Microsoft KB Archive/138613

= How to Use the SYS(3052) Function to Avoid Scrolling Error =

Article ID: 138613

Article Last Modified on 8/26/1999

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APPLIES TO


 * Microsoft Visual FoxPro 3.0 Standard Edition

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This article was previously published under Q138613



SUMMARY
The SYS(3052) function helps prevent the scrolling error message "Record Not Available, please wait" by specifying whether or not Visual FoxPro uses the SET REPROCESS settings when attempting to lock an index or a memo file. This article explains how to use the SYS(3052) function in multiuser applications.



MORE INFORMATION
The "Record not available, please wait" message is displayed when a table is updated but the index or memo file cannot be locked. There is not a way to escape or cancel this warning message until the contention has been resolved. By modifying the locking order of files, the SYS(3052) function can help suppress the scrolling message.

Currently, for performance optimization, Visual FoxPro performs record locks on a table and file locks on a memo and index file in the following order:

Lock table record

Write table record

Lock memo file

Write memo file

Lock index file

Write index file

When the index and memo attributes of the SYS(3052) function are set to True (.T.), the locking and updating order is as follows:

Lock table record

Lock memo file

Lock index file

Write table record

Write memo file

Write index file

As a result of using the SYS(3052) function, the scrolling "Record not available, please wait" message is less likely to occur. If this message is displayed, an abnormal shutdown would cause less discrepancy because neither the table nor the memo or index files have been updated.

The following example illustrates how to use the SYS(3052) function. To run it:


 * 1) Copy and paste the two sample programs into two program files, Server.prg and Client.prg.
 * 2) Start two instances of Visual FoxPro and run Server.prg.
 * 3) When the programs have run, issue an END TRANSACTION command in the instance of Visual FoxPro that ran Server.prg.

Sample Programs
*:*************************************************************************  SET SAFETY OFF SET EXCLUSIVE OFF
 * Procedure File Server.prg
 * SERVER
 * SERVER

CLOSE DATA ALL IF FILE('TSTSRVER.dbc') DELETE DATA TSTSRVER DELETETABLES ENDIF

=SYS(3052,1,.T.) =SYS(3052,2,.T.)

CREATE DATA TSTSRVER && Creates a database and a table CREATE TABLE xxx (dbkey i PRIMARY KEY, field2 c(5), field3 m)

INSERT INTO xxx VALUES (1, 'aaaaa', 'long string 1') INSERT INTO xxx VALUES (2, 'bbbbb', 'long string 2') INSERT INTO xxx VALUES (3, 'ccccc', 'long string 3') INSERT INTO xxx VALUES (4, 'ddddd', 'long string 4') INSERT INTO xxx VALUES (5, 'eeeee', 'long string 5')

CLOSE DATA ALL OPEN DATA TSTSRVER SHARED =MESSAGEBOX('Start the Client program on the second instance now.') USE xxx SHARED && Executes after the Client program is started

BEGIN TRANSACTION GOTO 2 REPLACE field3 WITH 'Changed String' SKIP ?'Return to client and press ok.'

SET SAFETY OFF SET EXCLUSIVE OFF CLOSE DATA ALL
 * Procedure File Client.prg
 * CLIENT
 * CLIENT
 * CLIENT

=SYS(3052,1,.T.) && Changes the lock and write order =SYS(3052,2,.T.)

USE XXX SHARED =MESSAGEBOX('Switch to server and press OK')

GOTO 1 REPLACE field3 WITH 'Changed String from client' SKIP When these programs are run, the message "Attempting To Lock. Press Cancel" is displayed. When you press the ESC key, the error "Record is in Use by another user" appears, or your ON ERROR routine is triggered.

If you change the settings of SYS(3052) to false (.F.) in Client.prg, the scrolling message "Record not available, please wait" is displayed.

Additional query words: VFoxWin rlock flock locking

Keywords: KB138613

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