/*
* Copyright (C) 2016 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.util;
import android.os.Parcel;
import android.os.ParcelFileDescriptor;
import android.os.Parcelable;
import android.os.Process;
import libcore.io.IoUtils;
import java.io.Closeable;
import java.io.IOException;
import java.util.UUID;
/**
* This class is an array of integers that is backed by shared memory.
* It is useful for efficiently sharing state between processes. The
* write and read operations are guaranteed to not result in read/
* write memory tear, i.e. they are atomic. However, multiple read/
* write operations are <strong>not</strong> synchronized between
* each other.
* <p>
* The data structure is designed to have one owner process that can
* read/write. There may be multiple client processes that can only read.
* The owner process is the process that created the array. The shared
* memory is pinned (not reclaimed by the system) until the owning process
* dies or the data structure is closed. This class is <strong>not</strong>
* thread safe. You should not interact with an instance of this class
* once it is closed. If you pass back to the owner process an instance
* it will be read only even in the owning process.
* </p>
*
* @hide
*/
public final class MemoryIntArray implements Parcelable, Closeable {
private static final String TAG = "MemoryIntArray";
private static final int MAX_SIZE = 1024;
private final boolean mIsOwner;
private final long mMemoryAddr;
private int mFd = -1;
/**
* Creates a new instance.
*
* @param size The size of the array in terms of integer slots. Cannot be
* more than {@link #getMaxSize()}.
* @param clientWritable Whether other processes can write to the array.
* @throws IOException If an error occurs while accessing the shared memory.
*/
public MemoryIntArray(int size) throws IOException {
if (size > MAX_SIZE) {
throw new IllegalArgumentException("Max size is " + MAX_SIZE);
}
mIsOwner = true;
final String name = UUID.randomUUID().toString();
mFd = nativeCreate(name, size);
mMemoryAddr = nativeOpen(mFd, mIsOwner);
}
private MemoryIntArray(Parcel parcel) throws IOException {
mIsOwner = false;
ParcelFileDescriptor pfd = parcel.readParcelable(null);
if (pfd == null) {
throw new IOException("No backing file descriptor");
}
mFd = pfd.detachFd();
mMemoryAddr = nativeOpen(mFd, mIsOwner);
}
/**
* @return Gets whether this array is mutable.
*/
public boolean isWritable() {
enforceNotClosed();
return mIsOwner;
}
/**
* Gets the value at a given index.
*
* @param index The index.
* @return The value at this index.
* @throws IOException If an error occurs while accessing the shared memory.
*/
public int get(int index) throws IOException {
enforceNotClosed();
enforceValidIndex(index);
return nativeGet(mFd, mMemoryAddr, index);
}
/**
* Sets the value at a given index. This method can be called only if
* {@link #isWritable()} returns true which means your process is the
* owner.
*
* @param index The index.
* @param value The value to set.
* @throws IOException If an error occurs while accessing the shared memory.
*/
public void set(int index, int value) throws IOException {
enforceNotClosed();
enforceWritable();
enforceValidIndex(index);
nativeSet(mFd, mMemoryAddr, index, value);
}
/**
* Gets the array size.
*
* @throws IOException If an error occurs while accessing the shared memory.
*/
public int size() throws IOException {
enforceNotClosed();
return nativeSize(mFd);
}
/**
* Closes the array releasing resources.
*
* @throws IOException If an error occurs while accessing the shared memory.
*/
@Override
public void close() throws IOException {
if (!isClosed()) {
nativeClose(mFd, mMemoryAddr, mIsOwner);
mFd = -1;
}
}
/**
* @return Whether this array is closed and shouldn't be used.
*/
public boolean isClosed() {
return mFd == -1;
}
@Override
protected void finalize() throws Throwable {
IoUtils.closeQuietly(this);
super.finalize();
}
@Override
public int describeContents() {
return CONTENTS_FILE_DESCRIPTOR;
}
@Override
public void writeToParcel(Parcel parcel, int flags) {
ParcelFileDescriptor pfd = ParcelFileDescriptor.adoptFd(mFd);
try {
parcel.writeParcelable(pfd, flags & ~Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
} finally {
pfd.detachFd();
}
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (this == obj) {
return true;
}
if (getClass() != obj.getClass()) {
return false;
}
MemoryIntArray other = (MemoryIntArray) obj;
return mFd == other.mFd;
}
@Override
public int hashCode() {
return mFd;
}
private void enforceNotClosed() {
if (isClosed()) {
throw new IllegalStateException("cannot interact with a closed instance");
}
}
private void enforceValidIndex(int index) throws IOException {
final int size = size();
if (index < 0 || index > size - 1) {
throw new IndexOutOfBoundsException(
index + " not between 0 and " + (size - 1));
}
}
private void enforceWritable() {
if (!isWritable()) {
throw new UnsupportedOperationException("array is not writable");
}
}
private native int nativeCreate(String name, int size);
private native long nativeOpen(int fd, boolean owner);
private native void nativeClose(int fd, long memoryAddr, boolean owner);
private native int nativeGet(int fd, long memoryAddr, int index);
private native void nativeSet(int fd, long memoryAddr, int index, int value);
private native int nativeSize(int fd);
/**
* @return The max array size.
*/
public static int getMaxSize() {
return MAX_SIZE;
}
public static final Parcelable.Creator<MemoryIntArray> CREATOR =
new Parcelable.Creator<MemoryIntArray>() {
@Override
public MemoryIntArray createFromParcel(Parcel parcel) {
try {
return new MemoryIntArray(parcel);
} catch (IOException ioe) {
throw new IllegalArgumentException("Error unparceling MemoryIntArray");
}
}
@Override
public MemoryIntArray[] newArray(int size) {
return new MemoryIntArray[size];
}
};
}