Ipc

General info

Interprocess communication in Hall B is based on package located in $CLON/src/ipc. Currently it is based on ActiveMQ, which can be replaced with another messager if necessary, for example jlab-developed xMsg. Switching between messagers is done by changing $CLON/src/Makefile.include and recompiling entire $CLON area. ActiveMQ or any other messager must be installed in /usr/local/src area.

Top level classes can be found in $CLON/src/ipc/ipc.s/ipc_lib.h, test program is $CLON/src/ipc/main/ipc_client.cc.

Sender subscribes to the 4-field topic

"TOPIC1"."TOPIC2"."TOPIC3"."TOPIC4"

and start message from message header in a form of character string

(char *)"FORMAT:TOPIC4:TOPIC3:TOPIC2:TOPIC1"

with following format:

Topic (defaults are NULL or '*'):

TOPIC1 - usually getenv("EXPID")
TOPIC2 - usually getenv("SESSION")
TOPIC3 - message class, for example 'control', 'epics', 'daq' etc
TOPIC4 - unique name of sender, usually program name

Message header:

FORMAT - message format, for example 'cmd', 'json' etc, 'MessageActionXXXX.h' must be provided for every format
TOPIC4 (optional, but preferrably sender program name)
TOPIC3 (optional, usually not used)
TOPIC2 (optional, usually not used)
TOPIC1 (optional, usually not used)

Typical user code includes following:

#include "ipc_lib.h"

#include "MessageActionControl.h"

#include "MessageActionXXXX.h" // XXXX is particular listener, like MessageActionEPICS.h

IpcServer &server = IpcServer::Instance(); // get ipc server instance, it is implemented as singleton

main()
{
  // following call sets topic for sender ("par1.par2.par3.par4") and receiver ("par1.par2.par5.par6")
  // 1st and 2nd params - usually EXPID and SESSION, or EXPID and NULL
  // 3rd and 4th params - 'class' and 'destination' for sender only, for example 'epics' and 'dbrouter' (sending to class 'epics' and destination 'dbrouter')
  // 5th and 6th params (optional) - 'class' and 'destination' for receiver only, for example 'epics' and '*' (listen for messages with class 'epics' and any destination)
  // for example:
  server.init(getenv("EXPID"), getenv("SESSION"), (char *)"epics", (char *)"dbrouter", (char *)"epics", (char *)"*");

  MessageActionControl  *control = new MessageActionControl((char *)"myname");
  MessageActionXXXX        *xxxx = new MessageActionXXXX();

  server.addActionListener(control);
  server.addActionListener(xxxx);

  server << clrm << ...stuff... << endm;

  server.close();
}

MessageActionControl.h

Sends commands and receives status. Command message sent by program 'myname' must has following format:

server.init(getenv("EXPID"), getenv("SESSION"), "control", destination);
server << clrm << "command:myname" << "quit" << endm;        // request to quit
server << clrm << "command:myname" << "status" << endm;      // request for status
server << clrm << "command:myname" << "statistics" << endm;  // request for statistics

If information is requested, program suppose to send back following:

server << clrm << "status:myname" << nelem << elem1 << elem2 << .. << endm;
server << clrm << "statistics:myname" << nelem << elem1 << elem2 << .. << endm;

In examples above message header contains two parts: message format and sender name, that header form shell be typically used for all messages in CLAS12.

MessageActionEPICS.h

Sends and receives EPICS messages. Message sent by program 'myname' must has following format:

server.init(getenv("EXPID"), getenv("SESSION"), "epics", destination);
server << clrm << "epics" << "myname" << "hostname" << "username" << unix_time << "channel_name" << "channel_type" << Nelements << element1 << element2 << ... << endm;

"channel_type" can be one of following:

char
uchar
short
ushort
int
uint
float
double
string (NOTE: 'Nelements' for 'string' can only be 1, array of strings not supported yet)