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boost::hashes status
by Martin Dyring-Andersen 14 Dec '11

14 Dec '11

Hello, I've been using (parts of) the boost::hashes library for some time, and it seems to work quite well. Thanks Scott! A few changes are necessary to compile without errors and warnings Visual Studio 10 (see attached). I was wondering what the plans are for making it an official library? IMO it would be a very nice addition. As I recall, a suggestion was made to rename the library to boost::digest instead, to avoid confusion with boost::hash and the plural form. That seems sensible to me. -- Best regards, Martin Dyring-Andersen

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Ambiguous boost::move
by Kelvin Chung 13 Dec '11

13 Dec '11

I'm having this compiler issue while trying to use boost::packaged_task (gcc, C++03, move emulation). When I try to compile, I get the following: src/KMBuilder.cpp:54: error: call of overloaded ‘move(boost::unique_future<long unsigned int>&)’ is ambiguous boost/include/boost/thread/detail/move.hpp:44: note: candidates are: typename boost::enable_if<boost::is_convertible<T&, boost::detail::thread_move_t<T> >, boost::detail::thread_move_t<T> >::type boost::move(T&) [with T = boost::unique_future<long unsigned int>] boost/include/boost/move/move.hpp:294: note: typename boost::move_detail::disable_if<boost::has_move_emulation_enabled<T>, T&>::type boost::move(T&) [with T = boost::unique_future<long unsigned int>] The offending line of code: futures.push_back(boost::move(taskResult)); // futures is a boost::container::deque Is there a way to force one version of boost::move over the other? If so, which one should I use?

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Using unique_future in C++03, boost 1.47.0
by Kelvin Chung 13 Dec '11

13 Dec '11

I have a bunch of boost::packaged_task<unsigned long>, which I intend to execute on separate boost::threads. Before I do that, though, I want to insert each boost::unique_future<unsigned long> in a container as I make them. Given that I am using C++03 and boost 1.47.0 (boost 1.48.0 craps out over an ambiguous overload of boost::move), I have something like the following: std::deque<boost::unique_future<unsigned long>> futures; // std::deque<boost::thread> evalThreads; TODO for (…) { boost::packaged_task<unsigned long> task = …; // Create the tasks, one at a time boost::unique_future<unsigned long> taskResult = task.get_future(); // boost::thread taskThread(boost::move(task)); TODO // boost::unique_future and boost::thread can't be copied, but can be moved futures.push_back(boost::move(taskResult)); // evalThreads.push_back(boost::move(taskThread)); TODO } boost::wait_for_all(futures.begin(), futures.end()); // Now we can do stuff with futures The problem is that the code above is failing to compile, saying that /usr/include/c++/4.1.2/ext/new_allocator.h:104: error: passing ‘const boost::unique_future<long unsigned int>’ as ‘this’ argument of ‘boost::unique_future<R>::operator boost::detail::thread_move_t<boost::unique_future<R> >() [with R = long unsigned int]’ discards qualifiers I don't fully understand the problem, but I blame the move emulation. How do I fix this?

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boost::shared_locks and boost::upgrade_locks
by Kelvin Chung 13 Dec '11

13 Dec '11

I'm trying to implement a read-write lock, and I was told to use boost::upgrade_lock. However, only one thread can have a boost::upgrade_lock, and everyone else gets blocked, so it's not much on the read end. (Correct me if I am wrong, but boost::upgrade_lock only waits if someone has exclusive, but someone with boost::upgrade_lock will cause everyone else to block) But reads are cheap in my case - I just need to use locks for a cache. So, suppose I have the following: class Cache { std::map<Input, Output> cache; boost::shared_mutex mutex; public: Output query(const Input& in); }; It would appear that the proper way to implement Cache::query() is as follows: Output query(const Input& in) { boost::shared_lock<boost::shared_mutex> readLock(mutex); if (cache.count(in) == 0) { readLock.unlock(); boost::unique_lock<boost::shared_mutex> writeLock(mutex); // Check to see if the result was added while waiting for lock if (cache.count(in) != 0) return cache[in]; cache[in] = compute_output(in); return cache[in]; } else { return cache[in]; } } Is this correct? Or maybe it should be this: Output query(const Input& in) { boost::shared_lock<boost::shared_mutex> readLock(mutex); if (cache.count(in) == 0) { readLock.unlock(); boost::upgrade_lock<boost::shared_mutex> rereadLock(mutex); // Check to see if the result was added while waiting for lock if (cache.count(in) != 0) { return cache[in]; } else { boost::upgrade_to_unique_lock<boost::shared_mutex> writeLock(rereadLock); cache[in] = compute_output(in); return cache[in]; } } else { return cache[in]; } } A side question is that if compute_output() is an expensive operation, should that be moved to the part between releasing the read lock and getting the write/reread lock?

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Priority task queues using Boost.Asio and Boost.Thread
by Kelvin Chung 13 Dec '11

13 Dec '11

Suppose I have this abstract class Task like so: struct Task { virtual int doStuff() = 0; }; I then also have this: class CompositeTask : public Task { std::vector<Task> tasks; public: int doStuff() { for (std::vector<Task>::const_iterator it = tasks.begin(); it != tasks.end(); ++it) { it->do_stuff(); } } }; Now suppose that there is a point where I have a list of Tasks and I want to have them executed concurrently. To do so, I've leveraged Boost.Asio to create a thread pool task queue construct (via boost::asio::io_service). The next step beyond that is that I want to evaluate each of the tasks in CompositeTasks in parallel. I have a few questions about this: * One idea is to make a separate task thread for each CompositeTask. I'm under the impression that there is an absolute limit to the number of threads that I can make, which is determined by boost::thread::hardware_concurrency(). Is this true? If so, if the main Task queue has that many threads, would making a second task queue fail because it can't get more? * If I keep to one task queue (ie. throw all the Tasks in the CompositeTask to the main Task queue), then the possiblity exists of some kind of starvation (eg. the queue is full of CompositeTasks, and they are all blocking due to dependencies on Tasks in the queue). Is there a way to prioritize Tasks in the queue so that this doesn't happen?

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Try-upgrade locking
by Kelvin Chung 13 Dec '11

13 Dec '11

Suppose I have a boost::upgrade_lock<boost::shared_mutex>. When I want to create the boost::upgrade_to_unique_lock<boost::shared_mutex> and upgrade to exclusive locking, this blocks until all the shared lock holders leave. However, it does not appear that there is a non-blocking version of this, unlike, say, making a boost::unique_lock<boost::shared_mutex> and passing in boost::try_to_lock. So what should I do in order to create my own "try-upgrade" lock? I'm trying to use it like so: boost::upgrade_lock<boost::shared_mutex> upgradeLock(mutex); ... if (...) { // Substitute for boost::upgrade_to_unique_lock<boost::shared_mutex>, but also with aspects of // boost::try_to_lock, basically my_upgrade_to_unique_lock<boost::shared_mutex> deferredWriteLock(lock); // Do stuff where it doesn't matter whether I have exclusive or not, while the readers leave if (!deferredWriteLock) deferredWriteLock.lock(); // Now we need exclusive // We have exclusive, do more stuff } // Back to regular upgrade_lock here

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Boost matix question from a newbie
by boostnewbie 13 Dec '11

13 Dec '11

Hello, I want to use the boost matrices, and I have examples how to deal with that. But now, I want to store those matrix in a std-Array or an std-list. To do this, I must be able to name the type of for example a 3X3 matrix. I mean I nbeed an expressione similar to std::vector<matrix<double>> trafos; but I don´t know how to say that the matrix is a 3X3 type. Thanks in advence Egon -- View this message in context: http://boost.2283326.n4.nabble.com/Boost-matix-question-from-a-newbie-tp418… Sent from the Boost - Users mailing list archive at Nabble.com.

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shared_ptr to object in stl set container?
by Galen 13 Dec '11

13 Dec '11

Hi, -- I'm trying to use shared_ptr in a stl set, but am having trouble with find() Any help? Documentation on this seems hard to find. -- Also, are the overloaded < and == useful or correct here? thanks! Output is: ------------------ 0 adding neighbor 1 0 adding neighbor 2 1 adding neighbor 0 2 adding neighbor 1 0's neighbors 1 has 1 neighbors 0 2 has 1 neighbors 1 NOT WORKING is 1 a neighbor of 0? 0 is 0 a neighbor of 1? 0 Code below: ------------------- #include<set> #include<iostream> #include<boost/shared_ptr.hpp> using namespace std; //use typedef instead in actual code #define NodePtr boost::shared_ptr<Node> // TODO: should this extend shared_ptr? class Node { private: int id; set<NodePtr> neighbors; public: Node() { } Node(int newID) { id = newID; } ~Node() { } int getID() { return id; } int addNeighbor(NodePtr newNode) { int newID; newID = newNode->id; // if not already a neighbor, add if (!isNeighbor(newID)) neighbors.insert(newNode); } set<NodePtr> getNeighbors() { return neighbors; } bool isNeighbor(int searchID) { set<NodePtr>::iterator it; // check if this neighbor already in list NodePtr searchNode(new Node(searchID)); it = neighbors.find(searchNode); // if not found, add to neighbors if (it == neighbors.end()) { return false; } //else return true; } //overload == for find() bool operator== (NodePtr otherNode) { cout << "==: " << otherNode->id << " " << id << endl; return (otherNode->id == id); } //overload < in case we want to sort bool operator< (NodePtr otherNode) { return (id < otherNode->id); } }; int main() { // the nodes are pointers to Node objects NodePtr n0(new Node(0)); NodePtr n1(new Node(1)); NodePtr n2(new Node(2)); cout << n0->getID() << " adding neighbor " << n1->getID() << endl; n0->addNeighbor(n1); cout << n0->getID() << " adding neighbor " << n2->getID() << endl; n0->addNeighbor(n2); cout << n1->getID() << " adding neighbor " << n0->getID() << endl; n1->addNeighbor(n0); // cout << n2->getID() << " adding neighbor " << n0->getID() << endl; // n2->addNeighbor(n0); cout << n2->getID() << " adding neighbor " << n1->getID() << endl; n2->addNeighbor(n1); set<NodePtr> neighbors = n0->getNeighbors(); set<NodePtr>::iterator NB; int id = n0->getID(); cout << id << "'s neighbors" << endl; for (NB = neighbors.begin(); NB != neighbors.end() ; NB++) { set<NodePtr> neighborsList = (*NB)->getNeighbors(); cout << (*NB)->getID() << " has " << neighborsList.size() << " neighbors" << endl; cout << (*neighborsList.begin())->getID() << endl; } // http://www.engr.sjsu.edu/wbarrett/SortFind.htm cout << "NOT WORKING" << endl; cout << "is 1 a neighbor of 0? " << n0->isNeighbor(1) << endl; cout << "is 0 a neighbor of 1? " << n1->isNeighbor(0) << endl; }

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Re: [Boost-users] Boost-users Digest, Vol 2933, Issue 5
by Marat Abrarov 13 Dec '11

13 Dec '11

Hi, Rory. > Is there a reason io_service::run does not set an appropriate error on the > passed boost::system::error_code object when this is encountered? Certainly > it seems like an error case and would help circuital circumstances such as > my own. With current behavior of asio::io_service we can continue working with io_service after it was stopped by calling asio::io_service::reset(). It's like pause on io_service. It's not often used feature but it is nice to know that such behavior is possible. Also note that invocation of handlers is done only within threads that executes asio::io_service::run (run_one, poll, poll_one - http://www.boost.org/doc/libs/1_48_0/doc/html/boost_asio/overview/core/thre…) When io_service switches to the "stopped" state asio::io_service::run have to exit as fast as possible. When io_service is already in the "stopped" state asio::io_service::run have to exit immediately. So if io_service is already in stopped state before any user thread calls asio::io_service::run how can Asio pass "appropriate error" to asynchronous completion handlers? IMHO, current design of Asio is very clear. Regards, Marat Abrarov.

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Re: [Boost-users] incompatible serialization format of boost::property_tree between 1.44 and 1.48 (Robert Ramey)
by kpzhang 13 Dec '11

13 Dec '11

Hi Robert, os: windows 7 compiler: visual studio 2008 sample code: #include <iostream> #include <string> #include <boost/property_tree/ptree.hpp> #include <boost/property_tree/json_parser.hpp> int main() { std::string str; { std::stringstream sstr; boost::property_tree::ptree pt; char a= '\0'; pt.put("a",a); boost::property_tree::write_json(sstr, pt); str = sstr.str(); std::cout << str << std::endl; } { std::stringstream sstr(str); boost::property_tree::ptree pt; boost::property_tree::read_json(sstr, pt); char a = '\1'; std::cout << (int)pt.get("a",a) << std::endl; } return 0; }

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