src/com/android/camera/CameraHolder.java

/*
 * Copyright (C) 2009 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 com.android.camera;

import static com.android.camera.Util.Assert;

import android.hardware.Camera.Parameters;
import android.os.Build;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Message;
import android.util.Log;

import java.io.IOException;

/**
 * The class is used to hold an {@code android.hardware.Camera} instance.
 *
 * <p>The {@code open()} and {@code release()} calls are similar to the ones
 * in {@code android.hardware.Camera}. The difference is if {@code keep()} is
 * called before {@code release()}, CameraHolder will try to hold the {@code
 * android.hardware.Camera} instance for a while, so if {@code open()} is
 * called soon after, we can avoid the cost of {@code open()} in {@code
 * android.hardware.Camera}.
 *
 * <p>This is used in switching between {@code Camera} and {@code VideoCamera}
 * activities.
 */
public class CameraHolder {
    private static final String TAG = "CameraHolder";
    private android.hardware.Camera mCameraDevice;
    private long mKeepBeforeTime = 0;  // Keep the Camera before this time.
    private final Handler mHandler;
    private int mUsers = 0;  // number of open() - number of release()

    // We store the camera parameters when we actually open the device,
    // so we can restore them in the subsequent open() requests by the user.
    // This prevents the parameters set by the Camera activity used by
    // the VideoCamera activity inadvertently.
    private Parameters mParameters;

    // Use a singleton.
    private static CameraHolder sHolder;
    public static synchronized CameraHolder instance() {
        if (sHolder == null) {
            sHolder = new CameraHolder();
        }
        return sHolder;
    }

    private static final int RELEASE_CAMERA = 1;
    private class MyHandler extends Handler {
        MyHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            switch(msg.what) {
                case RELEASE_CAMERA:
                    synchronized (CameraHolder.this) {
                        // In 'CameraHolder.open', the 'RELEASE_CAMERA' message
                        // will be removed if it is found in the queue. However,
                        // there is a chance that this message has been handled
                        // before being removed. So, we need to add a check
                        // here:
                        if (CameraHolder.this.mUsers == 0) releaseCamera();
                    }
                    break;
            }
        }
    }

    private CameraHolder() {
        HandlerThread ht = new HandlerThread("CameraHolder");
        ht.start();
        mHandler = new MyHandler(ht.getLooper());
    }

    public synchronized android.hardware.Camera open()
            throws CameraHardwareException {
        Assert(mUsers == 0);
        if (mCameraDevice == null) {
            try {
                mCameraDevice = android.hardware.Camera.open();
            } catch (RuntimeException e) {
                Log.e(TAG, "fail to connect Camera", e);
                throw new CameraHardwareException(e);
            }
            mParameters = mCameraDevice.getParameters();
        } else {
            try {
                mCameraDevice.reconnect();
            } catch (IOException e) {
                Log.e(TAG, "reconnect failed.");
                throw new CameraHardwareException(e);
            }
            mCameraDevice.setParameters(mParameters);
        }
        ++mUsers;
        mHandler.removeMessages(RELEASE_CAMERA);
        mKeepBeforeTime = 0;
        return mCameraDevice;
    }

    /**
     * Tries to open the hardware camera. If the camera is being used or
     * unavailable then return {@code null}.
     */
    public synchronized android.hardware.Camera tryOpen() {
        try {
            return mUsers == 0 ? open() : null;
        } catch (CameraHardwareException e) {
            // In eng build, we throw the exception so that test tool
            // can detect it and report it
            if ("eng".equals(Build.TYPE)) {
                throw new RuntimeException(e);
            }
            return null;
        }
    }

    public synchronized void release() {
        Assert(mUsers == 1);
        --mUsers;
        mCameraDevice.stopPreview();
        releaseCamera();
    }

    private synchronized void releaseCamera() {
        Assert(mUsers == 0);
        Assert(mCameraDevice != null);
        long now = System.currentTimeMillis();
        if (now < mKeepBeforeTime) {
            mHandler.sendEmptyMessageDelayed(RELEASE_CAMERA,
                    mKeepBeforeTime - now);
            return;
        }
        mCameraDevice.release();
        mCameraDevice = null;
    }

    public synchronized void keep() {
        // We allow (mUsers == 0) for the convenience of the calling activity.
        // The activity may not have a chance to call open() before the user
        // choose the menu item to switch to another activity.
        Assert(mUsers == 1 || mUsers == 0);
        // Keep the camera instance for 3 seconds.
        mKeepBeforeTime = System.currentTimeMillis() + 3000;
    }
}