Boost :: shared_mutex multitext with multiple readers / single writers

Question

I am trying to use boost :: shared_mutex to implement a mutex with multiple readers / single writers. My question is pretty simple, is it possible for a thread to get reader access to shared_mutex when another thread tries to lock this shared_mutex for writing? For example, I have 10 threads, only one of them can write,

• In stream 1 there is shared_lock for this shared_mutex and is trying to read something
• In stream 2 there is shared_lock for this shared_mutex and is trying to read something
• thread 3 has a unique_lock on this shared_mutex and is trying to write something
• thread 4 has shared_lock for this shared_mutex and is trying to read something
• In thread 5 there is shared_lock for this shared_mutex and is trying to read something

Currently shared_mutex is shared by thread 2 lock, my question is, is it possible for thread 4 to have read access to this shared_mutex, before thread 3 can write? Is it possible for reader / writer mutexes to ever get into a fasting situation, for example, 100 readers are against. 1 writer?

Thanks.

Answer 1

boost::shared_mutex leave a fairness policy before implementation. This may be true, reader-writer or writer-reader, therefore, depending on which version of your version may turn out to be hungry, it may be written.