howardhinnant / upgrade_mutex Goto Github PK

Why upgrade_lock have no

    upgrade_lock(std::shared_lock<mutex_type>&& sl)

constructor?

upgrade_mutex does not have unlock_shared_and_lock_upgrade, also. There is only timed version try_unlock_shared_and_lock_upgrade_for / try_unlock_shared_and_lock_upgrade_until.

P.S. It seems that boost have these timeless versions...

1. a. I believe that upgrade_mutex::try_unlock_shared_and_lock_until() should wait on gate1_ until there is no writer and no upgrader and then it should decrement the reader count and set the write_entered_ flag and then it should wait on gate2_ until there are no more readers. This prevents new readers from taking a shared or upgrade lock while this function is waiting to take the exclusive lock.
   b. Also, right now since it is only waiting on gate2_ it won't get signaled after any of the unlock*() functions are called.
2. I believe that upgrade_mutex::try_unlock_shared_and_lock_upgrade_until() should wait on gate1_ instead of gate2_. Right now since it is only waiting on gate2_ it won't get signaled after unlock_upgrade() is called.
3. a. I believe that upgrade_mutex::try_unlock_upgrade_and_lock_until() should decrement the reader count and set the write_entered_ flag and then it should wait on gate2_ until there are no more readers. This prevents new readers from taking a shared lock while this function is waiting to take the exclusive lock.
   b. Also, right now gate2_ only gets signaled when the reader count is zero but this function currently waits for the reader count to reach 1.

I've already fixed these issues in the copy of upgrade_mutex that exists in Boost.Thread: https://github.com/boostorg/thread/blob/develop/include/boost/thread/v2/shared_mutex.hpp.

Are these issues all valid or have I missed something? Thank you for taking a look at this.