pthread 没有为 class 个实例启动

Question

注意：C++98

你好，我对 c++ 有点陌生，我正在编写一个数据库程序，并试图使用 pthread 使用 boost::asio 包启动一个计时器。计时器的目的是在 sql 查询被放入缓冲区后启动，如果一段时间内没有收到任何内容，缓冲区将运行执行函数。我已经设法让它编译，但它看起来不像 pthread 实例正在启动。

我已经在我的 getInstance 方法中调用了 pthread，boost::asio 警报也已相应设置。我将在下面展示的是通过调用 io_run() 直接启动计时器在警报中陷入循环。

database.h

void *run_io(void *arg);

class Database
{
private:
    static Database *dbInstance; //= NULL;

public:
    boost::asio::io_service io_service;
    boost::posix_time::millisec interval;
    boost::asio::deadline_timer timer;
    pthread_t timerThread;

public:
    static Database &getInstance()
    {
        if (!dbInstance)
        {
            dbInstance = new Database();
            // pthread_create(&dbInstance->timerThread,NULL,run_io,&dbInstance->io_service);
            std::cout << " INSTANCE CREATED " << std::endl;
            pthread_create(&dbInstance->timerThread, NULL, run_io, (void *)&dbInstance->io_service);
            // pthread_join(&dbInstance->timerThread, NULL);
        }
        return *dbInstance;
    }
};

database.cpp

Database *Database::dbInstance = NULL;

Database::Database()
    : interval(2000), timer(io_service, interval) {}

Database::~Database()
{
    sqlite3_close(db);
}

void Database::setAlarm(const boost::system::error_code& /* e */)
{
    std::cout << "[TEST] WE ARE IN SET ALARM " << std::endl;
    DB_WRITE_TIME = 500;

    boost::posix_time::milliseconds interval(DB_WRITE_TIME);

    // Reschedule the timer for 1 second in the future:
    timer.expires_at(timer.expires_at() + interval);
    // Posts the timer event
    timer.async_wait(boost::bind(&Database::setAlarm, this, _1));
}

int Database::buffer()
{
    // DO BUFFER STUFF

    timer.async_wait(boost::bind(&Database::setAlarm, this, _1));
   // io_service.run() <-- uncommenting this results in the loop
    return rc ;
}

void *run_io(void *arg)
{
    boost::asio::io_service *io_service = (boost::asio::io_service *)arg;

    io_service->run();
}

所以我觉得 pthread 甚至都没有启动。我试着在里面放一个打印语句看它是否出来了，但我的终端里什么也没有出现。

---- 编辑 ----

我已按照 Sehe 的建议进行了更改，但看起来我仍然无法调用警报处理程序 (setAlarm())。我不得不稍微修改它以与整个程序兼容，但本质上是这样的（我将间隔时间的值设置为 5000 以使其有足够的时间进行测试）：

database.h

class Database
{
private:
    static boost::shared_ptr<Database> dbInstance;

private:
    typedef boost::asio::io_service io_service;
    io_service io;
    boost::scoped_ptr<io_service::work> work;
    boost::posix_time::millisec interval;
    boost::asio::deadline_timer timer;
    boost::thread timerThread;

    void run_io()
    {
        std::cout << "ENTER IO THREAD" << std::endl;
        io.run();
        std::cout << "LEAVE IO THREAD" << std::endl;
    }

public:
    static Database &getInstance()
    {
        if (!dbInstance)
        {
            std::cout << " INSTANCE CREATED " << std::endl;
            dbInstance.reset(new Database());
            dbInstance->timerThread = boost::thread(boost::bind(&Database::run_io,dbInstance));
        }
        return *dbInstance;
    }

    Database(); // <-- default constructor (doesn't take any args)
    ~Database();

database.cpp

boost::shared_ptr<Database> Database::dbInstance;
static const int DB_WRITE_TIME = 5000;

Database::Database()
    : work(new io_service::work(io)), interval(5000), timer(io, interval)
{
    // std::cout << " CONSTRUCTED " << std::endl;
}

Database::~Database()
{
    // std::cout << " DESTROYED " << std::endl;
    // sqlite3_close(db);
}

void Database::setAlarm(const boost::system::error_code& ec)
{
    std::cout << "[TEST] WE ARE IN SET ALARM - ec message = " << ec.message() << std::endl;

    executeSqlInBuffer(); // once timer expire, call the execute function

    if(!ec)
    {
        boost::posix_time::milliseconds interval(DB_WRITE_TIME);
        timer.expires_from_now(interval);
        timer.async_wait(boost::bind(&Database::setAlarm, this, _1));
    }
}

void Database::teardown()
{
    // std::cout << " INSTANCE SHUTTING DOWN " << std::endl;
    timer.cancel();             // stop timer loop
    work.reset();               // allows io.run() to exit
    if(timerThread.joinable())
    {
        std::cout << " JOINED " << std::endl;
        timerThread.join();     // releasing bound of shared_ptr
    }
    else std::cout << " NOT JOINED " << std::endl;
    dbInstance.reset();         // releasing instance
}

int Database::buffer()
{
    // do buffering
    if(buffer.size() == max_size)
    {    
        executeSqlInBuffer();
    }
    std::cout << timer.expires_from_now(interval) << std::endl;
    // std::cout << " ~ BEFORE TIMER ~ " << std::endl;
    timer.async_wait(boost::bind(&Database::setAlarm, this, _1));

    return 1;
}

main.cpp

int main()
{
    pthread_t thread1;        // a few pthreads in main that handle other areas of the program.
    pthread_create(&thread1,NULL,thread1Arg,NULL);

    pthread_t dbThread;        // my pthread for the database
    pthread_create(&dbThread,NULL,dbThreadArg,NULL);

    Database& database = Database::getInstance();
    database.teardown();

    pthread_join(thread1,NULL);
    pthread_join(dbThread,NULL);

    return 0;
}

你也可以在这里看到它进入和离开IO线程，并创建一个实例，加上timer.expires_from_now(interval)的调试输出：

 INSTANCE CREATED 

 JOINED 
ENTER IO THREAD
LEAVE IO THREAD
...
...
0 ---> first cycle
1 ---> second cycle
...
1 ---> nth cycle

Answer 1

我很困惑为什么使用 Boost 或 C++11（或两者...）的人会使用原始 pthread 线程（参见以获得良好的并置） .

真正的问题可能是工作中有 io_service 运行（参见 https://www.boost.org/doc/libs/1_57_0/doc/html/boost_asio/reference/io_service__work.html）。

如果您没有挂起的异步操作，线程就会退出。

另一个问题是

的准确性问题

timer.expires_at(timer.expires_at() + interval);

有些处理程序可能会花费太多时间，以至于在您安排下一个警报时，截止日期已经过期。使用

可能更好

timer.expires_from_now(interval);

Note this also matches the comment better. The comment suffers from comment already because it says "1 second" but it is actually some defined constant DB_WRITE_TIME

或者以其他方式将您的计时器与其他处理程序分开，以保证准确的调度。

最后，由于没有任何关机，您 UB 了。静态实例永远不会被销毁，但非分离线程的价值永远不会被加入，从而在关闭时产生未定义的行为。

This problem is actually almost identical to the one recently discussed here, where I also explains the way work guards work in more detail:

~~这是一个 c++11 重写，并进行了必要的修复：~~

既然我现在注意到你就是那个因为一些奇怪的原因而被困在 c++03 领域的人，一个 Boost Thread 版本：

C++03 DEMO/Boost线程

Live On Coliru

#include <boost/asio.hpp>
#include <boost/make_shared.hpp>
#include <boost/scoped_ptr.hpp>
#include <boost/thread.hpp>
#include <iostream>

static const int DB_WRITE_TIME = 500;

class Database
{
  private:
    static boost::shared_ptr<Database> dbInstance;

    Database()
        : work(new io_service::work(io)),
          interval(750),
          timer(io, interval)
    {
        std::cout << "INSTANCE CREATED" << std::endl;
    }

    void on_timer_completed(const boost::system::error_code& ec) {
        std::cout << "[on_timer_completed] " << ec.message() << std::endl;

        if (!ec) {
            boost::posix_time::milliseconds interval(DB_WRITE_TIME);

            // Reschedule the timer
            timer.expires_from_now(interval);
            timer.async_wait(boost::bind(&Database::on_timer_completed, this, _1));
        }
    }

    int buffer()
    {
        // DO BUFFER STUFF

        timer.expires_from_now(interval);
        timer.async_wait(boost::bind(&Database::on_timer_completed, this, _1));
        // io_service.run() <-- uncommenting this results in the loop
        return 1; // rc ;
    }

  public:
    void do_stuff() {
        buffer(); // whatever it does
    }

    void teardown() {
        std::cout << "INSTANCE SHUTTING DOWN\n";
        timer.cancel(); // stop timer loop
        work.reset();   // allows io.run() to exit
        if (timerThread.joinable()) {
            timerThread.join(); // releasing the bound shared_ptr
        }
        dbInstance.reset(); // releasing the instance
    }

    ~Database() {
        //sqlite3_close(db);
        std::cout << "INSTANCE DESTROYED\n";
    }

  private:
    typedef boost::asio::io_service io_service;
    io_service io;
    boost::scoped_ptr<io_service::work> work;
    boost::posix_time::millisec interval;
    boost::asio::deadline_timer timer;
    boost::thread timerThread;

    void run_io() {
        std::cout << "ENTER IO THREAD" << std::endl;
        io.run();
        std::cout << "LEAVE IO THREAD" << std::endl;
    }
public:
    static Database &getInstance()
    {
        if (!dbInstance)
        {
            dbInstance.reset(new Database());
            dbInstance->timerThread =
                boost::thread(boost::bind(&Database::run_io, dbInstance));
        }
        return *dbInstance;
    }
};

boost::shared_ptr<Database> Database::dbInstance;

int main() {
    Database& db = Database::getInstance();
    boost::this_thread::sleep_for(boost::chrono::seconds(1));

    db.do_stuff();
    boost::this_thread::sleep_for(boost::chrono::seconds(3));
    // ....

    db.teardown();
}

版画

INSTANCE CREATED
ENTER IO THREAD
[on_timer_completed] Success
[on_timer_completed] Success
[on_timer_completed] Success
[on_timer_completed] Success
[on_timer_completed] Success
INSTANCE SHUTTING DOWN
[on_timer_completed] Operation canceled
LEAVE IO THREAD
INSTANCE DESTROYED

pthread 没有为 class 个实例启动

pthread is not starting for class instance

io

asynchronous

pthreads

boost-asio

c++98

---- 编辑 ----

C++03 DEMO/Boost线程