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A library jar that provides APIs for Applications written for the Google Android Platform.
/*
* 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.compat.annotation.UnsupportedAppUsage;
import android.system.ErrnoException;
import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
/**
* MemoryFile is a wrapper for {@link SharedMemory} which can optionally be set to purgeable.
*
* Applications should generally prefer to use {@link SharedMemory} which offers more flexible
* access & control over the shared memory region than MemoryFile does.
*
* 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 'true' if purged, 'false' otherwise
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
private static native boolean native_pin(FileDescriptor fd, boolean pin) throws IOException;
@UnsupportedAppUsage
private static native int native_get_size(FileDescriptor fd) throws IOException;
private SharedMemory mSharedMemory;
private ByteBuffer mMapping;
private boolean mAllowPurging = false; // true if our ashmem region is unpinned
/**
* Allocates a new ashmem region. The region is initially not purgable.
*
* @param name optional name for the file (can be null).
* @param length of the memory file in bytes, must be positive.
* @throws IOException if the memory file could not be created.
*/
public MemoryFile(String name, int length) throws IOException {
try {
mSharedMemory = SharedMemory.create(name, length);
mMapping = mSharedMemory.mapReadWrite();
} catch (ErrnoException ex) {
ex.rethrowAsIOException();
}
}
/**
* Closes the memory file. If there are no other open references to the memory
* file, it will be deleted.
*/
public void close() {
deactivate();
mSharedMemory.close();
}
/**
* Unmaps the memory file from the process's memory space, but does not close it.
* After this method has been called, read and write operations through this object
* will fail, but {@link #getFileDescriptor()} will still return a valid file descriptor.
*
* @hide
*/
@UnsupportedAppUsage
void deactivate() {
if (mMapping != null) {
SharedMemory.unmap(mMapping);
mMapping = null;
}
}
private void checkActive() throws IOException {
if (mMapping == null) {
throw new IOException("MemoryFile has been deactivated");
}
}
private void beginAccess() throws IOException {
checkActive();
if (mAllowPurging) {
if (native_pin(mSharedMemory.getFileDescriptor(), true)) {
throw new IOException("MemoryFile has been purged");
}
}
}
private void endAccess() throws IOException {
if (mAllowPurging) {
native_pin(mSharedMemory.getFileDescriptor(), false);
}
}
/**
* Returns the length of the memory file.
*
* @return file length.
*/
public int length() {
return mSharedMemory.getSize();
}
/**
* Is memory file purging enabled?
*
* @return true if the file may be purged.
*
* @deprecated Purgable is considered generally fragile and hard to use safely. Applications
* are recommend to instead use {@link android.content.ComponentCallbacks2#onTrimMemory(int)}
* to react to memory events and release shared memory regions as appropriate.
*/
@Deprecated
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
*
* @deprecated Purgable is considered generally fragile and hard to use safely. Applications
* are recommend to instead use {@link android.content.ComponentCallbacks2#onTrimMemory(int)}
* to react to memory events and release shared memory regions as appropriate.
*/
@Deprecated
synchronized public boolean allowPurging(boolean allowPurging) throws IOException {
boolean oldValue = mAllowPurging;
if (oldValue != allowPurging) {
native_pin(mSharedMemory.getFileDescriptor(), !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.
* @throws IOException if the memory file has been purged or deactivated.
*/
public int readBytes(byte[] buffer, int srcOffset, int destOffset, int count)
throws IOException {
beginAccess();
try {
mMapping.position(srcOffset);
mMapping.get(buffer, destOffset, count);
} finally {
endAccess();
}
return count;
}
/**
* 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.
* @throws IOException if the memory file has been purged or deactivated.
*/
public void writeBytes(byte[] buffer, int srcOffset, int destOffset, int count)
throws IOException {
beginAccess();
try {
mMapping.position(destOffset);
mMapping.put(buffer, srcOffset, count);
} finally {
endAccess();
}
}
/**
* Gets a FileDescriptor for the memory file.
*
* The returned file descriptor is not duplicated.
*
* @throws IOException If the memory file has been closed.
*
* @hide
*/
@UnsupportedAppUsage
public FileDescriptor getFileDescriptor() throws IOException {
return mSharedMemory.getFileDescriptor();
}
/**
* 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.
*
* @throws IOException If fd is not a valid file descriptor.
*
* @hide
*/
@UnsupportedAppUsage
public static int getSize(FileDescriptor fd) throws IOException {
return native_get_size(fd);
}
private class MemoryInputStream extends InputStream {
private int mMark = 0;
private int mOffset = 0;
private byte[] mSingleByte;
@Override
public int available() throws IOException {
if (mOffset >= mSharedMemory.getSize()) {
return 0;
}
return mSharedMemory.getSize() - 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) {
return -1;
}
return mSingleByte[0];
}
@Override
public int read(byte buffer[], int offset, int count) throws IOException {
if (offset < 0 || count < 0 || offset + count > buffer.length) {
// readBytes() also does this check, but we need to do it before
// changing count.
throw new IndexOutOfBoundsException();
}
count = Math.min(count, available());
if (count < 1) {
return -1;
}
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 > mSharedMemory.getSize()) {
n = mSharedMemory.getSize() - 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);
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);
}
}
}