.
*/
public int readBytes(byte[] buffer, int srcOffset, int destOffset, int count)
throws IOException {
if (destOffset < 0 || destOffset > buffer.length || count < 0
|| count > buffer.length - destOffset
|| srcOffset < 0 || srcOffset > mLength
|| count > mLength - srcOffset) {
throw new IndexOutOfBoundsException();
}
return native_read(mFD, mAddress, buffer, srcOffset, destOffset, count, mAllowPurging);
}
/**
* Write bytes to the memory file.
* Will throw an IOException if the file has been purged.
*
* @param buffer byte array to write bytes from.
* @param srcOffset offset into the byte array buffer to write from.
* @param destOffset offset into the memory file to write to.
* @param count number of bytes to write.
*/
public void writeBytes(byte[] buffer, int srcOffset, int destOffset, int count)
throws IOException {
if (srcOffset < 0 || srcOffset > buffer.length || count < 0
|| count > buffer.length - srcOffset
|| destOffset < 0 || destOffset > mLength
|| count > mLength - destOffset) {
throw new IndexOutOfBoundsException();
}
native_write(mFD, mAddress, buffer, srcOffset, destOffset, count, mAllowPurging);
}
private class MemoryInputStream extends InputStream {
private int mMark = 0;
private int mOffset = 0;
private byte[] mSingleByte;
@Override
public int available() throws IOException {
if (mOffset >= mLength) {
return 0;
}
return mLength - mOffset;
}
@Override
public boolean markSupported() {
return true;
}
@Override
public void mark(int readlimit) {
mMark = mOffset;
}
@Override
public void reset() throws IOException {
mOffset = mMark;
}
@Override
public int read() throws IOException {
if (mSingleByte == null) {
mSingleByte = new byte[1];
}
int result = read(mSingleByte, 0, 1);
if (result != 1) {
throw new IOException("read() failed");
}
return mSingleByte[0];
}
@Override
public int read(byte buffer[], int offset, int count) throws IOException {
int result = readBytes(buffer, mOffset, offset, count);
if (result > 0) {
mOffset += result;
}
return result;
}
@Override
public long skip(long n) throws IOException {
if (mOffset + n > mLength) {
n = mLength - mOffset;
}
mOffset += n;
return n;
}
}
private class MemoryOutputStream extends OutputStream {
private int mOffset = 0;
private byte[] mSingleByte;
@Override
public void write(byte buffer[], int offset, int count) throws IOException {
writeBytes(buffer, offset, mOffset, count);
}
@Override
public void write(int oneByte) throws IOException {
if (mSingleByte == null) {
mSingleByte = new byte[1];
}
mSingleByte[0] = (byte)oneByte;
write(mSingleByte, 0, 1);
}
}
}