Intel Threading Building Blocks

Concurrent Access

The member classes const_accessor and accessor are called accessors. Accessors allow multiple threads to concurrently access pairs in a shared concurrent_hash_map. An accessor acts as a smart pointer to a pair in a concurrent_hash_map. It holds an implicit lock on a pair until the instance is destroyed or the release method is called on the accessor.

The const_accessor and accessor classes differ in the kind of access they permit, as shown in Table 5-4.

Table 5-4. Differences between const_accessor and accessor

Class	value_type	Implied lock on pair
const_accessor	const std::pair<const Key,T>	Reader lock: permits shared access with other readers
accessor	std::pair<const Key,T>	Writer lock: blocks access by other threads

Accessors cannot be assigned or copy-constructed because allowing that would greatly complicate the locking semantics.