Transcript Building Server Services with VFP - dFPUG

Session V17
Building Server Services
with Visual FoxPro
Rainer Becker
dFPUG, Germany
FoxTeach 2001
Who Am I?
• German FoxPro User Group
http://www.dfpug.de/forum
– German VFP DevCon
– FoxX Professional (4x200 pages)
• Wizards & Builders GmbH
http://www.wizards-builders.com
• MVP, MCSD, speaker/writer
– But I am not bilingual !
FoxTeach 2001
Defining the problem
What is the problem we solve with
a remote server service ?
FoxTeach 2001
Services on a Server
Multiply performance by direct table
access instead of network traffic for
(examples):
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Database reorg/reindex
Structure modification/update
Data synchronization
Data import (host)/export
Complex queries/reports
Long-running process (e.g. re-booking)
FoxTeach 2001
How to call a Server App
• CREATEOBJECT
– only local registration with /REGSERVER
or REGSRV32.EXE
• CREATEOBJECTX
– remote registration with CLIREG32.EXE
– But still no asynchronous connection...
But: Server Application must run
independent from Client App!
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Automatic Start on a Server
• AUTOEXEC.BAT
– Only for DOS Command
• AUTOSTART folder
– Only for active user
• SCHEDULER
– Configuration problem
• SERVICE
– Currently the most suitable solution
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Installing a “Service“
How to define a VFP server
service on Windows NT ?
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Installation of a “Service“
• Configuration / System Management /
Services
– Only allows changing of existing services
(e.g. execution type, used account)
– “Allow Interactive Relation to Desktop“
• Wizard “SRVINSTW.EXE“ allows
interactive installation of a service
• Interface for a service cannot be
supplied with VFP -> SRVANY.EXE
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Using the Install Wizard
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P1: [x] Install a service
P2: [x] Local Machine
P3: Service Name „Remote Server“
P4: Executable File „SRVANY.EXE“
P5: [x] Service is its own process
P6: [x] System account
– [x] Allow Service to interact with Desktop
• P7: [x] Automatic
• P8: Finish
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Configure SRVANY.EXE
• Call REGEDIT.EXE
• Navigate to “HKEY_LOCAL_MACHINE
\SYSTEM\CurrentControlSet\Services\”
• Navigate to your “Remote Service“
• Right mouse: Option “New“, Sub-option
“Key“, Value “Parameters“
• “New”, “Char”, “Application“, Value “
“<Drive>:<path>\<vgremote>.exe“
• “New”, “Char”, “AppDirectory“, Value
“<Drive>:\<path>“
• Optional “AppParameters“, Value “NONE“
FoxTeach 2001
How to start a Service
• Various Options to start/stop:
– Interactive with system configuration
– NET START/STOP “service name“
– SC START via SC commandline utility of
Windows NT
• Problem: Applet does not see VFPstatus but only SRVANY-status (even “
“QUIT“ still allows to start/stop/restart
the service) – confusing for admins!
FoxTeach 2001
Unattended Installation
• INSTSRV.EXE parameters
– Service name
– Exe location
– (-a account name)
– (-p account password)
– REMOVE
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Implementing Remote Server
How to implement a remote server
application ?
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Parameter Passing
• No access via object reference
• Parameter table instead
– User, Password (encrypted)
– Module, Object, Method, Parameter
Or
– Script-Memo (Single/Multi-Line)
– ErrorRetry
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Setup Methods
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Settings
SetVars / Properties
Set OnShutDown / Shutdown
Set OnError+ErrorHandler /
ErrorMethod
• OpenTable
• Endless Loop / Timer
(snp)
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Problems with Endless Loops
• Normally you get an endless loop by
accident with no work at all, but
– A typical endless loop produces 100%
workload in the Task Manager
– Additionally, it creates a GUI error with
SYS(2335,0) (unattended servermode)
• Solution: Use READ EVENTS with a
timer which fires CLEAR EVENTS
– (still you get problems with sys(2335,0)...)
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Job Execution Methods
• Scan Job-Table
• JobLock
• JobProcess
– Macro execution
– Script-compiling
– COM-Server creation/call
(snp)
• Repositioning
• JobUnlock
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Call COM Servers
• CREATEOBJECT
– Call an .EXE instead of .DLL to survive
execution failure
• LOGIN
– encryption for security
• Method-Call
– COMRETURNERROR if exclusive access
is needed but not available
• Return Value
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Configuration with Constants
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Name, Title, Caption
Table, Path
Retry on Error
Timer: Break between jobs
Master-User / -Password
Exclusive Access ComReturnError
For Discussion of constants see
session V18 Dynamic Constants
FoxTeach 2001
Logfile / Activity
• Low-Level Text File for Job-Log
– Datetime start/end, result/failure
• NT Eventlog not implemented yet
– WinAPI-problems occured
• Monitor activity from Client (snp)
• Restart via Starter Application
– CreateObjectX for Starter not Server
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Connect the Client
How to connect the client to the
remote server application ?
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Client Implementation
• Implementation as a service class
– Reusability needed
• Data access to job-table needed
– Place in a different class for later change
of table format or parameter passing type
• Read/Write Job-Table
– Read status information (see below)
– Timer for status information
• „Call once“ or „Call many“ jobs
FoxTeach 2001
Client Methods
• IsServerActive
• ServerStart
• JobCreate
• JobStatusGet
• JobTimerCreate (Thermometer)
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Thermometer Update
• Status information is wanted for
long-running remote jobs, but
– Server application cannot update
Job-Table as it is locked by the
remote server service
• Solution: 1:1-related table for
status information OR pass THIS
for a callback mechanism
– Use a wrapper object reference
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The “exclusive client“ Problem
• Some useful server jobs need
exclusive database access
(e.g. reorg, reindex, pack, backup)
• Client application can insert a job into
job-table, but that‘s it
– Server application will terminate again and
again as long as user is logged into app
• Depends on your implementation of
semaphores and locking
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Special Tricks
How can we
extend the
potential power
of remote server
services ?
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Multiple Server Services
• Even on a single processor server,
more than one instance might be
useful to shorten processing time
– See example in VFPSP3.CHM
– Just place a RUN-Task in job-table...
• Memory consumption problems
might be reduced by MultiThreaded VFP-Runtime (see SP3)
FoxTeach 2001
MQ / MSTS
• Parameter table can be replaced
by Message Queue Server
– No current experience
• Instantiation time might be
reduced by use of MS Transaction
Server
– No current experience
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Service as “WebService“
• Remote Server Service built as COM
Server convertable to Web service
– with Toolkit in Visual Studio 6.0 or VFP 7.0
• Build a table-interface-Webservice
– Send Job-Table entry as XML-record
– Implement Client functions for COM-server
• See Session V19 “Creating and Using
SOAP Web Services with Visual
FoxPro“ by Rick Strahl
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Additional Material
Where to go from here ? Where to
find additional information ?
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Visit other Sessions
• V14 “Building World-Class Visual
FoxPro COM Servers“
– Kevin McNeish
• V19 “Creating and Using SOAP
Web Services with Visual FoxPro“
– Rick Strahl
FoxTeach 2001
Tools/Docs on Companion CD
• SRVINSTW.EXE
• INSTSRV.EXE
• SRVANY.EXE
(install wizard)
(install tool)
(service interface)
• SRVANY.WRI
(documentation)
• W2RKTOOL.CHM (NT Resource Kit)
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www.dbcentral.com
This session will NOT have web updates.
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FoxTeach 2001