Re: @property problem
Re: @property problem
- Subject: Re: @property problem
- From: Bill Bumgarner <email@hidden>
- Date: Mon, 11 Feb 2008 15:46:46 -0800
On Feb 11, 2008, at 3:33 PM, Adam P Jenkins wrote:
Is there any performance penalty for using the 64 bit runtime? In
general what are the disadvantages of disabling 32 bit compatibility
other than the obvious fact that my program wouldn't run on 32 bit
machines?
If you are the first 64 bit app launched on the system, there will be
a slightly performance penalty as all of the 64 bit versions of the
various dylibs are mapped into memory.
Obviously, you can't deploy a 64 bit application to 32 bit only macs;
the performance is infinitely bad, in that case. :)
The performance characteristics of Objective-C changes slightly in 64
bit. Message dispatch and instance variable access changes
slightly. It is unlikely that this will change application
performance significantly.
The 64 bit ABI also features a unified ObjC/C++ exception model. It
is often called "zero cost". This is not really true; it simply
shifts the expense related to exception handling from the setup of the
handler to when an exception is actually thrown. It can have a huge
[positive] impact on your application's performance if you have lots
and lots of exception handlers but few exceptions are ever thrown.
Of course, your memory footprint will be slightly larger in that
everything that is pointer sized will be doubled in size. This is
both a direct and indirect impact in that some structures may have a
bit more padding to ensure correct alignment for pointers.
The Garbage Collector works just fine in 64 bits.
b.bum
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