Inter-Process Communications (IPC)

Message Passing

• queue is frequently on the recipient's machine: sender sends message to queue, possibly on a remote machine; recipient picks up message from its queue (or multiple recipients get messages from shared queue)
• queue could be on an intermediary machine; recipients from various machines all look to same address for queue
synchronous vs. asynchronous message passing
(or, from StackOverflow:
• synchronous and asynchronous data transmission between client and server,
• description of asynchronous programming)

Synchronous example

Client: Sends request, waits on response
Server: Gets first request. Returns response, waits for next interaction
Client: Gets response.  Continues on until sends next request
Server: Gets next request. Returns response, waits for next interaction

Need “handshake” to establish/close connection

Asynchronous example (e.g., mail)

Peer1: Sends information, goes on to do other things
Peer2: Gets information, acts on it, sends information (possibly),
        goes on to do other things.

No ongoing connection

Asynchronous server (e.g., http)

Client: Sends request, waits on response
Server: Gets new request, acts on it, sends response.
        Goes on to do other things.
Client: Gets response.  Continues on until sends next request.
Server: Gets new request, acts on it, sends response.
        Goes on to do other things.
Client: Gets response.  Continues on until sends next request.

No ongoing connection

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Alyce Brady, Kalamazoo College