// **********************************************************************
//
// Copyright (c) 2002
// ZeroC, Inc.
// Billerica, MA, USA
//
// All Rights Reserved.
//
// Ice is free software; you can redistribute it and/or modify it under
// the terms of the GNU General Public License version 2 as published by
// the Free Software Foundation.
//
// **********************************************************************

package IceInternal;

public final class ThreadPool
{
    private final static boolean TRACE_REGISTRATION = false;
    private final static boolean TRACE_INTERRUPT = false;
    private final static boolean TRACE_SHUTDOWN = false;
    private final static boolean TRACE_SELECT = false;
    private final static boolean TRACE_EXCEPTION = false;
    private final static boolean TRACE_THREAD = false;
    private final static boolean TRACE_STACK_TRACE = false;

    public
    ThreadPool(Instance instance, int threadNum, int timeout, String name)
    {
        _instance = instance;
        _destroyed = false;
        _timeout = timeout;
        _multipleThreads = false;
	_promote = true;
        _name = name;

        Network.SocketPair pair = Network.createPipe();
        _fdIntrRead = (java.nio.channels.ReadableByteChannel)pair.source;
        _fdIntrWrite = pair.sink;

        try
        {
            _selector = java.nio.channels.Selector.open();
            pair.source.configureBlocking(false);
            _fdIntrReadKey = pair.source.register(_selector, java.nio.channels.SelectionKey.OP_READ);
        }
        catch(java.io.IOException ex)
        {
            Ice.SyscallException sys = new Ice.SyscallException();
            sys.initCause(ex);
            throw sys;
        }

        //
        // The Selector holds a Set representing the selected keys. The
        // Set reference doesn't change, so we obtain it once here.
        //
        _keys = _selector.selectedKeys();

	if(threadNum < 1)
	{
	    threadNum = 1;
	}

        if(threadNum > 1)
        {
            _multipleThreads = true;
        }

        //
        // Use Ice.ProgramName as the prefix for the thread names.
        //
        String threadNamePrefix = "";
        String programName = _instance.properties().getProperty("Ice.ProgramName");
        if(programName.length() > 0)
        {
            threadNamePrefix = programName + "-";
        }

        try
        {
            _threads = new EventHandlerThread[threadNum];
            for(int i = 0; i < threadNum; i++)
            {
                _threads[i] = new EventHandlerThread(threadNamePrefix + _name + "-" + i);
                _threads[i].start();
            }
        }
        catch(RuntimeException ex)
        {
	    java.io.StringWriter sw = new java.io.StringWriter();
	    java.io.PrintWriter pw = new java.io.PrintWriter(sw);
	    ex.printStackTrace(pw);
	    pw.flush();
	    String s = "cannot create threads for thread pool:\n" + sw.toString();
	    _instance.logger().error(s);

            destroy();
	    joinWithAllThreads();
            throw ex;
        }
    }

    protected void
    finalize()
        throws Throwable
    {
        assert(_destroyed);
        if(_selector != null)
        {
            try
            {
                _selector.close();
            }
            catch(java.io.IOException ex)
            {
            }
        }
        if(_fdIntrWrite != null)
        {
            try
            {
                _fdIntrWrite.close();
            }
            catch(java.io.IOException ex)
            {
            }
        }
        if(_fdIntrRead != null)
        {
            try
            {
                _fdIntrRead.close();
            }
            catch(java.io.IOException ex)
            {
            }
        }

        super.finalize();
    }

    public synchronized void
    destroy()
    {
        if(TRACE_SHUTDOWN)
        {
            trace("destroy");
        }

        assert(!_destroyed);
	assert(_handlerMap.isEmpty());
	assert(_changes.isEmpty());
        _destroyed = true;
        setInterrupt(0);
    }

    public synchronized void
    _register(java.nio.channels.SelectableChannel fd, EventHandler handler)
    {
        if(TRACE_REGISTRATION)
        {
            trace("adding handler of type " + handler.getClass().getName() + " for channel " + fd);
        }
	assert(!_destroyed);
        _changes.add(new FdHandlerPair(fd, handler));
        setInterrupt(0);
    }

    public synchronized void
    unregister(java.nio.channels.SelectableChannel fd)
    {
        if(TRACE_REGISTRATION)
        {
            if(TRACE_STACK_TRACE)
            {
                java.io.StringWriter sw = new java.io.StringWriter();
                try
                {
                    throw new RuntimeException();
                }
                catch(RuntimeException ex)
                {
                    java.io.PrintWriter pw = new java.io.PrintWriter(sw);
                    ex.printStackTrace(pw);
                    pw.flush();
                }
                trace("removing handler for channel " + fd + "\n" + sw.toString());
            }
            else
            {
                trace("removing handler for channel " + fd);
            }
        }

	assert(!_destroyed);
        _changes.add(new FdHandlerPair(fd, null));
        setInterrupt(0);
    }

    public void
    promoteFollower()
    {
        if(_multipleThreads)
        {
	    if(!_promote) // Double-checked locking.
	    {
		synchronized(_promoteMonitor)
		{
		    if(!_promote)
		    {
			_promote = true;
			_promoteMonitor.notify();
		    }
		}
	    }
        }
    }

    public void
    initiateShutdown()
    {
        if(TRACE_SHUTDOWN)
        {
            trace("initiate server shutdown");
        }

        setInterrupt(1);
    }

    public void
    joinWithAllThreads()
    {
        //
        // _threads is immutable after the initial creation in the
        // constructor, therefore no synchronization is
        // needed. (Synchronization wouldn't be possible here anyway,
        // because otherwise the other threads would never terminate.)
        //
        for(int i = 0; i < _threads.length; i++)
        {
            while(true)
            {
                try
                {
                    _threads[i].join();
                    break;
                }
                catch(InterruptedException ex)
                {
                }
            }
        }
    }

    private boolean
    clearInterrupt()
    {
        if(TRACE_INTERRUPT)
        {
            trace("clearInterrupt");
            if(TRACE_STACK_TRACE)
            {
                try
                {
                    throw new RuntimeException();
                }
                catch(RuntimeException ex)
                {
                    ex.printStackTrace();
                }
            }
        }

        byte b = 0;

        java.nio.ByteBuffer buf = java.nio.ByteBuffer.allocate(1);
        try
        {
            while(true)
            {
                buf.rewind();
                if(_fdIntrRead.read(buf) != 1)
                {
                    break;
                }

                if(TRACE_INTERRUPT)
                {
                    trace("clearInterrupt got byte " + (int)buf.get(0));
                }

                b = buf.get(0);
                break;
            }
        }
        catch(java.io.IOException ex)
        {
            Ice.SocketException se = new Ice.SocketException();
            se.initCause(ex);
            throw se;
        }

        return b == (byte)1; // Return true if shutdown has been initiated.
    }

    private void
    setInterrupt(int b)
    {
        if(TRACE_INTERRUPT)
        {
            trace("setInterrupt(" + b + ")");
            if(TRACE_STACK_TRACE)
            {
                try
                {
                    throw new RuntimeException();
                }
                catch(RuntimeException ex)
                {
                    ex.printStackTrace();
                }
            }
        }

        java.nio.ByteBuffer buf = java.nio.ByteBuffer.allocate(1);
        buf.put(0, (byte)b);
        while(buf.hasRemaining())
        {
            try
            {
                _fdIntrWrite.write(buf);
            }
            catch(java.io.IOException ex)
            {
                Ice.SocketException se = new Ice.SocketException();
                se.initCause(ex);
                throw se;
            }
        }
    }

    //
    // Each thread supplies a BasicStream, to avoid creating excessive
    // garbage (Java only)
    //
    private void
    run(BasicStream stream)
    {
        while(true)
        {
            if(_multipleThreads)
            {
		synchronized(_promoteMonitor)
		{
		    while(!_promote)
		    {
			try
			{
			    _promoteMonitor.wait();
			}
			catch(InterruptedException ex)
			{
			}
		    }

		    _promote = false;
		}

                if(TRACE_THREAD)
                {
                    trace("thread " + Thread.currentThread() + " has the lock");
                }
            }

        repeatSelect:

            while(true)
            {
                if(TRACE_REGISTRATION)
                {
                    java.util.Set keys = _selector.keys();
                    trace("selecting on " + keys.size() + " channels:");
                    java.util.Iterator i = keys.iterator();
                    while(i.hasNext())
                    {
                        java.nio.channels.SelectionKey key = (java.nio.channels.SelectionKey)i.next();
                        trace("  " + key.channel());
                    }
                }

                select();
                if(_keys.size() == 0) // We initiate a shutdown if there is a thread pool timeout.
                {
                    if(TRACE_SELECT)
                    {
                        trace("timeout");
                    }

                    assert(_timeout > 0);
                    _timeout = 0;
                    initiateShutdown();
                    continue repeatSelect;
                }

                EventHandler handler = null;
                boolean finished = false;
		boolean shutdown = false;

                synchronized(this)
                {
                    if(_keys.contains(_fdIntrReadKey) && _fdIntrReadKey.isReadable())
                    {
                        if(TRACE_SELECT || TRACE_INTERRUPT)
                        {
                            trace("detected interrupt");
                        }

                        //
                        // There are three possibilities for an interrupt:
                        //
                        // - The thread pool has been destroyed.
                        //
                        // - Server shutdown has been initiated.
                        //
                        // - An event handler was registered or unregistered.
                        //

                        //
                        // Thread pool destroyed?
                        //
                        if(_destroyed)
                        {
                            if(TRACE_SHUTDOWN)
                            {
                                trace("destroyed, thread id = " + Thread.currentThread());
                            }

                            //
                            // Don't clear the interrupt fd if destroyed, so that
                            // the other threads exit as well.
                            //
                            return;
                        }

                        //
                        // Remove the interrupt channel from the selected key set.
                        //
                        _keys.remove(_fdIntrReadKey);

                        shutdown = clearInterrupt();

                        if(!shutdown)
                        {
			    //
			    // An event handler must have been
			    // registered or unregistered.
			    //
			    assert(!_changes.isEmpty());
			    FdHandlerPair change = (FdHandlerPair)_changes.removeFirst();
			    
			    if(change.handler != null) // Addition if handler is set.
			    {
				int op;
				if((change.fd.validOps() & java.nio.channels.SelectionKey.OP_READ) > 0)
				{
				    op = java.nio.channels.SelectionKey.OP_READ;
				}
				else
				{
				    op = java.nio.channels.SelectionKey.OP_ACCEPT;
				}
				
				java.nio.channels.SelectionKey key = null;
				try
				{
				    key = change.fd.register(_selector, op, change.handler);
				}
				catch(java.nio.channels.ClosedChannelException ex)
				{
				    assert(false);
				}
				_handlerMap.put(change.fd, new HandlerKeyPair(change.handler, key));
				
				if(TRACE_REGISTRATION)
				{
				    trace("added handler (" + change.handler.getClass().getName() + ") for fd " +
					  change.fd);
				}
				
				continue repeatSelect;
			    }
			    else // Removal if handler is not set.
			    {
				HandlerKeyPair pair = (HandlerKeyPair)_handlerMap.remove(change.fd);
				assert(pair != null);
				handler = pair.handler;
				finished = true;
				pair.key.cancel();
				
				if(TRACE_REGISTRATION)
				{
				    trace("removed handler (" + handler.getClass().getName() + ") for fd " +
					  change.fd);
				}
				
				// Don't goto repeatSelect; we have to
				// call finished() on the event
				// handler below, outside the thread
				// synchronization.
			    }
			}
		    }
		    else
                    {
                        java.nio.channels.SelectionKey key = null;
                        java.util.Iterator iter = _keys.iterator();
                        while(iter.hasNext())
                        {
                            //
                            // Ignore selection keys that have been cancelled
                            //
                            java.nio.channels.SelectionKey k = (java.nio.channels.SelectionKey)iter.next();
                            iter.remove();
                            if(k.isValid() && key != _fdIntrReadKey)
                            {
                                if(TRACE_SELECT)
                                {
                                    trace("found a key: " + keyToString(k));
                                }

                                key = k;
                                break;
                            }
                        }

                        if(key == null)
                        {
                            if(TRACE_SELECT)
                            {
                                trace("didn't find a valid key");
                            }

                            continue repeatSelect;
                        }

                        handler = (EventHandler)key.attachment();
                    }
                }

                assert(handler != null || shutdown);

                if(shutdown) // Shutdown has been initiated.
                {
                    if(TRACE_SHUTDOWN)
                    {
                        trace("shutdown detected");
                    }

                    ObjectAdapterFactory factory = _instance.objectAdapterFactory();
                    if(factory == null)
		    {
			continue repeatSelect;
		    }

		    promoteFollower();
		    factory.shutdown();
                }
		else
		{
		    if(finished)
		    {
			//
			// Notify a handler about it's removal from
			// the thread pool.
			//
			try
			{
			    handler.finished(this);
			}
			catch(Ice.LocalException ex)
			{
			    java.io.StringWriter sw = new java.io.StringWriter();
			    java.io.PrintWriter pw = new java.io.PrintWriter(sw);
			    ex.printStackTrace(pw);
			    pw.flush();
			    String s = "exception while calling finished():\n" + sw.toString() + "\n" +
				handler.toString();
			    _instance.logger().error(s);
			}
		    }
		    else
		    {
			//
			// If the handler is "readable", try to read a
			// message.
			//
			try
			{
			    if(handler.readable())
			    {
				try
				{
				    read(handler);
				}
				catch(Ice.TimeoutException ex) // Expected.
				{
				    continue repeatSelect;
				}
				catch(Ice.LocalException ex)
				{
				    if(TRACE_EXCEPTION)
				    {
					trace("informing handler (" + handler.getClass().getName() +
					      ") about exception " + ex);
					ex.printStackTrace();
				    }
				    
				    handler.exception(ex);
				    continue repeatSelect;
				}
				
				stream.swap(handler._stream);
				assert(stream.pos() == stream.size());
			    }
			    
			    handler.message(stream, this);
			}
			finally
			{
			    stream.reset();
			}
		    }
                }
		
                break; // Inner while loop.
            }
        }
    }

    private void
    read(EventHandler handler)
    {
        BasicStream stream = handler._stream;

        if(stream.size() == 0)
        {
            stream.resize(Protocol.headerSize, true);
            stream.pos(0);
        }

        if(stream.pos() != stream.size())
        {
            handler.read(stream);
            assert(stream.pos() == stream.size());
        }

        int pos = stream.pos();
        assert(pos >= Protocol.headerSize);
        stream.pos(0);
        byte protVer = stream.readByte();
        if(protVer != Protocol.protocolVersion)
        {
            throw new Ice.UnsupportedProtocolException();
        }
        byte encVer = stream.readByte();
        if(encVer != Protocol.encodingVersion)
        {
            throw new Ice.UnsupportedEncodingException();
        }
        byte messageType = stream.readByte();
        int size = stream.readInt();
        if(size < Protocol.headerSize)
        {
            throw new Ice.IllegalMessageSizeException();
        }
        if(size > 1024 * 1024) // TODO: Configurable
        {
            throw new Ice.MemoryLimitException();
        }
        if(size > stream.size())
        {
            stream.resize(size, true);
        }
        stream.pos(pos);

        if(stream.pos() != stream.size())
        {
            handler.read(stream);
            assert(stream.pos() == stream.size());
        }
    }

    private void
    selectNonBlocking()
    {
        while(true)
        {
            try
            {
                if(TRACE_SELECT)
                {
                    trace("non-blocking select on " + _selector.keys().size() + " keys, thread id = " +
                          Thread.currentThread());
                }

                _selector.selectNow();

                if(TRACE_SELECT)
                {
                    if(_keys.size() > 0)
                    {
                        trace("after selectNow, there are " + _keys.size() + " selected keys:");
                        java.util.Iterator i = _keys.iterator();
                        while(i.hasNext())
                        {
                            java.nio.channels.SelectionKey key = (java.nio.channels.SelectionKey)i.next();
                            trace("  " + keyToString(key));
                        }
                    }
                }

                break;
            }
            catch(java.io.InterruptedIOException ex)
            {
                continue;
            }
            catch(java.io.IOException ex)
            {
                //
                // Pressing Ctrl-C causes select() to raise an
                // IOException, which seems like a JDK bug. We trap
                // for that special case here and ignore it.
                // Hopefully we're not masking something important!
                //
                if(ex.getMessage().indexOf("Interrupted system call") != -1)
                {
                    continue;
                }

                Ice.SocketException se = new Ice.SocketException();
                se.initCause(ex);
                throw se;
            }
        }
    }

    private void
    select()
    {
        int ret = 0;

        while(true)
        {
            try
            {
                if(TRACE_SELECT)
                {
                    trace("select on " + _selector.keys().size() + " keys, thread id = " + Thread.currentThread());
                }

		if(_timeout > 0)
		{
		    ret = _selector.select(_timeout * 1000);
		}
		else
		{
		    ret = _selector.select();
		}
            }
            catch(java.io.InterruptedIOException ex)
            {
                continue;
            }
            catch(java.io.IOException ex)
            {
                //
                // Pressing Ctrl-C causes select() to raise an
                // IOException, which seems like a JDK bug. We trap
                // for that special case here and ignore it.
                // Hopefully we're not masking something important!
                //
                if(ex.getMessage().indexOf("Interrupted system call") != -1)
                {
                    continue;
                }

                Ice.SocketException se = new Ice.SocketException();
                se.initCause(ex);
                throw se;
            }

            if(TRACE_SELECT)
            {
                trace("select() returned " + ret + ", _keys.size() = " + _keys.size());
            }

            break;
        }
    }

    private void
    trace(String msg)
    {
        System.err.println(_name + ": " + msg);
    }

    private String
    keyToString(java.nio.channels.SelectionKey key)
    {
        String ops = "[";
        if(key.isAcceptable())
        {
            ops += " OP_ACCEPT";
        }
        if(key.isReadable())
        {
            ops += " OP_READ";
        }
        if(key.isConnectable())
        {
            ops += " OP_CONNECT";
        }
        if(key.isWritable())
        {
            ops += " OP_WRITE";
        }
        ops += " ]";
        return key.channel() + " " + ops;
    }

    private static final class FdHandlerPair
    {
        java.nio.channels.SelectableChannel fd;
        EventHandler handler;

        FdHandlerPair(java.nio.channels.SelectableChannel fd, EventHandler handler)
        {
            this.fd = fd;
            this.handler = handler;
        }
    }

    private static final class HandlerKeyPair
    {
        EventHandler handler;
        java.nio.channels.SelectionKey key;

        HandlerKeyPair(EventHandler handler, java.nio.channels.SelectionKey key)
        {
            this.handler = handler;
            this.key = key;
        }
    }

    private Instance _instance;
    private boolean _destroyed;
    private java.nio.channels.ReadableByteChannel _fdIntrRead;
    private java.nio.channels.SelectionKey _fdIntrReadKey;
    private java.nio.channels.WritableByteChannel _fdIntrWrite;
    private java.nio.channels.Selector _selector;
    private java.util.Set _keys;
    private java.util.LinkedList _changes = new java.util.LinkedList();
    private java.util.HashMap _handlerMap = new java.util.HashMap();
    private int _timeout;
    private boolean _promote;
    private java.lang.Object _promoteMonitor = new java.lang.Object();
    private boolean _multipleThreads;
    private String _name;

    private final class EventHandlerThread extends Thread
    {
        EventHandlerThread(String name)
        {
            super(name);
        }

        public void
        run()
        {
            BasicStream stream = new BasicStream(_instance);

            try
            {
		ThreadPool.this.run(stream);
            }
            catch(Ice.LocalException ex)
            {
                java.io.StringWriter sw = new java.io.StringWriter();
                java.io.PrintWriter pw = new java.io.PrintWriter(sw);
                ex.printStackTrace(pw);
                pw.flush();
                String s = "exception in thread pool thread " + getName() + ":\n" + sw.toString();
                _instance.logger().error(s);
            }
            catch(RuntimeException ex)
            {
                java.io.StringWriter sw = new java.io.StringWriter();
                java.io.PrintWriter pw = new java.io.PrintWriter(sw);
                ex.printStackTrace(pw);
                pw.flush();
                String s = "unknown exception in thread pool thread " + getName() + ":\n" + sw.toString();
                _instance.logger().error(s);
            }

            if(TRACE_THREAD)
            {
                trace("run() terminated - promoting follower");
            }

            promoteFollower();

            stream.destroy();
        }
    }
    private EventHandlerThread[] _threads;
}