Your explanation is very detailedand useful, I think I understood. Thank you very much! class7class@163.com From: boost-users-request Date: 2015-07-23 09:04 To: boost-users Subject: Boost-users Digest, Vol 4201, Issue 4 Send Boost-users mailing list submissions to boost-users@lists.boost.org To subscribe or unsubscribe via the World Wide Web, visit http://lists.boost.org/mailman/listinfo.cgi/boost-users or, via email, send a message with subject or body 'help' to boost-users-request@lists.boost.org You can reach the person managing the list at boost-users-owner@lists.boost.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Boost-users digest..." Today's Topics: 1. Re: Boost release 1.59.0 beta 1 is now available from SourceForge (Ben Pope) 2. Re: Boost release 1.59.0 beta 1 is now available from SourceForge (Vicky Vergara) 3. Re: Subject:[atomic] why atomic<>::store method can not support memory_order_consum memory_order_acquire and memory_order_acq_rel these memory_orders? (Gavin Lambert) 4. [filesystem] problem: is_regular_file and deduplified files (reparse+sparse) (Paul Harris) 5. Re: Subject:[atomic] why atomic<>::store method can not support memory_order_consum memory_order_acquire and memory_order_acq_rel (Isaac To) ---------------------------------------------------------------------- Message: 1 Date: Thu, 23 Jul 2015 05:20:39 +0800 From: Ben Pope To: boost-users@lists.boost.org Cc: boost@lists.boost.org Subject: Re: [Boost-users] Boost release 1.59.0 beta 1 is now available from SourceForge Message-ID: Content-Type: text/plain; charset=windows-1252; format=flowed On Thursday, July 23, 2015 02:23 AM, Marshall Clow wrote:

On Thu, Jul 16, 2015 at 6:16 AM, Marshall Clow mailto:mclow.lists@gmail.com> wrote:

Boost release 1.59.0 beta 1 is now available from SourceForge See http://sourceforge.net/projects/boost/files/boost/1.59.0.beta.1/ For details of what's in the release, see http://www.boost.org/users/history/version_1_59_0.html. Note that the links to files on this web page are for the final release - use the SourceForge link above to get the beta files. Please download the beta, give it a try, and report any problems you encounter.

Has anyone tried the beta release with new compilers?

Specifically, I'm thinking about: * GCC 5.2 * VS2015 * Clang 3.7rc1

For clang 3.7 rc1, the tests for master are up on the ftp, but they won't be published because I haven't submitted a pull request for them to be published on the test site, since I don't run them regularly. The dev results should be up on the test matrix at some point soon, but the entire run of dev and release takes a couple of days (which feels slow) and is still in progress. I intend to publish the results of asan, msan, tsan runs at some point but I haven't got round to figuring out the right way to present them yet, if you want the raw xml results and don't have access to the ftp, contact me. I'll probably run for gcc 5.2 when it arrives on Ubuntu's launchpad. Ben ------------------------------ Message: 2 Date: Wed, 22 Jul 2015 17:53:17 -0500 From: Vicky Vergara To: "boost-users@lists.boost.org" Subject: Re: [Boost-users] Boost release 1.59.0 beta 1 is now available from SourceForge Message-ID: Content-Type: text/plain; charset="iso-8859-1" We re working on the release of pgRouting. We use Boost.Graph. My Question is: Waht changes I have to do in Github travis to check that pgRouting is compatible with this beta release? Here is our travis file: https://github.com/pgRouting/pgrouting/blob/develop_2_1_0/.travis.yml Right now it runs with boost 1.46.1 https://travis-ci.org/pgRouting/pgrouting/jobs/72064827#L1834 Thanks

To: boost-users@lists.boost.org From: benpope81@gmail.com Date: Thu, 23 Jul 2015 05:20:39 +0800 CC: boost@lists.boost.org Subject: Re: [Boost-users] Boost release 1.59.0 beta 1 is now available from SourceForge

On Thursday, July 23, 2015 02:23 AM, Marshall Clow wrote:

...

On Thu, Jul 16, 2015 at 6:16 AM, Marshall Clow mailto:mclow.lists@gmail.com> wrote:

Boost release 1.59.0 beta 1 is now available from SourceForge See http://sourceforge.net/projects/boost/files/boost/1.59.0.beta.1/ For details of what's in the release, see http://www.boost.org/users/history/version_1_59_0.html. Note that the links to files on this web page are for the final release - use the SourceForge link above to get the beta files. Please download the beta, give it a try, and report any problems you encounter.

Has anyone tried the beta release with new compilers?

Specifically, I'm thinking about: * GCC 5.2 * VS2015 * Clang 3.7rc1

For clang 3.7 rc1, the tests for master are up on the ftp, but they won't be published because I haven't submitted a pull request for them to be published on the test site, since I don't run them regularly.

The dev results should be up on the test matrix at some point soon, but the entire run of dev and release takes a couple of days (which feels slow) and is still in progress.

I intend to publish the results of asan, msan, tsan runs at some point but I haven't got round to figuring out the right way to present them yet, if you want the raw xml results and don't have access to the ftp, contact me.

I'll probably run for gcc 5.2 when it arrives on Ubuntu's launchpad.

Ben

_______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

-------------- next part -------------- HTML attachment scrubbed and removed ------------------------------ Message: 3 Date: Thu, 23 Jul 2015 12:20:28 +1200 From: Gavin Lambert To: boost-users@lists.boost.org Subject: Re: [Boost-users] Subject:[atomic] why atomic<>::store method can not support memory_order_consum memory_order_acquire and memory_order_acq_rel these memory_orders? Message-ID: Content-Type: text/plain; charset=windows-1252; format=flowed On 22/07/2015 14:43, class7class@163.com wrote:

I am a SE and I program based on boost library, I have one question to ask as below:

When I use the atomic library included boost , I coded as following: atomic<bool> flag; //declare the var flag.store(true,boost::memory_order_acq_rel); // use store method to change the value of flag

but BOOST_ASSERT failed,and I read the code of base_atomic<> template class,I found the the store() method can not support several memory_orders metioned in the subject , and the other methods can not support all memory_orders,such as: 1.the load method can not support memory_order_release and memory_order_acq_rel 2. the compare_exchange_strong method can not support memory_order_release and memory_order_acq_rel 3. the compare_exchange_weak method can not support memory_order_release and memory_order_acq_rel

I really want to know the reason that why the methods of atomic can not support all memory_orders.

Because this is mandated by the standard, and because doing otherwise doesn't really make sense. Loads can't release, and stores can't acquire. Therefore those memory orders are nonsensical. memory_order_acq_rel exists for RMW operations such as compare_exchange. The "acq" applies to the load and the "rel" to the store. It's not sensible for a store alone.

If I need the methods of the atomic<> support all memory_orders,how can i do?

You can re-read the standard memory model and discover why that doesn't make sense. Memory ordering can be tricky to get your head around at first -- it's a good idea to run any atomic algorithm you implement through a sanity checker such as RRD or ThreadSanitizer to help catch subtle bugs. If in doubt, stick with seq_cst memory ordering (the default). On x86/x64 there is very little performance difference between seq_cst and the weaker orders -- cacheline sharing tends to be more problematic. ------------------------------ Message: 4 Date: Thu, 23 Jul 2015 08:56:21 +0800 From: Paul Harris To: boost-users Subject: [Boost-users] [filesystem] problem: is_regular_file and deduplified files (reparse+sparse) Message-ID: Content-Type: text/plain; charset="utf-8" Hi guys, I'm seeing a lot of failures all of a sudden, its a serious problem. I imagine some of you may start seeing the same failures too very soon. I'm seeing it with boost 1.58.0. There is a related bug already entered here: https://svn.boost.org/trac/boost/ticket/11057 I can't seem to log on and update this ticket. But the problem extends further than that ticket. Windows Server 2003 support has been dropped by Microsoft, and a lot of IT depts around the world are switching over to the latest Windows Server. With this server comes the new "dedup" feature, that can automatically deduplify files. This happens on a schedule, eg 2am saturday. So suddenly we are getting messages of failures of software from all over the place, due to fs::is_regular_file() Deduped files have the REPARSE and SPARSE flag set. On the command line, you can run FSUTIL REPARSEPOINT QUERY and the "Reparse Tag Value" is 0x80000013 Which is a relatively new flag known as IO_REPARSE_TAG_DEDUP https://msdn.microsoft.com/en-us/library/windows/desktop/aa365740%28v=vs.85%... These files act as normal files, you can fopen and fread them, so I assume they should be treated almost like symlink by boost... perhaps not quite a symlink because I assume the "lstat" link properties are identical to the file's stat properties. Typically, I iterate over directories and only process files if fs::is_regular_file(filename) is true. I wrote some code to check what the properties were on these files, and its not any of the possible enums detected by file_status::type(). ideas? Best regards, Paul -------------- next part -------------- HTML attachment scrubbed and removed ------------------------------ Message: 5 Date: Thu, 23 Jul 2015 09:04:57 +0800 From: Isaac To To: boost-users@lists.boost.org Subject: Re: [Boost-users] Subject:[atomic] why atomic<>::store method can not support memory_order_consum memory_order_acquire and memory_order_acq_rel Message-ID: Content-Type: text/plain; charset="utf-8" On Thu, Jul 23, 2015 at 12:00 AM, "class7class@163.com"

wrote:

I found the the store() method can not support several memory_orders metioned in the subject , and the other methods can not support all memory_orders,such as: 1.the load method can not support memory_order_release and memory_order_acq_rel 2. the compare_exchange_strong method can not support memory_order_release and memory_order_acq_rel 3. the compare_exchange_weak method can not support memory_order_release and memory_order_acq_rel

I really want to know the reason that why the methods of atomic can not support all memory_orders.

If I need the methods of the atomic<> support all memory_orders,how can i do?

You are asking into the area of C++ where the fewest people in the world understand, namely relaxed atomics. Before I tell my limited understanding of the issue, I have an advice: - Use mutexes like boost::mutex to ensure all your accesses to variables shared among threads are not accessed concurrently, and you'll be fine. If your circumstance forces you to ignore the above advice (like me, e.g., when you cannot afford the scheduling overheads of mutexes), here is yet another advice which may save your life: - Make all your variables that can be accessed concurrently from multiple threads (with at least one thread writing) atomic. (This makes your program "data race free".) - Always use the default memory_order_seq_cst memory ordering for accesses to your atomics, never use anything else. If your circumstance forces you to ignore the above advices (unlike me, I just learn them because I haven't heard about the second advice before; you'll have to be writing for old ARM (i.e., ones without the LDA and STL instructions) or POWER for you to have a real reason to use relaxed atomics, I write for neither), here is what I have learnt. tl;dr The boost atomic doesn't support all memory ordering because the C++11 standard doesn't support all of them. The C++ standard doesn't support all memory ordering because not all make sense in the "memory model" supported by C++. It is not likely to change in the near future, i.e., unless some genius devises some novel memory model which changes the status quo. Here "memory model" means what "loads" from memory is allowed to return. Because of compiler and hardware optimization, writes (including atomic writes) to memory locations may be reordered, so the load doesn't always return "the last value stored". Special hardware instructions are necessary to ensure a particular ordering that the programmer needs. The easiest way to understand a program is that "All memory operations by all threads looks as if they are done one after another, interleaving among threads". But it proves to be too tricky for hardware to provide any reasonable performance for this model. The C++ memory model without relaxed atomics is essentially "All *atomic* memory operations by all threads looks as if they are done one after another, interleaving among threads. All other memory operations of each thread looks as if they are completely done between adjacent atomic memory operations. But the programmer guarantees not to write a data race. The compiler uses this assumption in all its work, and your program can break in all mysterious ways if you break this rule." This is essentially the illusion provided by sequential consistency. Everybody should want it. Except some don't, because in some architectures it is essentially impossible to provide sequential consistency efficiently. To do sequential consistency, one has to ensure that (1) the compiler doesn't reorder the statements written by the programmer, which is controllable by compiler writer; and (2) the hardware doesn't reorder the instructions generated by the compiler, which is damn hard. It usually means the compiler must insert memory fences before and after memory accesses (i.e., tell the CPU "don't return to me until everything I do up to this point are visible by all other CPUs" or "don't return to me until everything other CPUs do up to this point are visible by me"), which is very slow. It is particularly bad because for these architectures, fences must be inserted not just for atomic stores, but for the supposedly fast atomic loads as well. (Recent architectures do better because they link the requirement into the accesses of the particular memory location: the "particular memory location" here limits the scope where the "fences" have to do, and this makes a big difference in performance.) That's why relaxed atomics (i.e., memory_order_acq, etc) exists in the standard. They allow those architectures to perform better than using full sequential consistency in some common cases. Because different architectures require different sort of fences, it doesn't make sense for these to mean "insert a fence after the load". Instead, the C++ standard uses a more programmer centric view when defining relaxed memory ordering: - If a thread X stores a value with release semantics into an atomic variable, and another thread Y loads this value with acquire semantics from that same atomic variable, then everything done by thread X before this releasing store are guaranteed to be visible to thread Y after this acquiring load. There is no other semantics attached to the acquire and release. This is why acquiring stores and releasing loads are meaningless: they are not assigned any semantics. But the deeper reason for the lack is that the computer industry cannot find a way to give additional guarantee without incurring hefty performance overheads. And at the same time, sequentially consistent atomics are not so expensive in the new architectures. As for what to do if you want more than the above release-acquire guarantee: Simple, just use sequentially consistent atomic operations. Regards, Isaac -------------- next part -------------- HTML attachment scrubbed and removed ------------------------------ Subject: Digest Footer _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users ------------------------------ End of Boost-users Digest, Vol 4201, Issue 4 ********************************************