119 DBMS_PIPE
The DBMS_PIPE package lets two or more sessions in the same instance communicate. Oracle pipes are similar in concept to the pipes used in UNIX, but Oracle pipes are not implemented using the operating system pipe mechanisms.
119.1 DBMS_PIPE Overview
Pipe functionality has several potential applications: external service interface, independent transactions, alerters (non-transactional), debugging, and concentrator.
-
External service interface: You can communicate with user-written services that are external to the RDBMS. This can be done effectively in a shared server process, so that several instances of the service are executing simultaneously. Additionally, the services are available asynchronously. The requestor of the service does not need to block a waiting reply. The requestor can check (with or without time out) at a later time. The service can be written in any of the 3GL languages that Oracle supports.
-
Independent transactions: The pipe can communicate to a separate session which can perform an operation in an independent transaction (such as logging an attempted security violation detected by a trigger).
-
Alerters (non-transactional): You can post another process without requiring the waiting process to poll. If an "after-row" or "after-statement" trigger were to alert an application, then the application would treat this alert as an indication that the data probably changed. The application would then read the data to get the current value. Because this is an "after" trigger, the application would want to do a "
SELECTFORUPDATE" to make sure it read the correct data. -
Debugging: Triggers and stored procedures can send debugging information to a pipe. Another session can keep reading out of the pipe and display it on the screen or write it to a file.
-
Concentrator: This is useful for multiplexing large numbers of users over a fewer number of network connections, or improving performance by concentrating several user-transactions into one DBMS transaction.
119.2 DBMS_PIPE Security Model
Security can be achieved by use of GRANT EXECUTE on the DBMS_PIPE package by creating a pipe using the private parameter in the CREATE_PIPE function and by writing cover packages that only expose particular features or pipenames to particular users or roles.
Depending upon your security requirements, you may choose to use either public pipes or private pipes, which are described in DBMS_PIPE Operational Notes.
119.3 DBMS_PIPE Constants
This is the maximum time to wait attempting to send or receive a message.
maxwait constant integer := 86400000; /* 1000 days */
119.4 DBMS_PIPE Operational Notes
Information sent through Oracle pipes is buffered in the system global area (SGA). All information in pipes is lost when the instance is shut down.
WARNING:
Pipes are independent of transactions. Be careful using pipes when transaction control can be affected.
The operation of DBMS_PIPE is considered with regard to the following topics:
-
Public Pipes
-
Writing and Reading Pipes
-
Private Pipes
Public Pipes
You may create a public pipe either implicitly or explicitly. For implicit public pipes, the pipe is automatically created when it is referenced for the first time, and it disappears when it no longer contains data. Because the pipe descriptor is stored in the SGA, there is some space usage overhead until the empty pipe is aged out of the cache.
You create an explicit public pipe by calling the CREATE_PIPE function with the private flag set to FALSE. You must deallocate explicitly-created pipes by calling the REMOVE_PIPE function.
The domain of a public pipe is the schema in which it was created, either explicitly or implicitly.
Reading and Writing Pipes
Each public pipe works asynchronously. Any number of schema users can write to a public pipe, as long as they have EXECUTE permission on the DBMS_PIPE package, and they know the name of the public pipe. However, once buffered information is read by one user, it is emptied from the buffer, and is not available for other readers of the same pipe.
The sending session builds a message using one or more calls to the PACK_MESSAGE procedure. This procedure adds the message to the session's local message buffer. The information in this buffer is sent by calling the SEND_MESSAGE function, designating the pipe name to be used to send the message. When SEND_MESSAGE is called, all messages that have been stacked in the local buffer are sent.
A process that wants to receive a message calls the RECEIVE_MESSAGE function, designating the pipe name from which to receive the message. The process then calls the UNPACK_MESSAGE procedure to access each of the items in the message.
Private Pipes
You explicitly create a private pipe by calling the CREATE_PIPE function. Once created, the private pipe persists in shared memory until you explicitly deallocate it by calling the REMOVE_PIPE function. A private pipe is also deallocated when the database instance is shut down.
You cannot create a private pipe if an implicit pipe exists in memory and has the same name as the private pipe you are trying to create. In this case, CREATE_PIPE returns an error.
Access to a private pipe is restricted to:
-
Sessions running under the same userid as the creator of the pipe
-
Stored subprograms executing in the same userid privilege domain as the pipe creator
-
Users connected as
SYSDBA
An attempt by any other user to send or receive messages on the pipe, or to remove the pipe, results in an immediate error. Any attempt by another user to create a pipe with the same name also causes an error.
As with public pipes, you must first build your message using calls to PACK_MESSAGE before calling SEND_MESSAGE. Similarly, you must call RECEIVE_MESSAGE to retrieve the message before accessing the items in the message by calling UNPACK_MESSAGE.
119.5 DBMS_PIPE Exceptions
DBMS_PIPE package subprograms can return the errors listed in the following table.
Table 119-1 DBMS_PIPE Errors
| Error | Description |
|---|---|
|
|
Pipename may not be null. This can be returned by the |
|
|
Insufficient privilege to access pipe. This can be returned by any subprogram that references a private pipe in its parameter list. |
119.6 DBMS_PIPE Examples
These examples show use of DBMS_PIPE in debugging PL/SQL, debugging Pro*C, executing system commands, and an external service interface.
Example 1: Debugging - PL/SQL
This example shows the procedure that a PL/SQL program can call to place debugging information in a pipe.
CREATE OR REPLACE PROCEDURE debug (msg VARCHAR2) AS
status NUMBER;
BEGIN
DBMS_PIPE.PACK_MESSAGE(LENGTH(msg));
DBMS_PIPE.PACK_MESSAGE(msg);
status := DBMS_PIPE.SEND_MESSAGE('plsql_debug');
IF status != 0 THEN
raise_application_error(-20099, 'Debug error');
END IF;
END debug;
Example 2: Debugging - Pro*C
The following Pro*C code receives messages from the PLSQL_DEBUG pipe in the previous example, and displays the messages. If the Pro*C session is run in a separate window, then it can be used to display any messages that are sent to the debug procedure from a PL/SQL program executing in a separate session.
#include <stdio.h>
#include <string.h>
EXEC SQL BEGIN DECLARE SECTION;
VARCHAR username[20];
int status;
int msg_length;
char retval[2000];
EXEC SQL END DECLARE SECTION;
EXEC SQL INCLUDE SQLCA;
void sql_error();
main()
{
-- Prepare username:
strcpy(username.arr, "HR/<password>");
username.len = strlen(username.arr);
EXEC SQL WHENEVER SQLERROR DO sql_error();
EXEC SQL CONNECT :username;
printf("connected\n");
-- Start an endless loop to look for and print messages on the pipe:
FOR (;;)
{
EXEC SQL EXECUTE
DECLARE
len INTEGER;
typ INTEGER;
sta INTEGER;
chr VARCHAR2(2000);
BEGIN
chr := '';
sta := dbms_pipe.receive_message('plsql_debug');
IF sta = 0 THEN
DBMS_PIPE.UNPACK_MESSAGE(len);
DBMS_PIPE.UNPACK_MESSAGE(chr);
END IF;
:status := sta;
:retval := chr;
IF len IS NOT NULL THEN
:msg_length := len;
ELSE
:msg_length := 2000;
END IF;
END;
END-EXEC;
IF (status == 0)
printf("\n%.*s\n", msg_length, retval);
ELSE
printf("abnormal status, value is %d\n", status);
}
}
void sql_error()
{
char msg[1024];
int rlen, len;
len = sizeof(msg);
sqlglm(msg, &len, &rlen);
printf("ORACLE ERROR\n");
printf("%.*s\n", rlen, msg);
exit(1);
} Example 3: Execute System Commands
This example shows PL/SQL and Pro*C code let a PL/SQL stored procedure (or anonymous block) call PL/SQL procedures to send commands over a pipe to a Pro*C program that is listening for them.
The Pro*C program sleeps and waits for a message to arrive on the named pipe. When a message arrives, the Pro*C program processes it, carrying out the required action, such as executing a UNIX command through the system() call or executing a SQL command using embedded SQL.
DAEMON.SQL is the source code for the PL/SQL package. This package contains procedures that use the DBMS_PIPE package to send and receive message to and from the Pro*C daemon. Note that full handshaking is used. The daemon always sends a message back to the package (except in the case of the STOP command). This is valuable, because it allows the PL/SQL procedures to be sure that the Pro*C daemon is running.
You can call the DAEMON packaged procedures from an anonymous PL/SQL block using SQL*Plus or Enterprise Manager. For example:
SQLPLUS> variable rv number
SQLPLUS> execute :rv := DAEMON.EXECUTE_SYSTEM('ls -la');
On a UNIX system, this causes the Pro*C daemon to execute the command system("ls -la").
Remember that the daemon needs to be running first. You might want to run it in the background, or in another window beside the SQL*Plus or Enterprise Manager session from which you call it.
The DAEMON.SQL also uses the DBMS_OUTPUT package to display the results. For this example to work, you must have execute privileges on this package.
DAEMON.SQL Example. This is the code for the PL/SQL DAEMON package:
CREATE OR REPLACE PACKAGE daemon AS
FUNCTION execute_sql(command VARCHAR2,
timeout NUMBER DEFAULT 10)
RETURN NUMBER;
FUNCTION execute_system(command VARCHAR2,
timeout NUMBER DEFAULT 10)
RETURN NUMBER;
PROCEDURE stop(timeout NUMBER DEFAULT 10);
END daemon;
/
CREATE OR REPLACE PACKAGE BODY daemon AS
FUNCTION execute_system(command VARCHAR2,
timeout NUMBER DEFAULT 10)
RETURN NUMBER IS
status NUMBER;
result VARCHAR2(20);
command_code NUMBER;
pipe_name VARCHAR2(30);
BEGIN
pipe_name := DBMS_PIPE.UNIQUE_SESSION_NAME;
DBMS_PIPE.PACK_MESSAGE('SYSTEM');
DBMS_PIPE.PACK_MESSAGE(pipe_name);
DBMS_PIPE.PACK_MESSAGE(command);
status := DBMS_PIPE.SEND_MESSAGE('daemon', timeout);
IF status <> 0 THEN
RAISE_APPLICATION_ERROR(-20010,
'Execute_system: Error while sending. Status = ' ||
status);
END IF;
status := DBMS_PIPE.RECEIVE_MESSAGE(pipe_name, timeout);
IF status <> 0 THEN
RAISE_APPLICATION_ERROR(-20011,
'Execute_system: Error while receiving.
Status = ' || status);
END IF;
DBMS_PIPE.UNPACK_MESSAGE(result);
IF result <> 'done' THEN
RAISE_APPLICATION_ERROR(-20012,
'Execute_system: Done not received.');
END IF;
DBMS_PIPE.UNPACK_MESSAGE(command_code);
DBMS_OUTPUT.PUT_LINE('System command executed. result = ' ||
command_code);
RETURN command_code;
END execute_system;
FUNCTION execute_sql(command VARCHAR2,
timeout NUMBER DEFAULT 10)
RETURN NUMBER IS
status NUMBER;
result VARCHAR2(20);
command_code NUMBER;
pipe_name VARCHAR2(30);
BEGIN
pipe_name := DBMS_PIPE.UNIQUE_SESSION_NAME;
DBMS_PIPE.PACK_MESSAGE('SQL');
DBMS_PIPE.PACK_MESSAGE(pipe_name);
DBMS_PIPE.PACK_MESSAGE(command);
status := DBMS_PIPE.SEND_MESSAGE('daemon', timeout);
IF status <> 0 THEN
RAISE_APPLICATION_ERROR(-20020,
'Execute_sql: Error while sending. Status = ' || status);
END IF;
status := DBMS_PIPE.RECEIVE_MESSAGE(pipe_name, timeout);
IF status <> 0 THEN
RAISE_APPLICATION_ERROR(-20021,
'execute_sql: Error while receiving.
Status = ' || status);
END IF;
DBMS_PIPE.UNPACK_MESSAGE(result);
IF result <> 'done' THEN
RAISE_APPLICATION_ERROR(-20022,
'execute_sql: done not received.');
END IF;
DBMS_PIPE.UNPACK_MESSAGE(command_code);
DBMS_OUTPUT.PUT_LINE
('SQL command executed. sqlcode = ' || command_code);
RETURN command_code;
END execute_sql;
PROCEDURE stop(timeout NUMBER DEFAULT 10) IS
status NUMBER;
BEGIN
DBMS_PIPE.PACK_MESSAGE('STOP');
status := DBMS_PIPE.SEND_MESSAGE('daemon', timeout);
IF status <> 0 THEN
RAISE_APPLICATION_ERROR(-20030,
'stop: error while sending. status = ' || status);
END IF;
END stop;
END daemon;daemon.pc Example. This is the code for the Pro*C daemon. You must precompile this using the Pro*C Precompiler, Version 1.5.x or later. You must also specify the USERID and SQLCHECK options, as the example contains embedded PL/SQL code.
Note:
To use a VARCHAR output host variable in a PL/SQL block, you must initialize the length component before entering the block.
proc iname=daemon userid=HR/<password> sqlcheck=semantics
Then C-compile and link in the normal way.
#include <stdio.h>
#include <string.h>
EXEC SQL INCLUDE SQLCA;
EXEC SQL BEGIN DECLARE SECTION;
char *uid = "HR/<password>";
int status;
VARCHAR command[20];
VARCHAR value[2000];
VARCHAR return_name[30];
EXEC SQL END DECLARE SECTION;
void
connect_error()
{
char msg_buffer[512];
int msg_length;
int buffer_size = 512;
EXEC SQL WHENEVER SQLERROR CONTINUE;
sqlglm(msg_buffer, &buffer_size, &msg_length);
printf("Daemon error while connecting:\n");
printf("%.*s\n", msg_length, msg_buffer);
printf("Daemon quitting.\n");
exit(1);
}
void
sql_error()
{
char msg_buffer[512];
int msg_length;
int buffer_size = 512;
EXEC SQL WHENEVER SQLERROR CONTINUE;
sqlglm(msg_buffer, &buffer_size, &msg_length);
printf("Daemon error while executing:\n");
printf("%.*s\n", msg_length, msg_buffer);
printf("Daemon continuing.\n");
}
main()
{
command.len = 20; /*initialize length components*/
value.len = 2000;
return_name.len = 30;
EXEC SQL WHENEVER SQLERROR DO connect_error();
EXEC SQL CONNECT :uid;
printf("Daemon connected.\n");
EXEC SQL WHENEVER SQLERROR DO sql_error();
printf("Daemon waiting...\n");
while (1) {
EXEC SQL EXECUTE
BEGIN
:status := DBMS_PIPE.RECEIVE_MESSAGE('daemon');
IF :status = 0 THEN
DBMS_PIPE.UNPACK_MESSAGE(:command);
END IF;
END;
END-EXEC;
IF (status == 0)
{
command.arr[command.len] = '\0';
IF (!strcmp((char *) command.arr, "STOP"))
{
printf("Daemon exiting.\n");
break;
}
ELSE IF (!strcmp((char *) command.arr, "SYSTEM"))
{
EXEC SQL EXECUTE
BEGIN
DBMS_PIPE.UNPACK_MESSAGE(:return_name);
DBMS_PIPE.UNPACK_MESSAGE(:value);
END;
END-EXEC;
value.arr[value.len] = '\0';
printf("Will execute system command '%s'\n", value.arr);
status = system(value.arr);
EXEC SQL EXECUTE
BEGIN
DBMS_PIPE.PACK_MESSAGE('done');
DBMS_PIPE.PACK_MESSAGE(:status);
:status := DBMS_PIPE.SEND_MESSAGE(:return_name);
END;
END-EXEC;
IF (status)
{
printf
("Daemon error while responding to system command.");
printf(" status: %d\n", status);
}
}
ELSE IF (!strcmp((char *) command.arr, "SQL")) {
EXEC SQL EXECUTE
BEGIN
DBMS_PIPE.UNPACK_MESSAGE(:return_name);
DBMS_PIPE.UNPACK_MESSAGE(:value);
END;
END-EXEC;
value.arr[value.len] = '\0';
printf("Will execute sql command '%s'\n", value.arr);
EXEC SQL WHENEVER SQLERROR CONTINUE;
EXEC SQL EXECUTE IMMEDIATE :value;
status = sqlca.sqlcode;
EXEC SQL WHENEVER SQLERROR DO sql_error();
EXEC SQL EXECUTE
BEGIN
DBMS_PIPE.PACK_MESSAGE('done');
DBMS_PIPE.PACK_MESSAGE(:status);
:status := DBMS_PIPE.SEND_MESSAGE(:return_name);
END;
END-EXEC;
IF (status)
{
printf("Daemon error while responding to sql command.");
printf(" status: %d\n", status);
}
}
ELSE
{
printf
("Daemon error: invalid command '%s' received.\n",
command.arr);
}
}
ELSE
{
printf("Daemon error while waiting for signal.");
printf(" status = %d\n", status);
}
}
EXEC SQL COMMIT WORK RELEASE;
exit(0);Example 4: External Service Interface
Put the user-written 3GL code into an OCI or Precompiler program. The program connects to the database and executes PL/SQL code to read its request from the pipe, computes the result, and then executes PL/SQL code to send the result on a pipe back to the requestor.
Below is an example of a stock service request. The recommended sequence for the arguments to pass on the pipe for all service requests is:
protocol_version VARCHAR2 - '1', 10 bytes or less
returnpipe VARCHAR2 - 30 bytes or less
service VARCHAR2 - 30 bytes or less
arg1 VARCHAR2/NUMBER/DATE
...
argn VARCHAR2/NUMBER/DATE
The recommended format for returning the result is:
success VARCHAR2 - 'SUCCESS' if OK,
otherwise error message
arg1 VARCHAR2/NUMBER/DATE
...
argn VARCHAR2/NUMBER/DATE
The "stock price request server" would do, using OCI or PRO* (in pseudo-code):
<loop forever>
BEGIN dbms_stock_server.get_request(:stocksymbol); END;
<figure out price based on stocksymbol (probably from some radio
signal), set error if can't find such a stock>
BEGIN dbms_stock_server.return_price(:error, :price); END;
A client would do:
BEGIN :price := stock_request('YOURCOMPANY'); end;
The stored procedure, dbms_stock_server, which is called by the preceding "stock price request server" is:
CREATE OR REPLACE PACKAGE dbms_stock_server IS
PROCEDURE get_request(symbol OUT VARCHAR2);
PROCEDURE return_price(errormsg IN VARCHAR2, price IN VARCHAR2);
END;
CREATE OR REPLACE PACKAGE BODY dbms_stock_server IS
returnpipe VARCHAR2(30);
PROCEDURE returnerror(reason VARCHAR2) IS
s INTEGER;
BEGIN
dbms_pipe.pack_message(reason);
s := dbms_pipe.send_message(returnpipe);
IF s <> 0 THEN
raise_application_error(-20000, 'Error:' || to_char(s) ||
' sending on pipe');
END IF;
END;
PROCEDURE get_request(symbol OUT VARCHAR2) IS
protocol_version VARCHAR2(10);
s INTEGER;
service VARCHAR2(30);
BEGIN
s := dbms_pipe.receive_message('stock_service');
IF s <> 0 THEN
raise_application_error(-20000, 'Error:' || to_char(s) ||
'reading pipe');
END IF;
dbms_pipe.unpack_message(protocol_version);
IF protocol_version <> '1' THEN
raise_application_error(-20000, 'Bad protocol: ' ||
protocol_version);
END IF;
dbms_pipe.unpack_message(returnpipe);
dbms_pipe.unpack_message(service);
IF service != 'getprice' THEN
returnerror('Service ' || service || ' not supported');
END IF;
dbms_pipe.unpack_message(symbol);
END;
PROCEDURE return_price(errormsg in VARCHAR2, price in VARCHAR2) IS
s INTEGER;
BEGIN
IF errormsg is NULL THEN
dbms_pipe.pack_message('SUCCESS');
dbms_pipe.pack_message(price);
ELSE
dbms_pipe.pack_message(errormsg);
END IF;
s := dbms_pipe.send_message(returnpipe);
IF s <> 0 THEN
raise_application_error(-20000, 'Error:'||to_char(s)||
' sending on pipe');
END IF;
END;
END;
The procedure called by the client is:
CREATE OR REPLACE FUNCTION stock_request (symbol VARCHAR2)
RETURN VARCHAR2 IS
s INTEGER;
price VARCHAR2(20);
errormsg VARCHAR2(512);
BEGIN
dbms_pipe.pack_message('1'); -- protocol version
dbms_pipe.pack_message(dbms_pipe.unique_session_name); -- return pipe
dbms_pipe.pack_message('getprice');
dbms_pipe.pack_message(symbol);
s := dbms_pipe.send_message('stock_service');
IF s <> 0 THEN
raise_application_error(-20000, 'Error:'||to_char(s)||
' sending on pipe');
END IF;
s := dbms_pipe.receive_message(dbms_pipe.unique_session_name);
IF s <> 0 THEN
raise_application_error(-20000, 'Error:'||to_char(s)||
' receiving on pipe');
END IF;
dbms_pipe.unpack_message(errormsg);
IF errormsg <> 'SUCCESS' THEN
raise_application_error(-20000, errormsg);
END IF;
dbms_pipe.unpack_message(price);
RETURN price;
END;
You would typically only GRANT EXECUTE on DBMS_STOCK_SERVICE to the stock service application server, and would only GRANT EXECUTE on stock_request to those users allowed to use the service.
See Also:
119.7 Summary of DBMS_PIPE Subprograms
This table lists the DBMS_PIPE subprograms and briefly describes them.
Table 119-2 DBMS_PIPE Package Subprograms
| Subprogram | Description |
|---|---|
|
Creates a pipe (necessary for private pipes) |
|
|
Returns datatype of next item in buffer |
|
|
Builds message in local buffer |
|
|
Purges contents of named pipe |
|
|
Copies message from named pipe into local buffer |
|
|
Removes the named pipe |
|
|
Purges contents of local buffer |
|
|
Sends message on named pipe: This implicitly creates a public pipe if the named pipe does not exist |
|
|
Returns unique session name |
|
|
Accesses next item in buffer |
119.7.1 CREATE_PIPE Function
This function explicitly creates a public or private pipe. If the private flag is TRUE, then the pipe creator is assigned as the owner of the private pipe.
Explicitly-created pipes can only be removed by calling REMOVE_PIPE, or by shutting down the instance.
Syntax
DBMS_PIPE.CREATE_PIPE ( pipename IN VARCHAR2, maxpipesize IN INTEGER DEFAULT 8192, private IN BOOLEAN DEFAULT TRUE) RETURN INTEGER;
Pragmas
pragma restrict_references(create_pipe,WNDS,RNDS);
Parameters
Table 119-3 CREATE_PIPE Function Parameters
| Parameter | Description |
|---|---|
|
|
Name of the pipe you are creating. You must use this name when you call Caution: Do not use pipe names beginning with |
|
|
The maximum size allowed for the pipe, in bytes. The total size of all of the messages on the pipe cannot exceed this amount. The message is blocked if it exceeds this maximum. The default The |
|
|
Uses the default, Public pipes can be implicitly created when you call |
Return Values
Table 119-4 CREATE_PIPE Function Return Values
| Return | Description |
|---|---|
|
|
Successful. If the pipe already exists and the user attempting to create it is authorized to use it, then Oracle returns 0, indicating success, and any data already in the pipe remains. If a user connected as |
|
|
Failure due to naming conflict. If a pipe with the same name exists and was created by a different user, then Oracle signals error |
Exceptions
Table 119-5 CREATE_PIPE Function Exception
| Exception | Description |
|---|---|
|
|
Permission error: Pipe with the same name already exists, and you are not allowed to use it. |
119.7.2 NEXT_ITEM_TYPE Function
This function determines the datatype of the next item in the local message buffer.
After you have called RECEIVE_MESSAGE to place pipe information in a local buffer, call NEXT_ITEM_TYPE.
Syntax
DBMS_PIPE.NEXT_ITEM_TYPE RETURN INTEGER;
Pragmas
pragma restrict_references(next_item_type,WNDS,RNDS);
Return Values
Table 119-6 NEXT_ITEM_TYPE Function Return Values
| Return | Description |
|---|---|
|
|
No more items |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
119.7.3 PACK_MESSAGE Procedures
This procedure builds your message in the local message buffer.
To send a message, first make one or more calls to PACK_MESSAGE. Then, call SEND_MESSAGE to send the message in the local buffer on the named pipe.
The procedure is overloaded to accept items of type VARCHAR2, NCHAR, NUMBER, DATE., RAW and ROWID items. In addition to the data bytes, each item in the buffer requires one byte to indicate its type, and two bytes to store its length. One additional byte is needed to terminate the message.The overhead for all types other than VARCHAR is 4 bytes.
Syntax
DBMS_PIPE.PACK_MESSAGE ( item IN VARCHAR2); DBMS_PIPE.PACK_MESSAGE ( item IN NCHAR); DBMS_PIPE.PACK_MESSAGE ( item IN NUMBER); DBMS_PIPE.PACK_MESSAGE ( item IN DATE); DBMS_PIPE.PACK_MESSAGE_RAW ( item IN RAW); DBMS_PIPE.PACK_MESSAGE_ROWID ( item IN ROWID);
Pragmas
pragma restrict_references(pack_message,WNDS,RNDS); pragma restrict_references(pack_message_raw,WNDS,RNDS); pragma restrict_references(pack_message_rowid,WNDS,RNDS);
Parameters
Table 119-7 PACK_MESSAGE Procedure Parameters
| Parameter | Description |
|---|---|
|
|
Item to pack into the local message buffer. |
Usage Notes
In Oracle database version 8.x, the char-set-id (2 bytes) and the char-set-form (1 byte) are stored with each data item. Therefore, the overhead when using Oracle database version 8.x is 7 bytes.
When you call SEND_MESSAGE to send this message, you must indicate the name of the pipe on which you want to send the message. If this pipe already exists, then you must have sufficient privileges to access this pipe. If the pipe does not already exist, then it is created automatically.
Exceptions
ORA-06558 is raised if the message buffer overflows (currently 4096 bytes). Each item in the buffer takes one byte for the type, two bytes for the length, plus the actual data. There is also one byte needed to terminate the message.
119.7.4 PURGE Procedure
This procedure empties the contents of the named pipe.
An empty implicitly-created pipe is aged out of the shared global area according to the least-recently-used algorithm. Thus, calling PURGE lets you free the memory associated with an implicitly-created pipe.
Syntax
DBMS_PIPE.PURGE ( pipename IN VARCHAR2);
Pragmas
pragma restrict_references(purge,WNDS,RNDS);
Parameters
Table 119-8 PURGE Procedure Parameters
| Parameter | Description |
|---|---|
|
|
Name of pipe from which to remove all messages. The local buffer may be overwritten with messages as they are discarded. Pipename should not be longer than 128 bytes, and is case-insensitive. |
Usage Notes
Because PURGE calls RECEIVE_MESSAGE, the local buffer might be overwritten with messages as they are purged from the pipe. Also, you can receive an ORA-23322 (insufficient privileges) error if you attempt to purge a pipe with which you have insufficient access rights.
Exceptions
Permission error if pipe belongs to another user.
119.7.5 RECEIVE_MESSAGE Function
This function copies the message into the local message buffer.
Syntax
DBMS_PIPE.RECEIVE_MESSAGE ( pipename IN VARCHAR2, timeout IN INTEGER DEFAULT maxwait) RETURN INTEGER;
Pragmas
pragma restrict_references(receive_message,WNDS,RNDS);
Parameters
Table 119-9 RECEIVE_MESSAGE Function Parameters
| Parameter | Description |
|---|---|
|
|
Name of the pipe on which you want to receive a message. Names beginning with |
|
|
Time to wait for a message, in seconds. The default value is the constant |
Return Values
Table 119-10 RECEIVE_MESSAGE Function Return Values
| Return | Description |
|---|---|
|
|
Success |
|
|
Timed out. If the pipe was implicitly-created and is empty, then it is removed. |
|
|
Record in the pipe is too large for the buffer. (This should not happen.) |
|
|
An interrupt occurred. |
|
|
User has insufficient privileges to read from the pipe. |
Usage Notes
To receive a message from a pipe, first call RECEIVE_MESSAGE. When you receive a message, it is removed from the pipe; hence, a message can only be received once. For implicitly-created pipes, the pipe is removed after the last record is removed from the pipe.
If the pipe that you specify when you call RECEIVE_MESSAGE does not already exist, then Oracle implicitly creates the pipe and waits to receive the message. If the message does not arrive within a designated timeout interval, then the call returns and the pipe is removed.
After receiving the message, you must make one or more calls to UNPACK_MESSAGE to access the individual items in the message. The UNPACK_MESSAGE procedure is overloaded to unpack items of type DATE, NUMBER, VARCHAR2, and there are two additional procedures to unpack RAW and ROWID items. If you do not know the type of data that you are attempting to unpack, then call NEXT_ITEM_TYPE to determine the type of the next item in the buffer.
Exceptions
Table 119-11 RECEIVE_MESSAGE Function Exceptions
| Exception | Description |
|---|---|
|
|
Permission error. Insufficient privilege to remove the record from the pipe. The pipe is owned by someone else. |
119.7.6 RESET_BUFFER Procedure
This procedure resets the PACK_MESSAGE and UNPACK_MESSAGE positioning indicators to 0.
Because all pipes share a single buffer, you may find it useful to reset the buffer before using a new pipe. This ensures that the first time you attempt to send a message to your pipe, you do not inadvertently send an expired message remaining in the buffer.
Syntax
DBMS_PIPE.RESET_BUFFER;
Pragmas
pragma restrict_references(reset_buffer,WNDS,RNDS);
119.7.7 REMOVE_PIPE Function
This function removes explicitly-created pipes.
Pipes created implicitly by SEND_MESSAGE are automatically removed when empty. However, pipes created explicitly by CREATE_PIPE are removed only by calling REMOVE_PIPE, or by shutting down the instance. All unconsumed records in the pipe are removed before the pipe is deleted.
This is similar to calling PURGE on an implicitly-created pipe.
Syntax
DBMS_PIPE.REMOVE_PIPE ( pipename IN VARCHAR2) RETURN INTEGER;
Pragmas
pragma restrict_references(remove_pipe,WNDS,RNDS);
Parameters
Table 119-12 REMOVE_PIPE Function Parameters
| Parameter | Description |
|---|---|
|
|
Name of pipe that you want to remove. |
Return Values
Table 119-13 REMOVE_PIPE Function Return Values
| Return | Description |
|---|---|
|
|
Success If the pipe does not exist, or if the pipe already exists and the user attempting to remove it is authorized to do so, then Oracle returns 0, indicating success, and any data remaining in the pipe is removed. |
|
|
Insufficient privileges. If the pipe exists, but the user is not authorized to access the pipe, then Oracle signals error |
Exceptions
Table 119-14 REMOVE_PIPE Function Exception
| Exception | Description |
|---|---|
|
|
Permission error: Insufficient privilege to remove pipe. The pipe was created and is owned by someone else. |
119.7.8 SEND_MESSAGE Function
This function sends a message on the named pipe.
The message is contained in the local message buffer, which was filled with calls to PACK_MESSAGE. You can create a pipe explicitly using CREATE_PIPE, otherwise, it is created implicitly.
Syntax
DBMS_PIPE.SEND_MESSAGE (
pipename IN VARCHAR2,
timeout IN INTEGER DEFAULT MAXWAIT,
maxpipesize IN INTEGER DEFAULT 8192)
RETURN INTEGER;Pragmas
pragma restrict_references(send_message,WNDS,RNDS);
Parameters
Table 119-15 SEND_MESSAGE Function Parameters
| Parameter | Description |
|---|---|
|
|
Name of the pipe on which you want to place the message. If you are using an explicit pipe, then this is the name that you specified when you called Caution: Do not use pipe names beginning with ' |
|
|
Time to wait while attempting to place a message on a pipe, in seconds. The default value is the constant |
|
|
Maximum size allowed for the pipe, in bytes. The total size of all the messages on the pipe cannot exceed this amount. The message is blocked if it exceeds this maximum. The default is 8192 bytes. The Specifying |
Return Values
Table 119-16 SEND_MESSAGE Function Return Values
| Return | Description |
|---|---|
|
|
Success. If the pipe already exists and the user attempting to create it is authorized to use it, then Oracle returns 0, indicating success, and any data already in the pipe remains. If a user connected as |
|
|
Timed out. This procedure can timeout either because it cannot get a lock on the pipe, or because the pipe remains too full to be used. If the pipe was implicitly-created and is empty, then it is removed. |
|
|
An interrupt occurred. If the pipe was implicitly created and is empty, then it is removed. |
|
|
Insufficient privileges. If a pipe with the same name exists and was created by a different user, then Oracle signals error |
Exceptions
Table 119-17 SEND_MESSAGE Function Exception
| Exception | Description |
|---|---|
|
|
Permission error. Insufficient privilege to write to the pipe. The pipe is private and owned by someone else. |
119.7.9 UNIQUE_SESSION_NAME Function
This function receives a name that is unique among all of the sessions that are currently connected to a database.
Multiple calls to this function from the same session always return the same value. You might find it useful to use this function to supply the PIPENAME parameter for your SEND_MESSAGE and RECEIVE_MESSAGE calls.
Syntax
DBMS_PIPE.UNIQUE_SESSION_NAME RETURN VARCHAR2;
Pragmas
pragma restrict_references(unique_session_name,WNDS,RNDS,WNPS);
Return Values
This function returns a unique name. The returned name can be up to 30 bytes.
119.7.10 UNPACK_MESSAGE Procedures
This procedure retrieves items from the buffer.
After you have called RECEIVE_MESSAGE to place pipe information in a local buffer, call UNPACK_MESSAGE.
Note:
The UNPACK_MESSAGE procedure is overloaded to return items of type VARCHAR2, NCHAR, NUMBER, or DATE. There are two additional procedures to unpack RAW and ROWID items.
Syntax
DBMS_PIPE.UNPACK_MESSAGE ( item OUT VARCHAR2); DBMS_PIPE.UNPACK_MESSAGE ( item OUT NCHAR); DBMS_PIPE.UNPACK_MESSAGE ( item OUT NUMBER); DBMS_PIPE.UNPACK_MESSAGE ( item OUT DATE); DBMS_PIPE.UNPACK_MESSAGE_RAW ( item OUT RAW); DBMS_PIPE.UNPACK_MESSAGE_ROWID ( item OUT ROWID);
Pragmas
pragma restrict_references(unpack_message,WNDS,RNDS); pragma restrict_references(unpack_message_raw,WNDS,RNDS); pragma restrict_references(unpack_message_rowid,WNDS,RNDS);
Parameters
Table 119-18 UNPACK_MESSAGE Procedure Parameters
| Parameter | Description |
|---|---|
|
|
Argument to receive the next unpacked item from the local message buffer. |
Exceptions
ORA-06556 or 06559 are generated if the buffer contains no more items, or if the item is not of the same type as that requested.