Re: Is C's parameter passing more-efficient than ObjC's message passing?
Re: Is C's parameter passing more-efficient than ObjC's message passing?
- Subject: Re: Is C's parameter passing more-efficient than ObjC's message passing?
- From: "Frederick C. Lee" <email@hidden>
- Date: Fri, 10 Feb 2006 17:14:07 -0800
I wasn't thinking about overhead when writing ObjC code.
I do a lot of [self <routine>] calls within my .m codes.
These internal calls would more-efficiently be made using C routines
instead.
The ObjC routines could then be used for accessors instead,
particularly called
from outside the class; or interfacing with the GUI/Controllers.
Ric.
On Feb 10, 2006, at 4:52 PM, David Hart wrote:
The overhead isn't so much in the parameter passing per say - but
the method
invocation as a whole. With a straight C function call, you
essentially just
need to branch + stack setup and tear down; with obj-c dynamic method
invocation, for example [obj foo] is really a call to objc_msg_send
(or
objc_msg_sendv) with the object id, the selector and arguments as
parameters. Then objc_msg_send will locate the function address
from the
selector, and branch to that + stack setup and teardown... So...
Basically
it comes down to this:
Straight C:
function call is branch + stack setup and teardown/paramater passing
Objective-C:
Method invocation is function call to objc_msg_send + normal
function call
overhead; so two times the function call overhead + the work
objc_msg_send
does to look up the appropriate function based on the selector.
This is a bit of a simplification, but is basically it, and after
having
said all of that... The overhead of a obj-c method is really a non-
issue for
MOST code...
PS there are ways to speed up objc method invocation with caching
of method
addresses, and i think the runtime has some caching of its own...
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