Re: [boost] [thread] thread_specific_ptr performance

Subject: Re: [boost] [thread] thread_specific_ptr performance
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2010-01-12 15:10:57

----- Original Message ----- 
From: <strasser_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Tuesday, January 12, 2010 4:58 PM
Subject: Re: [boost] [thread] thread_specific_ptr performance

Zitat von Vicente Botet Escriba <vicente.botet_at_[hidden]>:
> Peter Dimov-5 wrote:
>>
>> Vicente Botet Escriba wrote:
>>> For me it is unacceptable to use reallocation of the vector on the
>>> operator*.
>>
>> Operator* has a non-NULL precondition and doesn't need to reallocate.
>> reset() does, but only if you set a thread_specific_ptr that has been
>> created after the thread has started.
>>
>>
> I was responding to the proposition of Stefan, not to the current
> implementation.

peter´s right, no reallocation in operator*.

<snip code>
> My concrete example is to access the current transaction on a Software
> Transaction Memory. This operation can be required frequently. You should

but reallocation only happens once per thread, on first call to reset().

> I have no access to the code now. Please,could you show where the current
> implementation allocates and use a mutex on the operator*.

probably also only on reset(), the code is in libs/src/pthread/thread.cpp.
it inserts an element into a std::map, which allocates, which acquires  
a mutex.

> A library could not know if its users work on a Boost.Thread or on a native
> thread. So thread_specific_ptr needs to work in both cases. The current
> implementation of thread_specific_ptr satisfy already this. Any alternative
> proposal need to satisfy this requirement also.

ok, I wasn´t sure.

_______________________________________________

Stefan,
I have never talk about reset function but the operator*. Just quoting yourself
"thread_specific_ptr operator*:
one branch to make sure the vector is large enough(a new  
thread_specific_ptr might have been created by another thread), one  
indirection.
constant-time average, linear to vector if reallocation is necessary.  
but that can only happen when a new thread_specific_ptr was created."

>From this I deduce that the operator* you were proposing did a reallocation. Please don't mix allocation on the map and reallocation of the vector you were proposing.

Vicente