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0MQ Binding for Delphi

This is a binding for ZMQ. Should work with Delphi7+ versions and with FPC 2.6.0.

General

The package contains a wrapper (zmq.pas), and a higher level api (zmqapi.pas). It should work with ZMQ 2.2.x, and with 3.2.x. For version 2.2.x undefine zmq3, in zmq.inc. The dll's are not part of this repo, you can download the appropriate from the official distro, and rename it to libzmq.dll.

This is a work in progress, please open an issue if you find bugs, or have question, or proposal.

Usage

You should use the higher level api, which'll save you a lot of time, and incidentally the code'll be easier to read.

First, you need to create a context

context := TZMQContext.Create;

There are various socket types, see the Guide, each has a constant. To create for example a REP socket, just write this:

socket := context.Socket( stRep );

// binding the socket
socket.bind( 'tcp://*:5555' );

// connecting the socket
socket.connect( 'tcp://localhost:5555' );

To send messages the api has several methods. You can send single, or Multipart messages, in blocking or nonblocking (in the v3 it's called dontwait) mode.

// sending a Utf8String in blocking mode(default) is just as easy as this:
socket.send( 'Hello' );

// or in non-blocking mode
socket.send( 'Hello', [rsfNoBlock] );
// in this case if the message cannot be queued an EZMQException is raised,
// with a value EAGAIN.

// sending data from a stream (don't forget to set the position of the stream, to read to)
socket.send( stream, size );

// sending multipart messages.
// Utf8Strings:
socket.send( ['Hello','World'] );

//this is equivalent to:
socket.send( 'Hello', [rsfSndMore] );
socket.send( 'World' );

// or use TStrings. TString.Strings interpreted as Utf8Strings!
tsl := TStringList.Create;
tsl.Add( 'Hello' );
tsl.Add( 'World' );
socket.send( tsl );
tsl.Free;

Receiving messages is as easy as

msize := socket.recv( msg );
// the new message is in the msg, and msize holds the length of the message

// to a Stream
msize := socket.recv( stream );

// read multipart message
tsl := TStringList.Create;
mcount := socket.recv( tsl );
// this will add message parts to the stringlist, and returns
// the count of the messages received.

CTRL+C Handling

it's a bit tricky. On windows signal handling is different, than in posix systems. Blocking calls won't receive SIGINT, just block continuously. To overcome this issue, the installed handler terminates the contexts, so blocking calls like recv, poll, etc... will receive ETERM. It's just on Windows.

if you code your infinite loops like this, you can terminate cleanly.

while not context.Terminated do
try
  socket.recv( msg );
except
  // handle exception, or
  context.Terminate;
  // if CTRL+C was pressed, on windows the context already
  // terminated
end;
context.Free;

Polling

Polling can work in two different ways, let's call the first synchronous, the second asynchronous way. The asynchronous version creates a thread, and do the polling there.

  • synchronous

    // create context
context := TZMQContext.Create;
socket := context.Socket( stDealer );
socket.connect( address );

// Create the poller. The `true` parameter tells
// the poller to use synchronous polling
poller := TZMQPoller.Create( true );

// register the socket.
poller.register( socket, [pePollIn] );

timeout := 100; // 100ms
while not context.Terminated do
begin
  rc := poller.poll(timeout);
  if rc > 0 then
	do something...
end;

poller.Free;
socket.Free;
context.Free;

  • asynchronous way

    This implementation uses a kind of reactor pattern, the poller starts a new thread , and creates a pair socket connection between the class and the created thread. So this poller implementation is not thread safe, don't register, deregister sockets in different threads.

    procedure TMyClass.pollerEvent( socket: TZMQSocket; event: TZMQPollEvents );
  begin
	do something...
  end;

// create context.
context := TZMQContext.Create;

socket := context.Socket( stDealer );
socket.connect( address );

// create the poller. the second parameter can be nil, than
// the poller creates it's own context.
poller := TZMQPoller.Create( false, context );

poller.onEvent := pollerEvent;

// register the socket. If the third parameter is true,
// than the register block until the socket is registered.
poller.register( socket, [pePollIn], false );

Monitoring Sockets ( just available in v3.2.2)

// define a callback like this.
procedure TMyClass.MonitorCallback( event: TZMQEvent );
begin
  // do something.
end;

// Register the callback
socket.RegisterMonitor( MonitorCallback, cZMQMonitorEventsAll );

// The `MonitorCallback` is called from a separate thread,
// created by `RegisterMonitor`

// you can deregister the monitoring with calling.
socket.DeRegisterMonitor;

Threads

Similar to the czmq api. this binding also supports attached and detached thread creation. There are two ways to use this class, call the CreateDetached or CreateAttached constructors, with parameters, or create your own descendent class and override the DoExecute method.

  • Creating a detached thread.

    procedure TMyClass.DetachedMeth( args: Pointer; context: TZMQContext );
var
  socket: TZMQSocket;
begin
  socket := context.Socket( TZMQSocketType( Args^ ) );
  Dispose( args );
end;

var
  thr: TZMQThread;
  sockettype: ^TZMQSocketType;
begin
  New( sockettype );
  sockettype^ := stDealer;
  thr := TZMQThread.CreateDetached( DetachedMeth, sockettype );
  thr.FreeOnTerminate := true;
  thr.Resume;
end;

  • or

    // create descendant class
TMyZMQThread = class( TZMQThread )
protected
  procedure doExecute; override;
end;

procedure TMyZMQThread.doExecute
var
  socket: TZMQSocket;
begin
  // do something cool.
  socket := Context.socket( TZMQSocketType(Args^) );
end;

var
  myThread: TMyZMQThread;
  sockettype: ^TZMQSocketType;
begin
  New( sockettype );
  sockettype^ := stDealer;

  // the nil context means it will be a detached thread.
  myThread := TMyZMQThread.Create( sockettype, nil );
  myThread.Resume;
end;

  • Creating an attached thread.

    procedure TMyClass.AttachedMeth( args: Pointer; context: TZMQContext; pipe: TZMQSocket );
var
  socket: TZMQSocket;
  msg: Utf8String;
begin
  while not context.Terminated do
  begin
	// do some cool stuff.
	socket := Context.socket( TZMQSocketType(Args^) );
	
	// you can use pipe to communicate.
	pipe.recv( msg );
  end;
end;

var
  thr: TZMQThread;
  sockettype: ^TZMQSocketType;
begin
  New( sockettype );
  sockettype^ := stDealer;
  thr := TZMQThread.CreateAttached( AttachedMeth, context, sockettype );
  thr.FreeOnTerminate := true;
  thr.Resume;


  // use thr.pipe to send stuff to the thread.
  thr.pipe.send( 'hello thread' );
end;

  • or

    // create descendant class
TMyZMQThread = class( TZMQThread )
protected
  procedure doExecute; override;
end;

procedure TMyZMQThread.doExecute
var
  socket: TZMQSocket;
  msg: Utf8String;
begin
  // do something cool.
  socket := Context.socket( TZMQSocketType(Args^) );
  while true do
  begin
	pipe.recv( msg );
  end;
end;

var
  myThread: TMyZMQThread;
  sockettype: ^TZMQSocketType;
begin
  New( sockettype );
  sockettype^ := stDealer;

  myThread := TMyZMQThread.Create( sockettype, context )
  myThread.Resume;

  myThread.pipe.send( 'Hello thread' );
end;

Examples

examples are in the zguide examples/Delphi folder.

Changes

  • TZMQThread class
  • Fixed bug in context.Destroy
  • New poller class
  • poll function of TZMQPoller has a new optional parameter "pollCount".
  • Upgrade dll-s to v3.2.2 RC2
  • New monitoring logic implemented.
  • Default ZMQ version for the binding is now 3.2 ( can switch back to 2.2 by not defining zmq3 in the zmq.inc file )

Authors

The following people have contributed to the project:

Balazs Varga <[email protected]>
Stathis Gkotsis <[email protected]>
Stephane Carre <[email protected]>

Copying

Free use of this software is granted under the terms of the GNU Lesser General Public License (LGPL). For details see the files COPYING.LESSER included with the distribution.