How (GA) Global array library (an implementation of ARMCI) is used for communication between two process located on different remote machines.
Is that something similar to TCP socket programming where one process wait for data and the other transfers it ?
I try to see the documentation that ga_put() and ga_get() are two operation that used for inter-process communication. till now I only able to come up with a program running on the same machine that use shared-Memory architecture (I have used ga_put() and ga_get() to put data in Global array and to get it respectively ).
Now, I want use this program for communicating data (basically performaning one-sided communication) between two remote processes. Obiviously putting the program that I am running on single machine on the remote side will work out. It needs some way to tell which machine should we access and get the right data. And here is where I need your help. how can I do this? (what is its equivalent of TCP/IP listen, accept and connect ... on GA ? )
Or is that the case that GA also uses TCP/IP socket underneath ?
can some one please explain to me? and sample code of two remote processes communicating is also appreciable.
thanks,
I am answering my question after all. May be it will help some one looking for the same issue.
GA Library is implemented to work with MPI. So we have something like:
MPI_Init(..)
GA_Initialize()
MA_Init(..)
// .... do sothing here
GA_Terminate()
MPI_Finalize()
The answer to my question is:
MPI has the following primitives to be able to support client-server commuication:
//in the server side
MPI_Open_port()
MPI_Comm_accept()
//do MPI_Send() or MPI_Recv()
MPI_Close_port()
//client Side
MPI_Comm_connect()
//do MPI_Recv() or MPI_Send()
depending on the hardware support and the MPI implementation used, MPI might use sockets, or other mechanisms (e.g SAN (System area network)).
In general, most MPI implementations use sockets for TCP based communication.
So, yes GA also uses sockets underneath (of course depending on the MPI implementation used)
cheers,
Related
I've been asked to implement VPN capabilities in an existing software project on an embedded system, in order to make the device available via network to an external server while avoiding trouble with firewalls (no need for encryption, just to make it accessible).
Unfortunately, the embedded system is based on a Cortex-M4 MCU, therefore Linux, which would allow for VPN nearly out of the box, is not an option. All I've got is an RTOS and a working LwIP stack.
I've used VPNs in the past. However, my network knowledge is rather limited concerning implementing VPNs, so I'm rather stumped. As I think, I'd use the current LwIP instance for building up the tunnel connection, and the application would use a second instance for the actual network communication, while the network interface of the second instance is a virtual one (like a tap device on linux), encapsulating its low level data and tranceiving it via the tunnel connection of the first LwIP instance.
Maybe this way I'd be able to create a custom solution for the problem, but the solution should conform to any standards (as the server will be any kind of sophisticated system).
So I wonder if anyone has been confronted with a task like this, and would appreciate any hint what to do, at least a direction where to look at.
Thanks in advance!
I want to create a proxy server which routes incoming packets from REQ type sockets to one of the REP sockets on one of the computers in a cluster. I have been reading the guide and I think the proper structure is a combination of ROUTER and DEALER on the proxy server. Where the ROUTER passes messages to the dealer to be distributed. However, I cannot figure out how to create this connection scheme. Is this the correct architecture? If so how to I bind a dealer to multiple addresses. The flow I envision is like this REQ->ROUTER|DEALER->[REP, REP, ...] where only one REP socket would handle a single request.
NB: forget about packets -- think in terms of "Behaviour", that's the key
ZeroMQ is rather an abstract layer for certain communication-behavioral patterns, so while terms alike socket do sound similar to what one has read/used previously, the ZeroMQ-world is by far different from many points of view.
This very formalism allows ZeroMQ Formal-Communication-Patterns to grow in scale, to get assembled in higher-order-patterns ( for load-balancing, for fault-tolerance, for performance-scaling ). Mastering this style of thinkign, you forget about packets, thread-sync-issues, I/O-polling and focus on your higher-abstraction-based design -- on Behaviour -- rather than on underlying details. This makes your design both free from re-inventing wheel & very powerful, as you re-use a highly professional tools right for your problem-domain tasks.
DEALER->[REP,REP,...] Segment
That said, your DEALER-node ( in fact a ZMQsocket-access-node, having The Behaviour called a "DEALER" to resemble it's queue/buffering-style, it's round-robin dispatcher, it's send-out&expect-answer-in model ) may .bind() to multiple localhost address:port-s and these "service-points" may also operate over different TransportClass-es -- one working over tcp://, another over inproc://, if that makes sense for your Design Architecture -- ZeroMQ empowers you to use this transparently abstracted from all the "awfull&dangerous" lower level gritty-nitties.
ZeroMQ also allows to reverse .connect() / .bind()
In principle, where helpfull, one may reverse the .bind() and .connect() from DEALER to a known target address of the respective REP entity.
You leave a couple details out that are important to determining the correct architecture.
When you say "from REQ type sockets to one of the REP sockets on one of the computers in a cluster", how do you determine which computer gets the message? Is it addressed to a specific computer? Does a computer announce its availability before it can receive a message? Does each message just get passed to the next one in line in a round-robin fashion? (if it's not the last one, you probably don't want a DEALER socket)
When you say "how do I bind a dealer to multiple addresses", it's not clear what you mean by "addresses"... Do you mean to say that the proxy has a unique IP address that it uses to communicate with each computer in the cluster? Or are you just wondering how to manage the connection to multiple different peers with the same socket? The former is a special case, the latter is simple.
I'm going to work with the following assumptions:
You want a worker computer from the cluster to announce its availability for work before it receives any work, and any computer in the cluster can handle any job. A faster worker, or a worker working on a smaller job, will not have to wait behind some slow worker to finish their job and get a new job first.
The proxy/broker uses a single ip interface to communicate with all workers.
If those are true, then what you want will be closer to this:
REQ->ROUTER|ROUTER->[REQ, REQ, ...]
A worker will create a request to the backend router socket to announce its availability, and await a reply with work. Once it is finished, it will create a new request with the finished work, which again announces its availability. The other half of the pattern you've already worked out.
This is the Simple Pirate Pattern from the ZMQ guide. It's a good place to start, but it's not very robust. This is in the Reliable Request-Reply Patterns section of the guide, and I suggest you read or reread that section carefully as it will guide you well. In particular, they keep refining this pattern into more and more reliable implementations and wind up with the Majordomo pattern, which is very robust and fault tolerant. You should see if you need all the features that provides or if you can scale it back a little. Either way, you should learn and understand what these patterns are doing and why before you make the choice to do something different.
I'm dealing with network programming (especially P2P systems) lately. The usual program I deal with, somewhere has something like this (running in it's own thread):
while True:
handle(receive())
How do I deal with a series of dependent send/receive actions. For example when I want to have something like:
def inviteNode(receiver):
send(receiver, INVITE)
if receive() == OK:
send(receiver, SOME_INFORMATION)
...
I mean several send/receive actions that depend on each other and have a certain order. It would be nice to have something like the inviteNode() above (because all steps of the protocol are at the same location in the code, and you can retrace the order just by looking at the code), but receive() calls outside of my listen loop just won't do it, because how should it be decided which receive() gets to receive the data.
Is having a global state the only solution for this? After doing the first send(receiver, INVITE) do I have to memorize somewhere, that I expect to receive an OK from that specific Node, I just sent the INVITE to? Isn't this very complex when I have several different of these dependent send/receive actions?
PS: Just to make sure: This is about UDP connections.
Seems like you need to use the sockets polling. You can use select() system call (cross-platform solution, but it's not so fast as it can be with special, system dependent API) or if you're targeting linux, you can try to use the epoll API.
The main idea is: you have some network sockets, those can be in different states (for example, the data can be received).
You can query this socket set for some events (Read,Write,Exception) and perform needed actions dependent on what you need.
For example, Nginx http server uses this architecture.
Also, you will need to save the context, for example which sockets should be notified and checked and what data was already received or sended, and other information you may need.
This is a bit complex but can do the job: finite-state machines.
http://linux.die.net/man/2/select
http://msdn.microsoft.com/en-us/library/windows/desktop/ms740141%28v=vs.85%29.aspx
I would like to be able to communicated with PLC controllers, so that I can send and receive custom commands on the PLC.
My idea of being able to do this was to have a TCP listener on the PLC that could read TCP incoming packets on a specific port, and execute routines based on the commands in the packets. It could also send information back via TCP/IP.
This would allow me to write software in multiple languages such as C#, PHP, JavaScript, etc. so that software can be used on any platform such as Windows, iOS, Android, etc. to issue commands to the PLC. This would also mean you do not need the PLC software (which can be costly) to view or control the PLC.
I am not a PLC programmer, so I do not know if PLC has the capability of sending and receive custom TCP packets. I would like to know that a) if it is possible b) how feasible it would be to do this and c) what exactly I should research so that I can accomplish this.
Thanks.
It sounds a bit like reinventing the wheel. You want to make something like KepServerEX?
http://www.kepware.com/kepserverex/
There are also two things to consider - one is the ability to interface with the PLC to share data (ie: for a custom HMI) and the other is to program the PLC. For the latter you still need the control software from the manufacturer unless you're willing to reverse engineer and re-write it from the ground up.
Keep in mind, also, that PLCs don't work the same way that other software does. There are no functions or procedures or classes or objects or even really any "commands", per se. A PLC is a system which executes a continuous fixed program of mostly raw logic rules and calculations. A typical interface to an HMI involves reading and writing directly to/from logic bits and word data (ie:hardware memory locations) which represent the current state of the machine. OPC already does this just fine so I'm not quite sure what you're going for.
If you're looking for a cheap/free alternative to a full commercial package, something here may work for you :
http://www.opcconnect.com/freesrv.php
If I understand correctly, when referred to "Run/Stop" you mean for the PLC to 'Start' or 'Stop' scanning the code and updating its I/O. If this is the situation, it would be perfectly suitable to add a Scan_If_On bit (which will be written by a TCP Command) in parallel connection with the "Start" bit controlled by the HMI.
This way, there will be 2 forms of "Starting" the process controlled by the PLC. HMI and TCP.
I have a client which sends data via UDP-broadcast. (To let's say 127.0.0.255:12345)
Now I want to have multiple servers listening to this data. To do so on a local machine, they need to share the port 12345 for listening.
My question is, if that is possible, if there are any disadvantages and if there could be problems with this approach.
There is one alternative which unfortunately brings with a lot of overhead:
Implement some kind of registration-process. On startup, each server tells the client its port. The client then sends the messages to each port (having to send the data multiple times, some kind of handshaking needs to be implemented...)
Do you know any better alternative?
If that matters:
I'm using C++ with Boost::Asio. The software should be portable (mainly Linux and Windows).
You will have to bind the socket in both processes with the SO_REUSEPORT option. If you don't specify this option in the first process, binding in the second will fail. Likewise, if you specify this option in the first but not the second, binding in the second will fail. This option effectively specifies both a request ("I want to bind to this port even if it's already bound by another process") and a permission ("other processes may bind to this port too").
See section 4.12 of this document for more information.
This answer is referenced to the answer of cdhowie, who linked a document which states that SO_REUSEPORT would have the effect I'm trying to achieve.
I've researched how and if this option is implemented and focused mainly on Boost::Asio and Linux.
Boost::Asio does only set this option if the OS is equal to BSD or MacOSX. The code for that is contained in the file boost/asio/detail/reactive_socket_service.hpp (Boost Version 1.40, in newer versions, the code has been moved into other files).
I've wondered why Asio does not define this option for platforms like Linux and Windows.
There are several references discussing that this is not implemented in Linux:
https://web.archive.org/web/20120315052906/http://kerneltrap.org/mailarchive/linux-netdev/2008/8/7/2851754
http://kerneltrap.org/mailarchive/linux-kernel/2010/6/23/4586155
There also is a patch which should add this functionality to the kernel:
https://web-beta.archive.org/web/20110807043058/http://kerneltrap.org/mailarchive/linux-netdev/2010/4/19/6274993
I don't know if this option is existing for Windows, but by defining portable as an attribute for software which runs on Linux too, this means, that SO_REUSEPORT is OS specific and there is no portable solution for my question.
In one of the discussions I've linked it is recommended for UDP to implement a master-listener which then provides the incoming data to multiple slave-listeners.
I will mark this answer as accepted (though feeling kind of bad by accepting my own answer), because it points out why the approach of using SO_REUSEPORT will fail when trying to use it with portable software.
Several sources explain that you should use SO_REUSEADDR on windows. But none mention that it is possible to receive UDP message with and without binding the socket.
The code below binds the socket to a local listen_endpoint, that is essential, because without that you can and will still receive your UDP messages, but by default your will have exclusive ownership of the port.
However if you set reuse_address(true) on the socket (or on the acceptor when using TCP), and bind the socket afterwards, it will enable multiple applications, or multiple instances of your own application to do it again, and everyone will receive all messages.
// Create the socket so that multiple may be bound to the same address.
boost::asio::ip::udp::endpoint listen_endpoint(
listen_address, multicast_port);
// == important part ==
socket_.open(listen_endpoint.protocol());
socket_.set_option(boost::asio::ip::udp::socket::reuse_address(true));
socket_.bind(listen_endpoint);
// == important part ==
boost::array<char, 2000> recvBuffer;
socket_.async_receive_from(boost::asio::buffer(recvBuffer), m_remote_endpoint,
boost::bind(&SocketReader::ReceiveUDPMessage, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)