Subversion Repositories usb_fpga_2_14

/*%

   Java host software API of ZTEX SDK

   Copyright (C) 2009-2017 ZTEX GmbH.

   http://www.ztex.de

   This Source Code Form is subject to the terms of the Mozilla Public

   License, v. 2.0. If a copy of the MPL was not distributed with this file,

   You can obtain one at http://mozilla.org/MPL/2.0/.

   Alternatively, the contents of this file may be used under the terms

   of the GNU General Public License Version 3, as described below:

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License version 3 as

   published by the Free Software Foundation.

   This program is distributed in the hope that it will be useful, but

   WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

   General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program; if not, see http://www.gnu.org/licenses/.

%*/

package ztex;

import java.io.*;

import java.util.*;

import java.nio.*;

import org.usb4java.*;

/**

  * This class manages an USB context.

  * Because libusb_get_device_list does not return an up to date device list at least on some implementations

  * a new context must be created every time the bus is (re)discovered, i.e. every time re-numeration occurs.

  * This class creates a new USB context, initializes it and deinitializes it as soon it is not used anymore.

  * Used is tracked using a reference counter. Reference counter of a new instance is 1.

*/

public class ZtexContext {

    private int refCount = 0;

    private Context context;

/**

  * Constructs an new USB context and initializes it.

  */

    public ZtexContext () throws UsbException {

        context = new Context();

        refCount = 0;

        ref();

    }

/**

  * Returns the USB context.

  * @return the USB context.

  */

    public final Context context() {

        return context;

    }

/**

  * Increases the reference count.

  * @return the USB context.

  */

    public synchronized ZtexContext ref() throws UsbException {

        refCount ++;

        if ( refCount == 1 ) {

            int result = LibUsb.init(context);

            if (result < 0 ) throw new UsbException("Unable to initialize usb context", result);

//          System.out.println("created ZtexContext: " + context);

        }

        return this;

    }

/**

  * Decreases the reference count and deinitializes the context if reference counter reaches 0.

  */

    public synchronized void unref() {

        refCount --;

        if ( refCount == 0 ) {

//          System.out.println("disposing ZtexContext: " + context);

            LibUsb.exit(context);

        }

    }

// ******* finalize ************************************************************

/**

  * Releases all resources.

  */

    protected void finalize() throws Throwable {

        if (refCount > 0) refCount=1;

        unref();

        super.finalize();

    }

}