unordered_map thread safety

Question

I am changing a single thread program into multi thread using boost:thread library. The program uses unordered_map as a hasp_map for lookups. My question is..

At on

Answer 1

The existing answers cover the main points:

• you must have a lock to read or write to the map
• you could use a multiple-reader / single-writer lock to improve concurrency

Also, you should be aware that:

• using an earlier-retrieved iterator, or a reference or pointer to an item in the map, counts as a read or write operation

• write operations performed in other threads may invalidate pointers/references/iterators into the map, much as they would if they were done in the same thread, even if a lock is again acquired before an attempt is made to continue using them...