/*
* %CopyrightBegin%
*
* Copyright Ericsson AB 2000-2017. All Rights Reserved.
*
* 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.
*
* %CopyrightEnd%
*/
package com.ericsson.otp.erlang;
/**
* <p>
* Provides a simple mechanism for exchanging messages with Erlang processes or
* other instances of this class.
* </p>
*
* <p>
* Each mailbox is associated with a unique {@link OtpErlangPid pid} that
* contains information necessary for delivery of messages. When sending
* messages to named processes or mailboxes, the sender pid is made available to
* the recipient of the message. When sending messages to other mailboxes, the
* recipient can only respond if the sender includes the pid as part of the
* message contents. The sender can determine his own pid by calling
* {@link #self() self()}.
* </p>
*
* <p>
* Mailboxes can be named, either at creation or later. Messages can be sent to
* named mailboxes and named Erlang processes without knowing the
* {@link OtpErlangPid pid} that identifies the mailbox. This is necessary in
* order to set up initial communication between parts of an application. Each
* mailbox can have at most one name.
* </p>
*
* <p>
* Since this class was intended for communication with Erlang, all of the send
* methods take {@link OtpErlangObject OtpErlangObject} arguments. However this
* class can also be used to transmit arbitrary Java objects (as long as they
* implement one of java.io.Serializable or java.io.Externalizable) by
* encapsulating the object in a {@link OtpErlangBinary OtpErlangBinary}.
* </p>
*
* <p>
* Messages to remote nodes are externalized for transmission, and as a result
* the recipient receives a <b>copy</b> of the original Java object. To ensure
* consistent behaviour when messages are sent between local mailboxes, such
* messages are cloned before delivery.
* </p>
*
* <p>
* Additionally, mailboxes can be linked in much the same way as Erlang
* processes. If a link is active when a mailbox is {@link #close closed}, any
* linked Erlang processes or OtpMboxes will be sent an exit signal. As well,
* exit signals will be (eventually) sent if a mailbox goes out of scope and its
* {@link #finalize finalize()} method called. However due to the nature of
* finalization (i.e. Java makes no guarantees about when {@link #finalize
* finalize()} will be called) it is recommended that you always explicitly
* close mailboxes if you are using links instead of relying on finalization to
* notify other parties in a timely manner.
* </p>
*
* <p>
* When retrieving messages from a mailbox that has received an exit signal, an
* {@link OtpErlangExit OtpErlangExit} exception will be raised. Note that the
* exception is queued in the mailbox along with other messages, and will not be
* raised until it reaches the head of the queue and is about to be retrieved.
* </p>
*
*/
public class OtpMbox {
OtpNode home;
OtpErlangPid self;
GenericQueue queue;
String name;
Links links;
// package constructor: called by OtpNode:createMbox(name)
// to create a named mbox
OtpMbox(final OtpNode home, final OtpErlangPid self, final String name) {
this.self = self;
this.home = home;
this.name = name;
queue = new GenericQueue();
links = new Links(10);
}
// package constructor: called by OtpNode:createMbox()
// to create an anonymous
OtpMbox(final OtpNode home, final OtpErlangPid self) {
this(home, self, null);
}
/**
* <p>
* Get the identifying {@link OtpErlangPid pid} associated with this
* mailbox.
* </p>
*
* <p>
* The {@link OtpErlangPid pid} associated with this mailbox uniquely
* identifies the mailbox and can be used to address the mailbox. You can
* send the {@link OtpErlangPid pid} to a remote communicating part so that
* he can know where to send his response.
* </p>
*
* @return the self pid for this mailbox.
*/
public OtpErlangPid self() {
return self;
}
/**
* <p>
* Register or remove a name for this mailbox. Registering a name for a
* mailbox enables others to send messages without knowing the
* {@link OtpErlangPid pid} of the mailbox. A mailbox can have at most one
* name; if the mailbox already had a name, calling this method will
* supercede that name.
* </p>
*
* @param aname
* the name to register for the mailbox. Specify null to
* unregister the existing name from this mailbox.
*
* @return true if the name was available, or false otherwise.
*/
public synchronized boolean registerName(final String aname) {
return home.registerName(aname, this);
}
/**
* Get the registered name of this mailbox.
*
* @return the registered name of this mailbox, or null if the mailbox had
* no registered name.
*/
public String getName() {
return name;
}
/**
* Block until a message arrives for this mailbox.
*
* @return an {@link OtpErlangObject OtpErlangObject} representing the body
* of the next message waiting in this mailbox.
*
* @exception OtpErlangDecodeException
* if the message can not be decoded.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*/
public OtpErlangObject receive() throws OtpErlangExit,
OtpErlangDecodeException {
try {
return receiveMsg().getMsg();
} catch (final OtpErlangExit e) {
throw e;
} catch (final OtpErlangDecodeException f) {
throw f;
}
}
/**
* Wait for a message to arrive for this mailbox.
*
* @param timeout
* the time, in milliseconds, to wait for a message before
* returning null.
*
* @return an {@link OtpErlangObject OtpErlangObject} representing the body
* of the next message waiting in this mailbox.
*
* @exception OtpErlangDecodeException
* if the message can not be decoded.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*/
public OtpErlangObject receive(final long timeout) throws OtpErlangExit,
OtpErlangDecodeException {
try {
final OtpMsg m = receiveMsg(timeout);
if (m != null) {
return m.getMsg();
}
} catch (final OtpErlangExit e) {
throw e;
} catch (final OtpErlangDecodeException f) {
throw f;
} catch (final InterruptedException g) {
}
return null;
}
/**
* Block until a message arrives for this mailbox.
*
* @return a byte array representing the still-encoded body of the next
* message waiting in this mailbox.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*
*/
public OtpInputStream receiveBuf() throws OtpErlangExit {
return receiveMsg().getMsgBuf();
}
/**
* Wait for a message to arrive for this mailbox.
*
* @param timeout
* the time, in milliseconds, to wait for a message before
* returning null.
*
* @return a byte array representing the still-encoded body of the next
* message waiting in this mailbox.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*
* @exception InterruptedException
* if no message if the method times out before a message
* becomes available.
*/
public OtpInputStream receiveBuf(final long timeout)
throws InterruptedException, OtpErlangExit {
final OtpMsg m = receiveMsg(timeout);
if (m != null) {
return m.getMsgBuf();
}
return null;
}
/**
* Block until a message arrives for this mailbox.
*
* @return an {@link OtpMsg OtpMsg} containing the header information as
* well as the body of the next message waiting in this mailbox.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*
*/
public OtpMsg receiveMsg() throws OtpErlangExit {
final OtpMsg m = (OtpMsg) queue.get();
switch (m.type()) {
case OtpMsg.exitTag:
case OtpMsg.exit2Tag:
try {
final OtpErlangObject o = m.getMsg();
throw new OtpErlangExit(o, m.getSenderPid());
} catch (final OtpErlangDecodeException e) {
throw new OtpErlangExit("unknown", m.getSenderPid());
}
default:
return m;
}
}
/**
* Wait for a message to arrive for this mailbox.
*
* @param timeout
* the time, in milliseconds, to wait for a message.
*
* @return an {@link OtpMsg OtpMsg} containing the header information as
* well as the body of the next message waiting in this mailbox.
*
* @exception OtpErlangExit
* if a linked {@link OtpErlangPid pid} has exited or has
* sent an exit signal to this mailbox.
*
* @exception InterruptedException
* if no message if the method times out before a message
* becomes available.
*/
public OtpMsg receiveMsg(final long timeout) throws InterruptedException,
OtpErlangExit {
final OtpMsg m = (OtpMsg) queue.get(timeout);
if (m == null) {
return null;
}
switch (m.type()) {
case OtpMsg.exitTag:
case OtpMsg.exit2Tag:
try {
final OtpErlangObject o = m.getMsg();
throw new OtpErlangExit(o, m.getSenderPid());
} catch (final OtpErlangDecodeException e) {
throw new OtpErlangExit("unknown", m.getSenderPid());
}
default:
return m;
}
}
/**
* Send a message to a remote {@link OtpErlangPid pid}, representing either
* another {@link OtpMbox mailbox} or an Erlang process.
*
* @param to
* the {@link OtpErlangPid pid} identifying the intended
* recipient of the message.
*
* @param msg
* the body of the message to send.
*
*/
public void send(final OtpErlangPid to, final OtpErlangObject msg) {
try {
final String node = to.node();
if (node.equals(home.node())) {
home.deliver(new OtpMsg(to, (OtpErlangObject) msg.clone()));
} else {
final OtpCookedConnection conn = home.getConnection(node);
if (conn == null) {
return;
}
conn.send(self, to, msg);
}
} catch (final Exception e) {
}
}
/**
* Send a message to a named mailbox created from the same node as this
* mailbox.
*
* @param aname
* the registered name of recipient mailbox.
*
* @param msg
* the body of the message to send.
*
*/
public void send(final String aname, final OtpErlangObject msg) {
home.deliver(new OtpMsg(self, aname, (OtpErlangObject) msg.clone()));
}
/**
* Send a message to a named mailbox created from another node.
*
* @param aname
* the registered name of recipient mailbox.
*
* @param node
* the name of the remote node where the recipient mailbox is
* registered.
*
* @param msg
* the body of the message to send.
*
*/
public void send(final String aname, final String node,
final OtpErlangObject msg) {
try {
final String currentNode = home.node();
if (node.equals(currentNode)) {
send(aname, msg);
} else if (node.indexOf('@', 0) < 0
&& node.equals(currentNode.substring(0,
currentNode.indexOf('@', 0)))) {
send(aname, msg);
} else {
// other node
final OtpCookedConnection conn = home.getConnection(node);
if (conn == null) {
return;
}
conn.send(self, aname, msg);
}
} catch (final Exception e) {
}
}
/**
* Close this mailbox with the given reason.
*
* <p>
* After this operation, the mailbox will no longer be able to receive
* messages. Any delivered but as yet unretrieved messages can still be
* retrieved however.
* </p>
*
* <p>
* If there are links from this mailbox to other {@link OtpErlangPid pids},
* they will be broken when this method is called and exit signals will be
* sent.
* </p>
*
* @param reason
* an Erlang term describing the reason for the exit.
*/
public void exit(final OtpErlangObject reason) {
home.closeMbox(this, reason);
}
/**
* Equivalent to <code>exit(new OtpErlangAtom(reason))</code>.
*
* @see #exit(OtpErlangObject)
*/
public void exit(final String reason) {
exit(new OtpErlangAtom(reason));
}
/**
* <p>
* Send an exit signal to a remote {@link OtpErlangPid pid}. This method
* does not cause any links to be broken, except indirectly if the remote
* {@link OtpErlangPid pid} exits as a result of this exit signal.
* </p>
*
* @param to
* the {@link OtpErlangPid pid} to which the exit signal should
* be sent.
*
* @param reason
* an Erlang term indicating the reason for the exit.
*/
// it's called exit, but it sends exit2
public void exit(final OtpErlangPid to, final OtpErlangObject reason) {
exit(2, to, reason);
}
/**
* <p>
* Equivalent to <code>exit(to, new
* OtpErlangAtom(reason))</code>.
* </p>
*
* @see #exit(OtpErlangPid, OtpErlangObject)
*/
public void exit(final OtpErlangPid to, final String reason) {
exit(to, new OtpErlangAtom(reason));
}
// this function used internally when "process" dies
// since Erlang discerns between exit and exit/2.
private void exit(final int arity, final OtpErlangPid to,
final OtpErlangObject reason) {
try {
final String node = to.node();
if (node.equals(home.node())) {
home.deliver(new OtpMsg(OtpMsg.exitTag, self, to, reason));
} else {
final OtpCookedConnection conn = home.getConnection(node);
if (conn == null) {
return;
}
switch (arity) {
case 1:
conn.exit(self, to, reason);
break;
case 2:
conn.exit2(self, to, reason);
break;
}
}
} catch (final Exception e) {
}
}
/**
* <p>
* Link to a remote mailbox or Erlang process. Links are idempotent, calling
* this method multiple times will not result in more than one link being
* created.
* </p>
*
* <p>
* If the remote process subsequently exits or the mailbox is closed, a
* subsequent attempt to retrieve a message through this mailbox will cause
* an {@link OtpErlangExit OtpErlangExit} exception to be raised. Similarly,
* if the sending mailbox is closed, the linked mailbox or process will
* receive an exit signal.
* </p>
*
* <p>
* If the remote process cannot be reached in order to set the link, the
* exception is raised immediately.
* </p>
*
* @param to
* the {@link OtpErlangPid pid} representing the object to link
* to.
*
* @exception OtpErlangExit
* if the {@link OtpErlangPid pid} referred to does not exist
* or could not be reached.
*
*/
public void link(final OtpErlangPid to) throws OtpErlangExit {
try {
final String node = to.node();
if (node.equals(home.node())) {
if (!home.deliver(new OtpMsg(OtpMsg.linkTag, self, to))) {
throw new OtpErlangExit("noproc", to);
}
} else {
final OtpCookedConnection conn = home.getConnection(node);
if (conn != null) {
conn.link(self, to);
} else {
throw new OtpErlangExit("noproc", to);
}
}
} catch (final OtpErlangExit e) {
throw e;
} catch (final Exception e) {
}
links.addLink(self, to);
}
/**
* <p>
* Remove a link to a remote mailbox or Erlang process. This method removes
* a link created with {@link #link link()}. Links are idempotent; calling
* this method once will remove all links between this mailbox and the
* remote {@link OtpErlangPid pid}.
* </p>
*
* @param to
* the {@link OtpErlangPid pid} representing the object to unlink
* from.
*
*/
public void unlink(final OtpErlangPid to) {
links.removeLink(self, to);
try {
final String node = to.node();
if (node.equals(home.node())) {
home.deliver(new OtpMsg(OtpMsg.unlinkTag, self, to));
} else {
final OtpCookedConnection conn = home.getConnection(node);
if (conn != null) {
conn.unlink(self, to);
}
}
} catch (final Exception e) {
}
}
/**
* <p>
* Create a connection to a remote node.
* </p>
*
* <p>
* Strictly speaking, this method is not necessary simply to set up a
* connection, since connections are created automatically first time a
* message is sent to a {@link OtpErlangPid pid} on the remote node.
* </p>
*
* <p>
* This method makes it possible to wait for a node to come up, however, or
* check that a node is still alive.
* </p>
*
* <p>
* This method calls a method with the same name in {@link OtpNode#ping
* Otpnode} but is provided here for convenience.
* </p>
*
* @param node
* the name of the node to ping.
*
* @param timeout
* the time, in milliseconds, before reporting failure.
*/
public boolean ping(final String node, final long timeout) {
return home.ping(node, timeout);
}
/**
* <p>
* Get a list of all known registered names on the same {@link OtpNode node}
* as this mailbox.
* </p>
*
* <p>
* This method calls a method with the same name in {@link OtpNode#getNames
* Otpnode} but is provided here for convenience.
* </p>
*
* @return an array of Strings containing all registered names on this
* {@link OtpNode node}.
*/
public String[] getNames() {
return home.getNames();
}
/**
* Determine the {@link OtpErlangPid pid} corresponding to a registered name
* on this {@link OtpNode node}.
*
* <p>
* This method calls a method with the same name in {@link OtpNode#whereis
* Otpnode} but is provided here for convenience.
* </p>
*
* @return the {@link OtpErlangPid pid} corresponding to the registered
* name, or null if the name is not known on this node.
*/
public OtpErlangPid whereis(final String aname) {
return home.whereis(aname);
}
/**
* Close this mailbox.
*
* <p>
* After this operation, the mailbox will no longer be able to receive
* messages. Any delivered but as yet unretrieved messages can still be
* retrieved however.
* </p>
*
* <p>
* If there are links from this mailbox to other {@link OtpErlangPid pids},
* they will be broken when this method is called and exit signals with
* reason 'normal' will be sent.
* </p>
*
* <p>
* This is equivalent to {@link #exit(String) exit("normal")}.
* </p>
*/
public void close() {
home.closeMbox(this);
}
@Override
protected void finalize() {
close();
queue.flush();
}
/**
* Determine if two mailboxes are equal.
*
* @return true if both Objects are mailboxes with the same identifying
* {@link OtpErlangPid pids}.
*/
@Override
public boolean equals(final Object o) {
if (!(o instanceof OtpMbox)) {
return false;
}
final OtpMbox m = (OtpMbox) o;
return m.self.equals(self);
}
@Override
public int hashCode() {
return self.hashCode();
}
/*
* called by OtpNode to deliver message to this mailbox.
*
* About exit and exit2: both cause exception to be raised upon receive().
* However exit (not 2) causes any link to be removed as well, while exit2
* leaves any links intact.
*/
void deliver(final OtpMsg m) {
switch (m.type()) {
case OtpMsg.linkTag:
links.addLink(self, m.getSenderPid());
break;
case OtpMsg.unlinkTag:
links.removeLink(self, m.getSenderPid());
break;
case OtpMsg.exitTag:
links.removeLink(self, m.getSenderPid());
queue.put(m);
break;
case OtpMsg.exit2Tag:
default:
queue.put(m);
break;
}
}
// used to break all known links to this mbox
void breakLinks(final OtpErlangObject reason) {
final Link[] l = links.clearLinks();
if (l != null) {
final int len = l.length;
for (int i = 0; i < len; i++) {
exit(1, l[i].remote(), reason);
}
}
}
}
