Programming a Tuxedo ATMI Application Using C
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Writing Servers
This topic includes the following sections:
- BEA Tuxedo System main( )
- System-Supplied Server and Services
- Guidelines for Writing Servers
- Defining a Service
- Example: Checking the Buffer Type
- Example: Checking the Priority of the Service Request
- Terminating a Service Routine
- Advertising and Unadvertising Services
- Building ServersUsing a C++ Compiler
BEA Tuxedo System main( )
To facilitate the development of ATMI servers, the BEA Tuxedo system provides a predefined main() routine for server load modules. When you execute the buildserver command, the main() routine is automatically included as part of the server.
Note: The main() routine that the system provides is a closed abstraction; you cannot modify it.
In addition to joining and exiting from an application, the predefined main() routine accomplishes the following tasks on behalf of the server.
- Executes the process ignoring any hangups (that is, it ignores the
SIGHUPsignal). - Initiates the cleanup process on receipt of the standard operating system software termination signal (
SIGTERM). The server is shut down and must be rebooted if needed again. - Attaches to shared memory for bulletin board services.
- Creates a message queue for the process.
- Advertises the initial services to be offered by the server. The initial services are either all the services link edited with the predefined
main(), or a subset specified by the BEA Tuxedo system administrator in the configuration file. - Processes command-line arguments up to the double dash (
--), which indicates the end of system-recognized arguments. - Calls the function tpsvrinit() to process any command-line arguments listed after the double dash (
--) and optionally to open the resource manager. These command-line arguments are used for application-specific initialization. - Until ordered to halt, checks its request queue for service request messages.
- When a service request message arrives on the request queue,
main()performs the following tasks until ordered to halt: - If the
-roption is specified, records the starting time of the service request. - Updates the bulletin board to indicate that the server is
BUSY. - Allocates a buffer for the request message and dispatches the service; that is, calls the service subroutine.
- When the service returns from processing its input,
main()performs the following tasks until ordered to halt: - If the
-roption is specified, records the ending time of the service request. - Updates statistics.
- Updates the bulletin board to indicate that the server is
IDLE; that is, that the server is ready for work. - Checks its queue for the next service request.
- When the server is required to halt, calls tpsvrdone() to perform any required shutdown operations.
As indicated above, the main() routine handles all of the details associated with joining and exiting from an application, managing buffers and transactions, and handling communication.
Note: Because the system-supplied main() accomplishes the work of joining and leaving the application, you should not include calls to the tpinit() or tpterm() function in your code. If you do, the function encounters an error and returns TPEPROTO in tperrno. For more information on the tpinit() or tpterm() function, refer to Writing Clients.
System-Supplied Server and Services
The main() routine provides one system-supplied ATMI server, AUTHSVR, and two subroutines, tpsvrinit() and tpsvrdone(). The default versions of all three, which are described in the following sections, can be modified to suit your application.
Notes: If you want to write your own versions of tpsvrinit() and tpsvrdone(), remember that the default versions of these two routines call tx_open() and tx_close(), respectively. If you write a new version of tpsvrinit() that calls tpopen() rather than tx_open(), you should also write a new version of tpsvrdone() that calls tpclose(). In other words, both functions in an open/close pair must belong to the same set.
In addition to the subroutines described in this topic, the system provides two subroutines called tpsvrthrinit(3c) and tpsvrthrdone(3c). For more information, refer to Programming a Multithreaded and Multicontexted ATMI Application.
System-Supplied Server: AUTHSVR( )
You can use the AUTHSVR(5) server to provide individual client authentication for an application. The tpinit() function calls this server when the level of security for the application is TPAPPAUTH.
The service in AUTHSVR looks in the data field of the TPINIT buffer for a user password (not to be confused with the application password specified in the passwd field of the TPINIT buffer). By default, the system takes the string in data and searches for a matching string in the /etc/passwd file.
When called by a native-site client, tpinit() forwards the data field as it is received. This means that if the application requires the password to be encrypted, the client program must be coded accordingly.
When called by a Workstation client, tpinit() encrypts the data before sending it across the network.
System-Supplied Services: tpsvrinit( ) Function
When a server is booted, the BEA Tuxedo system main() calls tpsvrinit(3c) during its initialization phase, before handling any service requests.
If an application does not provide a custom version of this function within the server, the system uses the default function provided by main(), which opens the resource manager and logs an entry in the central event log indicating that the server has successfully started. The central user log is an automatically generated file to which processes can write messages by calling the userlog(3c) function. Refer to Managing Errors for more information on the central event log.
You can use the tpsvrinit() function for any initialization processes that might be required by an application, such as the following:
The following sections provide code samples showing how these initialization tasks are performed through calls to tpsvrinit(). Although it is not illustrated in the following examples, message exchanges can also be performed within this routine. However, tpsvrinit() fails if it returns with asynchronous replies pending. In this case, the replies are ignored by the BEA Tuxedo system, and the server exits gracefully.
You can also use the tpsvrinit() function to start and complete transactions, as described in Managing Errors.
Use the following signature to call the tpsvrinit() function:
int
tpsvrinit(int argc, char **argv)
Receiving Command-line Options
When a server is booted, its first task is to read the server options specified in the configuration file up to the point that it receives an EOF indication. To do so, the server calls the getopt(3) UNIX function. The presence of a double dash (--) on the command line causes the getopt() function to return an EOF. The getopt function places the argv index of the next argument to be processed in the external variable optind. The predefined main() then calls tpsvrinit().
The following code example shows how the tpsvrinit() function is used to receive command-line options.
Listing 5-1 Receiving Command-line Options in tpsvrinit( )
tpsvrinit(argc, argv)
int argc;
char **argv;
{
int c;
extern char *optarg;
extern int optind;
.
.
.
while((c = getopt(argc, argv, "f:x:")) != EOF)
switch(c){
.
.
.
}
.
.
.
}
When main() calls tpsvrinit(), it picks up any arguments that follow the double dash (--) on the command line. In the example above, options f and x each takes an argument, as indicated by the colon. optarg points to the beginning of the option argument. The switch statement logic is omitted.
Opening a Resource Manager
The following example illustrates another common use of tpsvrinit(): opening a resource manager. The BEA Tuxedo system provides functions to open a resource manager, tpopen(3c) and tx_open(3c). It also provides the complementary functions, tpclose(3c) and tx_close(3c). Applications that use these functions to open and close their resource managers are portable in this respect. They work by accessing the resource manager instance-specific information that is available in the configuration file.
Note: If writing a multithreaded server, you must use the tpsvrthrinit() function to open a resource manager, as described in Programming a Multithreaded and Multicontexted ATMI Application.
These function calls are optional and can be used in place of the resource manager specific calls that are sometimes part of the Data Manipulation Language (DML) if the resource manager is a database. Note the use of the userlog(3c) function to write to the central event log.
Note: To create an initialization function that both receives command-line options and opens a database, combine the following example with the previous example.
Listing 5-2 Opening a Resource Manager in tpsvrinit( )
tpsvrinit()
{
/* Open database */
if (tpopen() == -1) {
(void)userlog("tpsvrinit: failed to open database: ");
switch (tperrno) {
case TPESYSTEM:
(void)userlog("System error\n");
break;
case TPEOS:
(void)userlog("Unix error %d\n",Uunixerr);
break;
case TPEPROTO:
(void)userlog("Called in improper context\n");
break;
case TPERMERR:
(void)userlog("RM failure\n");
break;
}
return(-1); /* causes the server to exit */
}
return(0);
}
To guard against errors that may occur during initialization, tpsvrinit() can be coded to allow the server to exit gracefully before starting to process service requests.
System-Supplied Services: tpsvrdone( ) Function
The tpsvrdone() function calls tpclose() to close the resource manager, similarly to the way tpsvrinit() calls tpopen() to open it.
Note: If writing a multithreaded server, you must use the tpsvrthrdone() command to open a resource manager, as described in Programming a Multithreaded and Multicontexted ATMI Application.
Use the following signature to call the tpsvrdone() function:
void
tpsvrdone()/* Server termination routine */
The tpsvrdone() function requires no arguments.
If an application does not define a closing routine for tpsvrdone(), the BEA Tuxedo system calls the default routine supplied by main(). This routine calls tx_close() and userlog() to close the resource manager and write to the central event log, respectively. The message sent to the log indicates that the server is about to exit.
tpsvrdone() is called after the server has finished processing service requests but before it exits. Because the server is still part of the system, further communication and transactions can take place within the routine, as long as certain rules are followed. These rules are covered in Managing Errors.
The following example illustrates how to use the tpsvrdone() function to close a resource manager and exit gracefully.
Listing 5-3 Closing a Resource Manager with tpsvrdone( )
void
tpsvrdone()
{
/* Close the database */
if(tpclose() == -1)
(void)userlog("tpsvrdone: failed to close database: ");
switch (tperrno) {
case TPESYSTEM:
(void)userlog("BEA TUXEDO error\n");
break;
case TPEOS:
(void)userlog("Unix error %d\n",Uunixerr);
break;
case TPEPROTO:
(void)userlog("Called in improper context\n");
break;
case TPERMERR:
(void)userlog("RM failure\n");
break;
}
return;
}
return;
}
Guidelines for Writing Servers
Because the communication details are handled by the BEA Tuxedo system main() routine, you can concentrate on the application service logic rather than communication implementation. For compatibility with the system-supplied main(), however, application services must adhere to certain conventions. These conventions are referred to, collectively, as the service template for coding service routines. They are summarized in the following list. Refer to the tpservice(3c) reference page in the BEA Tuxedo ATMI C Function Reference for more information on these conventions.
- A request/response service can receive only one request at a time and can send only one reply.
- When processing a request, a request/response service works only on that request. It can accept another only after it has either sent a reply to the requester or forwarded the request to another service for additional processing.
- Service routines must terminate by calling either the tpreturn() or tpforward() function. These functions behave similarly to the C language
returnstatement except that after they finish executing, control returns to the BEA Tuxedo system'smain()instead of the calling function. - When communicating with another server via tpacall(), the initiating service must either wait for all outstanding replies or invalidate them with tpcancel() before calling tpreturn() or tpforward().
- Service routines are invoked with one argument,
svcinfo, which is a pointer to a service information structure (TPSVCINFO).
Defining a Service
You must define every service routine as a function that receives one argument consisting of a pointer to a TPSVCINFO structure. The TPSVCINFO structure is defined in the atmi.h header file and includes the following information:
charname[32];
longflags;
char *data;
longlen;
intcd;
intappkey;
CLIENTIDcltid;
The following table summarizes the TPSVCINFO data structure.
Table 5-1 TPSVCINFO Data Structure
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Specifies, to the service routine, the name used by the requesting process to invoke the service. |
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Notifies the service if it is in transaction mode or if the caller is expecting a reply. The various ways in which a service can be placed in transaction mode are discussed in Writing Global Transactions. The The |
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Pointer to a buffer that was previously allocated by tpalloc() within the |
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Contains the length of the request data that is in the buffer referenced by the |
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For conversational communication, specifies the connection descriptor. |
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Reserved for use by the application. If application-specific authentication is part of your design, the application-specific authentication server, which is called when a client joins the application, should return a client authentication key as well as an indication of success or failure. The BEA Tuxedo system holds the appkey on behalf of the client and passes the information to subsequent service requests in this field. By the time the appkey is passed to a service, the client has already been authenticated. However, the appkey field can be used within a service to identify the user invoking the service or some other parameters associated with the user. If this field is not used, the system assigns it a default value of |
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Structure of type |
When the data field in the TPSVCINFO structure is being accessed by a process, the following buffer types must agree:
- Type of the request buffer passed by the calling process
- Type of the corresponding buffer code defined within the called service
- Type of the associated buffer type defined for the called service in the configuration file
The following example illustrates a typical service definition. This code is borrowed from the ABAL (account balance) service routine that is part of the banking application provided with the BEA Tuxedo software. ABAL is part of the BAL server.
Listing 5-4 Typical Service Definition
#include <stdio.h> /* UNIX */
#include <atmi.h> /* BEA Tuxedo System */
#include <sqlcode.h> /* BEA Tuxedo System */
#include "bank.flds.h" /* bankdb fields */
#include "aud.h" /* BANKING view defines */
EXEC SQL begin declare section;
static long branch_id; /* branch id */
static float bal; /* balance */
EXEC SQL end declare section;
/*
* Service to find sum of the account balances at a SITE
*/
void
#ifdef __STDC__
ABAL(TPSVCINFO *transb)
#else
ABAL(transb)
TPSVCINFO *transb;
#endif
{
struct aud *transv; /* view of decoded message */
/* Set pointer to TPSVCINFO data buffer */
transv = (struct aud *)transb->data;
set the consistency level of the transaction
/* Get branch id from message, do query */
EXEC SQL declare acur cursor for
select SUM(BALANCE) from ACCOUNT;
EXEC SQL open acur; /* open */
EXEC SQL fetch acur into :bal; /* fetch */
if (SQLCODE != SQL_OK) { /* nothing found */
(void)strcpy (transv->ermsg,"abal failed in sql aggregation");
EXEC SQL close acur;
tpreturn(TPFAIL, 0, transb->data, sizeof(struct aud), 0);
}
EXEC SQL close acur;
transv->balance = bal;
tpreturn (TPSUCCESS, 0, transb->data, sizeof(struct aud), 0);
}
In the preceding example, the application allocates a request buffer on the client side by a call to tpalloc() with the type parameter set to VIEW and the subtype set to aud. The ABAL service is defined as supporting the VIEW typed buffer. The BUFTYPE parameter is not specified for ABAL and defaults to ALL. The ABAL service allocates a buffer of the type VIEW and assigns the data member of the TPSVCINFO structure that was passed to the ABAL subroutine to the buffer pointer. The ABAL server retrieves the appropriate data buffer by accessing the corresponding data member, as illustrated in the preceding example.
Note: After the buffer is retrieved, but before the first attempt is made to access the database, the service must specify the consistency level of the transaction. Refer to Writing Global Transactions for more details on transaction consistency levels.
Example: Checking the Buffer Type
The code example in this section shows how a service can access the data buffer defined in the TPSVCINFO structure to determine its type by using the tptypes() function. (This process is described in Checking for Buffer Type.) The service also checks the maximum size of the buffer to determine whether or not to reallocate space for the buffer.
This example is derived from the ABAL service that is part of the banking application provided with the BEA Tuxedo software. It shows how the service is written to accept a request either as an aud VIEW or an FML buffer. If its attempt to determine the message type fails, the service returns a string with an error message plus an appropriate return code; otherwise it executes the segment of code that is appropriate for the buffer type. For more information on the tpreturn() function, refer to Terminating a Service Routine.
Listing 5-5 Checking for Buffer Type
#define TMTYPERR 1 /* return code indicating tptypes failed */
#define INVALMTY 2 /* return code indicating invalid message type */
void
ABAL(transb)
TPSVCINFO *transb;
{
struct aud *transv; /* view message */
FBFR *transf; /* fielded buffer message */
int repc; /* tpgetrply return code */
char typ[TMTYPELEN+1], subtyp[TMSTYPELEN+1]; /* type, subtype of message */
char *retstr; /* return string if tptypes fails */
/* find out what type of buffer sent */
if (tptypes((char *)transb->data, typ, subtyp) == -1) {
retstr=tpalloc("STRING", NULL, 100);
(void)sprintf(retstr,
"Message garbled; tptypes cannot tell what type message\n");
tpreturn(TPFAIL, TMTYPERR, retstr, 100, 0);
}
/* Determine method of processing service request based on type */
if (strcmp(typ, "FML") == 0) {
transf = (FBFR *)transb->data;
... code to do abal service for fielded buffer ...
tpreturn succeeds and sends FML buffer in reply
}
else if (strcmp(typ, "VIEW") == 0 && strcmp(subtyp, "aud") == 0) {
transv = (struct aud *)transb->data;
... code to do abal service for aud struct ...
tpreturn succeeds and sends aud view buffer in reply
}
else {
retstr=tpalloc("STRING", NULL, 100);
(void)sprintf(retstr,
"Message garbled; is neither FML buffer nor aud view\n");
tpreturn(TPFAIL, INVALMTY, retstr, 100, 0);
}
}
Example: Checking the Priority of the Service Request
Note: The tpgprio() and tpsprio() functions, used for getting and setting priorities, respectively, are described in detail in Setting and Getting Message Priorities.
The example code in this section shows how a service called PRINTER tests the priority level of the request just received using the tpgprio() function. Then, based on the priority level, the application routes the print job to the appropriate destination printer and pipes the contents of pbufdata to that printer.
The application queries pbufflags to determine whether a reply is expected. If so, it returns the name of the destination printer to the client. For more information on the tpreturn() function, refer to Terminating a Service Routine.
Listing 5-6 Checking the Priority of a Received Request
#include <stdio.h>
#include "atmi.h"
char *roundrobin();
PRINTER(pbuf)
TPSVCINFO *pbuf; /* print buffer */
{
char prname[20], ocmd[30]; /* printer name, output command */
long rlen; /* return buffer length */
int prio; /* priority of request */
FILE *lp_pipe; /* pipe file pointer */
prio=tpgprio();
if (prio <= 20)
(void)strcpy(prname,"bigjobs"); /* send low priority (verbose)
jobs to big comp. center
laser printer where operator
sorts output and puts it
in a bin */
else if (prio <= 60)
(void)strcpy(prname,roundrobin()); /* assign printer on a
rotating basis to one of
many local small laser printers
where output can be picked
up immediately; roundrobin() cycles
through list of printers */
else
(void)strcpy(prname,"hispeed");
/* assign job to high-speed laser
printer; reserved for those who
need verbose output on a daily,
frequent basis */
(void)sprintf(ocmd, "lp -d%s", prname); /* output lp(1) command */
lp_pipe = popen(ocmd, "w"); /* create pipe to command */
(void)fprintf(lp_pipe, "%s", pbuf->data); /* print output there */
(void)pclose(lp_pipe); /* close pipe */
if ((pbuf->flags & TPNOREPLY))
tpreturn(TPSUCCESS, 0, NULL, 0, 0);
rlen = strlen(prname) + 1;
pbuf->data = tprealloc(pbuf->data, rlen); /* ensure enough space for name */
(void)strcpy(pbuf->data, prname);
tpreturn(TPSUCCESS, 0, pbuf->data, rlen, 0);
char *
roundrobin()
{
static char *printers[] = {"printer1", "printer2", "printer3", "printer4"};
static int p = 0;
if (p > 3)
p=0;
return(printers[p++]);
}
Terminating a Service Routine
The tpreturn(3c), tpcancel(3c), and tpforward(3c) functions specify that a service routine has completed with one of the following actions:
tpreturn()sends a reply to the calling client.tpcancel()cancels the current request.tpforward() forwards a request to another service for further processing.
Sending Replies
The tpreturn(3c) function marks the end of the service routine and sends a message to the requester. Use the following signature to call the tpreturn() function:
void
tpreturn(int rval, int rcode, char *data, long len, long flags)
The following table describes the arguments to the tpreturn() function.
Table 5-2 tpreturn( ) Function Arguments
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Indicates whether or not the service has completed successfully on an application-level. The value is an integer that is represented by a symbolic name. Valid settings include:
For a description of the effect that the value of this argument has on global transactions, refer to Writing Global Transactions. |
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Returns an application-defined return code to the caller. The client can access the value returned in |
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Pointer to the reply message that is returned to the client process. The message buffer must have been allocated previously by tpalloc(). If you use the same buffer that was passed to the service in the If you use another buffer (that is, a buffer other than the one passed to the service routine) to return the message, it is your responsibility to allocate it. The system frees the buffer automatically when the application calls the tpreturn() function. If no reply message needs to be returned, set this argument to the NULL pointer. Note: If no reply is expected by the client (that is, if |
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Length of the reply buffer. The application accesses the value of this argument through the Acting as the client, the process can use this returned value to determine whether the reply buffer has grown. If a reply is expected by the client and there is no data in the reply buffer (that is, if the The system ignores the value of this argument if the |
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The primary function of a service routine is to process a request and return a reply to a client process. It is not necessary, however, for a single service to do all the work required to perform the requested function. A service can act as a requester and pass a request call to another service the same way a client issues the original request: through calls to tpcall() or tpacall().
Note: The tpcall() and tpacall() functions are described in detail in Writing Request/Response Clients and Servers.
When tpreturn() is called, control always returns to main(). If a service has sent requests with asynchronous replies, it must receive all expected replies or invalidate them with tpcancel() before returning control to main(). Otherwise, the outstanding replies are automatically dropped when they are received by the BEA Tuxedo system main(), and an error is returned to the caller.
If the client invokes the service with tpcall(), after a successful call to tpreturn(), the reply message is available in the buffer referenced by *odata. If tpacall() is used to send the request, and tpreturn() returns successfully, the reply message is available in the tpgetrply() buffer that is referenced by *data.
If a reply is expected and tpreturn() encounters errors while processing its arguments, it sends a failed message to the calling process. The caller detects the error by checking the value placed in tperrno. In the case of failed messages, the system sets tperrno to TPESVCERR. This situation takes precedence over the value of the tpurcode global variable. If this type of error occurs, no reply data is returned, and both the contents and length of the caller's output buffer remain unchanged.
If tpreturn() returns a message in a buffer of an unknown type or a buffer that is not allowed by the caller (that is, if the call is made with flags set to TPNOCHANGE), the system returns TPEOTYPE in tperrno(5). In this case, application success or failure cannot be determined, and the contents and length of the output buffer remain unchanged.
The value returned in the tpurcode(5) global variable is not relevant if the tpreturn() function is invoked and a timeout occurs for the call waiting for the reply. This situation takes precedence over all others in determining the value that is returned in tperrno(5). In this case, tperrno(5) is set to TPETIME and the reply data is not sent, leaving the contents and length of the caller's reply buffer unchanged. There are two types of timeouts in the BEA Tuxedo system: blocking and transaction timeouts (discussed in Writing Global Transactions).
The example code in this section shows the TRANSFER service that is part of the XFER server. Basically, the TRANSFER service makes synchronous calls to the WITHDRAWAL and DEPOSIT services. It allocates a separate buffer for the reply message since it must use the request buffer for the calls to both the WITHDRAWAL and the DEPOSIT services. If the call to WITHDRAWAL fails, the service writes the message cannot withdraw on the status line of the form, frees the reply buffer, and sets the rval argument of the tpreturn() function to TPFAIL. If the call succeeds, the debit balance is retrieved from the reply buffer.
Note: In the following example, the application moves the identifier for the "destination account" (which is retrieved from the cr_id variable) to the zeroth occurrence of the ACCOUNT_ID field in the transf fielded buffer. This move is necessary because this occurrence of the field in an FML buffer is used for data-dependent routing. Refer to Setting Up a BEA Tuxedo Application for more information.
A similar scenario is followed for the call to DEPOSIT. On success, the service frees the reply buffer that was allocated in the service routine and sets the rval argument to TPSUCCESS, returning the pertinent account information to the status line.
Listing 5-7 tpreturn( ) Function
#include <stdio.h> /* UNIX */
#include <string.h> /* UNIX */
#include "fml.h" /* BEA Tuxedo System */
#include "atmi.h" /* BEA Tuxedo System */
#include "Usysflds.h" /* BEA Tuxedo System */
#include "userlog.h" /* BEA Tuxedo System */
#include "bank.h" /* BANKING #defines */
#include "bank.flds.h" /* bankdb fields */
/*
* Service to transfer an amount from a debit account to a credit
* account
*/
void
#ifdef __STDC__
TRANSFER(TPSVCINFO *transb)
#else
TRANSFER(transb)
TPSVCINFO *transb;
#endif
{
FBFR *transf; /* fielded buffer of decoded message */
long db_id, cr_id; /* from/to account id's */
float db_bal, cr_bal; /* from/to account balances */
float tamt; /* amount of the transfer */
FBFR *reqfb; /* fielded buffer for request message*/
int reqlen; /* length of fielded buffer */
char t_amts[BALSTR]; /* string for transfer amount */
char db_amts[BALSTR]; /* string for debit account balance */
char cr_amts[BALSTR]; /* string for credit account balance */
/* Set pointr to TPSVCINFO data buffer */
transf = (FBFR *)transb->data;
/* Get debit (db_id) and credit (cr_id) account IDs */
/* must have valid debit account number */
if (((db_id = Fvall(transf, ACCOUNT_ID, 0)) < MINACCT) || (db_id > MAXACCT)) {
(void)Fchg(transf, STATLIN, 0,"Invalid debit account number",(FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* must have valid credit account number */
if ((cr_id = Fvall(transf, ACCOUNT_ID, 1)) < MINACCT || cr_id > MAXACCT) {
(void)Fchg(transf,STATLIN, 0,"Invalid credit account number",(FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* get amount to be withdrawn */
if (Fget(transf, SAMOUNT, 0, t_amts, < 0) 0 || strcmp(t_amts,"") == 0) {
(void)Fchg(transf, STATLIN, 0, "Invalid amount",(FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
(void)sscanf(t_amts,"%f",tamt);
/* must have valid amount to transfer */
if (tamt = 0.0) {
(void)Fchg(transf, STATLIN, 0,
"Transfer amount must be greater than $0.00",(FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* make withdraw request buffer */
if ((reqfb = (FBFR *)tpalloc("FML",NULL,transb->len)) == (FBFR *)NULL) {
(void)userlog("tpalloc failed in transfer\n");
(void)Fchg(transf, STATLIN, 0,
"unable to allocate request buffer", (FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
reqlen = Fsizeof(reqfb);
/* put ID in request buffer */
(void)Fchg(reqfb,ACCOUNT_ID,0,(char *)&db_id, (FLDLEN)0);
/* put amount in request buffer */
(void)Fchg(reqfb,SAMOUNT,0,t_amts, (FLDLEN)0);
/* increase the priority of withdraw call */
if (tpsprio(PRIORITY, 0L) == -1)
(void)userlog("Unable to increase priority of withdraw\n");
if (tpcall("WITHDRAWAL", (char *)reqfb,0, (char **)&reqfb,
(long *)&reqlen,TPSIGRSTRT) == -1) {
(void)Fchg(transf, STATLIN, 0,
"Cannot withdraw from debit account", (FLDLEN)0);
tpfree((char *)reqfb);
tpreturn(TPFAIL, 0,transb->data, 0L, 0);
}
/* get "debit" balance from return buffer */
(void)strcpy(db_amts, Fvals((FBFR *)reqfb,SBALANCE,0));
void)sscanf(db_amts,"%f",db_bal);
if ((db_amts == NULL) || (db_bal < 0.0)) {
(void)Fchg(transf, STATLIN, 0,
"illegal debit account balance", (FLDLEN)0);
tpfree((char *)reqfb);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* put deposit account ID in request buffer */
(void)Fchg(reqfb,ACCOUNT_ID,0,(char *)&cr_id, (FLDLEN)0);
/* put transfer amount in request buffer */
(void)Fchg(reqfb,SAMOUNT,0,t_amts, (FLDLEN)0);
/* Up the priority of deposit call */
if (tpsprio(PRIORITY, 0L) == -1)
(void)userlog("Unable to increase priority of deposit\n");
/* Do a tpcall to deposit to second account */
if (tpcall("DEPOSIT", (char *)reqfb, 0, (char **)&reqfb,
(long *)&reqlen, TPSIGRSTRT) == -1) {
(void)Fchg(transf, STATLIN, 0,
"Cannot deposit into credit account", (FLDLEN)0);
tpfree((char *)reqfb);
tpreturn(TPFAIL, 0,transb->data, 0L, 0);
}
/* get "credit" balance from return buffer */
(void)strcpy(cr_amts, Fvals((FBFR *)reqfb,SBALANCE,0));
(void)sscanf(cr_amts,"%f",&cr_bal);
if ((cr_amts == NULL) || (cr_bal 0.0)) {
(void)Fchg(transf, STATLIN, 0,
"Illegal credit account balance", (FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* set buffer for successful return */
(void)Fchg(transf, FORMNAM, 0, "CTRANSFER", (FLDLEN)0);
(void)Fchg(transf, SAMOUNT, 0, Fvals(reqfb,SAMOUNT,0), (FLDLEN)0);
(void)Fchg(transf, STATLIN, 0, "", (FLDLEN)0);
(void)Fchg(transf, SBALANCE, 0, db_amts, (FLDLEN)0);
(void)Fchg(transf, SBALANCE, 1, cr_amts, (FLDLEN)0);
tpfree((char *)reqfb);
tpreturn(TPSUCCESS, 0,transb->data, 0L, 0);
}
Invalidating Descriptors
If a service calling tpgetrply() (described in detail in Writing Request/Response Clients and Servers) fails with TPETIME and decides to cancel the request, it can invalidate the descriptor with a call to tpcancel(3c). If a reply subsequently arrives, it is silently discarded.
Use the following signature to call the tpcancel() function:
void
tpcancel(int cd)
The cd (call descriptor) argument identifies the process you want to cancel.
tpcancel() cannot be used for transaction replies (that is, for replies to requests made without the TPNOTRAN flag set). Within a transaction, tpabort(3c) does the same job of invalidating the transaction call descriptor.
The following example shows how to invalidate a reply after timing out.
Listing 5-8 Invalidating a Reply After Timing Out
int cd1;
.
.
.
if ((cd1=tpacall(sname, (char *)audv, sizeof(struct aud),
TPNOTRAN)) == -1) {
.
.
.
}
if (tpgetrply(cd1, (char **)&audv,&audrl, 0) == -1) {
if (tperrno == TPETIME) {
tpcancel(cd1);
.
.
.
}
}
tpreturn(TPSUCCESS, 0,NULL, 0L, 0);
Forwarding Requests
The tpforward(3c) function allows a service to forward a request to another service for further processing.
Use the following signature to call the tpforward() function:
void
tpforward(char *svc, char *data, long len, long flags)
The following table describes the arguments to the tpreturn() function.
Table 5-3 tpreturn() Function Arguments
|
Character pointer to the name of the service to which the request is to be forwarded. |
|
|
Pointer to the reply message that is returned to the client process. The message buffer must have been allocated previously by tpalloc(). If you use the same buffer that was passed to the service in the If you use another buffer (that is, a buffer other than the one that is passed to the service routine) to return the message, it is your responsibility to allocate it. The system frees the buffer automatically when the application calls the tpreturn() function. If no reply message needs to be returned, set this argument to the NULL pointer. Note: If no reply is expected by the client (that is, if |
|
|
Length of the reply buffer. The application accesses the value of this argument through the Acting as the client, the process can use this returned value to determine whether the reply buffer has grown. If a reply is expected by the client and there is no data in the reply buffer (that is, if the The system ignores the value of this argument if the |
|
The functionality of tpforward() differs from a service call: a service that forwards a request does not expect a reply. The responsibility for providing the reply is passed to the service to which the request has been forwarded. The latter service sends the reply to the process that originated the request. It becomes the responsibility of the last server in the forward chain to send the reply to the originating client by invoking tpreturn().
The following figure shows one possible sequence of events when a request is forwarded from one service to another. Here a client initiates a request using the tpcall() function and the last service in the chain (SVC_C) provides a reply using the tpreturn() function.
Figure 5-1 Forwarding a Request
Service routines can forward requests at specified priorities in the same manner that client processes send requests, by using the tpsprio() function.
When a process calls tpforward(), the system-supplied main() regains control, and the server process is free to do more work.
Note: If a server process is acting as a client and a reply is expected, the server is not allowed to request services from itself. If the only available instance of the desired service is offered by the server process making the request, the call fails, indicating that a recursive call cannot be made. However, if a service routine sends a request (to itself) with the TPNOREPLY communication flag set, or if it forwards the request, the call does not fail because the service is not waiting for itself.
Calling tpforward() can be used to indicate success up to that point in processing the request. If no application errors have been detected, you can invoke tpforward(), otherwise, you can call tpreturn() with rval set to TPFAIL.
The following example is borrowed from the OPEN_ACCT service routine which is part of the ACCT server. This example illustrates how the service sends its data buffer to the DEPOSIT service by calling tpforward(). The code shows how to test the SQLCODE to determine whether the account insertion is successful. If the new account is added successfully, the branch record is updated to reflect the new account, and the data buffer is forwarded to the DEPOSIT service. On failure, tpreturn() is called with rval set to TPFAIL and the failure is reported on the status line of the form.
Listing 5-9 tpforward( ) Function
...
/* set pointer to TPSVCINFO data buffer */
transf = (FBFR *)transb->data;
...
/* Insert new account record into ACCOUNT*/
account_id = ++last_acct; /* get new account number */
tlr_bal = 0.0; /* temporary balance of 0 */
EXEC SQL insert into ACCOUNT (ACCOUNT_ID, BRANCH_ID, BALANCE,
ACCT_TYPE, LAST_NAME, FIRST_NAME, MID_INIT, ADDRESS, PHONE) values
(:account_id, :branch_id, :tlr_bal, :acct_type, :last_name,
:first_name, :mid_init, :address, :phone);
if (SQLCODE != SQL_OK) { /* Failure to insert */
(void)Fchg(transf, STATLIN, 0,
"Cannot update ACCOUNT", (FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* Update branch record with new LAST_ACCT */
EXEC SQL update BRANCH set LAST_ACCT = :last_acct where BRANCH_ID = :branch_id;
if (SQLCODE != SQL_OK) { /* Failure to update */
(void)Fchg(transf, STATLIN, 0,
"Cannot update BRANCH", (FLDLEN)0);
tpreturn(TPFAIL, 0, transb->data, 0L, 0);
}
/* up the priority of the deposit call */
if (tpsprio(PRIORITY, 0L) == -1)
(void)userlog("Unable to increase priority of deposit\n");
/* tpforward same buffer to deposit service to add initial balance */
tpforward("DEPOSIT", transb->data, 0L, 0);
Advertising and Unadvertising Services
When a server is booted, it advertises the services it offers based on the values specified for the CLOPT parameter in the configuration file.
Note: The services that a server may advertise are initially defined when the buildserver command is executed. The -s option allows a comma-separated list of services to be specified. It also allows you to specify a function with a name that differs from that of the advertised service that is to be called to process the service request. Refer to the buildserver(1) in the BEA Tuxedo Command Reference for more information.
The default specification calls for the server to advertise all services with which it was built. Refer to the UBBCONFIG(5) or servopts(5) reference page in the File Formats, Data Descriptions, MIBs, and System Processes Reference for more information.
Because an advertised service uses a service table entry in the bulletin board, and can therefore be resource-expensive, an application may boot its servers in such a way that only a subset of the services offered are available. To limit the services available in an application, define the CLOPT parameter, within the appropriate entry in the SERVERS section of the configuration file, to include the desired services in a comma-separated list following the -s option. The -s option also allows you to specify a function with a name other than that of the advertised service to be called to process the request. Refer to the servopts(5) reference page in the File Formats, Data Descriptions, MIBs, and System Processes Reference for more information.
A BEA Tuxedo application administrator can use the advertise and unadvertise commands of tmadmin(1) to control the services offered by servers. The tpadvertise() and tpunadvertise() functions enable you to dynamically control the advertisement of a service in a request/response or conversational server. The service to be advertised (or unadvertised) must be available within the same server as the service making the request.
Advertising Services
Use the following signature to call the tpadvertise(3c) function:
int
tpadvertise(char *svcname, void *func)
The following table describes the arguments to the tpadvertise() function.
Table 5-4 tpadvertise( ) Function Arguments
Unadvertising Services
The tpunadvertise(3c) function removes the name of a service from the service table of the bulletin board so that the service is no longer advertised.
Use the following signature for the tpunadvertise() function:
tpunadvertise(char *svcname)
char *svcname;
The tpunadvertise() function contains one argument, which is described in the following table.
Table 5-5 tpunadvertise( ) FunctionArguments
Example: Dynamic Advertising and Unadvertising of a Service
The following example shows how to use the tpadvertise() function. In this example, a server called TLR is programmed to offer only the service called TLR_INIT when booted. After some initialization, TLR_INIT advertises two services called DEPOSIT and WITHDRAW. Both are performed by the tlr_funcs function, and both are built into the TLR server.
After advertising DEPOSIT and WITHDRAW, TLR_INIT unadvertises itself.
Listing 5-10 Dynamic Advertising and Unadvertising
extern void tlr_funcs()
.
.
.
if (tpadvertise("DEPOSIT", (tlr_funcs)(TPSVCINFO *)) == -1)
check for errors;
if (tpadvertise("WITHDRAW", (tlr_funcs)(TPSVCINFO *)) == -1)
check for errors;
if (tpunadvertise("TLR_INIT") == -1)
check for errors;
tpreturn(TPSUCCESS, 0, transb->data,0L, 0);
Building Servers
To build an executable ATMI server, compile your application service subroutines with the BEA Tuxedo system server adaptor and all other referenced files using the buildserver(1) command.
Note: The BEA Tuxedo server adaptor accepts messages, dispatches work, and manages transactions (if transactions are enabled).
Use the following syntax for the buildserver command:
buildserver -ofilename-ffilenames-lfilenames-s -v
The following table describes the buildserver command-line options:
|
List of files that are link edited before the BEA Tuxedo system libraries. You can specify the |
|
|
List of files that are link edited after the BEA Tuxedo system libraries. You can specify the |
|
|
List of resource manager access libraries that are link edited with the executable server. The application administrator is responsible for predefining all valid resource manager information in the |
|
|
Name of service or services offered by the server and the name of the function that performs each service. You can specify the Typically, you should assign the same name to both the service and the function that performs that service. Alternatively, you can specify any names. To assign names, use the following syntax: |
|
|
Specifies that the server is coded in a thread-safe manner and may be booted as multithreaded if specified as such in the configuration file. |
Note: The BEA Tuxedo libraries are linked in automatically. You do not need to specify the BEA Tuxedo library names on the command line.
The order in which you specify the library files to be link edited is significant: it depends on the order in which functions are called and which libraries contain references to those functions.
By default, the buildserver command invokes the UNIX cc command. You can specify an alternative compile command and set your own flags for the compile and link-edit phases, however, by setting the CC and CFLAGS environment variables, respectively. For more information, refer to Setting Environment Variables.
The following command processes the acct.o application file and creates a server called ACCT that contains two services: NEW_ACCT, which calls the OPEN_ACCT function, and CLOSE_ACCT, which calls a function of the same name.
buildserver -o ACCT -f acct.o -s NEW_ACCT:OPEN_ACCT -s CLOSE_ACCT
See Also
- Building Clients
- buildclient(1) in the BEA Tuxedo Command Reference
Using a C++ Compiler
There are basically two differences between using a C++ compiler and a C compiler to develop application ATMI servers:
Declaring Service Functions
When declaring a service function for a C++ compiler, you must declare it to have "C" linkage using extern "C". Specify the function prototype as follows:
#ifdef __cplusplus
extern "C"
#endif
MYSERVICE(TPSVCINFO *tpsvcinfo)
By declaring the name of your service with "C" linkage, you ensure that the C++ compiler will not modify the name. Many C++ compilers change the function name to include type information for the parameters and function return.
This declaration also allows you to:
- Link both C and C++ service routines into a single server without indicating the type of each routine.
- Use dynamic service advertisement, which requires accessing the symbol table of the executable to find the function name.
Using Constructors and Destructors
C++ constructors are called to initialize class objects when those objects are created, and destructors are invoked when class objects are destroyed. For automatic (that is, local, non-static) variables that contain constructors and destructors, the constructor is called when the variable comes into scope and the destructor is called when the variable goes out of scope. However, when you call the tpreturn() or tpforward() function, the compiler performs a non-local goto (using longjmp(3)) such that destructors for automatic variables are not called. To avoid this problem, write the application so that you call tpreturn() or tpforward() from the service routine directly (instead of from any functions that are called from the service routine). In addition, one of the following should be true:
- The service routine should not have any automatic variables with destructors (they should be declared and used in a function called by the service routine).
- Automatic variables should be declared and used in a nested scope (contained within curly brackets {}) in such a way that the scope ends before calling the tpreturn() or tpforward() function.
In other words, you should define the application so that there are no automatic variables with destructors in scope in the current function or on the stack when the tpreturn() or tpforward() function is called.
For proper handling of global and static variables that contain constructors and destructors, many C++ compilers require that you compile main() using the C++ compiler.
Note: Special processing is included in the main() routine to ensure that any constructors are executed when the program starts and any destructors are executed when the program exits.
Because main() is provided by the BEA Tuxedo system, you do not compile it directly. To ensure that the file is compiled using C++, you must use the C++ compiler with the buildserver command. By default, the buildserver command invokes the UNIX cc command. You can specify that the buildserver command invoke the C++ compiler, instead, by setting the CC environment variable to the full path name for the C++ compiler. Also, you can set flags for any options that you want to include on the C++ command line by setting the CFLAGS environment variable. For more information, refer to Setting Environment Variables.
