c# barcode generator library open source This looks just like our previous example, Listing 6-4, except this time, we have the in Font

Creator Data Matrix 2d barcode in Font This looks just like our previous example, Listing 6-4, except this time, we have the

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BeginXAction message. This message calls the begin method with the transaction ID. private def begin(xActionId: Int) {
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We now capture the current state of the Actor both the info and the mechanism for servicing incoming messages:
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val oldInfo = info // capture val oldService = service
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CHAPTER 6 ACTORS AND CONCURRENCY
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Next, we build up a partial function that will service incoming requests. If there s a TIMEOUT, we roll back the transaction by replacing the current state with the state at the beginning of the transaction:
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val tmp: PartialFunction[Any, Unit] = { case TIMEOUT => // Rollback info = oldInfo service = oldService
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If we get a Pair that contains the current transaction ID and the RollbackXAction message, we roll back the transaction:
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case (n, RollbackXAction) if n == xActionId => info = oldInfo service = oldService
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If we get a Pair that contains the current transaction ID and the CommitXAction message, we commit the transaction by reverting to the old servicing mechanism and leaving the data the way it was mutated by the current transaction:
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case (n, CommitXAction) if n == xActionId => // Commit service = oldService
If we get any other message and it has the correct transaction ID and can be handled by the normal message handler, we pass it on to the normal message handler:
case (n, v) if n == xActionId && normal.isDefinedAt(v) => normal(v) }
Finally, we set the servicing mechanism to the new partial function:
service = (tmp, true) }
Next, we define our act loop. If we are outside of the transaction boundary, we process the message the normal way with react. However, if we re inside a transaction, we call reactWithin(500). This will process messages the same way as react, except if no message matching the pattern is received in 500 milliseconds, the Actor is sent a TIMEOUT message. This allows us to terminate our transaction automatically if there s no activity on the transaction in a 500 millisecond period. Any messages received outside the transaction will be left in the Actor s mailbox and will be processed after the transaction is complete.
def act = loop { service match { case (pf, false) => react(pf) case (pf, true) => reactWithin(500)(pf) } }
CHAPTER 6 ACTORS AND CONCURRENCY
And always remember to start the Actor.
this.start }
Testing the Transactional Actor
We ve defined a transactional Actor. Let s see how it works. Let s create accounts for two people, dpp and archer, and put funds into the checking and savings accounts.
val dpp = new Acct dpp ! Update("Savings", v => (v getOrElse 0) + 1000) dpp ! Update("Checking", v => (v getOrElse 0) + 100) val archer = new Acct archer ! Update("Savings", v => (v getOrElse 0) + 2000) archer ! Update("Checking", v => (v getOrElse 0) + 50) println("Initial balances:") println("dpp: "+(dpp ! GetInfo)) println("archer: "+(archer ! GetInfo))
Let s see what s printed on the console:
Initial balances: dpp: Info(Map(Savings -> 1000, Checking -> 100)) archer: Info(Map(Savings -> 2000, Checking -> 50))
Let s define a variable that keeps track of our transaction IDs:
var xid = 1
Next, let s define a method that will transactionally transfer money between accounts for a single Actor as long as there are sufficient funds:
def transfer(who: Actor, from: String, to: String, amount: Int): Unit = { xid += 1
who ! BeginXAction(xid)
We begin the transaction and get the current balances:
who ! (500, (xid, GetInfo)) match { case Some(Info(bal)) =>
CHAPTER 6 ACTORS AND CONCURRENCY
If the account has sufficient balances, then we debit one account and credit the other account and commit the transaction.
if (bal.getOrElse(from, 0) > amount) { who ! (xid, Update(from, v => (v getOrElse 0) - amount)) who ! (xid, Update(to, v => (v getOrElse 0) + amount)) who ! (xid, CommitXAction) } else {
If we don t get the balance within 500 milliseconds or there s not sufficient funds, roll back the transaction.
who ! (xid, RollbackXAction) } case _ => who ! (xid, RollbackXAction) } }
Let s test out the transactional transfer and see whether it works by trying to transfer $700 from savings to checking twice. The first transaction should succeed, but the second should fail.
transfer(dpp, println("xfer transfer(dpp, println("xfer "Savings", "Checking", 700) 1 dpp: "+(dpp ! GetInfo)) "Savings", "Checking", 700) 2 dpp: "+(dpp ! GetInfo))
The console says:
xfer 1 dpp: Info(Map(Savings -> 300, Checking -> 800)) xfer 2 dpp: Info(Map(Savings -> 300, Checking -> 800))
Next, let s define a method that transfers money between two accounts on two separate Actors. Once again, there must be sufficient funds for the transfer, or the transaction will be rolled back.
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