C++17 std::shared_mutex的替代方案boost::shared_mutex

std::shared_mutex

http://en.cppreference.com/w/cpp/thread/shared_mutex

GCC5.1才会支持C++17 std::shared_mutex，替代方案是boost::shared_mutex。

boost::shared_mutex官方文档：http://www.boost.org/doc/libs/1_60_0/doc/html/thread/synchronization.html#thread.synchronization.mutex_types.shared_mutex

需要的lib：

Cpp代码

#pragma comment(lib, "libboost_chrono-vc140-mt-1_60.lib")
#pragma comment(lib, "libboost_date_time-vc140-mt-1_60.lib")
#pragma comment(lib, "libboost_system-vc140-mt-1_60.lib")
#pragma comment(lib, "libboost_system-vc140-mt-1_60.lib")
#pragma comment(lib, "libboost_thread-vc140-mt-1_60.lib")

boost::shared_mutex用法示例：

参考自：http://stackoverflow.com/questions/3896717/example-of-how-to-use-boost-upgradeable-mutexes

Cpp代码

#include <boost/thread/locks.hpp>    
#include <boost/thread/shared_mutex.hpp>    
  
int  
main()  
{  
    typedef boost::shared_mutex Mutex;  
    typedef boost::shared_lock<Mutex> ReadLock;  
    typedef boost::unique_lock<Mutex> WriteLock;  
    Mutex mutex;  
  
    {  
        // acquire read lock  
        ReadLock read( mutex );  
  
        // do something to read resource  
    }  
  
    {  
        // acquire write lock  
        WriteLock write( mutex, boost::adopt_lock_t() );  
  
        // do something to write resource  
    }  
}

参考自：http://stackoverflow.com/questions/989795/example-for-boost-shared-mutex-multiple-reads-one-write

Cpp代码

boost::shared_mutex _access;  
void reader()  
{  
  // get shared access  
  boost::shared_lock<boost::shared_mutex> lock(_access);  
  
  // now we have shared access  
}  
  
void writer()  
{  
  // get upgradable access  
  boost::upgrade_lock<boost::shared_mutex> lock(_access);  
  
  // get exclusive access  
  boost::upgrade_to_unique_lock<boost::shared_mutex> uniqueLock(lock);  
  // now we have exclusive access  
}

其他参考：

How to make a multiple-read/single-write lock from more basic synchronization primitives?

http://stackoverflow.com/questions/27860685/how-to-make-a-multiple-read-single-write-lock-from-more-basic-synchronization-pr

使用boost::shared_mutex实现读写锁

伟大的Boost库给我们提供了 shared_mutex 类，结合 unique_lock 与 shared_lock 的使用，可以实现读写锁。

通常读写锁需要完成以下功能：

1.当 data 被线程A读取时，其他线程仍可以进行读取却不能写入

2.当 data 被线程A写入时，其他线程既不能读取也不能写入

对应于功能1,2我们可以这样来描述：

1.当线程A获得共享锁时，其他线程仍可以获得共享锁但不能获得独占锁

2.当线程A获得独占锁时，其他线程既不能获得共享锁也不能获得独占锁

typedef boost::shared_lock<boost::shared_mutex> read_lock;
typedef boost::unique_lock<boost::shared_mutex> write_lock;
 
boost::shared_mutex read_write_mutex;
int32_t data = 1;
 
//线程A,读data
{
    read_lock rlock(read_write_mutex);
    std::cout << data << std:; endl;
}
 
//线程B,读data
{
    read_lock rlock(read_write_mutex);
    std::cout << data << std:; endl;
}
 
//线程C,写data
{
    write_lock rlock(read_write_mutex);
    data = 2;
}

通过 shared_lock 为 shared_mutex 上锁之后，线程将获得其共享锁，此时其他线程仍可以获得共享锁来读取 data，但是此时 unique_lock 将无法为 shared_mutex 上独占锁，功能1实现了。通过 unique_lock 为 shared_lock 上锁之后，线程将获得独占锁，此时无法再被上锁，功能2页实现了。