| package org.onlab.onos.store.service; |
| |
| /** |
| * A lock is a tool for controlling access to a shared resource by multiple processes. |
| * Commonly, a lock provides exclusive access to a resource such as a network device |
| * or exclusive permission to a controller to perform a particular role such as serve |
| * as the master controller for a device. |
| * At any given time one and only process can acquire the lock. |
| */ |
| public interface Lock { |
| |
| /** |
| * Acquires the lock. |
| * If the lock is not available then the caller thread becomes |
| * disabled for thread scheduling purposes and lies dormant until |
| * the lock has been acquired. |
| * <p> |
| * Locks are reentrant. A thread invoking this method multiple times |
| * without an intervening unlock or lease expiration must invoke unlock() |
| * the same number of times before the lock is released (unless the lease expires). |
| * When this method is invoked for a lock that is already acquired, |
| * the lease time will be set to the maximum of the remaining lease time |
| * from the previous invocation, or leaseDurationMillis. |
| * @param leaseDurationMillis the number of milliseconds to hold the |
| * lock after granting it, before automatically releasing it if it hasn't |
| * already been released by invoking unlock(). Must be in the range |
| * (0, MAX_LEASE_MILLIS] |
| */ |
| void lock(long leaseDurationMillis); |
| |
| /** |
| * Acquires the lock only if it is free at the time of invocation. |
| * @param leaseDurationMillis the number of milliseconds the must be |
| * locked after it is granted, before automatically releasing it if it hasn't |
| * already been released by an invocation of unlock(). Must be in the range |
| * (0, MAX_LEASE_MILLIS] |
| * @return true if the lock was acquired and false otherwise |
| */ |
| boolean tryLock(long leaseDurationMillis); |
| |
| /** |
| * Acquires the lock if it is free within the given waiting |
| * time and the current thread has not been interrupted. |
| * @param waitTimeMillis the maximum time (in milliseconds) to wait for the lock |
| * @param leaseDurationMillis the number of milliseconds to hold the |
| * lock after granting it, before automatically releasing it if it hasn't |
| * already been released by invoking unlock(Object). Must be in the range |
| * (0, MAX_LEASE_MILLIS] |
| * @return true if the lock was acquired and false if the waiting time |
| * elapsed before the lock was acquired |
| */ |
| boolean tryLock(long waitTimeMillis, long leaseDurationMillis); |
| |
| /** |
| * Returns true if this Lock instance currently holds the lock. |
| * @return true if this instance is the owner of the lock. |
| */ |
| boolean isLocked(); |
| |
| /** |
| * Releases the lock. |
| */ |
| void unlock(); |
| |
| /** |
| * Extends the lease for this lock. |
| * @param extensionDurationMillis is the amount of additional |
| * time to add to the end of the current expiration time. For example, |
| * if the lock is currently set to expire at time T, a successful call to |
| * extendLease with an argument of 5000 will cause the lock to |
| * now expire at 5 seconds past T. |
| * @return true if the extension is successful, false otherwise. Note |
| * that a failure to extend the lease does not result in unlocking. The lock |
| * will be released either by an explicit call to unlock or when previously |
| * acquired lease runs out. |
| */ |
| boolean extendLease(long extensionDurationMillis); |
| } |