Communication Between or Among Separate Running Programs

[raleeper]

Two or more separate running programs can communicate in a limited manner by the SendMessage and GetMessage functions - provided they know each other's handle.
One way they can share handles is by a disk file.

My question is: "What are the best words or phrases to search for further information on this subject?"

Thanks, Robert

[qWord]

Interprocess Communication (IPC)

[hutch--]

Robert,

One of the useful ways is SendMessage with the HWND_BROADCAST handle and your own defined custom messages. That handles the contact between running processes, then you can use a memory mapped file opened between consenting apps to transfer data using the messages as the triggers.

[dedndave]

i was a little surprised how well WM_COPYDATA works   :U

[ToutEnMasm]

Two programs can communicate with atoms
RegisterWindowMessage

[raleeper]

Interprocess Communication (IPC)

That appears to hit the nail on the head.
Thank you.

[raleeper]

Two programs can communicate with atoms
RegisterWindowMessage

Yes, I see I'd better give a little more thought to defining the mssages,  I had assumed I could just pick a number.
Thanks,

[raleeper]

Robert,

One of the useful ways is SendMessage with the HWND_BROADCAST handle and your own defined custom messages. That handles the contact between running processes, then you can use a memory mapped file opened between consenting apps to transfer data using the messages as the triggers.

Yes.  That makes sense,
Thanks.

[redskull]

Real Men(tm) use COM  :8)

http://msdn.microsoft.com/en-us/library/ms688421(v=VS.85).aspx

[raleeper]

Real Men(tm) use COM  :8)

http://msdn.microsoft.com/en-us/library/ms688421(v=VS.85).aspx

Thanks.
At this point I don't understand this at all, but I have filed the reference for later.  (I'm not asking for an explanation.  It will make sense when I know more [something] about OLE).

[dedndave]

COM looks great, but - a lot of documentation to pour through   :P
WM_COPYDATA is simple   :U

it depends a lot on what you want to do

[dedndave]

here's a quick little example

you open UserApp
it runs PmApp, sending the UserApp window handle on the command line
PmApp sends its' handle back to UserApp via WM_COPYDATA
once both windows have the handle of the other, you can send stuff back and forth with WM_COPYDATA

[raleeper]

Thanks to all who responded, with a wealth of information that I'm sure I'll be referring to frequently.

For now, I'm going to try a very simple method in which every participating program or instance puts its main window handle in a special file and sends a "new process active" message to the owner of any handle already there.  And so on.  I'll look at WM_COPYDATA - it may be better, but I don't see why I can't just use the clipboard.

The only messages I'll need are, roughly:
    Get Your Mail
    OK
    Error; Resend
    Failure
    Shut down

SendMessage with the HWND_BROADCAST handle may be useful, but I'm going to want the special file anyway, and it seems to me that broadcasting may interfere with other unrelated processes if I make errors during the development process.

Thank you all very much.

Best wishes, Robert

[hutch--]

Robert,

The HWND_BROADCAST message works fine, the trick is to register a custom message so that nothing else can interfere with it then any two or more running processes can communicate through that channel with safety.

This is what I use in QE to handle the multiple instance communiction.

Code Select Expand


    mov WM_INTSETTINGSCHANGE, rv(RegisterWindowMessage,"unique string here")
    mov WM_SHUTDOWN,          rv(RegisterWindowMessage,"another unique string here")
    mov WM_REFRESHMENUS,      rv(RegisterWindowMessage,"yet another unique string here")


Then you just send your registered windows message using the HWND_BROADCAST handle and any app that recognises the message can respond to it.

[raleeper]

Robert,

The HWND_BROADCAST message works fine, the trick is to register a custom message so that nothing else can interfere with it then any two or more running processes can communicate through that channel with safety.

This is what I use in QE to handle the multiple instance communiction.

Code Select Expand


    mov WM_INTSETTINGSCHANGE, rv(RegisterWindowMessage,"unique string here")
    mov WM_SHUTDOWN,          rv(RegisterWindowMessage,"another unique string here")
    mov WM_REFRESHMENUS,      rv(RegisterWindowMessage,"yet another unique string here")


Then you just send your registered windows message using the HWND_BROADCAST handle and any app that recognises the message can respond to it.

Well, to tell the truth I was thinking of doing it the lazy way - send to a known handle and just pick any number I want without worrying about whether it's unique or even assigning a string, except in my notes.  But that's not the right way, I know.  And I guess if I register the messages, I might as well broadcast.

OK, I'll forget about the lazy way,

Thanks, Robert

[later] I'm still leery of broadcasting.  Suppose my program crashes into a loop that does nothing but broadcast the same message repeatedly as fast as the os can process the SendMessages.  Mightn't that clog the other processes' message queues?