Subject: Re: [boost] How to get the size of an C-array?
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2009-10-15 16:19:44
vicente.botet wrote:
>> I'm not sure I understand you here. Are you saying that other threads
>> may be accessing the array elements during the destruction?
>
> Yes. This is the case I try to solve.
Why not locking the mutex (or whatever you use to synchronize the
threads) in the destructor? It will block if another thread is working
with the object.
>> All in all, the overall scheme is as follows:
>>
>> static void* operator new[] (std::size_t size)
>> {
>> void* p = std::malloc(sizeof(info_t) + gap_size + size);
>> if (p)
>> {
>> new (p) info_t();
>> static_cast< info_t* >(p)->m_Count = size / sizeof(T);
>
> Are you sure the size given as parameter consider only the user info?
> Doesn't this size includes any additional part needed by the standard
> library to know if the the allocation corresponds to a single element
> or to an array and whatever is needed to call the destructors of all
> the array elements?
Hmm... Looks like you're right here. The Standard doesn't say what the
size will be and at least gcc does add a little to the size. However, if
sizeof(T) is big enough, you may not notice this extra increase in size.
Well, unless you want to tweak your code for every compiler/platform to
take that additional info into account, I don't see how this can be
solved. You might want to use an additional argument to the operator
new[] to pass the array size twice, but this essentially eliminates the
advantage of using the regular operator new. Still, you will be able to
use scoped_array, shared_array, etc.