使用scoped try_shared_lock和upgrade lock in boost的示例

答案似乎是您可以提供增强:尝试将锁定作为这些作用域锁中的几个的参数。

例如

boost::shared_mutex mutex;

// The reader version
boost::shared_lock<boost::shared_mutex> lock(mutex, boost::try_to_lock);
if (lock){
  // We have obtained a shared lock
}

// Writer version
boost::upgrade_lock<boost::shared_mutex> write_lock(mutex, boost::try_to_lock);
if (write_lock){
  boost::upgrade_to_unique_lock<boost::shared_mutex> unique_lock(write_lock);
  // exclusive access now obtained.
}

编辑: 我还通过实验发现,如果没有升级锁,升级到唯一锁将失败。您也可以这样做:

boost::upgrade_to_unique_lock<boost::shared_mutex> unique_lock(write_lock);
if (unique_lock){
  // we are the only thread in here... safe to do stuff to our shared resource
}

// If you need to downgrade then you can also call
unique_lock.release();

// And if you want to release the upgrade lock as well (since only one thread can have upgraded status at a time)
write_lock.unlock().

注意:您必须先调用release,然后调用unlock,否则将引发锁定异常。 当然,您可以让unique-lock和write-lock超出范围,从而释放锁,尽管我发现有时您希望更早地释放它,您应该在这种状态下花费最少的时间。