Example for boost shared_mutex (multiple reads/one write)?

Question

I have a multithreaded app that has to read some data often, and occasionally that data is updated. Right now a mutex keeps access to that data safe, but it\'s expensive bec

Answer 1

Just to add some more empirical info, I have been investigating the whole issue of upgradable locks, and Example for boost shared_mutex (multiple reads/one write)? is a good answer adding the important info that only one thread can have an upgrade_lock even if it is not upgraded, that is important as it means you cannot upgrade from a shared lock to a unique lock without releasing the shared lock first. (This has been discussed elsewhere but the most interesting thread is here http://thread.gmane.org/gmane.comp.lib.boost.devel/214394)

However I did find an important (undocumented) difference between a thread waiting for an upgrade to a lock (ie needs to wait for all readers to release the shared lock) and a writer lock waiting for the same thing (ie a unique_lock).

1. The thread that is waiting for a unique_lock on the shared_mutex blocks any new readers coming in, they have to wait for the writers request. This ensures readers do not starve writers (however I believe writers could starve readers).

2. The thread that is waiting for an upgradeable_lock to upgrade allows other threads to get a shared lock, so this thread could be starved if readers are very frequent.

This is an important issue to consider, and probably should be documented.