FoxTeach 2001 Building Server Services with Visual FoxPro Session V17 Rainer Becker dFPUG, Germany
Jan 30, 2016
FoxTeach 2001
Building Server Services with Visual FoxPro
Session V17
Rainer BeckerdFPUG, Germany
FoxTeach 2001
Who Am I?
• German FoxPro User Grouphttp://www.dfpug.de/forum
– German VFP DevCon– FoxX Professional (4x200 pages)
• Wizards & Builders GmbHhttp://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):– 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
FoxTeach 2001
Using the Install Wizard
• 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 VFP-status but only SRVANY-status (even “ “QUIT“ still allows to start/stop/restart the service) – confusing for admins!
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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
• 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
• 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
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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
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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
FoxTeach 2001
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 Multi-Threaded VFP-Runtime (see SP3)
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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 ?
FoxTeach 2001
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 (install wizard)
• INSTSRV.EXE (install tool)
• SRVANY.EXE (service interface)
• SRVANY.WRI (documentation)
• W2RKTOOL.CHM (NT Resource Kit)
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FoxTeach Web Update Page
www.dbcentral.com
This session will NOT have web updates.
FoxTeach 2001
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