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Re: Garbage collector vs variable lifetime
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Re: Garbage collector vs variable lifetime


  • Subject: Re: Garbage collector vs variable lifetime
  • From: Antonio Nunes <email@hidden>
  • Date: Sat, 7 Jun 2008 05:48:21 +0200

On 7 Jun 2008, at 01:42, Bill Bumgarner wrote:

The easiest way to do this is to simply to use data once after the for() loop:

	NSData* data = <get it from somewhere>;
	const unsigned char* bytes = [data bytes];
	NSUInteger count = [data length];
	for (NSUInteger i = 0; i < count; i++)
		something = bytes [i];
	[data self];

Yup. I don't particularly like it either. Fortunately, it is an uncommon case -- most of the objects in the AppKit/Foundation "just work". This kind of a problem arises when something leverages the C in Objective-C.

Quincey Morris wrote:
A little inner voice insists on asking, though, how we know some future version of the compiler might not optimize '[data self]' upwards before the loop, if it decides that nothing inside the loop references anything non-local:

Why not explicitly turn off collection for the data pointer:

NSData* data = <get it from somewhere>;
[[NSGarbageCollector defaultCollector] disableCollectorForPointer:data];
const unsigned char* bytes = [data bytes];
NSUInteger count = [data length];
for (NSUInteger i = 0; i < count; i++)
something = bytes [i];
[[NSGarbageCollector defaultCollector] enableCollectorForPointer:data];

It's slightly longer, but straightforward and clear about it's purpose, and should be future proof.

António

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  • Follow-Ups:
    • Re: Garbage collector vs variable lifetime
      • From: Ken Thomases <email@hidden>
References: 
 >Garbage collector vs variable lifetime (From: Quincey Morris <email@hidden>)
 >Re: Garbage collector vs variable lifetime (From: Bill Bumgarner <email@hidden>)
 >Re: Garbage collector vs variable lifetime (From: Ricky Sharp <email@hidden>)
 >Re: Garbage collector vs variable lifetime (From: Bill Bumgarner <email@hidden>)

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