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The Actual-Time Control System (RCS) library is really a class library meant for multi-platform real-time distributed applications. Nowadays there are 2 versions from the library, one out of C++ and yet another in Java. The Java version presently doesn’t provide all the functionality from the C++ version, however the client-side communications courses of instruction for NML happen to be re-designed in Java. This document describes using the Neutral Message Language (NML) aspects of the library.

The Communication Management System (CMS) provides use of a set-size buffer of general data to multiple readers or author processes on a single processor, across a backplane, or higher a network. Whatever the communication method needed, the interface to CMS is uniform. Methods are supplied to encode all the fundamental C/Java data types inside a machine independent or neutral format, and also to send them back towards the native format. A CMS_HEADER is put into each buffer which supplies details about if the buffer continues to be written or read from last, if the buffer is totally new to particular process and how big the final email the buffer. CMS utilizes a configuration file to ensure that users can alter communications protocols or parameters without recompiling or relinking the applications.

The Neutral Message Language (NML) supplies a greater level interface to CMS. It possesses a mechanism to handle multiple kinds of messages within the same buffer in addition to simplifying the interface for encoding and decoding buffers in neutral format and also the configuration mechanism.

The figure below illustrates the dwelling of the RCS application using NML. The applying is shipped across three computers.

Narima lopes nml writing services the server in

Processes 1, 2, and three can write into the shared memory buffers they will use since they’re found in the same computer or backplane. It’s because of this that they’re labeled “LOCAL”. Processes 4,5 and 6 are only able to connect to the buffers with an NML Server and therefore are therefore labeled “REMOTE”. The outline should be complicated inside a system with buffers in several machine. Processes would then have to be referred to as local or remote regarding a specific buffer.

NML servers should be run for every buffer that’ll be utilized by remote processes. They read towards the buffer in the same manner as local processes around the account of remote processes.

NML uses configuration files to keep details about which processes talk to which buffers and just how. The majority of the possibilities to NML programmers are selected by indicating them within the configuration file. (The configuration files are ascii text files having a format described under “Writing NML Configuration Files” .)

NML is message-based instead of stream-based. Each effective read operation retrieves the information submitted exactly one write operation. Unless of course queuing is enabled, each write operation moves one message in to the buffer replacing any previous message.

Several kind of message can be delivered to exactly the same buffer so a distinctive type identifier is definitely within the message. Following a read operation, the procedure must make use of this identifier to look for the kind of message before using the data within the message.

Narima lopes nml writing services removed from the queue

Each kind of message implies a specific data structure. Most messages are user-defined.

Messages are known as encoded should they have been converted right into a machine-independent or neutral format like the exterior Data Representation (XDR). Buffers are known as encoded when the messages inside them should be encoded that is established within the configuration file. NML servers can encode and decode messages with respect to remote processes. An NML vocabulary defines the group of messages which may be utilized in a credit card applicatoin and offers the required functions for encoding and decoding the messages.

All the necessary header files is going to be incorporated if rcs.hh is incorporated.

The next classes supply the programming interface for CMS and NML:

These courses are detailed within the following sections.

NML Application Structure

The following figure shows the dwelling of merely one concurrent process module using NML (the memory buffer seems to become close to the applying)

The applications routines initialize and employ objects from class NML and NMLmsg which rely on some user-defined functions. The format function selects from some user defined update functions for every aggregate type the consumer will have to pass towards the memory buffer. The update function for every aggregate type is made by updating each member individually using CMS routines for that fundamental C data types. These fundamental update routines email and browse from internal CMS buffers that are themselves read or written to memory buffers that are offered with other concurrent processes while using CMS Communications Routines.

Because NML is configurable, programmers can pick between protocols with greater performance but which can be smaller or want more costly hardware or individuals which are less restrictive or require less costly more broadly available hardware. By looking into making a buffer close to a procedure you are able to enhance the performance of this process. By moving processes you might be able to lessen the strain on one CPU or increase the amount of processes able to utilize the faster local protocol. Using servers to supply remote use of buffers frees local processes from being slowed lower through the communications with remote processes. Presently the NML communications servers and many-likely the actual-time modules have to be designed in C++, however GUI’s, diagnostics tools, and 2nd floor supervisors with less-rigid time deadlines could be designed in Java and employ NML to talk with C++ areas of the applying.

A controller for any robot must poll a number of inputs and carry out some computations every “n” milliseconds along with a remote supervisor will be able to look into the status from the robot if needed.

The following figure shows one possible the perception of this application. Since the controller can write straight to the shared memory buffer, writing the status requires a minimum here we are at the controller. While using NML server enables the supervisor to become located almost anywhere as well as on just about any host.

Review of Design Suggestions.

  1. Avoid overloading any CPU by assigning a lot of ways to it or creating a single process which should do an excessive amount of work.
  2. Place buffers so they might be utilized in your area through the most time-critical process(es).
  3. Make use of the “LOCAL” protocol whenever you can.
  4. Just use neutrally encoded buffers at the appropriate interval.(i.e. backplane communications between various kinds of processors)

NML applications programmers need to produce a message vocabulary and connected format function, write a configuration file, create an NML object, and employ the read member functions.

The content vocabulary is some C++/Java classes, produced from NMLmsg, which may be regarded as data structures which are copied in to the NML buffer throughout a write operation, and copied out throughout a read operation. Each class is connected having a unique identifier, an optimistic integer, that enables readers to recognize which message exists within the buffer. Aside from the particular data people from the class, each class also needs an update function which calls CMS techniques to convert the information people to types CMS are designed for. Presently, CMS provides support for that fundamental C/Java language built-in types. However, stay away from enums or lengthy doubles in NML messages. (See “Problem Solving – Inadequate Arguments Error” )

To allow CMS to neutrally format the information within the buffer in order to allow NML servers to encode and decode the information for remote processes, a format function is needed. This format function is simply a switch statement, connecting NML identifiers using the update functions of particular NML message classes. The format function could be by hand programmed and so will be described below, or it may be instantly generated while using NML Code Generator .

Files needed let’s imagine include: nml_ex1MsgDict.java, EXAMPLE_MSG.java

Both EXAMPLE_MSG.java, and nml_ex1MsgDict.java were produced by nml_ex1.hh while using NML Code Generator. nml_ex1.hh can also be utilized in the C++ examples.

/* *New Java File starts here. *This file ought to be named nml_ex1_MsgDict.java *Instantly generated by NML CodeGen Java Applet. *with command line arguments. generate_for_java=true generate_for_cpp=false HHFile=nml_ex1.hh *RCS_VERSION=2009.12.17_1575* *.gen script. *:load nml_ex1.hh *1:obvious *2:select_from_file nml_ex1.hh *3:generate Java dictnml_ex1_MsgDict.java *4:generate Java classes * *5:exit * */ // Import NML classes and interfaces import rcs.nml.* import java.util.Hashtable /* *Class definition for nml_ex1_MsgDict *Instantly generated by NML CodeGen Java Applet. */ public class nml_ex1_MsgDict implements NMLMessageDictionary < // Define an object of every message class. private EXAMPLE_MSG EXAMPLE_MSG_object = null; // ID Type Constants public static final int EXAMPLE_MSG_TYPE = 101; // Sizes useful for C++ compat and preallocating byte storage. //(not used for normal NML reads/writes). public long getEstimatedSize(final int _type) < switch(_type) < case EXAMPLE_MSG_TYPE: /*101*/ return 232; default: break; > return 232 /* maximum */ > public lengthy getMaxEstimatedSize() < return 232; > //Define an NML_ENUM_INFO object for that type ID’s NML_ENUM_INFO nml_enum_info_for_type_names =null //Produce a constructor to put together the NML_ENUM_INFO object. public nml_ex1_MsgDict() < nml_enum_info_for_type_names= new NML_ENUM_INFO(); nml_enum_info_for_type_names.name="nml_ex1_MsgDict"; Hashtable h1 = new Hashtable(); Hashtable h2 = new Hashtable(); Integer I = null; String S = null; I=new Integer(EXAMPLE_MSG_TYPE); S="EXAMPLE_MSG"; h1.put(I,S); h2.put(S,I); nml_enum_info_for_type_names.int_to_string_hash=h1; nml_enum_info_for_type_names.string_to_int_hash=h2; > // Miscellaneous Pre-Defined Values // Enumerated Type Constants // NML Format Function public int formatMsg(NMLFormatConverter nml_fc) < int return_val=0; nml_fc.check_type_info(nml_enum_info_for_type_names); switch(nml_fc.msg_type) < case EXAMPLE_MSG_TYPE: /*101*/ if(null == EXAMPLE_MSG_object) < EXAMPLE_MSG_object = new EXAMPLE_MSG(); > nml_fc.msg_to_update = EXAMPLE_MSG_object EXAMPLE_MSG_object.update(nml_fc) break default: return_val=-1 break > return(return_val) > > /* *New Java File starts here. *This file ought to be named EXAMPLE_MSG.java */ // Import all NML, CMS, and RCS classes and interfaces import rcs.* import rcs.nml.* import rcs.nml.NMLFormatConverter import rcs.nml.NMLMessageDictionary import rcs.nml.NMLmsg import rcs.nml.RCS_CMD_MSG import rcs.nml.RCS_STAT_MSG /* *Class definition for instance_MSG *Instantly generated by RCS Java Diagnostics Tool. *on Thu Jun 05 13:38:12 EDT 1997 */ public class EXAMPLE_MSG extends NMLmsg < float f = 0; byte c = 0; int i = 0; // Constructor public EXAMPLE_MSG() < super(101); > public void update(NMLFormatConverter nml_fc) < super.update(nml_fc); f = nml_fc.update(f ); c = nml_fc.update(c ); i = nml_fc.update(i ); > >

Both of these files may be generated using the command.

java -jar CodeGenCmdLine.jar generate_for_java=true generate_for_cpp=false nml_ex1.hh

Regardless of whether you create the source files or download them, the ought to be compiled with this particular command.

javac -classpath rcs.jar EXAMPLE_MSG.java nml_ex1_MsgDict.java

It is perfectly normal to determine the next notes. (We’re able to alter the code to make use of safer checked functions however the code would no more compile with older jdk’s. The files rcs.jar and CodeGenCmdLine.jar can be found around the NIST ftp site o r could be constructed with the rcslib found in the bin directory or plat/java/lib directory.

Note: nml_ex1_MsgDict.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details.

NOTE: All of the NML updates are similar with the exception that your body should call the NMLFormatConverter update function for every member within the class. The update function continues to be overloaded to simply accept references to all the fundamental data types (ints, floats, etc.) With respect to the NMLFormatConverter mode the update functions will either store their argument inside a neutrally encoded buffer or decode the buffer and keep output within the variables passed towards the update functions. Just like the format function, the update functions could be either by hand coded or generated instantly using the NML Code Generator.

NMLConnection has lots of constructors, but many users uses the next.

NMLConnection(NMLMessageDictionary msg_dict, String buf, String proc, String file) throws NMLException

The parameters are:
msg_dict = message dictionary resist use
buf = name from the buffer to hook up with as specified by configuration file
proc = name to which to gain access to the buffer
file = name from the configuration file

/* nml_ex2.java */ //Import the custom message dictionary // Normally you might have something similar to import package.nml_ex1_MsgDict // consider we’re not using packages we do not require the import. // Import all NML, CMS, and RCS classes and interfaces import rcs.* import rcs.nml.* public class nml_ex2 < public static void main(String args[]) throws Exception < /* NML( format function, buffer name, process name, configuration file ) */ NMLConnection example_nml = new NMLConnection(new nml_ex1_MsgDict(), "ex_buf1","ex2_proc", "ex_cfg.nml"); > >

javac -classpath rcs.jar nml_ex2.java nml_ex1_MsgDict.java EXAMPLE_MSG.java

To operate it you have to begin the server without anyone’s knowledge. The server should be designed in C++ and it is example 9 within the NML C++ Programmer’s Guide .

# Compile command depends upon OS and compiler versions. g++ nml_ex9.cc nml_ex1.cc rcslib/lib/librcs.a -lpthread -o nml_ex9 ./nm_ex9

To operate the java application.

java -classpath rcs.jar nml_ex2

This situation commonly has no output or effect.

Fundamental essentials member functions accustomed to perform reads:

  • public NMLmsg look() throws NMLException ()
    Read an NMLmsg but don’t alter the was_read flag.
  • public String peekDataString() throws NMLException ()
    Reads an NMLmsg using look() and converts it to some String.
  • public NMLmsg read() throws NMLException ()
    Read a NMLmsg.
  • public String readDataString() throws NMLException ()
    Reads an NMLmsg and converts it to some String.

There’s a noticeable difference between these characteristics and also the C++ versions. The C++ functions NML::read() and NML::look() return an integer indicating which kind of message or no was read and also the actual information is stored in the region available by calling NML::get_address(). However in java these characteristics return references to NMLmsg objects or null if there wasn’t any message to see, and there’s no get_address function. (References are as near as Java will get to pointers.) This is because Java has two features that aren’t generally obtainable in C++: Run-time type checking and automatic garbage collection. In Java, it’s not easy to simply create one static memory place to deposit all of the NML messages recieved there, however when the objects are produced, casting these to the incorrect class leads to a ClassCastException unlike C++ which may let the item be utilized in inappropriate ways as lengthy because there was an explicit cast.

If the error occurs which makes it impossible to see out of this NML buffer, an NMLException is tossed.

Look works exactly like read with the exception that the flag that lets others know once the buffer is read isn’t altered and when queuing is enabled the content isn’t taken off the queue. This may be helpful if you want to monitor a buffer without letting other processes while using buffer know.

javac -classpath rcs.jar nml_ex3.java nml_ex1_MsgDict.java EXAMPLE_MSG.java

To operate it you have to begin the server without anyone’s knowledge. The server should be designed in C++ and it is example 9 within the NML C++ Programmer’s Guide .

# Compile command depends upon OS and compiler versions. g++ nml_ex9.cc nml_ex1.cc rcslib/lib/librcs.a -lpthread -o nml_ex9 ./nm_ex9

To operate the java application.

java -classpath rcs.jar nml_ex3

By trying to operate this situation, it’ll watch for something to become written in to the buffer. To create something in to the buffer, you should use the instance in “Writing NML Data”. Additionally, you will require an NML server. This program nml_ex9 that is described within the C++ form of this informative guide under “While using run_nml_servers function.” can be used the NML server.

Fundamental essentials member functions accustomed to perform writes:

write public int write(NMLmsg msg)
Writes an NMLmsg. Parameters: msg – the NMLmsg to create. Returns: when the writ*e was effective, -1 if there is a mistake writeDataString public int writeDataString(String dataString)
Convert a String for an NMLmsg after which write it towards the buffer. Parameters: dataString – string to create Returns: when the write was effective, -1 otherwise

The same as the write_if_read() function in C++ is not implemented yet.

javac -classpath rcs.jar nml_ex4.java nml_ex1_MsgDict.java EXAMPLE_MSG.java

Before you run start the NML server, see previous examples.

To operate the java application.

java -classpath rcs.jar. nml_ex4

It ought to print:

Sent message: f = 3.14, c = 49, i = 1024

This situation writes a note right into a buffer. To see the content make use of the example in Studying NML Data

Errors from NML could be worked with increased rigorously by catching NMLException.

Last Modified: February 1,2010

For those who have questions or comments in regards to this page or you want to be notified of changes towards the RCS library via email, please contact Will Shackleford at shackle@cme.nist.gov

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