我正在使用从这个网站获取的阻塞队列示例,认为它非常不错。 这个阻塞队列使用了boost::mutex。 有时会抛出异常:
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::system::system_error> >'
what(): 坏的文件描述符
这是阻塞队列的代码:
#include <boost/thread/mutex.hpp>
#include <boost/thread/thread.hpp>
#include <boost/thread/condition_variable.hpp>
#include <exception>
#include <list>
#include <stdio.h>
struct BlockingQueueTerminate
: std::exception
{};
namespace tools {
template<class T>
class BlockingQueue
{
private:
boost::mutex mtx_;
boost::condition_variable cnd_;
std::list<T> q_;
unsigned blocked_;
bool stop_;
public:
BlockingQueue()
: blocked_()
, stop_()
{}
~BlockingQueue()
{
this->stop(true);
}
void stop(bool wait)
{
// tell threads blocked on BlockingQueue::pull() to leave
boost::mutex::scoped_lock lock(mtx_);
stop_ = true;
cnd_.notify_all();
if(wait) // wait till all threads blocked on the queue leave BlockingQueue::pull()
while(blocked_)
cnd_.wait(lock);
}
void put(T t)
{
boost::mutex::scoped_lock lock(mtx_); // The exception is thrown here !
q_.push_back(t);
cnd_.notify_one();
}
T pull()
{
boost::mutex::scoped_lock lock(mtx_);
++blocked_;
while(!stop_ && q_.empty())
cnd_.wait(lock);
--blocked_;
if(stop_) {
cnd_.notify_all(); // tell stop() this thread has left
throw BlockingQueueTerminate();
}
T front = q_.front();
q_.pop_front();
return front;
}
};
}
有没有人能发现这里出了什么问题?我已经试图整天找出问题,但是徒劳无功。我想我需要外部的视角来看待这个问题。
请查找“//The exception is thrown here!”的注释,以确定问题发生的确切位置。
编辑1:
背景:我正在使用这个阻塞队列来创建一个MySQL异步包装器。
这是我的MySQL.hh文件。
#ifndef MYSQL_HH_
# define MYSQL_HH_
# include <boost/asio.hpp>
# include <boost/thread.hpp>
# include <boost/function.hpp>
# include <mysql++/mysql++.h>
# include <queue>
# include "async_executor.hh"
# include "BlockingQueue.hh"
class t_mysql_event {
public:
t_mysql_event(std::string query, boost::function<void(mysqlpp::StoreQueryResult)> cb) :
m_query(query), m_store_cb(cb), m_store_bool(true) {}
t_mysql_event(std::string query, boost::function<void()> cb) :
m_query(query), m_exec_cb(cb), m_store_bool(false) {}
bool is_store_query() {
return m_store_bool;
}
std::string toString() {
return m_query;
}
std::string m_query;
boost::function<void(mysqlpp::StoreQueryResult)> m_store_cb;
boost::function<void()> m_exec_cb;
private:
bool m_store_bool;
};
namespace pools {
class MySQL {
public:
~MySQL() {}
static MySQL* create_instance(boost::asio::io_service& io);
static MySQL* get_instance();
void exec(std::string query, boost::function<void()> cb);
void store(std::string query, boost::function<void(mysqlpp::StoreQueryResult)> cb);
private:
MySQL(boost::asio::io_service& io) : executor(io, 100), parent_io(io), m_strand(io)
{
for (int i=0; i < 100; ++i) {
boost::thread(boost::bind(&MySQL::retreive, this));
}
}
void async_exec(std::string query, boost::function<void()> cb, mysqlpp::Connection& conn);
void async_store(std::string query, boost::function<void(mysqlpp::StoreQueryResult)> cb, mysqlpp::Connection& conn);
void retreive();
private:
tools::async_executor executor;
boost::asio::io_service& parent_io;
boost::asio::strand m_strand;
tools::BlockingQueue<t_mysql_event*> m_events;
std::queue<mysqlpp::Connection*> m_stack;
};
}
#endif //MYSQL_HH_
这里是MySQL.cc文件:
#include "MySQL.hh"
static pools::MySQL* _instance = 0;
namespace pools {
MySQL* MySQL::create_instance(boost::asio::io_service& io) {
if (!_instance)
_instance = new MySQL(io);
return _instance;
}
MySQL* MySQL::get_instance() {
if (!_instance) {
exit(1);
}
return _instance;
}
void MySQL::exec(std::string query, boost::function<void()> cb) {
m_events.put(new t_mysql_event(query, cb));
}
void MySQL::store(std::string query, boost::function<void(mysqlpp::StoreQueryResult)> cb) {
m_events.put(new t_mysql_event(query, cb));
}
void MySQL::retreive() {
mysqlpp::Connection conn("***", "***", "***", "***");
for(;;) {
t_mysql_event *event = m_events.pull();
if (event->is_store_query())
async_store(event->m_query, event->m_store_cb, conn);
else
async_exec(event->m_query, event->m_exec_cb, conn);
delete event;
}
}
void MySQL::async_exec(std::string query, boost::function<void()> cb, mysqlpp::Connection& conn) {
mysqlpp::Query db_q = conn.query(query.c_str());
db_q.exec();
parent_io.post(cb);
}
void MySQL::async_store(std::string query, boost::function<void(mysqlpp::StoreQueryResult)> cb, mysqlpp::Connection& conn) {
mysqlpp::Query db_q = conn.query(query.c_str());
mysqlpp::StoreQueryResult res = db_q.store();
parent_io.post(boost::bind(cb, res));
}
}
之后:
class MyClass {
public:
MyClass() : _mysql(pools::MySQL::get_instance()) {}
startQueries();
private:
void Query1() {
std::stringstream query("");
query << "INSERT INTO Table1 ***";
_mysql->exec(query.str(),
boost::bind(&MyClass::Query2, this, _1));
}
void Query2() {
std::stringstream query("");
query << "INSERT INTO Table2 ***";
_mysql->exec(query.str(),
boost::bind(&MyClass::Query3, this, _1));
}
void Query3() {
std::stringstream query("");
query << "INSERT INTO Table3 ***";
_mysql->exec(query.str(),
boost::bind(&MyClass::done, this, _1));
}
void done() {}
pools::MySQL *_mysql;
};
希望这能回答有关更多信息的请求...
有趣的事情:
如果我将每个“_mysql”替换为“pools::MySQL::get_instance()”,似乎不会崩溃。但我怀疑下面还有更重要的错误...