org.ros.android.acm_serial.PollingInputStream.java Source code

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Here is the source code for org.ros.android.acm_serial.PollingInputStream.java

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/*
 * Copyright (C) 2011 Google Inc.
 *
 * 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 org.ros.android.acm_serial;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.ros.concurrent.CancellableLoop;
import org.ros.exception.RosRuntimeException;

import java.io.IOException;
import java.io.InputStream;
import java.util.concurrent.ExecutorService;

/**
 * Constantly reads from an {@link InputStream} into a buffer.
 * 
 * @author damonkohler@google.com (Damon Kohler)
 */
public class PollingInputStream extends InputStream {

    private final static boolean DEBUG = false;
    private final static Log log = LogFactory.getLog(PollingInputStream.class);

    private final static int BUFFER_CAPACITY = 512 * 1024;
    private final static int READ_SIZE = 256;

    private final byte[] readBuffer;

    private int readPosition;
    private int writePosition;

    /**
     * @param inputStream
     *          the {@link InputStream} to read from
     * @param executorService
     *          used to execute the read loop
     */
    public PollingInputStream(final InputStream inputStream, ExecutorService executorService) {
        readBuffer = new byte[BUFFER_CAPACITY];
        readPosition = 0;
        writePosition = 0;
        executorService.execute(new CancellableLoop() {
            @Override
            protected void loop() throws InterruptedException {
                try {
                    while (remaining() < READ_SIZE) {
                        if (readPosition < remaining()) {
                            // There isn't enough room to compact the buffer yet. We will most
                            // likely start dropping messages.
                            log.error("Not enough room to compact buffer.");
                            Thread.yield();
                            continue;
                        }
                        synchronized (readBuffer) {
                            int remaining = remaining();
                            System.arraycopy(readBuffer, writePosition, readBuffer, 0, remaining);
                            writePosition = remaining;
                            readPosition = 0;
                            if (DEBUG) {
                                log.info(String.format("Buffer compacted. %d bytes remaining.", remaining()));
                            }
                        }
                    }
                    int bytesRead = inputStream.read(readBuffer, writePosition, READ_SIZE);
                    if (bytesRead < 0) {
                        throw new IOException("Stream closed.");
                    }
                    writePosition += bytesRead;
                } catch (IOException e) {
                    throw new RosRuntimeException(e);
                }
            }
        });
    }

    @Override
    public synchronized int read(byte[] buffer, int offset, int length) throws IOException {
        int bytesRead = 0;
        if (length > 0) {
            while (available() == 0) {
                // Block until there are bytes to read.
                Thread.yield();
            }
            synchronized (readBuffer) {
                bytesRead = Math.min(length, available());
                System.arraycopy(readBuffer, readPosition, buffer, offset, bytesRead);
                readPosition += bytesRead;
            }
        }
        return bytesRead;
    }

    @Override
    public int read() throws IOException {
        byte[] buffer = new byte[1];
        return read(buffer, 0, 1);
    }

    @Override
    public int available() throws IOException {
        return writePosition - readPosition;
    }

    private int remaining() {
        return BUFFER_CAPACITY - writePosition;
    }
}