All Known Subinterfaces:

PersistentLockManager

All Known Implementing Classes:

PersistentLockManagerImpl, TransientLockManager
```
public interface LockManager
```
A service to obtain/manage locks, e.g. to functionally synchronize workflow instances. Currently, two implementations exist for the LockManager. - One of them is for persistent engines and synchronizes workflow instances through a database lock which thus also works on distributed engines operating on a single data base (Only one workflow at a time obtains the lock with the symbolic lockId) - The second implementation is provided to be used in transient engines. There is no synchronization possibility for distributed transient engines and thus, only one workflow at a time obtains the lock on a single engine. If you run multiple engines, it can happen that multiple workflows (each on a different engine) operate concurrently on the same lock (i.e same symbolic lockId)!

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`java.lang.String`	`acquireLock(java.lang.String lockId, java.lang.String workflowInstanceId)`	Acquires a lock with the specified id.
`void`	`releaseLock(java.lang.String lockId, java.lang.String workflowInstanceId)`	Releases the specified lock.

Method Detail

acquireLock

java.lang.String acquireLock(java.lang.String lockId,
                             java.lang.String workflowInstanceId)

Acquires a lock with the specified id. If the lock is free, then the lock is assigned to the caller and the methods return null.

Otherwise, if the lock is currently held by another entity, then the method returns a correlationId that the caller has to use to wait for. As soon as this lock is assigned to the caller, the lock manager creates a Response for this specified correlationId, containing the LockResult.

Example:

 private void acquireLock(final String lockId) throws Interrupt {
     for (;;) {
         logger.info("Going to acquire lock '{}'", lockId);
         final String cid = lockManager.acquireLock(lockId, this.getId());
         if (cid == null) {
             logger.info("Successfully acquired lock '{}'", lockId);
             return;
         }
         else {
             logger.info("Lock '{}' is currently not free - calling wait...", lockId);
             wait(WaitMode.ALL, 10000, cid);
             final Response<LockResult> result = getAndRemoveResponse(cid);
             logger.info("lock result={}", result);
             if (result.isTimeout()) {
                 logger.info("Failed to acquire lock: Timeout - trying again...");
             }
             else if (result.getResponse() != LockResult.OK) {
                 logger.error("Failed to acquire lock: {} - trying again...", result.getResponse());
             }
             else {
                 logger.info("Successfully acquired lock '{}'", lockId);
                 return;
             }
         }
     }
 }

Parameters:: lockId - symbolic lock id; workflowInstanceId - requestor/owner of this lock
Returns:: null if the lock was free and was assigned to the caller (workflowInstanceId) otherwise a correlationId to wait for.
Throws:: java.lang.RuntimeException - in case of technical problems

releaseLock
```
void releaseLock(java.lang.String lockId,
                 java.lang.String workflowInstanceId)
```
Releases the specified lock. If the workflow with the specified workflowId is not yet the owner of the lock (i.e. it is still waiting to retrieve the lock), the acquireLock request is removed from the queue.

Parameters:

lockId - symbolic lock id

workflowInstanceId - requestor/owner of this lock

Throws:

java.lang.RuntimeException - in case of technical problems

Interface LockManager

Method Summary

Method Detail

acquireLock

releaseLock