/*
* Process a request of a lock for the variable with @variableIndex
* @transactionNumber is the transaction number of the trasaction requesting the lock
* @isLockRequestReadOnly refers to the type of lock to request
* @return the lock or null if not successful
*
*/
public Lock requestLock(
int currentTimestamp,
int transactionNumber,
int variableIndex,
boolean isLockRequestReadOnly) {
Lock candidateLock =
new Lock(transactionNumber, this.siteIndex, variableIndex, isLockRequestReadOnly);
for (Lock lock : this.activeLocks) {
// Loop through all the active locks.
// If there is a write lock already on @variableIndex, no other transaction may access it, so
// return null
// If a different transaction has a read lock and the requesting lock is a write lock, do not
// give the lock i.e. return null
if ((lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& !lock.isReadOnly())
|| (lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& lock.isReadOnly()
&& !isLockRequestReadOnly)) {
System.out.println(
"Site: T"
+ transactionNumber
+ " found conflicting lock held by T"
+ lock.getTransactionNumber());
System.out.println(
"Site: "
+ (isLockRequestReadOnly ? "Read" : "Exclusive")
+ " Lock denied for T"
+ transactionNumber
+ " on x"
+ variableIndex
+ "."
+ siteIndex);
return null;
}
}
// At this point, the check is successful and add the lock to the active locks
this.activeLocks.add(candidateLock);
System.out.println(
"Site: "
+ (isLockRequestReadOnly ? "Read" : "Exclusive")
+ " Lock give to T"
+ transactionNumber
+ " on x"
+ variableIndex
+ "."
+ siteIndex);
// Give lock and record in the site
String[] details =
new String[] {
"give lock", "" + transactionNumber, "" + variableIndex, "" + isLockRequestReadOnly
};
siteLog.addEvent(currentTimestamp, details);
// Return the lock to the requesting transaction
return candidateLock;
}
/*
* Process an upgrade request of a lock from read to exclusive for the variable with @variableIndex
* @transactionNumber is the transaction number of the transaction requesting the lock
* @return the lock or null if not successful
*
*/
public Lock upgradeRequest(int currentTimestamp, int transactionNumber, int variableIndex) {
Lock candidateLock = new Lock(transactionNumber, this.siteIndex, variableIndex, false);
for (Lock lock : this.activeLocks) {
// Loop through all the active locks.
// If there is a write lock already on @variableIndex, no other transaction may access it, so
// return null
// If a different transaction has a read lock and the requesting lock is a write lock, do not
// give the lock i.e. return null
if ((lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& !lock.isReadOnly())
|| (lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& lock.isReadOnly())) {
System.out.println(
"Site: T"
+ transactionNumber
+ " found conflicting lock held by T"
+ lock.getTransactionNumber());
System.out.println(
"Site: Upgrade to exclusive lock denied for T"
+ transactionNumber
+ " on x"
+ variableIndex
+ "."
+ siteIndex);
return null;
}
}
// If successful, remove the lock from the activeLocks and add the candidate to the activeLocks
int index = 0;
while (index < this.activeLocks.size()) {
if (this.activeLocks.get(index).getLockedVariableIndex() == variableIndex
&& this.activeLocks.get(index).getTransactionNumber() == transactionNumber) {
this.activeLocks.remove(index);
break;
}
index++;
}
this.activeLocks.add(candidateLock);
System.out.println(
"Site: Upgrade to exclusive lock give to T"
+ transactionNumber
+ " on x"
+ variableIndex
+ "."
+ siteIndex);
// Give lock and record in the site
String[] details =
new String[] {"give lock", "" + transactionNumber, "" + variableIndex, "" + false};
siteLog.addEvent(currentTimestamp, details);
return candidateLock;
}
/*
* Return the lock that is conflicting with a hypothetical lock of the following properties:
* @transactionNumber is the transaction number of the transaction requesting the lock
* @variableIndex is the variable index the hypothetical lock would hold on
* @isLockRequestReadOnly refers to the type of the hypothetical lock
* @return the lock or null if not successful
*/
public Lock getConflictingLock(
int transactionNumber, int variableIndex, boolean isLockRequestReadOnly) {
for (Lock lock : this.activeLocks) {
// Loop through all the active locks.
// If there is a conflicting lock on @variableIndex, return that lock
if ((lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& !lock.isReadOnly())
|| (lock.getTransactionNumber() != transactionNumber
&& lock.getLockedVariableIndex() == variableIndex
&& lock.isReadOnly()
&& !isLockRequestReadOnly)) {
return lock;
}
}
return null;
}
/*
* Release all locks for a particular transaction from @activeLocks
* @transactionNumber refers to the transaction in which his locks should be released
*/
public void releaseLocks(int transactionNumber, int currentTimestamp) {
int i = 0;
while (i < this.activeLocks.size()) {
Lock lock = this.activeLocks.get(i);
if (lock.getTransactionNumber() == transactionNumber) {
System.out.println(
"Site: Release lock from T"
+ transactionNumber
+ " on x"
+ lock.getLockedVariableIndex()
+ "."
+ siteIndex);
// Give lock and record in the site
String[] details =
new String[] {
"release lock",
"" + transactionNumber,
"" + lock.getLockedVariableIndex(),
"" + lock.isReadOnly()
};
siteLog.addEvent(currentTimestamp, details);
this.activeLocks.remove(lock);
} else {
if (debug)
System.out.println(
"Site: Lock not released on x"
+ lock.getLockedVariableIndex()
+ "."
+ siteIndex
+ " held by T"
+ lock.getTransactionNumber());
i++;
}
}
}
