Need clarification on file_lock documentation

The documentation of boost::interprocess::file_lock has some cautions on synchronization limitations:
* It's unspecified if a file_lock synchronizes two threads from the same process.
* It's unspecified if a process can use two file_lock objects pointing to the same file.

But then gives the guidance:
* For each file, use a single file_lock object per process.
* Use the same thread to lock and unlock a file.

I then created the following example:
https://wandbox.org/permlink/3CNfkA3RcMkwbd2v

```
#include
#include
#include
#include
#include
#include
#include
#include
#include
int main()
{
std::ofstream("f.txt");
boost::interprocess::file_lock lock("f.txt");
std::mutex mtx;
const size_t max = 100;
size_t t1Count = 0;
std::thread
t1
(
[&lock,&t1Count,&mtx,max]()
{
while(t1Count < max)
{
//std::lock_guard mtxLock(mtx);
boost::interprocess::scoped_lock guard(lock);
std::cout << "Number 1" << std::endl;
t1Count++;
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
}
);
size_t t2Count = 0;
std::thread
t2
(
[&lock,&t2Count,&mtx,max]()
{
while(t2Count < max)
{
//std::lock_guard mtxLock(mtx);
boost::interprocess::scoped_lock guard(lock);
std::cout << "Number 2" << std::endl;
t2Count++;
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
}
);
t1.join();
t2.join();
return 0;
}
```

It only works properly if the std::mutex is used in addition to the file_lock. That was originally my thought when I read "It's unspecified if a file_lock synchronizes two threads from the same process.", but it seemed like I was following the guidance "Use the same thread to lock and unlock a file.". If I haven't messed anything up, I would probably update the documentation to say something like:
"If utilitizing the file_lock from multiple threads within the same process, synchronize access to the file_lock with an intraprocess synchronization mechanism such as a mutex."

Otherwise, is it a bug?

Thanks,
Rob

boost::interprocess::file_lock のドキュメントから始め、issue に含まれている C++ の例を使って動作を再現してください。文書化されているスレッドとプロセスに関する指針が誤っているのか、単に不明確なのかを判断してください。ドキュメントまたは実装に関する問題について、解決済みで検証された説明が得られれば完了です。

索引モデルが issue の本文から書いたものです。