Re: Accessing array in thread safe way
Re: Accessing array in thread safe way
- Subject: Re: Accessing array in thread safe way
- From: CoGe - Tamas Nagy <email@hidden>
- Date: Thu, 08 Mar 2012 21:02:37 +0100
Thanks for the great explanation Brian. Having a dual-processor system is a need for my app, so that's why I chose SpinLocks. But using dispatch blocks is could be an other option, I guess.
On Mar 8, 2012, at 8:19 PM, Brian Lambert wrote:
> Spin locks are useful in certain situations.
>
> First of all, on a single-processor system, it's never a good idea to use a
> spin lock because all it will do is burn up the waiting thread's scheduling
> quantum while preventing a thread that's holding the lock from getting
> scheduled so that it can complete its work and release the lock.
>
> A spin lock is useful in multi-processor environments when you know that a
> lock will be held for a *very short period of time*. In this case, spin
> locks can help you avoid excessive context switching because a waiting
> thread will often be able to spin (do something else) while waiting for a
> lock to be released, acquire the lock, and do its work, all within its
> scheduling quantum.
>
> In many simple scenarios, especially when contention is very low,
> @synchronized will be the best choice because it's trivial to get right and
> high-performance.
>
> In other scenarios, a fair readers-writers lock will be ideal.
>
>
> On Thu, Mar 8, 2012 at 9:52 AM, Jan E. Schotsman <email@hidden> wrote:
>
>>
>> On Mar 8, 2012, at 3:22 PM, CoGe - Tamas Nagy wrote:
>>
>> Maybe this will helps you, here is my thread-safe subclass of
>>> NSMutableArray: http://code.google.com/p/**cogeopensource/source/browse/*
>>> *trunk/CoGeOpenSource/**CoGeThreadSafeMutableArray.m<http://code.google.com/p/cogeopensource/source/browse/trunk/CoGeOpenSource/CoGeThreadSafeMutableArray.m>
>>>
>>
>> Thanks for the code.
>> I have two questions:
>>
>> 1. If you believe that OSSpinLock is faster than NSLock why don't you use
>> it for your thread-safe mutable array class too?
>>
>> 2. Once you start using an enumerator for the array you probably need a
>> explicit mutex after all. Isn't it simpler to just use
>> @synchronized(array) wherever the array is accessed?
>>
>> Jan E.
>>
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Tamas Nagy
-----------------
CoGe VJ Software
http://cogevj.hu
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