Re: alloc init thread safe?
Re: alloc init thread safe?
- Subject: Re: alloc init thread safe?
- From: David Carlisle <email@hidden>
- Date: Thu, 8 Mar 2007 09:37:40 -0700
I can't see a way around believing alloc isn't thread safe in this
case for some reason. I've had NSZombie enabled while looking for
this bug. I re checked my hierarchy of init methods and they are all
quite simple. So I don't see a way that my inits could randomly
change an allocated object into a null. The nulls make no response
at all to the messages sent to them, which was no help in finding the
problem. I do an NSLog on the object returned from C2_alloc_init
right after the call, so nothing in the calling procedure is
affecting the result. I'm using a core 2 duo, so both threads could
be running concurrently at that point.
I just don't understand the general principle involved so I can be
sure to avoid it in the future.
On Mar 8, 2007, at 4:15 AM, Chris Suter wrote:
On 08/03/2007, at 5:25 PM, email@hidden wrote:
I have one object of Class1. This object has a method
- (id) C2_alloc_init {
return [[Class2 alloc] init];
}
This method can be called from multiple threads simultaneously.
Sometimes this would return null, and it appears from the trace
messages that this occurs when it is being called from two threads
at about the same time. Both classes are subclasses of NSObject.
The problem seems to be solved by putting a lock around the alloc
init calls, doing an unlock before returning the value.
So did I miss some documentation that says alloc init are not
thread safe? Or at least alloc?
They should be thread-safe provided you've put Cocoa in
multithreaded mode and provided your init method is thread-safe.
You need to detach an NSThread but you can have it promptly exit if
you don't need it.
- Chris
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