/**
* performs the read operation for both Read-Write and Read-Only Transactions
*
* @param transactionID
* @param variable
* @param typeOfTransaction
*/
private void read(String transactionID, int variable, int typeOfTransaction) {
Transaction transactionForReading = this.currentTransactions.get(transactionID);
if (typeOfTransaction == Constants.RO) { // for read only transaction
boolean hasItBeenRead = false;
for (int i = 1; i <= Constants.SITES && !hasItBeenRead; i++) {
Site tempSite = sites.get(i);
if (tempSite.isDown()) {
// site is down
// Do not do anything, go to next site
} else {
// site is not down
ArrayList<Variable> variablesInTempSite = (ArrayList<Variable>) tempSite.getVariables();
for (int j = 0; j < variablesInTempSite.size(); j++) {
if (variablesInTempSite.get(j).getID() == variable
&& variablesInTempSite.get(j).getAvailableForRead()) {
// variable we are looking for found in tempSite and they are available for reading
// We have parse the VariableHistory of this Variable and choose the correct value
ArrayList<VariableHistory> history =
(ArrayList<VariableHistory>) variablesInTempSite.get(j).getHistoricalData();
int currentMax = -1; // time counter
int maxIndex = -1; // index in the ArrayList which has max
for (int k = 0; k < history.size(); k++) {
if (history.get(k).getTime() > currentMax
&& history.get(k).getTime() < transactionForReading.getStartTime()) {
maxIndex = k;
currentMax = history.get(k).getTime();
}
}
if (maxIndex != -1) {
hasItBeenRead = true;
System.out.println("The value that is read is " + history.get(maxIndex).getValue());
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
transactionForReading.insertOperation(op);
}
}
}
}
}
if (hasItBeenRead == false) {
// variable could not be read for any site so this operation has to wait
System.out.println(transactionID + "(R,x" + variable + ") has to wait");
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
insertToWaitList(op, transactionID);
}
} else { // for read-write transaction
if (this.doesThisTransactionAlreadyHaveReadLockOnVariable(transactionForReading, variable)) {
// transaction already has a read lock on variable at some site
int index = -1;
for (int q = 1; q <= Constants.SITES; q++) {
if (!this.sites.get(q).isDown()) {
if (this.sites
.get(q)
.lockInfo
.doesThisTableContainLockWith(variable, transactionID, Constants.RL)) {
index = q;
}
}
}
ArrayList<Variable> varsInSite = (ArrayList<Variable>) this.sites.get(index).getVariables();
Variable var = varsInSite.get(0);
for (int m = 0; m < varsInSite.size(); m++) {
if (varsInSite.get(m).getID() == variable) {
var = varsInSite.get(m);
}
}
System.out.println("The value that is read is " + var.getValue());
} else {
// the transaction does not have a read lock on this variable
boolean hasItBeenRead = false;
for (int i = 1; i <= Constants.SITES && !hasItBeenRead; i++) {
Site tempSite = sites.get(i);
if (tempSite.isDown()) {
// site is down
// Do not do anything
} else {
// site is not down
ArrayList<Variable> variablesInTempSite = (ArrayList<Variable>) tempSite.getVariables();
for (int j = 0; j < variablesInTempSite.size(); j++) {
if (variablesInTempSite.get(j).getID() == variable
&& variablesInTempSite.get(j).getAvailableForRead()) {
// variable we are looking for found in tempSite and they are available for
// reading(in term of recovery)
if (tempSite.lockInfo.canWeGetReadLockOnVariable(variable, transactionID)) {
// we can get read lock on the variable
if (tempSite.lockInfo.doesThisTableContainLockWith(
variable, transactionID, Constants.WL)) {
// this transaction has a write lock on the this variable at this site
hasItBeenRead = true;
Variable currentVariable = tempSite.getVariableWithID(variable);
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
transactionForReading.insertOperation(op);
transactionForReading.sitesAccessed.add(i);
System.out.println(
"The value that is read is " + currentVariable.getCurrValue());
// value read is the current value because transaction already has read lock on
// the variable
} else {
// this transaction does not have a write lock on this variable
hasItBeenRead = true;
tempSite.lockInfo.addLock(variable, transactionID, Constants.RL);
Variable currentVariable = tempSite.getVariableWithID(variable);
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
transactionForReading.insertOperation(op);
transactionForReading.sitesAccessed.add(i);
transactionForReading.addLockToAlreadyLocked(variable, Constants.RL);
System.out.println("The value that is read is " + currentVariable.getValue());
}
} else {
// this is the variable that we want to lock
// but we can't get a read lock on it
// so implement wait-die
hasItBeenRead = true;
ArrayList<Lock> tempList = tempSite.lockInfo.getAllLocksForVariable(variable);
Lock writeLock = tempList.get(0);
String tidWithWriteLock = writeLock.getTransactionId();
String tidWithoutWriteLock = transactionID;
boolean answer = isAbort(tidWithWriteLock, tidWithoutWriteLock);
if (answer == false) {
// This operation has to wait
this.putThisTransactionIntoWaitListingOfTransactionThatHaveLock(
transactionID, variable);
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
insertToWaitList(op, transactionID);
System.out.println(transactionID + "(R,x" + variable + ") has to wait");
}
}
}
}
}
}
if (hasItBeenRead == false) {
// variable could not be read for any site so this operation has to wait
Operation op = new Operation(0, variable, 0, Constants.OP_READ);
insertToWaitList(op, transactionID);
System.out.println(transactionID + "(R,x" + variable + ") has to wait");
}
}
}
}
