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Communication between 2 instances of the same program

Posted on 2006-07-19
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Last Modified: 2010-04-30
I have a program that acts as a scheduler. It is possible to open mutliple instances of this program on the same machine (several people can edit the different schedules at one time ). Only one program however should be acting as the scheduler.

When an instance of the program is started I want it to check for other instances
- if there are no other instances then it should become the scheduler

When an instance of the program closes and it is the scheduler, it needs to look for another instance and tell that instance to become the scheduler.

Also, the apps will be running on a terminal server by different users.


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Question by:tricks801
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by:EDDYKT
ID: 17145373
you only need to write 1 server and 1 client.

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Rob_Jeffrey earned 2000 total points
ID: 17147574
You can do that many ways.
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On startup you can check the number that is returned from app.PrevInstance.  If > 0 then you set the program as a client - else it becomes a server.  A communication method such as TCP-IP will need to be set up and when the server exits a poll will need to be taken to decide who becomes the next server.
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On startup open a common database and add itself using app.hInstance to a table.  If the autonum ID generated is the lowest (or there is only one row in the table) then it is the server - else it is a client.  On exit - delete the row from the table.  When an event hapes that needs to be acted on - only the app with the lowest autonum will act on it - becomming the server

These are only two I can think of off the top of my head.  It all depends on what you are comfortable with and familiar with.  If you know databases or TCPip - or even Windows Messaging.  It will also depend on the method you are already using for data storage and retrieval - what you are scheduling.

Rob
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by:JRCSystems
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Tricks801: Is this still open? Where did you get with this?
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