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[atomic] When to load/store
by Michael Powell 22 May '13

22 May '13

Hello, I have some thread synchronization to do, probably will end up using some sort of internally synchronized cancelation or other state to message between parent and child thread. If the state uses boost::atomic<bool> _canceled, for instance, how do I go about setting/getting the value? I am assuming that we do something like this: //To get the value. return _canceled.load(boost::memory_order::memory_order_acq_rel); //To set the value. _canceled.store(canceled, boost::memory_order::memory_order_acq_rel); Using acquire/release to get in, do what we need with the value, and get out, type thing. Also bearing in mind this is targeting ARM architecture (ARM5 I think). Also, how complex a value can be protected? Are we talking primitive types only? Basic data types like bool, int, float, that sort of thing? Thank you... Regards, Michael Powell

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[Atomic] / PPC / error: impossible constraint in 'asm'
by nicolas.danet＠free.fr 22 May '13

22 May '13

Hello, I get the error below compiling with (Xcode 2.5 / OS X 10.4.11) only for PPC arch. boost_1_53_0/boost/atomic/detail/gcc-ppc.hpp:1204: error: impossible constraint in 'asm' The related code is: static boost::atomic<long> messageCount_(0); number_ = messageCount_.fetch_add(1, boost::memory_order_relaxed); Is this a known bug ? Is there any way to fix it ? Thanks.

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[accumulator] with complex domain model
by Michael Powell 21 May '13

21 May '13

Hello, We've got a complex domain model which must be accumulated and eventually averaged together. I am already overloading the operators for that model. We could roll our own with just the operators we'll need to accommodate, like +, +=, /, etc, but would like to take a gander at Boost.Accumulator first. Would be much better, obviously, rather than having to reinvent the wheel. How doable would it be to accumulate an arbitrarily complex domain model. That's assuming that it is sensible to add, average, and so on, the model, which it is. Regards, Michael Powell

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endless loop and/or crash in boost::interprocess
by Charanga 21 May '13

21 May '13

How do I debug a potential endless loop and heap corruption issue involving boost::interprocess "new managed_shared_memory" freezing forever or crashing? I posted this on stackoverflow but I am hopeful that a real expert in Boost::Interprocess may have seen this freeze-up and crash before. Outside the debugger it manifests as a freeze-up, inside the debugger it manifests as a series of exceptions inside an endless try-catch-ignore loop which is coded into the boost implementation code. http://stackoverflow.com/questions/16651878/how-do-i-debug-a-potential-endl… Warren

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[SmartPtr] enable_shared_from_raw / weak_from_raw remains not associated
by Slava 20 May '13

20 May '13

I'm converting existing code with parent-child object tree to boost shared_ptr/weak_ptr with parents having [now shared] ownership over the children and children having weak reference to the parent. In the existing code a parent usually becomes the children as constructor parameters, and thus I have to extract the weak_ptr to "this" in constructor, which does not work with current boost::enable_shared_from_this implementation. So I am looking to enable_shared_from_raw alternative, which is promising, but unfortunately does not quite work for my case. Here is a small example demonstrating the issue: test.cpp: #include <boost/smart_ptr/enable_shared_from_raw.hpp> #include <iostream> struct Parent; struct Child { Child() { std::cout << "Construct Child" << std::endl; } ~Child() { std::cout << "Destruct Child" << std::endl; } boost::weak_ptr<Parent> parent; }; struct Parent : public boost::enable_shared_from_raw { Parent(boost::shared_ptr<Child> _child) { std::cout << "Construct Parent" << std::endl; this->child = _child; this->child->parent = boost::weak_from_raw(this); } ~Parent() { std::cout << "Destruct Parent" << std::endl; } boost::shared_ptr<Child> child; }; int main() { boost::shared_ptr<Child> child(new Child()); boost::shared_ptr<Parent> parent(new Parent(child)); std::cout << "child->parent is " << (child->parent.lock() ? "not null" : "null") << std::endl; parent.reset(); std::cout << "child must be alone" << std::endl; std::cout << "child->parent is " << (child->parent.lock() ? "not null" : "null") << std::endl; return 0; } `g++ -g -O0 test.cpp && valgrind a.out` produces: ==8467== Memcheck, a memory error detector ==8467== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al. ==8467== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info ==8467== Command: a.out ==8467== Construct Child Construct Parent child->parent is null Destruct Parent child must be alone child->parent is null Destruct Child ==8467== ==8467== HEAP SUMMARY: ==8467== in use at exit: 0 bytes in 0 blocks ==8467== total heap usage: 4 allocs, 4 frees, 112 bytes allocated ==8467== ==8467== All heap blocks were freed -- no leaks are possible ==8467== ==8467== For counts of detected and suppressed errors, rerun with: -v ==8467== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2) The problem is that the weak_ptr to parent in child does not get associated properly, when shared_ptr to parent is finally complete. Do I expect too much from enable_shared_from_raw or did I hit some bug in the implementation? I'm using boost 1.53.0-2 on Archlinux. -- Slava

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[boost][thread] Future's scheduler
by Klaim - Joël Lamotte 20 May '13

20 May '13

I'm using boost.thread V4 in my projects because I would like to use futures. I understand that boost 1.53 implementation of future.then() is incomplete but I think it's ok for my current use. However I think there might be something missing. I'm in a case where the user of my library provide his own task scheduler (or executor) which means that when I have functions that return futures, they will use that scheduler. I would like to limit the boilerplate necessary for the user to schedule tasks properly when one task is finished, so I assume the user will use then() with just lambdas or function pointers. The documentation of then() says: - When the scheduler or launch policy is not provided the continuation inherits the parent's launch policy or scheduler. Which is perfect to me as I just have to associate the first future with the scheduler, the user that will use .then() will not have to specify which scheduler to use. My problem is that I can't find how to associate a scheduler to a future (without using .then()). There is apparently no way to do this in boost::future or boost::promise interfaces. Am I missing something? I see that I could use a dummy initial future just to build another future with .then() which would associate the second future with the scheduler, but this is clearly just ductapping. Joel Lamotte

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64 bit or 32 bit?
by Scott Alexander 20 May '13

20 May '13

Hi, I have a Windows 8 64 bit OS and would like to use Visual Studio Express 2012 for Windows 8. Should I install a 64 bit or 32 bit version of Boost? Thanks, Scott

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[asio] schedule work on all threads of a single io_service::run() pool?
by Anthony Foiani 18 May '13

18 May '13

Greetings -- Is there a way to ask the io_service to distribute a particular handler to every thread that is running the service? My use case is per-thread watchdogs, and I need the worker threads to ping the watchdog on some regular interval (e.g., every 5 seconds). I didn't see anything like this in the docs, and I didn't see anything that looked promising when I looked through the source. (I'll freely admit that the ASIO source is beyond my ability to comprehend it without much more study, however.) I can approximate it by having my worker threads do something like this (pseudocode): while ( true ) { boost::system::error_code ec; io_service::poll_one( ec ); if ( ec == stopped ) break; watchdog::ping(); sleep( 500ms ); // trying to balance lag and wakeups } But that has the obvious problems of lag and more wakeups than I really need. To make this hack work, I think I need some calls that probably don't exist; instead of that "sleep" call, I would like to be able to do something like a timed wait on a condition variable: io_service::all_threads_cond.timed_wait( 5s ); That way, I would only wake up every 5 seconds (to feed the watchdog), unless the io_service sent a "notify_one" to the condition variable and this thread happened to be picked. Extra pings aren't much of an issue, but it would be nice to minimize them. Anyway. I'll continue digging, but if anyone has suggestions, I'd love to hear them. Thanks in advance! Best regards, Anthony Foiani

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[smart_ptr] Migrating from boost::shared_ptr<> to std::shared_ptr<>
by Szymon Gatner 18 May '13

18 May '13

Hi, with recently acquired (semi) C++11 compiler (YEY!) I started to think which of BOOST functionality could be replaced by standard counterparts. First obvious candidates are smart pointers. Thing is, there is lots of functions that take boost::shared_ptr<> as arguments (or return them) and it is just not easy to do do. My questions: - does it even make sense to switch to std::shared_ptr<> (should new functions use std instead of boost) - is there a way to easily convert one to another - what are (if any) differences between std and boost versions Regards, Szymon Gatner

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(no subject)
by Yeni Lora 18 May '13

18 May '13

Hi I have a problem with my code I using mpi. The error is with mca_btl_tcp_frag_recv, and I don´t know what mean... The error complete [../../../../../../ompi/mca/btl/tcp/btl_tcp_frag.c:216:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection timed out (110) and [btl_tcp_frag.c:216:mca_btl_tcp_frag_recv] mca_btl_tcp_frag_recv: readv failed: Connection reset by peer (104) I need some help...

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