[haiku-development] Re: BMessenger and synchronous replies

  • From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
  • To: haiku-development@xxxxxxxxxxxxx
  • Date: Fri, 30 Apr 2010 09:08:29 +0200

Chris Peel <chris.gsi@xxxxxxxxxxxx> wrote:
> My question is - how does the reply message _actually_ get back to  
> BMessenger->SendMessage()?  Is it:
> (a) by copying memory between processes

Generally, messaging works using ports. A BMessenger combines the target 
port, plus its team as well as a target token that identifies a 
specific handler.
The synchronous reply mechanism just uses one of a cached list of reply 
ports that are only used for this case. See src/kits/app/Message.cpp 
line 2177ff.

While messaging uses ports (and with them, memory copies between 
processes), the actual data might be sent using an area after some 
threshold is reached (IIRC 64K).


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