Question

在解释如何使用Boost实现读取器/写入器锁时，

This thread是金牌。它似乎相对简单，我真的很喜欢它，但它似乎也使用一个非命名的锁，我需要一个进程间解决方案（不需要是可移植的，可以只有Windows）。

有没有办法进行进程间shared_mutex？我看到有一个named_mutex但我无法使用shared_lock其他锁定。

任何指针都表示赞赏。

[编辑]

与此同时，我遇到this thread几乎击中头部的钉子。我有两个问题：

它没有显示完整的代码（我猜我需要使用named_upgradable_mutex但我不太确定）和
我不喜欢修改后的“编写器”的答案，它不使用在析构函数中解锁的现成类，而是使用互斥锁上的3个原始调用序列。

仍然欢迎评论或好的解决方案。

Answer 1

Boost.Interprocess文档描述了它支持的所谓upgradable mutexes和两个支持的可升级互斥锁类型的upgradable mutex operations：

boost::interprocess::interprocess_upgradable_mutex，一种非递归，匿名可升级的互斥锁，可放置在共享内存或内存映射文件中。
boost::interprocess::named_upgradable_mutex，一种非递归的，名为可升级的互斥锁。

编辑：我相信这有效：

#include <iostream>
#include <string>
#include <unistd.h>

#include <boost/scope_exit.hpp>
#include <boost/interprocess/mapped_region.hpp>
#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/sync/interprocess_upgradable_mutex.hpp>
#include <boost/interprocess/sync/scoped_lock.hpp>
#include <boost/interprocess/sync/sharable_lock.hpp>
#include <boost/interprocess/sync/upgradable_lock.hpp>

// http://stackoverflow.com/questions/12439099/interprocess-reader-writer-lock-with-boost/

#define SHARED_MEMORY_NAME "SO12439099-MySharedMemory"

struct shared_data {
private:
    typedef boost::interprocess::interprocess_upgradable_mutex upgradable_mutex_type;

    mutable upgradable_mutex_type mutex;
    volatile int counter;

public:
    shared_data()
        : counter(0)
    {
    }

    int count() const {
        boost::interprocess::sharable_lock<upgradable_mutex_type> lock(mutex);
        return counter;
    }

    void set_counter(int counter) {
        boost::interprocess::scoped_lock<upgradable_mutex_type> lock(mutex);
        this->counter = counter;
    }
};

int main(int argc, char *argv[])
{
    using namespace boost::interprocess;

    if (argc != 2) {
        std::cerr << "Usage: " << argv[0] << " WHICH" << std::endl;
        return 1;
    }

    const std::string which = argv[1];
    if (which == "parent") {
        shared_memory_object::remove(SHARED_MEMORY_NAME);
        shared_memory_object shm(create_only, SHARED_MEMORY_NAME, read_write);

        BOOST_SCOPE_EXIT(argc) {
            shared_memory_object::remove(SHARED_MEMORY_NAME);
        } BOOST_SCOPE_EXIT_END;

        shm.truncate(sizeof (shared_data));

        // Map the whole shared memory into this process.
        mapped_region region(shm, read_write);

        // Construct the shared_data.
        new (region.get_address()) shared_data;

        // Go to sleep for a minute.
        sleep(60);

        return 0;
    } else if (which == "reader_child") {
        shared_memory_object shm(open_only, SHARED_MEMORY_NAME, read_write);

        mapped_region region(shm, read_write);
        shared_data& d = *static_cast<shared_data *>(region.get_address());

        for (int i = 0; i < 100000; ++i) {
            std::cout << "reader_child: " << d.count() << std::endl;
        }
    } else if (which == "writer_child") {
        shared_memory_object shm(open_only, SHARED_MEMORY_NAME, read_write);

        mapped_region region(shm, read_write);
        shared_data& d = *static_cast<shared_data *>(region.get_address());

        for (int i = 0; i < 100000; ++i) {
            d.set_counter(i);
            std::cout << "writer_child: " << i << std::endl;
        }
    }
}

我在Mac上尝试使用以下脚本：

#!/usr/bin/env sh
./a.out reader_child &
./a.out reader_child &
./a.out writer_child &
./a.out reader_child &
./a.out reader_child &

（您必须先启动父级：./a.out parent）

输出显示“reader_child”和“writer_child”行的交错（所有“reader_child”行在第一个“writer_child”行之后显示非零值），因此它似乎正在工作。

使用Boost进行进程间读写器锁定

1 个答案: