org.alfresco.repo.lock

Interface JobLockService

All Known Implementing Classes:

JobLockServiceImpl

@AlfrescoPublicApi
public interface JobLockService

Service interface for managing job locks.

Locks are identified by a fully qualified name (QName) and follow a hierarchical naming convention i.e. locks higher up a hierarchy can be shared but will prevent explicit (exclusive) locks from being taken. For example: If exclusive lock a.a.a has been taken, then a.a and a are all implicitly taken as shared locks. Exclusive lock a.a.b can be taken by another process and will share locks a.a and a with the first process. It will not be possible for a third process to take a lock on a.a, however.

LOCK ORDERING:
The transactional locks will be applied in strict alphabetical order. A very basic deadlock prevention system (at least) must be in place when applying or reapplying locks and be biased against locks applied non-alphabetically.

Since:

3.2

Author:

Derek Hulley

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	JobLockService.JobLockRefreshCallback Interface for implementations that need a timed callback in order to refresh the lock.

Method Summary

Modifier and Type	Method and Description
String	getLock(org.alfresco.service.namespace.QName lockQName, long timeToLive) Take a manually-managed lock.
String	getLock(org.alfresco.service.namespace.QName lockQName, long timeToLive, JobLockService.JobLockRefreshCallback callback) Take a manually-managed lock and provide a callback to refresh it periodically.
String	getLock(org.alfresco.service.namespace.QName lockQName, long timeToLive, long retryWait, int retryCount) Take a manually-managed lock.
void	getTransactionalLock(org.alfresco.service.namespace.QName lockQName, long timeToLive) Take a transactionally-managed lock.
void	getTransactionalLock(org.alfresco.service.namespace.QName lockQName, long timeToLive, long retryWait, int retryCount) Take a transactionally-managed lock.
void	refreshLock(String lockToken, org.alfresco.service.namespace.QName lockQName, long timeToLive) Refresh the lock using a valid lock token.
void	refreshLock(String lockToken, org.alfresco.service.namespace.QName lockQName, long timeToLive, JobLockService.JobLockRefreshCallback callback) Provide a callback to refresh a lock using a valid lock token, pushing responsibility for regular lock refreshing onto the service implementation code.
void	releaseLock(String lockToken, org.alfresco.service.namespace.QName lockQName) Release the lock using a valid lock token.
boolean	releaseLockVerify(String lockToken, org.alfresco.service.namespace.QName lockQName) Release the lock using a valid lock token.

Method Detail

getTransactionalLock

void getTransactionalLock(org.alfresco.service.namespace.QName lockQName,
                          long timeToLive)

Take a transactionally-managed lock. This method can be called repeatedly to both initially acquire the lock as well as to maintain the lock. This method should be called repeatedly during the transaction to ensure that the lock remains refreshed. DO NOT use a long-lived lock to avoid calling this method at intervals; long-lived locks get left behind during server crashes, amongst other things.

The following rules apply to taking and releasing locks:
- Expired locks can be taken by any process
- Lock expiration does not prevent a lock from being refreshed or released
- Only locks that were manipulated using another token will cause failure

The locks are automatically released when the transaction is terminated.

Any failure to acquire the lock (after retries), refresh the lock or subsequently release the owned locks will invalidate the transaction and cause rollback.

Parameters:

lockQName - the name of the lock to acquire

timeToLive - the time (in milliseconds) for the lock to remain valid. This value must not be larger than either the anticipated operation time or a server startup time. Typically, it should be a few seconds.

Throws:

LockAcquisitionException - if the lock could not be acquired

IllegalStateException - if a transaction is not active

getTransactionalLock

void getTransactionalLock(org.alfresco.service.namespace.QName lockQName,
                          long timeToLive,
                          long retryWait,
                          int retryCount)

Take a transactionally-managed lock. This method can be called repeatedly to both initially acquire the lock as well as to maintain the lock. This method should be called repeatedly during the transaction to ensure that the lock remains refreshed. DO NOT use a long-lived lock to avoid calling this method at intervals; long-lived locks get left behind during server crashes, amongst other things.

The following rules apply to taking and releasing locks:
- Expired locks can be taken by any process
- Lock expiration does not prevent a lock from being refreshed or released
- Only locks that were manipulated using another token will cause failure

The locks are automatically released when the transaction is terminated.

Any failure to acquire the lock (after retries), refresh the lock or subsequently release the owned locks will invalidate the transaction and cause rollback.

If the lock cannot be immediately acquired, the process will wait and retry. Note that second and subsequent attempts to get the lock during a transaction cannot make use of retrying; the lock is actually being refreshed and will therefore never become valid if it doesn't refresh directly.

Parameters:

lockQName - the name of the lock to acquire

timeToLive - the time (in milliseconds) for the lock to remain valid. This value must not be larger than either the anticipated operation time or a server startup time. Typically, it should be a few seconds.

retryWait - the time (in milliseconds) to wait before trying again

retryCount - the maximum number of times to attempt the lock acquisition

Throws:

LockAcquisitionException - if the lock could not be acquired

IllegalStateException - if a transaction is not active

getLock

String getLock(org.alfresco.service.namespace.QName lockQName,
               long timeToLive)

Take a manually-managed lock. The lock current thread or transaction will not be tagged - the returned lock token must be used for further management of the lock.

No lock management is provided: the lock must be released manually or will only become available by expiry. No deadlock management is provided, either.

Parameters:

lockQName - the name of the lock to acquire

timeToLive - the time (in milliseconds) for the lock to remain valid. This value must not be larger than either the anticipated operation time or a server startup time. Typically, it should be a few seconds.

Returns:

Returns the newly-created lock token

Throws:

LockAcquisitionException - if the lock could not be acquired

getLock

String getLock(org.alfresco.service.namespace.QName lockQName,
               long timeToLive,
               long retryWait,
               int retryCount)

Take a manually-managed lock. The lock current thread or transaction will not be tagged - the returned lock token must be used for further management of the lock.

No lock management is provided: the lock must be released manually or will only become available by expiry. No deadlock management is provided, either.

If the lock cannot be immediately acquired, the process will wait and retry.

Parameters:

lockQName - the name of the lock to acquire

timeToLive - the time (in milliseconds) for the lock to remain valid. This value must not be larger than either the anticipated operation time or a server startup time. Typically, it should be a few seconds.

retryWait - the time (in milliseconds) to wait before trying again

retryCount - the maximum number of times to attempt the lock acquisition

Throws:

LockAcquisitionException - if the lock could not be acquired

getLock

String getLock(org.alfresco.service.namespace.QName lockQName,
               long timeToLive,
               JobLockService.JobLockRefreshCallback callback)

Take a manually-managed lock and provide a callback to refresh it periodically. A convenience wrapper around getLock(QName,long) and refreshLock(String,QName,long,JobLockRefreshCallback).

Parameters:

lockQName - the name of the lock to acquire

timeToLive - the time (in milliseconds) for the lock to remain valid. This value must not be larger than either the anticipated operation time or a server startup time. Typically, it should be a few seconds.

callback - the object that will be called at intervals of timeToLive/2 (about)

Returns:

Returns the newly-created lock token, or null if callback not active.

Throws:

LockAcquisitionException - if the lock could not be acquired

refreshLock

void refreshLock(String lockToken,
                 org.alfresco.service.namespace.QName lockQName,
                 long timeToLive)

Refresh the lock using a valid lock token.

Parameters:

lockQName - the name of the previously-acquired lock

timeToLive - the time (in milliseconds) for the lock to remain valid

Throws:

LockAcquisitionException - if the lock could not be refreshed or acquired

refreshLock

void refreshLock(String lockToken,
                 org.alfresco.service.namespace.QName lockQName,
                 long timeToLive,
                 JobLockService.JobLockRefreshCallback callback)

Provide a callback to refresh a lock using a valid lock token, pushing responsibility for regular lock refreshing onto the service implementation code. This method should only be called once for a given lock token to prevent unnecessary refreshing.

Since the lock is not actually refreshed by this method, there will be no LockAcquisitionException.

The TTL (time to live) will be divided by two and the result used to trigger a timer thread to initiate the callback. The first refresh will occur after TTL/2 and no significant work should be done between acquiring a lock and calling this method, to prevent expiration.

Parameters:

lockToken - the lock token returned when the lock was acquired

lockQName - the name of the previously-acquired lock

timeToLive - the time (in milliseconds) for the lock to remain valid

callback - the object that will be called at intervals of timeToLive/2 (about)

Since:

3.4.0a

releaseLock

void releaseLock(String lockToken,
                 org.alfresco.service.namespace.QName lockQName)

Release the lock using a valid lock token.

Parameters:

lockToken - the lock token returned when the lock was acquired

lockQName - the name of the previously-acquired lock

Throws:

LockAcquisitionException - if the lock has been taken over by another process

releaseLockVerify

boolean releaseLockVerify(String lockToken,
                          org.alfresco.service.namespace.QName lockQName)

Release the lock using a valid lock token. The lock can have been taken by another process (i.e. the lock token will no longer be valid); none of this will prevent the method from succeeding.

Parameters:

lockToken - the lock token returned when the lock was acquired

lockQName - the name of the previously-acquired lock

Returns:

true if the lock was valid and released otherwise false if the lock was already held by another token