Re: Accessing member variables from another thread crashes
Re: Accessing member variables from another thread crashes
- Subject: Re: Accessing member variables from another thread crashes
- From: Dave Fernandes <email@hidden>
- Date: Sun, 10 Aug 2008 11:50:46 -0400
This isn't really a multithreading issue, it is a memory management
issue. the string you have created is autoreleased, you must retain
it if you want it to remain in memory. See:
http://developer.apple.com/documentation/Cocoa/Conceptual/MemoryMgmt/
MemoryMgmt.html
On Aug 9, 2008, at 8:24 PM, Dennis Harms wrote:
I'm new to Cocoa and objective C development and I've got a big
problem with
multithreading:
I've created a class with some member variables of type NSString*.
In the
init function of the class, I write something into those strings.
Now I call
a function of the initialized class instance as a new thread and
try to read
from those member variables. This leads to a crash... Can someone
give me a
hint as to why this won't work?
Here's my code, shrunk down to just the problematic part:
---------- MyClass.h -----------------------------
@interface MyClass: NSObject
{
@private
NSString* baseURL;
}
- (id) initWithHost: (NSString*) _url;
- (void) doSomething: (id) object;
@end
----------------------------------------------------------
---------- MyClass.m -----------------------------
@implementation MyClass
- (id) initWithHost: (NSString*) _url
{
self = [super init];
baseURL = [NSString stringWithString: _url];
return self;
}
- (void) doSomething: (id) object
{
NSString *url = [NSString stringWithString: baseURL]; // <--
the crash
occurs even when just reading the member
}
@end
----------------------------------------------------------
I've tried calling the function in the same thread, as well as three
different ways of calling it in a seperate thread. Every time there's
another thread involved, it crashes when accessing the member
variable. If
the function doesn't access any members, the code works just fine...
instance = [[MyClass alloc] initWithHost: txtHost.text];
[instance doSomething: nil]; // Works
[instance performSelectorInBackground: @selector(doSomething:)
withObject:
nil]; // Doesn't work
[[[NSThread alloc] initWithTarget: instance selector:
@selector(doSomething:) object: nil] start]; // Doesn't work
[NSThread detachNewThreadSelector: @selector(doSomething:) toTarget:
instance withObject: nil]; // Doesn't work
Thanks,
Dennis
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