Is try_lock() +unlock() valid way to check whether boost::interprocess::file_lock is locked?

Question

I need to check whether a file is locked using boost::interprocess::file_lock. I produced this, but I'm worried what it's gonna do:

bool DataCache::isLocked() const {
    bool res = lock_->try_lock();
    if(res)
        lock_->unlock();
    return res;
}

Is it a good idea? Isn't there a way to check it without locking it?

Answer 1

As this doesn't fit in a comment: You could create "interface functions" for tryLock and unlock externally.

e.g.:

bool DataCache::try_lock() const {
    return lock_->try_lock();
}

void DataCache::unlock() const {
    lock_->unlock();
}

Usage:

DataCache cache;
if(cache.try_lock())
{
    cache.doSomething();
    cache.unlock();
}
else
{
    //....
}

I'm not sure if the const will work here. I just copied it from the question code.