hudson.remoting

Class Channel

java.lang.Object

hudson.remoting.Channel

All Implemented Interfaces:

VirtualChannel, Closeable, AutoCloseable

public class Channel
extends Object
implements VirtualChannel, Closeable

Represents a communication channel to the remote peer.

A Channel is a mechanism for two JVMs to communicate over bi-directional InputStream/OutputStream pair. Channel represents an endpoint of the stream, and thus two Channels are always used in a pair.

Communication is established as soon as two Channel instances are created at the end fo the stream pair until the stream is terminated via close().

The basic unit of remoting is an executable Callable object. An application can create a Callable object, and execute it remotely by using the call(Callable) method or callAsync(Callable) method.

In this sense, Channel is a mechanism to delegate/offload computation to other JVMs and somewhat like an agent system. This is bit different from remoting technologies like CORBA or web services, where the server exposes a certain functionality that clients invoke.

Callable object, as well as the return value / exceptions, are transported by using Java serialization. All the necessary class files are also shipped over Channel on-demand, so there's no need to pre-deploy such classes on both JVMs.

Implementor's Note

Channel builds its features in a layered model. Its higher-layer features are built on top of its lower-layer features, and they are called layer-0, layer-1, etc.

• Layer 0: See Command for more details. This is for higher-level features, and not likely useful for applications directly.
• Layer 1: See Request for more details. This is for higher-level features, and not likely useful for applications directly.

Author:

Kohsuke Kawaguchi

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Channel.Listener Callback "interface" for changes in the state of Channel.
static class	Channel.Mode Communication mode used in conjunction with ClassicCommandTransport.

Field Summary

Fields

Modifier and Type	Field and Description
AtomicInteger	classLoadingCount Total counts of remote classloading activities.
AtomicInteger	classLoadingPrefetchCacheCount Prefetch cache hits.
AtomicLong	classLoadingTime Total number of nanoseconds spent for remote class loading.
static int	PIPE_WINDOW_SIZE Default pipe window size.
Capability	remoteCapability Capability of the remote Channel.
AtomicInteger	resourceLoadingCount Total count of remote resource loading.
AtomicLong	resourceLoadingTime Total number of nanoseconds spent for remote resource loading.

Constructor Summary

Constructors

Constructor and Description
Channel(String name, ExecutorService exec, Channel.Mode mode, InputStream is, OutputStream os) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, Channel.Mode mode, InputStream is, OutputStream os, OutputStream header) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, Channel.Mode mode, InputStream is, OutputStream os, OutputStream header, boolean restricted) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, Channel.Mode mode, InputStream is, OutputStream os, OutputStream header, boolean restricted, ClassLoader base) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, CommandTransport transport, boolean restricted, ClassLoader base) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, CommandTransport transport, boolean restricted, ClassLoader base, JarCache jarCache) Deprecated. as of 2.38
Channel(String name, ExecutorService exec, InputStream is, OutputStream os) Deprecated. as of 2.24 Use ChannelBuilder
Channel(String name, ExecutorService exec, InputStream is, OutputStream os, OutputStream header) Deprecated. as of 2.24 Use ChannelBuilder

Method Summary

Methods

Modifier and Type	Method and Description
void	addListener(Channel.Listener l) Registers a new Channel.Listener.
void	addLocalExecutionInterceptor(CallableFilter filter) Adds a CallableFilter that gets a chance to decorate every Callables that run locally sent by the other peer.
<V,T extends Throwable> V	call(Callable<V,T> callable) Makes a remote procedure call.
<V,T extends Throwable> Future<V>	callAsync(Callable<V,T> callable) Makes an asynchronous remote procedure call.
void	close() Performs an orderly shut down of this channel (and the remote peer.)
void	close(Throwable diagnosis) Closes the channel.
ListeningPort	createLocalToRemotePortForwarding(int recvPort, String forwardHost, int forwardPort) Starts a local to remote port forwarding (the equivalent of "ssh -L").
ListeningPort	createRemoteToLocalPortForwarding(int recvPort, String forwardHost, int forwardPort) Starts a remote to local port forwarding (the equivalent of "ssh -R").
static Channel	current() This method can be invoked during the serialization/deserialization of objects when they are transferred to the remote Channel, as well as during Callable.call() is invoked.
void	dumpExportTable(PrintWriter w) Dumps the list of exported objects and their allocation traces to the given output.
void	dumpPerformanceCounters(PrintWriter w) Print the performance counters.
<T> T	export(Class<T> type, T instance) Exports an object for remoting to the other Channel by creating a remotable proxy.
JarCache	getJarCache() If this channel is built with jar file caching, return the object that manages this cache.
long	getLastHeard()
String	getName()
<T> T	getProperty(ChannelProperty<T> key)
Object	getProperty(Object key) Gets the application specific property set by setProperty(Object, Object).
<T> T	getRemoteProperty(ChannelProperty<T> key)
Object	getRemoteProperty(Object key) Gets the property set on the remote peer.
OutputStream	getUnderlyingOutput() Deprecated. Future version of the remoting module may add other modes of creating channel that doesn't involve stream pair. Therefore, we aren't committing to this method. This method isn't a part of the committed API of the channel class.
boolean	isClosingOrClosed() Returns true if the channel is either in the process of closing down or has closed down.
boolean	isInClosed() If the receiving end of the channel is closed (that is, if we are guaranteed to receive nothing further), this method returns true.
boolean	isOutClosed() Is the sender side of the transport already closed?
boolean	isRestricted() Returns true if this channel is currently does not load classes from the remote peer.
void	join() Waits for this Channel to be closed down.
void	join(long timeout) Waits for this Channel to be closed down, but only up the given milliseconds.
void	pin(Object instance) Increase reference count so much to effectively prevent de-allocation.
void	pinClassLoader(ClassLoader cl) Pin down the exported classloader.
boolean	preloadJar(Callable<?,?> classLoaderRef, Class... classesInJar) Preloads jar files on the remote side.
boolean	preloadJar(ClassLoader local, Class... classesInJar)
boolean	preloadJar(ClassLoader local, URL... jars)
boolean	removeListener(Channel.Listener l) Removes a listener.
void	removeLocalExecutionInterceptor(CallableFilter filter) Rmoves the filter introduced by addLocalExecutionInterceptor(CallableFilter).
void	resetPerformanceCounters() Resets all the performance counters.
void	setJarCache(JarCache jarCache) You can change the JarCache while the channel is in operation, but doing so doesn't impact RemoteClassLoaders that are already created.
void	setMaximumBytecodeLevel(short level) Sets the maximum bytecode version (~ JDK) that we expect this channel to be able to load.
<T> T	setProperty(ChannelProperty<T> key, T value)
Object	setProperty(Object key, Object value) Sets the property value on this side of the channel.
void	setRestricted(boolean b)
hudson.remoting.ExportTable.ExportList	startExportRecording()
void	syncIO() Blocks until all the I/O packets sent before this gets fully executed by the remote side, then return.
void	syncLocalIO() Blocks until all the I/O packets sent from remote is fully locally executed, then return.
void	terminate(IOException e) Aborts the connection in response to an error.
String	toString()
<T> T	waitForProperty(ChannelProperty<T> key)
Object	waitForProperty(Object key) Works like getProperty(Object) but wait until some value is set by someone.
<T> T	waitForRemoteProperty(ChannelProperty<T> key) Deprecated. Because ChannelProperty is identity-equality, this method would never work. This is a design error.
Object	waitForRemoteProperty(Object key) Gets the property set on the remote peer.

Methods inherited from class java.lang.Object

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

Field Detail

classLoadingTime

public final AtomicLong classLoadingTime

Total number of nanoseconds spent for remote class loading.

Remote code execution often results in classloading activity (more precisely, when the remote peer requests some computation on this channel, this channel often has to load necessary classes from the remote peer.)

This counter represents the total amount of time this channel had to spend loading classes from the remote peer. The time measurement doesn't include the time locally spent to actually define the class (as the local classloading would have incurred the same cost.)

classLoadingCount

public final AtomicInteger classLoadingCount

Total counts of remote classloading activities. Used in a pair with classLoadingTime.

classLoadingPrefetchCacheCount

public final AtomicInteger classLoadingPrefetchCacheCount

Prefetch cache hits. Out of all the counts in classLoadingCount, how many times were we able to resolve them by ourselves, saving a remote roundtrip call?

Since:

2.24

resourceLoadingTime

public final AtomicLong resourceLoadingTime

Total number of nanoseconds spent for remote resource loading.

See Also:

classLoadingTime

resourceLoadingCount

public final AtomicInteger resourceLoadingCount

Total count of remote resource loading.

See Also:

classLoadingCount

remoteCapability

public final Capability remoteCapability

Capability of the remote Channel.

PIPE_WINDOW_SIZE

public static final int PIPE_WINDOW_SIZE

Default pipe window size.

This controls the amount of bytes that can be in flight. Value too small would fail to efficiently utilize a high-latency/large-bandwidth network, but a value too large would cause the risk of a large memory consumption when a pipe clogs (that is, the receiver isn't consuming bytes we are sending fast enough.)

If we have a gigabit ethernet (with effective transfer rate of 100M bps) and 20ms latency, the pipe will hold (100M bits/sec * 0.02sec / 8 bits/byte = 0.25MB. So 1MB or so is big enough for most network, and hopefully this is an acceptable enough memory consumption in case of clogging.

See Also:

PipeWindow

Constructor Detail

Channel

public Channel(String name,
       ExecutorService exec,
       InputStream is,
       OutputStream os)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       Channel.Mode mode,
       InputStream is,
       OutputStream os)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       InputStream is,
       OutputStream os,
       OutputStream header)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       Channel.Mode mode,
       InputStream is,
       OutputStream os,
       OutputStream header)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       Channel.Mode mode,
       InputStream is,
       OutputStream os,
       OutputStream header,
       boolean restricted)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       Channel.Mode mode,
       InputStream is,
       OutputStream os,
       OutputStream header,
       boolean restricted,
       ClassLoader base)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Creates a new channel.

Parameters:

restricted -

Throws:

IOException

Channel

public Channel(String name,
       ExecutorService exec,
       CommandTransport transport,
       boolean restricted,
       ClassLoader base)
        throws IOException

Deprecated. as of 2.24 Use ChannelBuilder

Throws:

IOException

Since:

2.13

Channel

public Channel(String name,
       ExecutorService exec,
       CommandTransport transport,
       boolean restricted,
       ClassLoader base,
       JarCache jarCache)
        throws IOException

Deprecated. as of 2.38

Creates a new channel.

Parameters:

name - See Channel(String, ExecutorService, Mode, InputStream, OutputStream, OutputStream, boolean, ClassLoader)

exec - See Channel(String, ExecutorService, Mode, InputStream, OutputStream, OutputStream, boolean, ClassLoader)

transport - The transport that we run Channel on top of.

base - See Channel(String, ExecutorService, Mode, InputStream, OutputStream, OutputStream, boolean, ClassLoader)

restricted - See Channel(String, ExecutorService, Mode, InputStream, OutputStream, OutputStream, boolean, ClassLoader)

jarCache -

Throws:

IOException

Since:

2.24

Method Detail

isOutClosed

public boolean isOutClosed()

Is the sender side of the transport already closed?

isClosingOrClosed

public boolean isClosingOrClosed()

Returns true if the channel is either in the process of closing down or has closed down.

Since:

2.33

export

public <T> T export(Class<T> type,
           T instance)

Exports an object for remoting to the other Channel by creating a remotable proxy.

All the parameters and return values must be serializable.

Specified by:

export in interface VirtualChannel

Parameters:

type - Interface to be remoted.

Returns:

the proxy object that implements T. This object can be transfered to the other Channel, and calling methods on it from the remote side will invoke the same method on the given local instance object.

pin

public void pin(Object instance)

Increase reference count so much to effectively prevent de-allocation.

See Also:

ExportTable.Entry.pin()

pinClassLoader

public void pinClassLoader(ClassLoader cl)

Pin down the exported classloader.

preloadJar

public boolean preloadJar(Callable<?,?> classLoaderRef,
                 Class... classesInJar)
                   throws IOException,
                          InterruptedException

Preloads jar files on the remote side.

This is a performance improvement method that can be safely ignored if your goal is just to make things working.

Normally, classes are transferred over the network one at a time, on-demand. This design is mainly driven by how Java classloading works — we can't predict what classes will be necessarily upfront very easily.

Classes are loaded only once, so for long-running Channel, this is normally an acceptable overhead. But sometimes, for example when a channel is short-lived, or when you know that you'll need a majority of classes in certain jar files, then it is more efficient to send a whole jar file over the network upfront and thereby avoiding individual class transfer over the network.

That is what this method does. It ensures that a series of jar files are copied to the remote side (AKA "preloading.") Classloading will consult the preloaded jars before performing network transfer of class files.

Beware that this method is not useful in all configurations. If a RemoteClassLoader has another RemoteClassLoader as a parent, which would be typical, then preloading a JAR in it will not reduce network round-trips: each class load still has to call loadClass on the parent, which will wind up checking the remote side just to get a negative answer.

Parameters:

classLoaderRef - This parameter is used to identify the remote classloader that will prefetch the specified jar files. That is, prefetching will ensure that prefetched jars will kick in when this Callable object is actually executed remote side.

RemoteClassLoaders are created wisely, one per local ClassLoader, so this parameter doesn't have to be exactly the same Callable to be executed later — it just has to be of the same class.

classesInJar - Class objects that identify jar files to be preloaded. Jar files that contain the specified classes will be preloaded into the remote peer. You just need to specify one class per one jar.

Returns:

true if the preloading actually happened. false if all the jars are already preloaded. This method is implemented in such a way that unnecessary jar file transfer will be avoided, and the return value will tell you if this optimization kicked in. Under normal circumstances your program shouldn't depend on this return value. It's just a hint.

Throws:

IOException - if the preloading fails.

InterruptedException

preloadJar

public boolean preloadJar(ClassLoader local,
                 Class... classesInJar)
                   throws IOException,
                          InterruptedException

Throws:

IOException

InterruptedException

preloadJar

public boolean preloadJar(ClassLoader local,
                 URL... jars)
                   throws IOException,
                          InterruptedException

Throws:

IOException

InterruptedException

getJarCache

public JarCache getJarCache()

If this channel is built with jar file caching, return the object that manages this cache.

Since:

2.24

setJarCache

public void setJarCache(JarCache jarCache)

You can change the JarCache while the channel is in operation, but doing so doesn't impact RemoteClassLoaders that are already created. So to best avoid performance loss due to race condition, please set a JarCache in the constructor, unless your call sequence guarantees that you call this method before remote classes are loaded.

Since:

2.24

call

public <V,T extends Throwable> V call(Callable<V,T> callable)
       throws IOException,
              T extends Throwable,
              InterruptedException

Makes a remote procedure call.

Sends Callable to the remote system, executes it, and returns its result.

Specified by:

call in interface VirtualChannel

Throws:

IOException - If there's any error in the communication between Channels.

InterruptedException - If the current thread is interrupted while waiting for the completion.

T extends Throwable

callAsync

public <V,T extends Throwable> Future<V> callAsync(Callable<V,T> callable)
                    throws IOException

Makes an asynchronous remote procedure call.

Similar to VirtualChannel.call(Callable) but returns immediately. The result of the Callable can be obtained through the Future object.

Specified by:

callAsync in interface VirtualChannel

Returns:

The Future object that can be used to wait for the completion.

Throws:

IOException - If there's an error during the communication.

terminate

public void terminate(IOException e)

Aborts the connection in response to an error. This is an SPI for CommandTransport implementation to notify Channel when the underlying connection is severed.

Parameters:

e - The error that caused the connection to be aborted. Never null.

addListener

public void addListener(Channel.Listener l)

Registers a new Channel.Listener.

See Also:

removeListener(Listener)

removeListener

public boolean removeListener(Channel.Listener l)

Removes a listener.

Returns:

false if the given listener has not been registered to begin with.

addLocalExecutionInterceptor

public void addLocalExecutionInterceptor(CallableFilter filter)

Adds a CallableFilter that gets a chance to decorate every Callables that run locally sent by the other peer. This is useful to tweak the environment those closures are run, such as setting up the thread context environment.

removeLocalExecutionInterceptor

public void removeLocalExecutionInterceptor(CallableFilter filter)

Rmoves the filter introduced by addLocalExecutionInterceptor(CallableFilter).

join

public void join()
          throws InterruptedException

Waits for this Channel to be closed down. The close-down of a Channel might be initiated locally or remotely.

Specified by:

join in interface VirtualChannel

Throws:

InterruptedException - If the current thread is interrupted while waiting for the completion.

isInClosed

public boolean isInClosed()

If the receiving end of the channel is closed (that is, if we are guaranteed to receive nothing further), this method returns true.

isRestricted

public boolean isRestricted()

Returns true if this channel is currently does not load classes from the remote peer.

setRestricted

public void setRestricted(boolean b)

setMaximumBytecodeLevel

public void setMaximumBytecodeLevel(short level)
                             throws IOException,
                                    InterruptedException

Sets the maximum bytecode version (~ JDK) that we expect this channel to be able to load. If attempts are made to load remote classes using newer bytecode, they are immediately rejected, even if the remote JVM is actually new enough to load it. This helps maintain compatibility by making tests fail immediately without the need for an old JDK installation. By default, the remote class loader will try to load any bytecode version.

Parameters:

level - e.g. 5 for JDK 5 (the minimum sensible value)

Throws:

IOException

InterruptedException

Since:

2.29

join

public void join(long timeout)
          throws InterruptedException

Waits for this Channel to be closed down, but only up the given milliseconds.

Specified by:

join in interface VirtualChannel

Throws:

InterruptedException - If the current thread is interrupted while waiting for the completion.

Since:

1.299

resetPerformanceCounters

public void resetPerformanceCounters()

Resets all the performance counters.

dumpPerformanceCounters

public void dumpPerformanceCounters(PrintWriter w)
                             throws IOException

Print the performance counters.

Throws:

IOException

Since:

2.24

close

public void close()
           throws IOException

Performs an orderly shut down of this channel (and the remote peer.)

Specified by:

close in interface VirtualChannel

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - if the orderly shut-down failed.

close

public void close(Throwable diagnosis)
           throws IOException

Closes the channel.

Parameters:

diagnosis - If someone (either this side or the other side) tries to use a channel that's already closed, they'll get a stack trace indicating that the channel has already been closed. This diagnosis, if provided, will further chained to that exception, providing more contextual information about why the channel was closed.

Throws:

IOException

Since:

2.8

getProperty

public Object getProperty(Object key)

Gets the application specific property set by setProperty(Object, Object). These properties are also accessible from the remote channel via getRemoteProperty(Object).

This mechanism can be used for one side to discover contextual objects created by the other JVM (as opposed to executing Callable, which cannot have any reference to the context of the remote Channel.

getProperty

public <T> T getProperty(ChannelProperty<T> key)

waitForProperty

public Object waitForProperty(Object key)
                       throws InterruptedException

Works like getProperty(Object) but wait until some value is set by someone.

Throws:

IllegalStateException - if the channel is closed. The idea is that channel properties are expected to be the coordination mechanism between two sides of the channel, and this method in particular is a way of one side to wait for the set by the other side of the channel (via waitForRemoteProperty(Object). If we don't abort after the channel shutdown, this method will block forever.

InterruptedException

waitForProperty

public <T> T waitForProperty(ChannelProperty<T> key)
                  throws InterruptedException

Throws:

InterruptedException

setProperty

public Object setProperty(Object key,
                 Object value)

Sets the property value on this side of the channel.

See Also:

getProperty(Object)

setProperty

public <T> T setProperty(ChannelProperty<T> key,
                T value)

getRemoteProperty

public Object getRemoteProperty(Object key)

Gets the property set on the remote peer.

Returns:

null if the property of the said key isn't set.

getRemoteProperty

public <T> T getRemoteProperty(ChannelProperty<T> key)

waitForRemoteProperty

public Object waitForRemoteProperty(Object key)
                             throws InterruptedException

Gets the property set on the remote peer. This method blocks until the property is set by the remote peer.

Throws:

InterruptedException

waitForRemoteProperty

public <T> T waitForRemoteProperty(ChannelProperty<T> key)
                        throws InterruptedException

Deprecated. Because ChannelProperty is identity-equality, this method would never work. This is a design error.

Throws:

InterruptedException

getUnderlyingOutput

public OutputStream getUnderlyingOutput()

Deprecated. Future version of the remoting module may add other modes of creating channel that doesn't involve stream pair. Therefore, we aren't committing to this method. This method isn't a part of the committed API of the channel class.

Obtain the output stream passed to the constructor.

Returns:

While the current version always return a non-null value, the caller must not make that assumption for the above reason. This method may return null in the future version to indicate that the Channel is not sitting on top of a stream pair.

createLocalToRemotePortForwarding

public ListeningPort createLocalToRemotePortForwarding(int recvPort,
                                              String forwardHost,
                                              int forwardPort)
                                                throws IOException,
                                                       InterruptedException

Starts a local to remote port forwarding (the equivalent of "ssh -L").

Parameters:

recvPort - The port on this local machine that we'll listen to. 0 to let OS pick a random available port. If you specify 0, use ListeningPort.getPort() to figure out the actual assigned port.

forwardHost - The remote host that the connection will be forwarded to. Connection to this host will be made from the other JVM that this Channel represents.

forwardPort - The remote port that the connection will be forwarded to.

Returns:

Throws:

IOException

InterruptedException

createRemoteToLocalPortForwarding

public ListeningPort createRemoteToLocalPortForwarding(int recvPort,
                                              String forwardHost,
                                              int forwardPort)
                                                throws IOException,
                                                       InterruptedException

Starts a remote to local port forwarding (the equivalent of "ssh -R").

Parameters:

recvPort - The port on the remote JVM (represented by this Channel) that we'll listen to. 0 to let OS pick a random available port. If you specify 0, use ListeningPort.getPort() to figure out the actual assigned port.

forwardHost - The remote host that the connection will be forwarded to. Connection to this host will be made from this JVM.

forwardPort - The remote port that the connection will be forwarded to.

Returns:

Throws:

IOException

InterruptedException

syncIO

public void syncIO()
            throws IOException,
                   InterruptedException

Blocks until all the I/O packets sent before this gets fully executed by the remote side, then return.

Throws:

IOException - If the remote doesn't support this operation, or if sync fails for other reasons.

InterruptedException

syncLocalIO

public void syncLocalIO()
                 throws InterruptedException

Description copied from interface: VirtualChannel

Blocks until all the I/O packets sent from remote is fully locally executed, then return.

Specified by:

syncLocalIO in interface VirtualChannel

Throws:

InterruptedException

getName

public String getName()

toString

public String toString()

Overrides:

toString in class Object

dumpExportTable

public void dumpExportTable(PrintWriter w)
                     throws IOException

Dumps the list of exported objects and their allocation traces to the given output.

Throws:

IOException

startExportRecording

public hudson.remoting.ExportTable.ExportList startExportRecording()

getLastHeard

public long getLastHeard()

See Also:

lastHeard

current

public static Channel current()

This method can be invoked during the serialization/deserialization of objects when they are transferred to the remote Channel, as well as during Callable.call() is invoked.

Returns:

null if the calling thread is not performing serialization.