Automatically delete containers sent to asynchronous functions/io_service - c++

Question

I would like to use an unordered_map as a job or session context object. So, I would like to allocate in some function bundle it with a static function in a function object and send this function object to an io_service. And obviously, I do not worry about deallocating it.
Any ideas on how to do that?
Thank you!
#include <iostream>
#include <unordered_map>
#include "boost/asio.hpp"
#include "boost/thread.hpp"
using namespace std;
namespace asio = boost::asio;
typedef std::unique_ptr<asio::io_service::work> work_ptr;
typedef boost::function<void(void) > boost_void_void_fun;
class job_processor {
public:
job_processor(int threads) : thread_count(threads) {
service = new asio::io_service();
work = new work_ptr(new asio::io_service::work(*(service)));
for (int i = 0; i < this->thread_count; ++i)
workers.create_thread(boost::bind(&asio::io_service::run, service));
}
void post_task(boost_void_void_fun job) {
this->service->post(job);
}
void drain() {
this->work->reset();
}
void wait() {
this->workers.join_all();
}
private:
int thread_count;
work_ptr * work;
asio::io_service* service;
boost::thread_group workers;
};
typedef std::unordered_map<string, unsigned long> map_t;
class with_static_function {
public:
static void print_map(map_t map) {
for(map_t::iterator it = map.begin(); it != map.end(); ++it)
std::cout << it->first << ":" << it->second << std::endl;
}
static void print__heap_map(map_t* map) {
if(!map) return;
for(map_t::iterator it = map->begin(); it != map->end(); ++it)
std::cout << it->first << ":" << it->second << std::endl;
}
};
int main(int argc, char** argv) {
map_t words;
words["one"] = 1;
// pass the reference;
with_static_function::print_map(words);
job_processor *pr = new job_processor(4);
{
map_t* heap_map = new map_t;
(*heap_map)["two"] = 2;
// I need this variable to the job_processor;
// and I do not want to worry about deallocation.
// should happen automatically somehow.
// I am ok with changing the variable to be a shared_ptr or
// anything else that works.
boost_void_void_fun fun = boost::bind(
&with_static_function::print__heap_map,
heap_map);
fun(); // if binding was done right this should have worked.
pr->post_task(fun);
}
pr->drain();
pr->wait();
delete pr;
return 0;
}

Answer 1

A number of observations:
Stop Emulating Java. Do not use new unless you're implementing an ownership primitive (smart handle/pointer type). Specifically, just create a pr:
job_processor pr(4);
Same goes for all the members of job_processor (you were leaking everything, and if job_processor were copied, you'd get double-free Undefined Behaviour
The code
// pass the reference;
with_static_function::print_map(words);
passes by value... meaning the whole map is copied
to avoid that copy, fix the print_map signature:
static void print_map(map_t const& map) {
for(map_t::const_iterator it = map.begin(); it != map.end(); ++it)
std::cout << it->first << ":" << it->second << std::endl;
}
Of course, consider just writing
static void print_map(map_t const& map) {
for(auto& e : map)
std::cout << e.first << ":" << e.second << "\n";
}
The "heap" overload of that could be, as my wording implies, an overload. Be sure to remove the useless duplication of code (!):
static void print_map(map_t const* map) {
if (map) print_map(*map);
}
You don't even need that overload because you can simply use a lambda to bind (instead of boost::bind):
auto heap_map = boost::make_shared<map_t>();
heap_map->insert({{"two", 2}, {"three", 3}});
boost_void_void_fun fun = [heap_map] { with_static_function::print_map(*heap_map); };
Complete working program:
Live On Coliru
#include <iostream>
#include <unordered_map>
#include <boost/asio.hpp>
#include <boost/make_shared.hpp>
#include <boost/thread.hpp>
#include <boost/function.hpp>
#include <boost/bind.hpp>
namespace asio = boost::asio;
typedef boost::function<void(void)> boost_void_void_fun;
class job_processor {
public:
job_processor(int threads) : service(), work(boost::asio::io_service::work(service))
{
for (int i = 0; i < threads; ++i)
workers.create_thread(boost::bind(&asio::io_service::run, &service));
}
void post_task(boost_void_void_fun job) {
service.post(job);
}
void drain() {
work.reset();
}
void wait() {
workers.join_all();
}
private:
asio::io_service service;
boost::optional<asio::io_service::work> work;
boost::thread_group workers;
};
typedef std::unordered_map<std::string, unsigned long> map_t;
namespace with_static_function {
static void print_map(map_t const& map) {
for(auto& e : map)
std::cout << e.first << ":" << e.second << "\n";
}
}
int main() {
// pass the reference;
with_static_function::print_map({ { "one", 1 } });
job_processor pr(4);
{
auto heap_map = boost::make_shared<map_t>();
heap_map->insert({{"two", 2}, {"three", 3}});
boost_void_void_fun fun = [heap_map] { with_static_function::print_map(*heap_map); };
pr.post_task(fun);
}
pr.drain();
pr.wait();
}
Prints
one:1
three:3
two:2