Class WsRemoteEndpointImplServer

java.lang.Object

org.apache.tomcat.websocket.WsRemoteEndpointImplBase

org.apache.tomcat.websocket.server.WsRemoteEndpointImplServer

All Implemented Interfaces:

RemoteEndpoint

public class WsRemoteEndpointImplServer
extends WsRemoteEndpointImplBase

This is the server side RemoteEndpoint implementation - i.e. what the server uses to send data to the client.

Nested Class Summary

Nested classes/interfaces inherited from interface javax.websocket.RemoteEndpoint

RemoteEndpoint.Async, RemoteEndpoint.Basic

Field Summary

Fields inherited from class org.apache.tomcat.websocket.WsRemoteEndpointImplBase

messagePartInProgress, SENDRESULT_OK

Constructor Summary

Constructors

Constructor	Description
WsRemoteEndpointImplServer(SocketWrapperBase<?> socketWrapper, UpgradeInfo upgradeInfo, WsServerContainer serverContainer, WebConnection connection)

Method Summary

Modifier and Type	Method	Description
protected boolean	acquireMessagePartInProgressSemaphore(byte opCode, long timeoutExpiry)	Acquire the semaphore that allows a message part to be written.
protected void	doClose()
protected void	doWrite(SendHandler handler, long blockingWriteTimeoutExpiry, ByteBuffer... buffers)
protected Lock	getLock()
protected long	getTimeoutExpiry()
protected final boolean	isMasked()
protected void	onTimeout(boolean useDispatch)
void	onWritePossible(boolean useDispatch)
protected void	setTransformation(Transformation transformation)
protected void	updateStats(long payloadLength)	Hook for updating server side statistics.

Methods inherited from class org.apache.tomcat.websocket.WsRemoteEndpointImplBase

close, flushBatch, getBatchingAllowed, getSendStream, getSendTimeout, getSendWriter, sendBytes, sendBytesByCompletion, sendBytesByFuture, sendObject, sendObjectByCompletion, sendObjectByFuture, sendPartialBytes, sendPartialString, sendPing, sendPong, sendString, sendStringByCompletion, sendStringByFuture, setBatchingAllowed, setEncoders, setSendTimeout, setSession

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

WsRemoteEndpointImplServer

public WsRemoteEndpointImplServer(SocketWrapperBase<?> socketWrapper,
 UpgradeInfo upgradeInfo,
 WsServerContainer serverContainer,
 WebConnection connection)

Method Details

isMasked

protected final boolean isMasked()

Specified by:

isMasked in class WsRemoteEndpointImplBase

acquireMessagePartInProgressSemaphore

protected boolean acquireMessagePartInProgressSemaphore(byte opCode,
 long timeoutExpiry)
                                                 throws InterruptedException

Acquire the semaphore that allows a message part to be written.

The close message is a special case. It needs to be blocking else implementing the clean-up that follows the sending of the close message gets a lot more complicated. On the server, this creates additional complications as a deadlock may occur in the following scenario:

1. Application thread writes message using non-blocking
2. Write does not complete (write logic holds message pending lock)
3. Socket is added to poller (or equivalent) for write
4. Client sends close message
5. Container processes received close message and tries to send close message in response
6. Container holds socket lock and is blocked waiting for message pending lock
7. Poller fires write possible event for socket
8. Container tries to process write possible event but is blocked waiting for socket lock
9. Processing of the WebSocket connection is deadlocked until the original message write times out

The purpose of this method is to break the above deadlock. It does this by returning control of the processor to the socket wrapper and releasing the socket lock while waiting for the pending message write to complete. Normally, that would be a terrible idea as it creates the possibility that the processor is returned to the pool more than once under various error conditions. In this instance it is safe because these are upgrade processors (isUpgrade() returns true) and upgrade processors are never pooled.

TODO: Despite the complications it creates, it would be worth exploring the possibility of processing a received close frame in a non-blocking manner.

Overrides:

acquireMessagePartInProgressSemaphore in class WsRemoteEndpointImplBase

Parameters:

opCode - The OPCODE for the message to be written

timeoutExpiry - The time when the attempt to acquire the semaphore should expire

Returns:

true if the semaphore is obtained, otherwise false.

Throws:

InterruptedException - If the wait for the semaphore is interrupted

doWrite

protected void doWrite(SendHandler handler,
 long blockingWriteTimeoutExpiry,
 ByteBuffer... buffers)

Specified by:

doWrite in class WsRemoteEndpointImplBase

updateStats

protected void updateStats(long payloadLength)

Description copied from class: WsRemoteEndpointImplBase

Hook for updating server side statistics. Called on every frame written (including when batching is enabled and the frames are buffered locally until the buffer is full or is flushed).

Overrides:

updateStats in class WsRemoteEndpointImplBase

Parameters:

payloadLength - Size of message payload

onWritePossible

public void onWritePossible(boolean useDispatch)

doClose

protected void doClose()

Specified by:

doClose in class WsRemoteEndpointImplBase

getTimeoutExpiry

protected long getTimeoutExpiry()

onTimeout

protected void onTimeout(boolean useDispatch)

setTransformation

protected void setTransformation(Transformation transformation)

Overrides:

setTransformation in class WsRemoteEndpointImplBase

getLock

protected Lock getLock()

Specified by:

getLock in class WsRemoteEndpointImplBase