Re: [boost] [log] Boost.Log formal review result

Subject: Re: [boost] [log] Boost.Log formal review result
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2010-03-25 13:15:33

On 25.03.2010 19:15, Stewart, Robert wrote:
>>> - The library should not reinvent wheels. In particular, custom
>>> implementations of TSS and RW mutex seems like a very bad idea.
>>
>> I have noted that during the review that these tools were
>> implemented for a reason. They make the library faster and lighter
>> in terms of memory footprint. They allow to avoid including
>> Boost.Thread headers in public headers of Boost.Log, which also
>> speeds up the compilation. I think these matters are more important
>> than having the code dispersion they add.
>
> I'd like to know the real effect of using off-the-Boost-shelf
> components rather than your special sauce.  That is, I'd like to know
> the performance and compilation tradeoffs for them before commenting
> further.

Here are the numbers regarding the memory footprint and the lightness:

On Linux x86_64, GCC 4.4:
=========================

$ g++ -I. -E ./boost/log/detail/thread_specific.hpp >bl_tss.pp
$ g++ -I. -E ./boost/thread/tss.hpp >bt_tss.pp
$ g++ -I. -E ./boost/log/detail/light_rw_mutex.hpp >bl_rw.pp
$ g++ -I. -E ./boost/thread/shared_mutex.hpp >bt_rw.pp
$ ls -la
    82157 2010-03-25 19:26 bl_rw.pp
   157431 2010-03-25 19:24 bl_tss.pp
  1205108 2010-03-25 19:26 bt_rw.pp
   347240 2010-03-25 19:24 bt_tss.pp

sizeof(shared_mutex) = 192, sizeof(light_rw_mutex) = 56

On Windows, x64, MSVC 9:
========================

E:\Sources\_SVN\boost-release>cl -I. /TP /EHsc -E 
boost\log\detail\thread_specific.hpp >bl_tss.pp
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.30729.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

thread_specific.hpp

E:\Sources\_SVN\boost-release>cl -I. /TP /EHsc -E boost\thread\tss.hpp 
 >bt_tss.pp
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.30729.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

tss.hpp

E:\Sources\_SVN\boost-release>cl -I. /TP /EHsc 
-DBOOST_LOG_USE_WINNT6_API -E boost\log\detail\light_rw_mutex.hpp >bl_rw.pp
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.30729.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

light_rw_mutex.hpp

E:\Sources\_SVN\boost-release>cl -I. /TP /EHsc -E 
boost\thread\shared_mutex.hpp >bt_rw.pp
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.30729.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

shared_mutex.hpp

E:\Sources\_SVN\boost-release>dir
  Volume in drive E is Dev
  Volume Serial Number is E050-708C

  Directory of E:\Sources\_SVN\boost-release

25.03.2010  19:52           394 755 bl_rw.pp
25.03.2010  19:55           776 216 bl_tss.pp
25.03.2010  19:51         4 360 402 bt_rw.pp
25.03.2010  19:49         3 823 468 bt_tss.pp

E:\Sources\_SVN\boost-release>cl -I. /TP /EHsc 
-DBOOST_LOG_USE_WINNT6_API -DBOOST_ALL_NO_LIB size_test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.30729.01 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

size_test.cpp
Microsoft (R) Incremental Linker Version 9.00.30729.01
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:size_test.exe
size_test.obj

E:\Sources\_SVN\boost-release>size_test.exe
sizeof(shared_mutex) = 48, sizeof(light_rw_mutex) = 8

I draw your attention to that a typical MT logger (at least, ones 
provided by the library) contains a rw mutex, which makes it a 
significant addition if loggers are used as class members.

Regarding performance, Boost.Log TSS relies on raw pthread/WinAPI calls, 
while Boost.Thread TSS adds to that a logarithmic lookup along all 
thread_specific_ptrs in the application, so it definitely cannot be 
faster. Also, using thread_specific_ptr to manage a tiny thing like an 
integer (the severity level) is an overkill since it would require 
several memory allocations per thread, one of which is for shared_ptr, 
IIRC. That's opposed to no allocations at all for Boost.Log TSS.