Module org.cojen.tupl

Package org.cojen.tupl

Enum Class LockMode

java.lang.Object

java.lang.Enum<LockMode>

org.cojen.tupl.LockMode

All Implemented Interfaces:

Serializable, Comparable<LockMode>, Constable

public enum LockMode
extends Enum<LockMode>

Various lock modes for use within transactions. Except for UNSAFE, all modes follow the same policy when modifying entries. They all differ with respect to entries which are being read.

When an entry is modified, an exclusive lock is acquired, which is typically held until the end of the transaction. When transaction scopes are committed, all held locks transfer to the parent scope. Uncommitted scopes release all of their acquired locks.

Modes ordered from strongest to weakest:

• UPGRADABLE_READ (default)
• REPEATABLE_READ
• READ_COMMITTED
• READ_UNCOMMITTED
• UNSAFE

See Also:

• Transaction.lockMode(org.cojen.tupl.LockMode)

Nested Class Summary

Nested classes/interfaces inherited from class java.lang.Enum

Enum.EnumDesc<E extends Enum<E>>

Enum Constant Summary

Enum Constants

Enum Constant	Description
READ_COMMITTED	Lock mode which acquires shared locks when reading entries and releases them as soon as possible.
READ_UNCOMMITTED	Lock mode which never acquires locks when reading entries.
REPEATABLE_READ	Lock mode which acquires shared locks when reading entries and retains them to the end of the transaction or scope.
UNSAFE	Lock mode which never acquires locks.
UPGRADABLE_READ	Lock mode which acquires upgradable locks when reading entries and retains them to the end of the transaction or scope.

Method Summary

Modifier and Type	Method	Description
boolean	isRepeatable()	Returns true if acquired locks are retained for the duration of the transaction.
static LockMode	valueOf(String name)	Returns the enum constant of this class with the specified name.
static LockMode[]	values()	Returns an array containing the constants of this enum class, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, describeConstable, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Details

UPGRADABLE_READ

public static final LockMode UPGRADABLE_READ

Lock mode which acquires upgradable locks when reading entries and retains them to the end of the transaction or scope. If an entry guarded by an upgradable lock is modified, the lock is first upgraded to be exclusive.

REPEATABLE_READ

public static final LockMode REPEATABLE_READ

Lock mode which acquires shared locks when reading entries and retains them to the end of the transaction or scope. Attempting to modify entries guarded by a shared lock is illegal. Consider using UPGRADABLE_READ instead.

See Also:

• LockUpgradeRule

READ_COMMITTED

public static final LockMode READ_COMMITTED

Lock mode which acquires shared locks when reading entries and releases them as soon as possible.

READ_UNCOMMITTED

public static final LockMode READ_UNCOMMITTED

Lock mode which never acquires locks when reading entries. Modifications made by concurrent transactions are visible for reading, but they might get rolled back.

UNSAFE

public static final LockMode UNSAFE

Lock mode which never acquires locks. This mode bypasses all transactional safety, permitting modifications even when locked by other transactions. These modifications are immediately committed, and so rollback is not possible.

Method Details

values

public static LockMode[] values()

Returns an array containing the constants of this enum class, in the order they are declared.

Returns:

an array containing the constants of this enum class, in the order they are declared

valueOf

public static LockMode valueOf(String name)

Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum class has no constant with the specified name

NullPointerException - if the argument is null

isRepeatable

public boolean isRepeatable()

Returns true if acquired locks are retained for the duration of the transaction. Applicable to UPGRADABLE_READ and REPEATABLE_READ.