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On Friday 12 February 2010 04:24:33 walt wrote: |
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> On 02/11/2010 03:03 PM, Volker Armin Hemmann wrote: |
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> > ... |
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> > |
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> > And don't start with sockets. That will result in a nightmare. dbus is a |
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> > clean solution to a huge problem. Apps have to talk to each other. The |
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> > only way to keep it sane is a standardized IPC daemon like dbus. |
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> |
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> Aha! This is a question that has confused me since I was still in diapers. |
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> (And may be in them again soon enough :) |
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> |
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> Could you (or anyone else here) give us a really dumbed-down summary |
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> of why a dev would want/need to use a socket, versus a pipe, versus |
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> a signal, versus dbus, versus, well, whatever else is out there? |
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A pipe is a quick and dirty means of connecting two processes. Shove stuff in |
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one end and it comes out the other end. What the other end does with it is up |
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to the other end. A pipe (|) in a shell is the same thing, built for you |
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automagically. Used within an app you must construct the pipe in code. An |
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example would be reading a text file and inserting the line into a database. |
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On the command line you would do |
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tail -f /path/to/data/file | /path/to/insert/script |
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A socket does the same thing in the style of networking as opposed to a raw |
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pipe. All your local X clients do this, the X server created a socket and the |
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clients plug into it. This is good because X is a networked gui system so you |
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just do networking everywhere even if the server and client are on the same |
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box. |
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You use dbus if any old app needs to get an idea across to any other old app |
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and you don't know who is doing what. You are always aware of what is at the |
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end of a pipe (you built the thing) but if your jabber client wants a |
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notification to be sent of an incoming message, it doesn't know or care how |
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this is done - that is up to the notification apps. This is analogous to |
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posting to a mailing list and asking anyone who knows the answer to a question |
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to please speak up. |
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A signal is a specific message you send to a specific process via the kernel. |
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Send signal 15 to a process's PID and the kernel will relay it. The message |
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will be interpreted as "shut yourself down now". |
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-- |
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alan dot mckinnon at gmail dot com |
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