Using Transactions

Transactions Sample Application

#pragma prefix "beasys.com"
module UniversityT

{
	typedef unsigned long CourseNumber;
	typedef sequence<CourseNumber> CourseNumberList;

	struct CourseSynopsis
	{
		CourseNumber   course_number;
		string         title;
	};
	typedef sequence<CourseSynopsis> CourseSynopsisList;

	interface CourseSynopsisEnumerator
	{
	//Returns a list of length 0 if there are no more entries
	CourseSynopsisList get_next_n(
		in  unsigned long number_to_get, // 0 = return all
		out unsigned long number_remaining
	);

	void destroy();
};
	typedef unsigned short Days;
	const Days MONDAY    =  1;
	const Days TUESDAY   =  2;
	const Days WEDNESDAY =  4;
	const Days THURSDAY  =  8;
	const Days FRIDAY    = 16;

//Classes restricted to same time block on all scheduled days, 
//starting on the hour

struct ClassSchedule
{
	Days           class_days; // bitmask of days
	unsigned short start_hour; // whole hours in military time
	unsigned short duration;   // minutes
};

struct CourseDetails
{
	CourseNumber   course_number;
	double         cost;
	unsigned short number_of_credits;
	ClassSchedule  class_schedule;
	unsigned short number_of_seats;
	string         title;
	string         professor;
	string         description;
};
	typedef sequence<CourseDetails> CourseDetailsList;
	typedef unsigned long StudentId;

struct StudentDetails
{
	StudentId         student_id;
	string            name;
	CourseDetailsList registered_courses;
};

enum NotRegisteredReason
{
	AlreadyRegistered,
	NoSuchCourse
};

struct NotRegistered
{
	CourseNumber        course_number;
	NotRegisteredReason not_registered_reason;
};
	typedef sequence<NotRegistered> NotRegisteredList;

exception TooManyCredits
{
	unsigned short maximum_credits;
};

//The Registrar interface is the main interface that allows
//students to access the database.
interface Registrar
{
	CourseSynopsisList
	get_courses_synopsis(
		in string                    search_criteria,
	 	in unsigned long             number_to_get,
	 	out unsigned long            number_remaining,
		out CourseSynopsisEnumerator rest
);

   	CourseDetailsList get_courses_details(in CourseNumberList
	 courses);
	StudentDetails get_student_details(in StudentId student);
	NotRegisteredList register_for_courses(
		in StudentId        student,
		in CourseNumberList courses
	) raises (
		TooManyCredits
	);

};

// The RegistrarFactory interface finds Registrar interfaces.

interface RegistrarFactory
{
	Registrar find_registrar(
	);
};

Step 2: Defining Transaction Policies for the Interfaces

CORBA::Object_var var_transaction_current_oref =  
     Bootstrap.resolve_initial_references("TransactionCurrent");
CosTransactions::Current_var transaction_current_oref=
     CosTransactions::Current::_narrow(var_transaction_current_oref.in());
//Begin the transaction
var_transaction_current_oref->begin();
try {
//Perform the operation inside the transaction
     pointer_Registar_ref->register_for_courses(student_id, course_number_list);
     ...
//If operation executes with no errors, commit the transaction:
     CORBA::Boolean report_heuristics = CORBA_TRUE;
     var_transaction_current_ref->commit(report_heuristics);
    }
catch (...) {
//If the operation has problems executing, rollback the 
//transaction. Then throw the original exception again.
//If the rollback fails,ignore the exception and throw the
//original exception again.        
try {
     var_transaction_current_ref->rollback();
    }
catch (...) {
            TP::userlog("rollback failed");
            }
throw;
}

Step 4: Writing the Server Application

CORBA::Boolean Server::initialize(int argc, char* argv[])
{
	TRACE_METHOD("Server::initialize");
	try {
		open_database();
		begin_transactional();
		register_fact();
		return CORBA_TRUE;
}
	catch (CORBA::Exception& e) {
		LOG("CORBA exception : " <<e);
	}
	catch (SamplesDBException& e) {
		LOG("Can't connect to database");
	}
	catch (...) {
		LOG("Unexpected database error : " <<e);
	}
	catch (...) {
		LOG("Unexpected exception");
	}
	cleanup();
	return CORBA_FALSE;
}

void Server::release()
{
	TRACE_METHOD("Server::release");
	cleanup();
}

static void cleanup()
{
	unregister_factory();
	end_transactional();
	close_database();
}
//Utilities to manage transaction resource manager

CORBA::Boolean s_became_transactional = CORBA_FALSE;
static void begin_transactional()
{
	TP::open_xa_rm();
	s_became_transactional = CORBA_TRUE;
}
static void end_transactional()
{
	if(!s_became_transactional){
	return//cleanup not necessary
}
try {
	TP::close_xa_rm ();
}
	catch (CORBA::Exception& e) {
	       LOG("CORBA Exception : " << e);
	}
	catch (...) {
	       LOG("unexpected exception");
 	}

	s_became_transactional = CORBA_FALSE;
}

Step 5: Creating a Configuration File

*RESOURCES
	IPCKEY    55432
	DOMAINID  university
	MASTER    SITE1
	MODEL     SHM
	LDBAL     N
	SECURITY  APP_PW				

*MACHINES
	BLOTTO
	LMID = SITE1
	APPDIR = C:\TRANSACTION_SAMPLE
	TUXCONFIG=C:\TRANSACTION_SAMPLE\tuxconfig
	TLOGDEVICE=C:\APP_DIR\TLOG
	TLOGNAME=TLOG
	TUXDIR="C:\WLEdir"
	MAXWSCLIENTS=10

*GROUPS
	SYS_GRP
	  LMID      = SITE1
	  GRPNO     = 1
	ORA_GRP
	  LMID      = SITE1
	  GRPNO     = 2

	OPENINFO  = "ORACLE_XA:Oracle_XA+SqlNet=ORCL+Acc=P
	/scott/tiger+SesTm=100+LogDir=.+MaxCur=5"
	OPENINFO  = "ORACLE_XA:Oracle_XA+Acc=P/scott/tiger
	+SesTm=100+LogDir=.+MaxCur=5"
	CLOSEINFO = ""
	TMSNAME   = "TMS_ORA"

*SERVERS
	DEFAULT:
	RESTART = Y
	MAXGEN  = 5

	TMSYSEVT
	  SRVGRP  = SYS_GRP
	  SRVID   = 1

	TMFFNAME
	  SRVGRP  = SYS_GRP
	  SRVID   = 2
	  CLOPT   = "-A -- -N -M"

	TMFFNAME
	  SRVGRP  = SYS_GRP
	  SRVID   = 3
	  CLOPT   = "-A -- -N"

	TMFFNAME
	  SRVGRP  = SYS_GRP
	  SRVID   = 4
	  CLOPT   = "-A -- -F"

	TMIFRSVR
	  SRVGRP  = SYS_GRP
	  SRVID   = 5

	UNIVT_SERVER
	  SRVGRP  = ORA_GRP
	  SRVID   = 1
	  RESTART = N

   	ISL
	  SRVGRP  = SYS_GRP
	  SRVID   = 6
	  CLOPT   = -A -- -n //MACHINENAME:2500

*SERVICES