Re: NSInvocation driving me nuts
Re: NSInvocation driving me nuts
- Subject: Re: NSInvocation driving me nuts
- From: Ondra Cada <email@hidden>
- Date: Sat, 8 Apr 2006 14:59:53 +0200
Pierre,
On 8.4.2006, at 13:24, Pierre Bernard wrote:
Can you spot the difference between:
[delegate _managedObjectContextEditor:self didCommit:YES
contextInfo:contextInfo];
and this:
SEL selector = @selector
(_managedObjectContextEditor:didCommit:contextInfo:);
NSInvocation *invocation = [NSInvocation
invocationWithMethodSignature:[delegate
methodSignatureForSelector:selector]];
BOOL success = YES;
[invocation setTarget:delegate]; // 0
[invocation setSelector:selector]; // 1
[invocation setArgument:&self atIndex:2];
[invocation setArgument:&success atIndex:3];
[invocation setArgument:&contextInfo atIndex:4];
[invocation retainArguments];
In this case retaining arguments seems superfluous, since the
invocation self-evidently is never stored.
[invocation invoke];
This should work all right.
[invocation release];
This should crash as soon as the current autorelease pool (which
contains the already released invocation) gets released.
Check this:
23 /tmp> <q.m
#import <Cocoa/Cocoa.h>
@interface Delegate:NSObject @end
@implementation Delegate
-(void)_managedObjectContextEditor:editor didCommit:(BOOL)dc
contextInfo:(void*)ci {
NSLog(@"delegate method called all right with %@/%d/%
x",editor,dc,ci);
}
@end
int main() {
SEL sel=@selector
(_managedObjectContextEditor:didCommit:contextInfo:);
id p=[NSAutoreleasePool new],del=[Delegate new],inv=[NSInvocation
invocationWithMethodSignature:[del methodSignatureForSelector:sel]];
BOOL succ=YES;
[inv setTarget:del];
[inv setSelector:sel];
[inv setArgument:&del atIndex:2]; // have no self here, of course
[inv setArgument:&succ atIndex:3];
[inv setArgument:&sel atIndex:4]; // why not, any address does
[inv retainArguments]; // superfluous, harmless
NSLog(@"delegate method about to be called now");
[inv invoke];
[inv release]; // overreleasing here
NSLog(@"overrelease crash about to happen now");
[p release];
NSLog(@"never seen");
return 0;
}
24 /tmp> cc -Wall q.m -framework Cocoa && ./a.out
2006-04-08 14:58:59.551 a.out[1126] delegate method about to be
called now
2006-04-08 14:58:59.552 a.out[1126] delegate method called all right
with <Delegate: 0x504240>/1/940a5170
2006-04-08 14:58:59.552 a.out[1126] overrelease crash about to happen
now
zsh: bus error ./a.out
25 /tmp>
---
Ondra Čada
OCSoftware: email@hidden http://www.ocs.cz
private email@hidden http://www.ocs.cz/oc
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