INTRODUCTION

C-API: MQ_C_API - theLink - a API to link multiple package-items together to act as one application …

PHILOSOPHY

The theLink project is an infrastructure that allows multiple package-items to be linked together to act as one application.
To link, you need to distribute the work from one package-item to another package-item and wait for an answer or not.

Philosophy: Write Once → Run Everywhere

The package-item can be a thread, a separate local process that is started by fork or spawn, or even a network of multiple services on multiple hosts.

The package-item can be written in any language that is supported by the Programming-Language-Micro-Kernel (PLMK) support.
It even supports running multiple programming languages in a single piece of software.
Supported Languages are: (C,C++,C#,VB.NET,Java,Python,Ruby,Perl,PHP,Tcl or GO)

Strategy: It takes 4 years to write a programming-language, but it only takes 4 weeks to insert a micro-kernel.

The package-item is connected to one another via a pipe or a socket and is based on packages which are sent from one package-item to another package-item and back.

Conclusion: theLink is used to manage a network of multiple package-items using an API that is available in all major programming-languages.

PROGRAMMING

theLink is responsible for:

establishing and managing the package-items, local or remote
establishing and managing the connections between package-items
establishing and managing the routing between package-items
sending and receiving the package data, calling up a service
reading and writing data from or into a data-package
setup and maintain event-handling and scheduling
interception, distribution and processing of error messages

The LibMsgque library is separted into three programming-layers:

The foundation-layer, used by theLink library programmer
The kernel-layer, used by the Programming-Language-Micro-Kernel programmer
The implementation-layer, used by the target-language programmer

foundation-layer

The foundation-layer implement the libmqmsgque library and is also responsible for the quality-target of the entire project.

establishing and managing the package-items
establishing and managing the connections
memory-management and garbage-collection
error-handling
logging and debugging
written in plain C

kernel-layer

The kernel-layer implement the Programming-Language-Micro-Kernel and is also responsible to generate and maintain the target-language-API source-code.

implementation of the managed-object technology
implementation of the token-stream-compiler technology
written in plain C, TCL and the target-language-API

implementation-layer

The implementation-layer is the API used by the target-language-programmer.

written in plain Target-Programming-Language (TPL)

Target: !! This documentation describe the implementation-layer and target the Java programmer. !!

SERVICE CALL

C-API: MqContextC_ServiceApi_C_API - MqContextC - create and manage a service …

To provide a service is the main purpose of a server and the main-purpose of a client/server connection is to call a service and to process the result.
A service can be defined on the server or on the client. On the server a service can be initial setup with IServerSetup method and finally cleanup with IServerCleanup.

‍A service is created with the MqServiceCreate and deleted with the MqServiceDelete.

A service can be created and deleted during the entire life-cycle of the server or the client. If the server/client-context is deleted all services of the are deleted also.

‍A MqServiceDelete is not required.

Creating or deleting a service is like granting or revoking the right to access a single feature.

eventloop

To receive a data-package on a service the event-loop have to be active. The event-loop ia always active on an synchronous-service-call . On a server the event-loop is started with MqProcessEvent at startup.

synchronous-service-call: A synchronous-service-call always block and enter the event-loop to wait for an answer

asynchronous-service-call: A asynchronous-service-call always return immediately and the possible result is received on a callback

callback

A callback is the function called by a service and required to receive data from remote.
A callback is created with MqServiceCreate or is part of the service-call.
A callback can be a service-identifer or a service-callback.

service-call with callback: SendEND_AND_CALLBACK, SendEND_AND_SUB, SendEND_AND_TRANSACTION

service-call without callback: SendEND, SendEND_AND_WAIT

Example from MyServer.java → define the service SRV1 on the server-link-setup

package example;

import jvmsgque.mkkernel.*;
import jvmsgque.mqmsgque.*;

// package-item
final class MyServer extends MqContextC implements IServerSetup {

  // Factory Constructor
  public MyServer(MqContextC tmpl) {
    super(tmpl);
  }

  // service to serve all incoming requests for token "HLWO"
  class MyFirstCallback implements MqServiceIF {
    public void Callback(MqContextC ctx) {
      SendSTART();
      SendSTR(ReadSTR() + " World");
      SendRETURN();
    }
  }

  // define a service as link between the token "HLWO" and the class "MyFirstService"
  public void ServerSetup() {
    ServiceCreate("HLWO", new MyFirstCallback());
  }

  // -------------------------------------------------------------

  // package-main
  public static void main(String[] argv) {
  
    // create the "MyServer" factory… and return the initial (top) object
    MqContextC srv = MqFactoryC.Add(MyServer.class).New();

    try {
      srv.LinkCreate(argv);
      srv.ProcessEvent(MqWaitOnEventE.FOREVER);
    } catch (Throwable e) {
      srv.ErrorCatch(e);
    }
    srv.Exit();
  }
}

asynchronous-service-call

A asynchronous-service-call always return immediately and the possible result is received on a callback.

SendEND	MqContextC - finish the send-data-block and call synchronous/asynchronous a remote-service …
SendEND_AND_CALLBACK	finish the send-data-block, call the remote service, do not-wait for the result but expect the result on a callback …
SendEND_AND_TRANSACTION	finish the send-data-block, call the remote service to do a longterm-transaction-call …

synchronous-service-call

A synchronous-service-call always block and enter the event-loop to wait for an answer.

SendEND_AND_WAIT	finish the send-data-block, call the remote service and wait for result…
SendEND_AND_SUB	finish the send-data-block, call the remote service, do wait for the result and expect multiple sub-results on a callback …

SENDING data

C-API: MqContextC_SendApi_C_API - MqContextC - construct an outgoing send-data-package …

A data-package is send in two different scenarios:

on a client to call a service on the server
on a server to answer a service call from the client

Sending data is an active task and the opposite of reading data, which is a passive task. Active means that the send process is triggered by the software workflow or by the user.
For each basic type defined in MkBufferC, there is a send function and some help functions.

Send-Safe: Sending data is an atomic task and must not be interrupted between MqSendSTART and MqSendEND. The MqContextC HIGH API is uninterruptible by design.
Basic rule: process first and send all data last.

If timeout != 0 is used, the application enters the event loop and waits in the current process or thread for timeout seconds until the service call is finished.
While waiting for a result, the application can continue to work on other events that are in the same or in a different process or thread.

Recursion-Safe: If another-service-call arrives while waiting for a response from a previous-service-call, the previous-service-call will NOT end until processing of the other-service-call is complete.

Example-1: a service call, send and read a data-package

On a client: perform a service call

send the service-call	MqSendSTART → SendTT... → MqSendEND_AND_WAIT
read the result package	ReadTT... → ...

on a server: answer a service call

read the service-call	ReadTT... → ...
send the result package	MqSendSTART → SendTT... → MqSendRETURN

Important in the code from above is the last command MqSendEND_AND_WAIT because this is just one of five possibilities:

command	synchron	database	result
MqSendEND	no	no	no
MqSendEND_AND_WAIT	yes	no	single return data
MqSendEND_AND_SUB	yes	no	multiple return data
MqSendEND_AND_CALLBACK	no	no	single return data
MqSendEND_AND_TRANSACTION	no	yes	two return data

To send a data-package is one task, to send it to the right receiver is an other one. The right receiver is identified using the token parameter argument. This parameter have to be a 4 character string. You'll probably ask "why 4?" the answer is that this string should be "human" readable and easy to "compare". As solution this string is mapped to a 4 byte integer used to find the proper key/value entry in the service-hash-table on the server. (in short: to search an integer is much faster as to search a string)

Example-2: (in C) At the client, calling the service and wait for an answer

...
enum MkErrorE MyServiceCall(MQ_CTX const ctx) {
  // ... do some work
    MqSendSTART_E(ctx);                     // init the Send-Buffer object
    MqSendI32_E(ctx,int_value);               // 1. argument: a MK_I32 value
    MqSendSTR_E(ctx,"num:01");                // 2. argument: a MK_STRN value
    MqSendBIN_E(ctx,mypicture,size);          // 3. argument: a MK_BIN picture of size length
    MqSendEND_AND_WAIT_E(ctx,"SRV1",60);    // call service "SRV1" and wait max 60sec for the results
  // ... get the results
    MK_I32 retI = MqReadI32_e(ctx);           // expect ONE integer as result
  // ... do some work
    return MK_OK;
  error:                                    // default error-handler
    return MkErrorStack_1X(ctx);              // on error, build up the error-stack
}

... or using the MqContextC HIGH API

...
enum MkErrorE MyServiceCall(MQ_CTX const ctx) {
  // ... do some work
    MqSend_E(ctx, "W", "SRV1:ICB", int_value, "num:01", mypicture, size);
  // ... get the results
    MK_I32 retI = MqReadI32_e(ctx);           // expect ONE integer as result
  // ... do some work
    return MK_OK;
  error:                                    // default error-handler
    return MkErrorStack_1X(ctx);              // on error, build up the error-stack
}

Example-3: (in C) At the server, answer the service call

...
static MkErrorE SRV1(MQ_CTX const ctx, MK_PTR data) {   // the name "SRV1" can be free chosen
  // ... do some work
    MK_I32 myInt = MqReadI32_e(ctx);          // read a MK_I32 value
    MK_STRN myStr = MqReadSTR_e(ctx);          // read a MK_STR value
    MK_BUF myPic = MqReadBUF_e(ctx);          // read a MkBuffer64S object to store the picture data
  // ... do some work
    MqSendSTART_E(ctx);                     // init the Send-Buffer object
    MqSendI32_E(ctx,int_ret);                 // return argument: a MK_I32 value
  error:                                    // something is wrong, error back
    return MqSendRETURN(ctx);                   // send the package as an answer of a previous service-call
}

... or using the MqContextC HIGH API

...
static MkErrorE SRV1(MQ_CTX const ctx, MK_PTR data) {   // the name "SRV1" can be free chosen
  // ... do some work
    MK_I32 myInt = MqReadI32_e(ctx);          // read a MK_I32 value
    MK_STRN myStr = MqReadSTR_e(ctx);          // read a MK_STR value
    MK_BUF myPic = MqReadBUF_e(ctx);          // read a MkBuffer64S object to store the picture data
  // ... do some work
  error:
    return MqSend(ctx, "R", "I", int_ret);  // send the package as an answer of a previous service-call
}

READING data

C-API: MqContextC_ReadApi_C_API - MqContextC - extract data from an incoming read-data-package …

A data-package is read in two different scenarios:

on a server to serve an incoming service-call from the client
on a client to process the return-data from a previous service-call

Reading data is a passive-task and the opposite of sending data, which is an active-task. Passive means that the reading process is triggered by an incoming-data-package and not by the software workflow or by the user.
There is a read function and some help functions for each basic type defined in MkBufferC .

Read-Safe: Each service-call has a private read-data-package. This means that during a service-call that is in progress, another service-call can be served without damaging the read-data-package of the current service-call.

Type-Safe: A data-item in a read-data-package is type safe, this mean that every read of a data-item have to match the data-type of the previous write. One exception is available, the cast from and to the string data-type (TYPE=C) is allowed.

Example from server.java → read-safety: Make a nested service-call

class CSV1 implements MqServiceIF {
  public void Callback(MqContextC ctx) {
    // read the input-data from the CSV1-service-call
    // Client → server
    int inI = ctx.ReadI32() + 1;

    // call the CSV2-service at the Client, wait 10sec for timeout
    // server → Client → server
    int retI = ((int)ctx.Send("Wt", 10L, "CSV2:I@I", inI)) + 1;

    // answer the CSV1-service-call with the result from the CSV2-service-call
    // server → Client
    ctx.Send("R", "I", retI);
  }
}

STORAGE

internal storage

C-API: MqContextC_StorageApi_C_API - MqContextC - setup and manage a storage used to persist data-packages …

The storage is divided into: INTERNAL and EXTERNAL storage. Only the read-data-package can be stored or dumped into the storage.

The read-data-package is saved into the storage using:

ServiceStorage	setup a service listen on a MqContextC_ServiceApi_Identifer and save all read-data-package into the STORAGE …
StorageExport	export the read-data-package into the STORAGE …

The read-data-package is restored from the storage using:

StorageImport	import the storage-package into the read-data-package …
ProxyForward	send the entire read-data-package-data to the link-target …
All this usually happen in an Event Handler

Some important facts of the storage-feature:

The internal-storage depends on SQLite.
The package-storage can be used to save all kind of package-data.
The longterm-transaction-package-data is allways saved into storage.
By default only an in-memory storage is in use, but this can be changed with MqStorageOpen or Storage
An entire service-call can be saved with MqServiceStorage

The following internal storages are supported:

default: The default-storage is set with the configuration parameter --storage fileName and defaults to "#memdb#". If a package have to be saved into the storage and the storage is not open the default-storage id used. The open will always be performed. If an explicit storage is required the default can be changed or a storage can explicit be opened with MqStorageOpen. Keep in mind that the default-storage is a per-context configuration but only one storage per process or thread is currently supported.

memdb: This is the default storage and can be set explicitly with MqStorageOpen using the "#memdb#" parameter.

tmpdb: This storage is like an in-memory-storage but export data to the TEMPORARY filesystem if the application run out of memory. This storage can explicit be set with MqStorageOpen with the parameter "#tmpdb#".

filedb: This storage always work on files. Only this storage is persistent and can explicit be set with MqStorageOpen with the storageFile parameter.

Performance analyse:

The performance is tested with: Nhi1Exec perfclient.c --all --storage VALUE @ perfserver.c.
The parameter VALUE is set to #memdb#, #tmpdb# or a filedb file.
If –storage is not set the filedb database is used together with an internal file-name.

database	performance	host crash	application crash	info
memdb	30.000	data lost	data lost	non persistent
tempdb	< 30.000	data lost	data lost	uses memory and/or temporary file
filedb (mem)	10.000	data lost	data safe	in memory filesystem
filedb (disc)	50	data safe	data safe	disc-speed is the key factor

external storage

C-API: MqDumpC_C_API - MqDumpC - the class known as dmp or dump is used to export a jvmqmsgque data package as binary …

The dump is used to exchange data with external counterparts such as a database or a user-specific infrastructure.

There are 3 different function that deal with a dump:

The MqDumpExport export the read-data-package from the calling context to a dump.
The MqDumpImport imports the dump into the read-data-package of the calling context. All MqContextC READ API functions can be used to read the data from the read-data-package.
The MqProxyForward imports the dump into the send-data-package of the calling context. All MqContextC SEND API functions can be used to write the data into the send-data-package

See also: MqContextC PROXY API

LONG TERM TRANSACTION

C-API: MqSendEND_AND_TRANSACTION_RT - finish the send-data-block, call the remote service to do a longterm-transaction-call …

A longterm-transaction is a service-call with guaranteed delivery. guaranteed mean that the transaction is using the MqContextC STORAGE API to keep every step persistent being able to recover a step if something unexpected happen.

To link the result with the calling-environment a private transaction-item is used to save the calling-environment to the local-storage. If the local-storage is persistent, the calling-environment will even survive an application restart.
If the result from the public service-call arrives, the transaction-item will be extracted from the result and the private calling-environment will be initialized from the local-storage.

To create a persistent-transaction the MqContextC STORAGE API have to be setup as persistent. By default, an in-memory MqContextC STORAGE API is used.

The longterm-transaction-call has TWO results…

the FIRST result is a acknowledge that the longterm-transaction was stored in the remote database
the SECOND result is the result of the service-call

In difference to MqSendEND_AND_WAIT and MqSendEND_AND_CALLBACK a longterm-transaction-call have to survive an application restart. To achieve this goal… two features have to be available to process the results:

a transaction-callback as a service created with MqServiceCreate
a transaction-item as a environment created with MqSendT_START … MqSendT_END and stored into an internal database.

transaction-item

The transaction-item is the entry-id from the local internal database and is the public handle of the private data. If the transaction-item-private-data should be persistent (survive an application restart) the internal database have to be persistent using the Storage option.
The transaction-item-private-data requires a MqSendT_START … MqSendT_END at the beginning of the send-data-package.
The list of data-items in the transaction-item-private-data have to be provided by the programmer and is used to initialise the environment in the callback (for example an external database-entry-id).
In the transaction-callback the transaction-item-private-data have to be extracted with MqReadT_START … MqReadT_END at the beginning of the read-data-package.

transaction-callback

The transaction-callback have to be a MqContextC_ServiceApi_Identifer defined with MqServiceCreate in the application setup code (like IServerSetup) and have to be available after an application restart.

If an error is raised on the server during the database-insert the function will return this error immediately. During waiting for the return the event-loop is used to process other events. Use IEvent to add your tasks into the event loop.

Parameters

[in]	mkrt	the MkRuntimeS instance to work on - the runtime argument, used by MK_RT_CALL (C-only)
[in]	ctx	the MqContextS instance to work on
[in]	token	the MqContextC SERVICE API to identify the service
[in]	callback	the MqContextC_ServiceApi_Identifer of the MqContextC_ServiceApi_Callback
[in]	timeout	in seconds until a timeout-error is raised (possible values like ProcessEvent) (`MK_TIMEOUT_DEFAULT=MK_TIMEOUT_USER`)

Exceptions

MkExceptionC → The default-exception from the Programming-Language-Micro-Kernel (PLMK)

Example from MyTransaction.java → make a logterm-transaction-call using the LOW and the HIGH api

package example;

import jvmsgque.mqmsgque.*;
import jvmsgque.mkkernel.*;

final class MyTransaction extends MqContextC {

  static class CallbackC implements MqServiceIF {
    public void Callback(MqContextC ctx) {
      ctx.ReadT_START();
      String myPrivateHandle = ctx.ReadSTR();
      ctx.ReadT_END();
      int myServiceResult = ctx.ReadI32();

      System.out.println("myPrivateHandle=" + myPrivateHandle + ", myServiceResult=" + myServiceResult);
    }
  }

  public static void main(String[] argv) {
    MyTransaction ctx = new MyTransaction();
    try {
      ctx.ConfigSetName("MyTransaction");

      // setup commandline arguments used for parsing
      MkBufferListC args = new MkBufferListC(argv);

      // check if the '--token' option is available, default "SRVC"
      String token = args.CheckOptionSTR("--token", "SRVC");

      // connect to the server
      ctx.LinkCreate(args);

      // register callback
      ctx.ServiceCreate("CLB1", new CallbackC());
       
      // send block using the LOW-Api
      ctx.SendSTART();
      ctx.SendT_START();
      ctx.SendSTR("Privat_Data_1");
      ctx.SendT_END();
      ctx.SendI32(11111);
      ctx.SendEND_AND_TRANSACTION(token, "CLB1");
       
      // send block using the HIGN-Api -> same as above, but shorter
      ctx.Send("T", "CLB1", token + ":(C)I", "Privat_Data_2", 22222);
       
      // now we wait for exact ONE result of the "ctx"
      ctx.ProcessEvent(MqWaitOnEventE.OWN);

    } catch (Throwable e) {
      ctx.ErrorCatch(e);
    }
    ctx.Exit();
  }
}

SERVER

A jvmqmsgque server requires the following setup:

file: example/java/MyServer.java
an instance of the abstract class ContextCreate
the interface MqFactoryC to create a new application instance
the interface IServerSetup and or IServerCleanup

Example from MyServer.java → The minimal server looks like:

package example;

import jvmsgque.mkkernel.*;
import jvmsgque.mqmsgque.*;

// package-item
final class MyServer extends MqContextC implements IServerSetup {

  // Factory Constructor
  public MyServer(MqContextC tmpl) {
    super(tmpl);
  }

  // service to serve all incoming requests for token "HLWO"
  class MyFirstCallback implements MqServiceIF {
    public void Callback(MqContextC ctx) {
      SendSTART();
      SendSTR(ReadSTR() + " World");
      SendRETURN();
    }
  }

  // define a service as link between the token "HLWO" and the class "MyFirstService"
  public void ServerSetup() {
    ServiceCreate("HLWO", new MyFirstCallback());
  }

  // -------------------------------------------------------------

  // package-main
  public static void main(String[] argv) {
  
    // create the "MyServer" factory… and return the initial (top) object
    MqContextC srv = MqFactoryC.Add(MyServer.class).New();

    try {
      srv.LinkCreate(argv);
      srv.ProcessEvent(MqWaitOnEventE.FOREVER);
    } catch (Throwable e) {
      srv.ErrorCatch(e);
    }
    srv.Exit();
  }
}

The server is started as network visible TCP server listen on PORT 2345 using a THREAD for every new connection request:


java MyServer –tcp –port 2345 –thread

If you are using UNIX and if you want to setup a high-performance local server then use the build-in UDS (Unix-Domain-Sockets) capability to listen on the FILE /path/to/any/file.uds instead on a network port:


java MyServer –uds –file /path/to/any/file.uds –thread

Three things are important:

the send style of functions
the ctx.ServiceCreate(String token, MqServiceIF callback) function
a connected context of type [constructor,static] MqContextC MqContextC.Create(?MqContextC tmpl = null?)

Sending data is done using a minimum of 2 steps:

First: start a data package with ctx.SendSTART()
Last: submit the a data package to the link target using one of:

The first three ctx.SendEND(String token, ?long timeout = MkTimeoutE.DEFAULT.get()?)... functions are used to call a remote service and the last one is used to answer an incoming service call. In-between ctx.SendSTART() and ctx.SendEND(String token, ?long timeout = MkTimeoutE.DEFAULT.get()?) ... other MqContextC SEND API style commands are available to fill the data package with data.

Services are created with the ctx.ServiceCreate(String token, MqServiceIF callback) function. The first parameter is a 4 byte Token as public name. 4 byte is required because this string is mapped to a 4 byte integer for speed reason. The second parameter is an object providing the MqContextC_ServiceApi_Callback interface.

The MqContextC_ServiceApi_Callback is called for every incoming service-request which belongs to token.

CLIENT

A jvmqmsgque client requires the following setup:

an instance of the abstract class ContextCreate

Example from MyClient.java → The minimal client looks like:

package example;
import jvmsgque.mqmsgque.*;
import jvmsgque.mkkernel.*;

class MyClient extends MqContextC {
  public static void main(String[] argv) {
    MyClient c = new MyClient();
    try {
      c.ConfigSetName("MyClient");
      c.LinkCreate(argv);
      c.SendSTART();
      c.SendSTR("Hello");
      c.SendEND_AND_WAIT("HLWO", 5);
      System.out.println(c.ReadSTR());
    } catch (Throwable e) {
      c.ErrorCatch(e);
    }
    c.Exit();
  }
}

Example: To call a network visible TCP server listen on PORT 2345 use:


java MyClient –tcp –port 2345
Hello World

Example: To call a network visible UDP server listen on FILE /path/to/any/file.uds use:


java MyClient –uds –file /path/to/any/file.uds
Hello World

Example: To call a local server started by the client using PIPE communication use:


java MyClient @ java MyServer
Hello World

FILTER

The FILTER MODE is used to define a command pipeline.

Example from manfilter.java → A minimal filter looks like:

package example;

import jvmsgque.mqmsgque.*;
import jvmsgque.mkkernel.*;

class manfilter extends MqContextC {
  public manfilter(MqContextC tmpl) {
    super(tmpl);
  }
  private static class FTR implements MqServiceIF {
    public void Callback(MqContextC ctx) {
      MqContextC ftr = ctx.SlaveGetFilter();
      ftr.SendSTART();
      while (ctx.ReadItemExists()) {
	ftr.SendSTR("<" + ctx.ReadSTR() + ">");
      }
      ftr.SendEND_AND_WAIT("+FTR");
      ctx.SendRETURN();
    }
  }
  public static void main(String[] argv) {
    MqContextC srv = MqFactoryC.Add(manfilter.class).New();
    try {
      srv.ConfigSetName("filter");
      srv.ConfigSetIsServer(true);
      srv.LinkCreate(argv);
      srv.ServiceCreate("+FTR", new manfilter.FTR()); 
      srv.ServiceProxy ("+EOF"); 
      srv.ProcessEvent(MqWaitOnEventE.FOREVER);
    } catch (Throwable e) {
      srv.ErrorCatch(e);
    }
    srv.Exit();
  }
}

Use manfilter in a LibMqMsgque command pipeline:


echo -e "1:2:3\na:b:c" | atool split -d : @ java manfilter @ atool join -d :

Table of Contents