org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock Class Reference

List of all members.

Public Member Functions
boolean	acquire (AbstractRequest request)
synchronized void	release ()
boolean	isLocked ()
long	getLocker ()
ArrayList	getWaitingList ()
synchronized boolean	isWaiting (long transactionId)

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Detailed Description

A TransactionExclusiveLock is an exclusive lock that let the owner of the lock acquire several times the lock (but it needs to be released only once). Acquire supports timeout and graceful withdrawal of timed out requests.

Author:

Emmanuel Cecchet

Version:

1.0

Definition at line 40 of file TransactionExclusiveLock.java.

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Member Function Documentation

boolean org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.acquire (  AbstractRequest  request  )

Acquires an exclusive lock on this table. If the lock is already held by the same transaction as the given request, this method is non-blocking else the caller is blocked until the transaction holding the lock releases it at commit/rollback time. Parameters: request  request asking for the lock (timeout field is used and updated upon waiting) Returns: boolean true is the lock has been successfully acquired, false on timeout or error See also: release() Definition at line 107 of file TransactionExclusiveLock.java. References org.objectweb.cjdbc.common.sql.AbstractRequest.getTimeout(), org.objectweb.cjdbc.common.sql.AbstractRequest.getTransactionId(), org.objectweb.cjdbc.common.sql.AbstractRequest.isAutoCommit, and org.objectweb.cjdbc.common.sql.AbstractRequest.setTimeout(). { long tid = request.getTransactionId(); synchronized (Thread.currentThread()) { WaitingListElement wle = null; synchronized (this) { if (!isLocked) { // Lock is free, take it locker = tid; isLocked = true; return true; } else { if ((!request.isAutoCommit()) && (locker == tid)) return true; // We already have the lock else { // Wait for the lock wle = new WaitingListElement(Thread.currentThread(), tid); waitingList.add(wle); } } } // At this point, we have to wait for the lock. try { int timeout = request.getTimeout(); if (timeout == 0) { Thread.currentThread().wait(); // No timeout // Note: isLocked and locker are already set. return true; } else { // Wait with timeout long start = System.currentTimeMillis(); // Convert seconds to milliseconds for wait call long lTimeout = timeout * 1000; Thread.currentThread().wait(lTimeout); long end = System.currentTimeMillis(); int remaining = (int) (lTimeout - (end - start)); if (remaining > 0) { // Ok request.setTimeout(remaining); // Note: isLocked and locker are already set. return true; } else { // Too late, remove ourselves from the waiting list synchronized (this) { int idx = waitingList.indexOf(wle); if (idx == -1) // We got the lock before being able to acquire the lock on // this. Give the lock to the next one. release(); else waitingList.remove(idx); } return false; } } } catch (InterruptedException ie) { synchronized (this) { // Something wrong happened, remove ourselves from the waiting list waitingList.remove(Thread.currentThread()); } return false; } } }

long org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.getLocker (   )

Returns the transaction id of the lock owner. The return value is undefined if the lock is not owned (usually it is the last owner). Returns: int the transaction id. Definition at line 223 of file TransactionExclusiveLock.java. Referenced by org.objectweb.cjdbc.controller.scheduler.raidb1.RAIDb1OptimisticTransactionLevelScheduler.scheduleNonSuspendedWriteRequest(). { return locker; }

ArrayList org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.getWaitingList (   )

Returns the waitingList. Returns: an ArrayList of WaitingListElement Definition at line 233 of file TransactionExclusiveLock.java. Referenced by org.objectweb.cjdbc.controller.scheduler.raidb1.RAIDb1OptimisticTransactionLevelScheduler.scheduleNonSuspendedWriteRequest(). { return waitingList; }

boolean org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.isLocked (   )

Returns true if the lock is owned by someone. Returns: boolean value Definition at line 212 of file TransactionExclusiveLock.java. { return isLocked; }

synchronized boolean org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.isWaiting (  long  transactionId  )

Returns true if the given transaction id is contained in this lock waiting queue. Parameters: transactionId  a transaction id Returns: a boolean value Definition at line 245 of file TransactionExclusiveLock.java. Referenced by org.objectweb.cjdbc.controller.scheduler.raidb1.RAIDb1OptimisticTransactionLevelScheduler.scheduleNonSuspendedWriteRequest(). { WaitingListElement e; int size = waitingList.size(); for (int i = 0; i < size; i++) { e = (WaitingListElement) waitingList.get(i); if (e.getTransactionId() == transactionId) return true; } return false; }

synchronized void org.objectweb.cjdbc.controller.scheduler.schema.TransactionExclusiveLock.release (   )

Releases the lock on this table. See also: acquire(AbstractRequest) Definition at line 189 of file TransactionExclusiveLock.java. References org.objectweb.cjdbc.common.sql.AbstractRequest.getTransactionId(). Referenced by org.objectweb.cjdbc.controller.scheduler.raidb1.RAIDb1OptimisticTransactionLevelScheduler.notifyWriteCompleted(). { while (!waitingList.isEmpty()) { // Wake up the first waiting thread and update locker transaction id WaitingListElement e = (WaitingListElement) waitingList.remove(0); Thread thread = e.getThread(); locker = e.getTransactionId(); synchronized (thread) { thread.notify(); // isLocked remains true return; } } isLocked = false; }

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The documentation for this class was generated from the following file:

• TransactionExclusiveLock.java

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