locklib

Interface LockPolicy<LockType>

Type Parameters:

LockType - the type of lock

All Known Implementing Classes:

MutexLockPolicy, SxLockPolicy

public interface LockPolicy<LockType>

A lock policy defines how a locking mechanism works. It is parameterized by a class LockType which represents a type of lock. The policy defines how different lock types operate with each other.

Method Summary

Modifier and Type	Method and Description
boolean	is_compatible(LockType lock_type_1, LockType lock_type_2) Checks if two locks are compatible.
LockType	parent_lock(LockType lock_type) Determines what is the type of lock a parent of a target should have.
boolean	starvation_allowed() If starvation is allowed compatible locks can be acquired even if there are locks waiting.

Method Detail

is_compatible

boolean is_compatible(LockType lock_type_1,
                      LockType lock_type_2)

Checks if two locks are compatible. Two locks are compatible if different holders can hold them in the same target.

Parameters:

lock_type_1 - the type of lock of one holder

lock_type_2 - the type of lock of another holder

Returns:

are both locks compatible?

parent_lock

LockType parent_lock(LockType lock_type)

Determines what is the type of lock a parent of a target should have.

Parameters:

lock_type - the type of lock held by the target

Returns:

the type of lock that a parent should hold if its child has lock lock_type; this must not return null as the parent must have some lock type to generate the lock chain

starvation_allowed

boolean starvation_allowed()

If starvation is allowed compatible locks can be acquired even if there are locks waiting. For example, in SX locks, it means a S lock can be acquired for a target when there is an X lock waiting. This means that the X lock can be held forever if S locks keep coming and going. If starvation is not allowed, then, in the previous example, an S lock is disallowed if there is an X lock waiting, even if the S lock is compatible with the currently-held lock. Whether starvation is allowed or not is irrelevant for lock types that are always exclusive.

Returns:

is starvation allowed