- Boost-users - lists.preview.boost.org

[asio] How to deal with no-connect and/or read-timeout
by Michael Powell 25 Jun '13

25 Jun '13

Hello, I posted previously, but this is a bit of a follow-on thought. Did some searching, and SO has this note: http://stackoverflow.com/questions/13126776/asioread-with-timeout Pardon me while I stare in disbelief. Seriously? Okay, I'd like to use Boost.Asio to facilitate things. Is this the way (one proposed way) of handling read-with-timeout? Our scenario goes similar to this I think: * Client may (or may not) connect, depending on the integration scenario. The main service thread should tolerate either, with plausibly the socket connection/session operating in another thread "asynchronously". * When client connects, the session logic is pretty straightforward: read if/when there is something to read, and pass it through a message framing unwrapper. Completed message gets deserialized and published into a thread-safe queue. * Events may be generated from the main service thread and subsequently published to the client: effectively a write operation, after passing a serialized message through a message framing wrapper. Doable? Feasible, possibly with some sort of a ping-ponging-back-and-forth type of session handling callback mechanism? I am cautiously optimistic that this has more to do with connection/session callback/state-machine type things, than it does Asio? Regards, Michael

2 2

[asio] Grasping the proto-typical socket server
by Michael Powell 25 Jun '13

25 Jun '13

Hello, I've dealt with sockets, and socket servers, in the past, so am familiar with them. Abstracting out a prototypical server details, drawing from the plethora of examples, this is what I can determine. I see three primary abstractions, the server itself, with endpoint binding, socket connection acceptor, so far so good. Then there's a connection, which is a sort of io_service to socket adapter. Followed closely by a session concern, where reads and writes are actually performed. Studying the examples, however, it seems to me that by design io_service wants to be *the* first class citizen that runs, with asynchronous callbacks being the mode of choice. How might we go about mixing this code, presumably in the main thread (?), with any worker service-oriented thread that might be going on. For instance, I start a thread and wait for it to finish and rejoin for a main service loop. Socket connection sessions are secondary to this service behavior taking place IMO. If a client connects, great, we'll interact with it. If not, that should be transparent to the application. Possibly session is a second thread worker with a thread-local-scope io_service, that we pub/sub messages to the main service loop. Thoughts on this type of approach? Much appreciated... Regards, Michael

2 1

Mutex synchronised wrapper class for boost::interprocess shared memory vector of strings
by Riskybiz 24 Jun '13

24 Jun '13

I'm trying to create a wrapper class to control a managed shared memory segment using Boost::Interprocess. I'm having trouble reading data from the shared memory vector of strings... When the vector is instantiated in the managed shared segment I place in the first vector element a test string; "testing testing 1 2 3". Immediately after placing it there and in the scope of the same code block I can access the vector element and print out the string using std::cout. However when I try to read the vector element using the read() function the test program crashes. The problem is with the line: std::string stdStr = sharedSegmentVector->at(index).c_str(); Question is how to fix this? I'm confused because at instantiation time this same code will access the shared memory vector; later on in the read() function it will not. I've as yet been unable to test the write() function; because I can't yet read() the vector! Any help to get this working is much appreciated, With thanks, Riskybiz Class Definition: #ifndef SHARED_MEMORY_WRAPPER_H//if not defined already #define SHARED_MEMORY_WRAPPER_H//then define it #include <boost/interprocess/managed_shared_memory.hpp> #include <boost/interprocess/containers/vector.hpp> #include <boost/interprocess/containers/string.hpp> #include <boost/interprocess/allocators/allocator.hpp> #include <boost/interprocess/sync/named_mutex.hpp> #include <iostream> #include <stdexcept> using namespace boost::interprocess; class SharedMemoryWrapper { public: SharedMemoryWrapper(const std::string &name, bool server) : m_name(name), m_server(server) { if (server) { named_mutex::remove("named_mutex"); shared_memory_object::remove(m_name.c_str()); //Create shared memory managed_shared_memory m_segment(create_only, m_name.c_str(), 10000); //Create allocators CharAllocator charallocator(m_segment.get_segment_manager()); StringAllocator stringallocator(m_segment.get_segment_manager()); //This string is in only in this process (the pointer pointing to the //buffer that will hold the text is not in shared memory). //But the buffer that will hold "this is my text" is allocated from //shared memory MyShmString mystring(charallocator); mystring = "testing testing 1 2 3"; //This vector is fully constructed in shared memory. All pointers //buffers are constructed in the same shared memory segment //This vector can be safely accessed from other processes. MyShmStringVector *sharedSegmentVector = m_segment.construct<MyShmStringVector>("sharedSegmentVector")(stringallocato r); sharedSegmentVector->push_back(mystring); std::string outStr = sharedSegmentVector->at(0).c_str(); std::cout << "Shared Memory Vector Instantiated: Index 0 Data is: " << outStr << std::endl; } else { //Open the shared segment managed_shared_memory m_segment(open_only, name.c_str()); //Find the vector using the c-string name and open it MyShmStringVector *sharedSegmentVector = m_segment.find<MyShmStringVector>("sharedSegmentVector").first; } m_mutex = new named_mutex(open_or_create, "named_mutex"); } ~SharedMemoryWrapper() { if (m_server) { named_mutex::remove("named_mutex"); //Destroy the vector from the managed_shared_memory //m_segment->destroy_ptr(sharedSegmentVector);//This will free all strings that the vector contains m_segment->destroy<MyShmStringVector>("sharedSegmentVector");//Destroy the vector //Is it necessary to destroy the allocators here? //Remove the managed_shared_memory; this may fail if the memory does not exist or is mapped or opened by another process shared_memory_object::remove(m_name.c_str()); } delete m_mutex; delete m_segment; } //Writer void write(const std::string &in) { try { CharAllocator charallocator(m_segment->get_segment_manager()); scoped_lock<named_mutex> lock(*m_mutex); MyShmString shmStr(in.c_str(), charallocator); sharedSegmentVector->push_back(shmStr); } catch(...) { std::cout << "Error in SharedMemoryWrapper::write(): unknown error" << std::endl; } } //Reader std::string read(int index) { try { scoped_lock<named_mutex> lock(*m_mutex); std::cout << "Shared Memory Vector Entered Read(), Passed Index: " << index << std::endl; std::string stdStr = sharedSegmentVector->at(index).c_str(); std::cout << "Shared Memory Vector Read At: Index" << index << "Data is: " << stdStr << std::endl; return stdStr; } catch(std::range_error err) { std::cout << "Error in SharedMemoryWrapper::read(): range_error" << std::endl; } catch(...) { std::cout << "Error in SharedMemoryWrapper::read(): unknown error " << std::endl; } return "ERROR IN SharedMemoryWrapper::read()"; } private: //Typedefs typedef boost::interprocess::allocator<char, managed_shared_memory::segment_manager> CharAllocator; typedef boost::interprocess::basic_string<char, std::char_traits<char>, CharAllocator> MyShmString; typedef boost::interprocess::allocator<MyShmString, managed_shared_memory::segment_manager> StringAllocator; typedef boost::interprocess::vector<MyShmString, StringAllocator> MyShmStringVector; bool m_server; std::string m_name; managed_shared_memory *m_segment; MyShmStringVector *sharedSegmentVector; named_mutex *m_mutex; };//class #endif//header guard Test Programme: #include "stdafx.h" #include "SharedMemoryWrapper.h" #include <iostream> #include <string> int main(int argc, char *argv[]) { SharedMemoryWrapper *smw = new SharedMemoryWrapper("SharedMemory1", true); std::string outStr = smw->read(0); std::cout << outStr << std::endl; return 0; }

2 1

Re: [Boost-users] Mutex synchronised wrapper class for boost::interprocess shared memory vector of strings
by Riskybiz 24 Jun '13

24 Jun '13

Date: Wed, 19 Jun 2013 22:05:32 +0200 From: Ion Gazta?aga <igaztanaga(a)gmail.com> To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] Mutex synchronised wrapper class for boost::interprocess shared memory vector of strings Message-ID: <51C20F0C.8090408(a)gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed El 18/06/2013 16:28, Riskybiz escribi?: > I'm trying to write a wrapper class in C++ to give mutex synchronised > interprocess access to a shared memory vector of strings. This is my first > foray into boost::interprocess and allocators are proving something of a > mystery. > > Is anyone able to see why on compilation I get the error: When you build any container in shared memory it must be constructed with an allocator. Change your push function to (not charallocator is passed to MyShmString): void push(const std::string & in) { CharAllocator charallocator(m_segment->get_segment_manager()); scoped_lock<named_mutex> lock(*m_mutex); MyShmString inStr(in.c_str(), charallocator); sharedSegmentVector->push_back(inStr); } Best, Ion Thanks for the reply Ion. I'm now having trouble reading from the vector in the shared memory. I get an exception when calling read(0) or read(1). What I'm trying to do is read "testing testing 123" from the first element of the sharedSegmentVector. Is it necessary to use some particular type conversion technique in the reader function to access a sharedSegmentVector string element? Any help to get this working is much appreciated; I've been trying for more than a month to get to this point! Code below..... Thanks Riskybiz #ifndef SHARED_MEMORY_WRAPPER_H//if not defined already #define SHARED_MEMORY_WRAPPER_H//then define it #include <boost/interprocess/managed_shared_memory.hpp> #include <boost/interprocess/containers/vector.hpp> #include <boost/interprocess/containers/string.hpp> #include <boost/interprocess/allocators/allocator.hpp> #include <boost/interprocess/sync/named_mutex.hpp> using namespace boost::interprocess; class SharedMemoryWrapper { public: SharedMemoryWrapper(const std::string &name, bool server) : m_name(name), m_server(server) { if (server) { named_mutex::remove("named_mutex"); shared_memory_object::remove(m_name.c_str()); //Create shared memory managed_shared_memory m_segment(create_only, m_name.c_str(), 10000); //Create allocators CharAllocator charallocator(m_segment.get_segment_manager()); StringAllocator stringallocator(m_segment.get_segment_manager()); //This string is in only in this process (the pointer pointing to the //buffer that will hold the text is not in shared memory). //But the buffer that will hold "this is my text" is allocated from //shared memory MyShmString mystring(charallocator); mystring = "testing testing 1 2 3"; //This vector is fully constructed in shared memory. All pointers //buffers are constructed in the same shared memory segment //This vector can be safely accessed from other processes. MyShmStringVector *sharedSegmentVector = m_segment.construct<MyShmStringVector>("sharedSegmentVector")(stringallocato r); sharedSegmentVector->push_back(mystring); } else { //Open the shared segment managed_shared_memory m_segment(open_only, name.c_str()); //Find the vector using the c-string name and open it MyShmStringVector *sharedSegmentVector = m_segment.find<MyShmStringVector>("sharedSegmentVector").first; } m_mutex = new named_mutex(open_or_create, "named_mutex"); } ~SharedMemoryWrapper() { if (m_server) { named_mutex::remove("named_mutex"); //Destroy the vector from the managed_shared_memory m_segment->destroy_ptr(sharedSegmentVector);//This will free all strings that the vector contains m_segment->destroy<MyShmStringVector>("sharedSegmentVector");//Destroy the vector //Is it necessary to destroy the allocators here? //Remove the managed_shared_memory; this may fail if the memory does not exist or is mapped or opened by another process shared_memory_object::remove(m_name.c_str()); } delete m_mutex; delete m_segment; } //Writer void write(const std::string &in) { CharAllocator charallocator(m_segment->get_segment_manager()); scoped_lock<named_mutex> lock(*m_mutex); MyShmString shmStr(in.c_str(), charallocator); sharedSegmentVector->push_back(shmStr); } //Reader std::string read(long index) { CharAllocator charallocator(m_segment->get_segment_manager()); scoped_lock<named_mutex> lock(*m_mutex); MyShmString shmStr(sharedSegmentVector->at(index), charallocator); std::string stdStr = std::string(shmStr.begin(), shmStr.end()); return stdStr; } private: //Typedefs typedef boost::interprocess::allocator<char, managed_shared_memory::segment_manager> CharAllocator; typedef boost::interprocess::basic_string<char, std::char_traits<char>, CharAllocator> MyShmString; typedef boost::interprocess::allocator<MyShmString, managed_shared_memory::segment_manager> StringAllocator; typedef boost::interprocess::vector<MyShmString, StringAllocator> MyShmStringVector; bool m_server; std::string m_name; managed_shared_memory *m_segment; MyShmStringVector *sharedSegmentVector; named_mutex *m_mutex; };//class #endif//header guard

2 1

[interprocess]shared_memory_object stores content in disk?
by Adrian Yu 24 Jun '13

24 Jun '13

I'm training multiple networks based on a single database. So to accelerate speed and reduce disk reading, I use shared_memory_object class provided by boost. Since the lab workstation is currently unavailable, I migrated my code to my personal computer. On the lab workstation, the host program successfully reads all data to memory. But on my PC, strangely it creates a file on system drive rather than storing the data in memory. The whole database is about 3.7 GB; the lab workstation has 32 GB memory and runs Windows Server 2008 R2; my PC has 8 GB memory and runs Windows 7. There should be enough memory to store the data. So why? Are there certain ways to force the program to keep all data in memory?

2 1

[Interprocess] Allocation algorithms
by Oodini 24 Jun '13

24 Jun '13

Hello, I need to allocate and fill about 10 big memories areas (several Gb) at the startup of my program. The data will never be modified or freed after during the program lifetime, and will be *only read* an other processes. What allocation algorithm should I take from the ones provided by the library ? Should I create a new one, more efficient (no reallocations, no race conditions...) ? Thanks.

3 3

[Interprocess] Minimal size of a managed_shared_memory
by Oodini 24 Jun '13

24 Jun '13

Hello, A managed_shared_memory is a typedef for a basic_managed_shared_memory using rbtree_best_fit as allocation algorithm. In the documentation : http://www.boost.org/doc/libs/1_53_0/doc/html/interprocess/memory_algorithm… It is said at the and of the page : "In most 32 systems with 8 byte alignment the minimum size of a block is 24 byte". I am on Windows XP SP3 32 bits. The alignement is 8 byte. But if I create a managed_shared_memory with a size lesser than 120 bytes, my app crashes. This value comes from several get_min_size function, the deepest being in the rbtree_best_fit class. So I wonder which value we can grant to the documentation above. How are the 120 bytes used ?

2 1

Boost::Interprocess Documentation request
by Riskybiz 24 Jun '13

24 Jun '13

In the Boost::Interprocess documentation and under the heading "Where is this being allocated?"; is an example of how to create a vector of strings in a managed_shared_memory segment. Link to Boost::Interprocess documentation here: http://www.boost.org/doc/libs/1_53_0/doc/html/interprocess/allocators_contai ners.html#interprocess.allocators_containers.containers_explained Please could this example be extended to demonstrate; 1. How to add string elements to the shared memory vector from a different process? 2. How to access and copy strings from the shared memory vector from a different process? This really would be invaluable to people trying to use Boost::Interprocess for the first time! My particular project has ground to a halt for over a month simply trying to get a working implementation of a Boost::Interprocess mutex synchronised shared memory vector of strings. I would like one process to add strings to the shared memory vector and several other processes to read string data from the vector. Right now I don't know if I'll ever get it to work! Running out of ideas here! Hope someone can help. Thanks, Riskybiz.

1 0

[property_tree] Serializing ptree to/from JSON
by Michael Powell 24 Jun '13

24 Jun '13

Hello, I am writing some code to serialize a package to/from JSON. Overall, it is working well, except for what appears to be a weak link in the ptree chain of events. I take a POCO (for all intents) and populate a ptree, then parse that to JSON using the property_tree JSON parser. No problem. Then I take that same string and want to parse it into another ptree. In and of itself, seems like it is no problem. The new ptree has a count, so I gather the parse worked. However, when I try to use ptree.count(path), or ptree.find(path), neither of these work. They are returning 0 or not_found(), respectively. I may be able to bypass that check for the moment and run it through ptree.get<Type>(path) for the time being, but that seems less desirable. Any insights on ptree along these lines? Thanks! Regards, Michael Powell

3 3

[FunctionTypes] Getting functor/lambda parameters (VS2012)
by Mateusz Loskot 23 Jun '13

23 Jun '13

Hi, I'm using C++ compiler from the latest VS2012. I'm trying this simple technique to determined type of functor or lambda call parameter, it works well: #include <boost/function_types/parameter_types.hpp> int main() { auto foo = [](int) -> void {}; typedef decltype(foo) foo_type; typedef boost::function_types::parameter_types < decltype(&foo_type::operator()) >::type parameter_types; } Next, I move the typedef into class template, in constructor body, it works well too: template <typename T> struct A { A(T t) { typedef typename boost::function_types::parameter_types < decltype(&T::operator()) >::type parameter_types; } }; Finally, I move further with the technique, so I can access parameter types within class template scope: template <typename T> struct B { typedef typename boost::function_types::parameter_types < decltype(&T::operator()) >::type parameter_types; }; This example does compile with clang 3.4 (svn trunk) and GCC 4.8.1, but it does not compile with Visual C++ 11.0. Does anyone understand what C++11 feaure VS2012 is lacking so it prevents compilation of the sample with B template above? Here is complete .cpp file https://gist.github.com/mloskot/5846468 Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

1 0