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previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/TestSuite.scala deleted 100644 → 0
View file @ 2396bbb9
package m20
import scala.concurrent._
import scala.concurrent.duration._
import scala.collection.mutable.HashMap
import scala.util.Random
import instrumentation._
import instrumentation.TestHelper._
import instrumentation.TestUtils._
enum ThreadResult:
case WriteError(error: String)
case WriteSuccess
case Read(result: (Int, Int))
import ThreadResult._
class M20Suite extends munit.FunSuite:
/** If at least one thread resulted in an error,
* return `(false, errorMessage)` otherwise return `(true, "")`.
*/
def processResults(results: List[ThreadResult]): (Boolean, String) =
val success = (true, "")
results.foldLeft(success) {
case (acc @ (false, _), _) =>
// Report the first error found
acc
case (_, WriteError(error)) =>
(false, error)
case (_, Read((x, y))) if x + 1 != y =>
(false, s"Read ($x, $y) but expected y to be ${x + 1}")
case (_, _: Read | WriteSuccess) =>
success
}
def randomList(length: Int): List[Int] =
List.fill(length)(Random.nextInt)
test("SeqCount: single-threaded write and copy (1 pts)") {
val sc = new SeqCount
randomList(100).lazyZip(randomList(100)).foreach { (x, y) =>
sc.write(x, y)
assertEquals(sc.copy(), (x, y))
}
}
test("SeqCount: one write thread, two copy threads (4 pts)") {
testManySchedules(3, sched =>
val sc = new SchedulableSeqCount(sched)
// Invariant in this test: y == x + 1
sc.write(0, 1)
val randomValues = randomList(length = 5)
def writeThread(): ThreadResult =
randomValues.foldLeft(WriteSuccess) {
case (res: WriteError, _) =>
// Report the first error found
res
case (_, i) =>
sc.write(i, i + 1)
val writtenValues = (i, i + 1)
val readBack = sc.copy()
if writtenValues != readBack then
WriteError(s"Wrote $writtenValues but read back $readBack")
else
WriteSuccess
}
def copyThread(): ThreadResult =
Read(sc.copy())
val threads = List(
() => writeThread(),
() => copyThread(),
() => copyThread()
)
(threads, results => processResults(results.asInstanceOf[List[ThreadResult]]))
)
}
test("MultiWriterSeqCount: single-threaded write and copy (1 pts)") {
val sc = new MultiWriterSeqCount
randomList(100).lazyZip(randomList(100)).foreach { (x, y) =>
sc.write(x, y)
assertEquals(sc.copy(), (x, y))
}
}
test("MultiWriterSeqCount: two write threads, two copy threads (4 pts)") {
testManySchedules(4, sched =>
val msc = new SchedulableMultiWriterSeqCount(sched)
// Invariant in this test: y == x + 1
msc.write(0, 1)
val randomValues = randomList(length = 5)
def writeThread(): ThreadResult =
randomValues.foreach(i => msc.write(i, i + 1))
// Unlke in the SeqCount test, we do not verify that we can read back
// the values we wrote, because the other writer thread might have
// overwritten them already.
WriteSuccess
def copyThread(): ThreadResult =
Read(msc.copy())
val threads = List(
() => writeThread(),
() => writeThread(),
() => copyThread(),
() => copyThread()
)
(threads, results => processResults(results.asInstanceOf[List[ThreadResult]]))
)
}
import scala.concurrent.duration._
override val munitTimeout = 200.seconds
end M20Suite
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/instrumentation/MockedMonitor.scala deleted 100644 → 0
View file @ 2396bbb9
package m20.instrumentation
trait MockedMonitor extends Monitor {
def scheduler: Scheduler
// Can be overriden.
override def waitDefault() = {
scheduler.log("wait")
scheduler updateThreadState Wait(this, scheduler.threadLocks.tail)
}
override def synchronizedDefault[T](toExecute: =>T): T = {
scheduler.log("synchronized check")
val prevLocks = scheduler.threadLocks
scheduler updateThreadState Sync(this, prevLocks) // If this belongs to prevLocks, should just continue.
scheduler.log("synchronized -> enter")
try {
toExecute
} finally {
scheduler updateThreadState Running(prevLocks)
scheduler.log("synchronized -> out")
}
}
override def notifyDefault() = {
scheduler mapOtherStates {
state => state match {
case Wait(lockToAquire, locks) if lockToAquire == this => SyncUnique(this, state.locks)
case e => e
}
}
scheduler.log("notify")
}
override def notifyAllDefault() = {
scheduler mapOtherStates {
state => state match {
case Wait(lockToAquire, locks) if lockToAquire == this => Sync(this, state.locks)
case SyncUnique(lockToAquire, locks) if lockToAquire == this => Sync(this, state.locks)
case e => e
}
}
scheduler.log("notifyAll")
}
}
trait LockFreeMonitor extends Monitor {
override def waitDefault() = {
throw new Exception("Please use lock-free structures and do not use wait()")
}
override def synchronizedDefault[T](toExecute: =>T): T = {
throw new Exception("Please use lock-free structures and do not use synchronized()")
}
override def notifyDefault() = {
throw new Exception("Please use lock-free structures and do not use notify()")
}
override def notifyAllDefault() = {
throw new Exception("Please use lock-free structures and do not use notifyAll()")
}
}
abstract class ThreadState {
def locks: Seq[AnyRef]
}
trait CanContinueIfAcquiresLock extends ThreadState {
def lockToAquire: AnyRef
}
case object Start extends ThreadState { def locks: Seq[AnyRef] = Seq.empty }
case object End extends ThreadState { def locks: Seq[AnyRef] = Seq.empty }
case class Wait(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState
case class SyncUnique(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState with CanContinueIfAcquiresLock
case class Sync(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState with CanContinueIfAcquiresLock
case class Running(locks: Seq[AnyRef]) extends ThreadState
case class VariableReadWrite(locks: Seq[AnyRef]) extends ThreadState
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/instrumentation/Scheduler.scala deleted 100644 → 0
View file @ 2396bbb9
package m20.instrumentation
import java.util.concurrent._;
import scala.concurrent.duration._
import scala.collection.mutable._
import Stats._
import java.util.concurrent.atomic.AtomicInteger
sealed abstract class Result
case class RetVal(rets: List[Any]) extends Result
case class Except(msg: String, stackTrace: Array[StackTraceElement]) extends Result
case class Timeout(msg: String) extends Result
/**
* A class that maintains schedule and a set of thread ids.
* The schedules are advanced after an operation of a SchedulableBuffer is performed.
* Note: the real schedule that is executed may deviate from the input schedule
* due to the adjustments that had to be made for locks
*/
class Scheduler(sched: List[Int]) {
val maxOps = 500 // a limit on the maximum number of operations the code is allowed to perform
private var schedule = sched
private var numThreads = 0
private val realToFakeThreadId = Map[Long, Int]()
private val opLog = ListBuffer[String]() // a mutable list (used for efficient concat)
private val threadStates = Map[Int, ThreadState]()
/**
* Runs a set of operations in parallel as per the schedule.
* Each operation may consist of many primitive operations like reads or writes
* to shared data structure each of which should be executed using the function `exec`.
* @timeout in milliseconds
* @return true - all threads completed on time, false -some tests timed out.
*/
def runInParallel(timeout: Long, ops: List[() => Any]): Result = {
numThreads = ops.length
val threadRes = Array.fill(numThreads) { None: Any }
var exception: Option[Except] = None
val syncObject = new Object()
var completed = new AtomicInteger(0)
// create threads
val threads = ops.zipWithIndex.map {
case (op, i) =>
new Thread(new Runnable() {
def run(): Unit = {
val fakeId = i + 1
setThreadId(fakeId)
try {
updateThreadState(Start)
val res = op()
updateThreadState(End)
threadRes(i) = res
// notify the master thread if all threads have completed
if (completed.incrementAndGet() == ops.length) {
syncObject.synchronized { syncObject.notifyAll() }
}
} catch {
case e: Throwable if exception != None => // do nothing here and silently fail
case e: Throwable =>
log(s"throw ${e.toString}")
exception = Some(Except(s"Thread $fakeId crashed on the following schedule: \n" + opLog.mkString("\n"),
e.getStackTrace))
syncObject.synchronized { syncObject.notifyAll() }
//println(s"$fakeId: ${e.toString}")
//Runtime.getRuntime().halt(0) //exit the JVM and all running threads (no other way to kill other threads)
}
}
})
}
// start all threads
threads.foreach(_.start())
// wait for all threads to complete, or for an exception to be thrown, or for the time out to expire
var remTime = timeout
syncObject.synchronized {
timed { if(completed.get() != ops.length) syncObject.wait(timeout) } { time => remTime -= time }
}
if (exception.isDefined) {
exception.get
} else if (remTime <= 1) { // timeout ? using 1 instead of zero to allow for some errors
Timeout(opLog.mkString("\n"))
} else {
// every thing executed normally
RetVal(threadRes.toList)
}
}
// Updates the state of the current thread
def updateThreadState(state: ThreadState): Unit = {
val tid = threadId
synchronized {
threadStates(tid) = state
}
state match {
case Sync(lockToAquire, locks) =>
if (locks.indexOf(lockToAquire) < 0) waitForTurn else {
// Re-aqcuiring the same lock
updateThreadState(Running(lockToAquire +: locks))
}
case Start => waitStart()
case End => removeFromSchedule(tid)
case Running(_) =>
case _ => waitForTurn // Wait, SyncUnique, VariableReadWrite
}
}
def waitStart(): Unit = {
//while (threadStates.size < numThreads) {
//Thread.sleep(1)
//}
synchronized {
if (threadStates.size < numThreads) {
wait()
} else {
notifyAll()
}
}
}
def threadLocks = {
synchronized {
threadStates(threadId).locks
}
}
def threadState = {
synchronized {
threadStates(threadId)
}
}
def mapOtherStates(f: ThreadState => ThreadState) = {
val exception = threadId
synchronized {
for (k <- threadStates.keys if k != exception) {
threadStates(k) = f(threadStates(k))
}
}
}
def log(str: String) = {
if((realToFakeThreadId contains Thread.currentThread().getId())) {
val space = (" " * ((threadId - 1) * 2))
val s = space + threadId + ":" + "\n".r.replaceAllIn(str, "\n" + space + " ")
opLog += s
}
}
/**
* Executes a read or write operation to a global data structure as per the given schedule
* @param msg a message corresponding to the operation that will be logged
*/
def exec[T](primop: => T)(msg: => String, postMsg: => Option[T => String] = None): T = {
if(! (realToFakeThreadId contains Thread.currentThread().getId())) {
primop
} else {
updateThreadState(VariableReadWrite(threadLocks))
val m = msg
if(m != "") log(m)
if (opLog.size > maxOps)
throw new Exception(s"Total number of reads/writes performed by threads exceed $maxOps. A possible deadlock!")
val res = primop
postMsg match {
case Some(m) => log(m(res))
case None =>
}
res
}
}
private def setThreadId(fakeId: Int) = synchronized {
realToFakeThreadId(Thread.currentThread.getId) = fakeId
}
def threadId =
try {
realToFakeThreadId(Thread.currentThread().getId())
} catch {
case e: NoSuchElementException =>
throw new Exception("You are accessing shared variables in the constructor. This is not allowed. The variables are already initialized!")
}
private def isTurn(tid: Int) = synchronized {
(!schedule.isEmpty && schedule.head != tid)
}
def canProceed(): Boolean = {
val tid = threadId
canContinue match {
case Some((i, state)) if i == tid =>
//println(s"$tid: Runs ! Was in state $state")
canContinue = None
state match {
case Sync(lockToAquire, locks) => updateThreadState(Running(lockToAquire +: locks))
case SyncUnique(lockToAquire, locks) =>
mapOtherStates {
_ match {
case SyncUnique(lockToAquire2, locks2) if lockToAquire2 == lockToAquire => Wait(lockToAquire2, locks2)
case e => e
}
}
updateThreadState(Running(lockToAquire +: locks))
case VariableReadWrite(locks) => updateThreadState(Running(locks))
}
true
case Some((i, state)) =>
//println(s"$tid: not my turn but $i !")
false
case None =>
false
}
}
var threadPreference = 0 // In the case the schedule is over, which thread should have the preference to execute.
/** returns true if the thread can continue to execute, and false otherwise */
def decide(): Option[(Int, ThreadState)] = {
if (!threadStates.isEmpty) { // The last thread who enters the decision loop takes the decision.
//println(s"$threadId: I'm taking a decision")
if (threadStates.values.forall { case e: Wait => true case _ => false }) {
val waiting = threadStates.keys.map(_.toString).mkString(", ")
val s = if (threadStates.size > 1) "s" else ""
val are = if (threadStates.size > 1) "are" else "is"
throw new Exception(s"Deadlock: Thread$s $waiting $are waiting but all others have ended and cannot notify them.")
} else {
// Threads can be in Wait, Sync, SyncUnique, and VariableReadWrite mode.
// Let's determine which ones can continue.
val notFree = threadStates.collect { case (id, state) => state.locks }.flatten.toSet
val threadsNotBlocked = threadStates.toSeq.filter {
case (id, v: VariableReadWrite) => true
case (id, v: CanContinueIfAcquiresLock) => !notFree(v.lockToAquire) || (v.locks contains v.lockToAquire)
case _ => false
}
if (threadsNotBlocked.isEmpty) {
val waiting = threadStates.keys.map(_.toString).mkString(", ")
val s = if (threadStates.size > 1) "s" else ""
val are = if (threadStates.size > 1) "are" else "is"
val whoHasLock = threadStates.toSeq.flatMap { case (id, state) => state.locks.map(lock => (lock, id)) }.toMap
val reason = threadStates.collect {
case (id, state: CanContinueIfAcquiresLock) if !notFree(state.lockToAquire) =>
s"Thread $id is waiting on lock ${state.lockToAquire} held by thread ${whoHasLock(state.lockToAquire)}"
}.mkString("\n")
throw new Exception(s"Deadlock: Thread$s $waiting are interlocked. Indeed:\n$reason")
} else if (threadsNotBlocked.size == 1) { // Do not consume the schedule if only one thread can execute.
Some(threadsNotBlocked(0))
} else {
val next = schedule.indexWhere(t => threadsNotBlocked.exists { case (id, state) => id == t })
if (next != -1) {
//println(s"$threadId: schedule is $schedule, next chosen is ${schedule(next)}")
val chosenOne = schedule(next) // TODO: Make schedule a mutable list.
schedule = schedule.take(next) ++ schedule.drop(next + 1)
Some((chosenOne, threadStates(chosenOne)))
} else {
threadPreference = (threadPreference + 1) % threadsNotBlocked.size
val chosenOne = threadsNotBlocked(threadPreference) // Maybe another strategy
Some(chosenOne)
//threadsNotBlocked.indexOf(threadId) >= 0
/*
val tnb = threadsNotBlocked.map(_._1).mkString(",")
val s = if (schedule.isEmpty) "empty" else schedule.mkString(",")
val only = if (schedule.isEmpty) "" else " only"
throw new Exception(s"The schedule is $s but$only threads ${tnb} can continue")*/
}
}
}
} else canContinue
}
/**
* This will be called before a schedulable operation begins.
* This should not use synchronized
*/
var numThreadsWaiting = new AtomicInteger(0)
//var waitingForDecision = Map[Int, Option[Int]]() // Mapping from thread ids to a number indicating who is going to make the choice.
var canContinue: Option[(Int, ThreadState)] = None // The result of the decision thread Id of the thread authorized to continue.
private def waitForTurn = {
synchronized {
if (numThreadsWaiting.incrementAndGet() == threadStates.size) {
canContinue = decide()
notifyAll()
}
//waitingForDecision(threadId) = Some(numThreadsWaiting)
//println(s"$threadId Entering waiting with ticket number $numThreadsWaiting/${waitingForDecision.size}")
while (!canProceed()) wait()
}
numThreadsWaiting.decrementAndGet()
}
/**
* To be invoked when a thread is about to complete
*/
private def removeFromSchedule(fakeid: Int) = synchronized {
//println(s"$fakeid: I'm taking a decision because I finished")
schedule = schedule.filterNot(_ == fakeid)
threadStates -= fakeid
if (numThreadsWaiting.get() == threadStates.size) {
canContinue = decide()
notifyAll()
}
}
def getOperationLog() = opLog
}
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/instrumentation/Stats.scala deleted 100644 → 0
View file @ 2396bbb9
/* Copyright 2009-2015 EPFL, Lausanne */
package m20.instrumentation
import java.lang.management._
/**
* A collection of methods that can be used to collect run-time statistics about Leon programs.
* This is mostly used to test the resources properties of Leon programs
*/
object Stats {
def timed[T](code: => T)(cont: Long => Unit): T = {
var t1 = System.currentTimeMillis()
val r = code
cont((System.currentTimeMillis() - t1))
r
}
def withTime[T](code: => T): (T, Long) = {
var t1 = System.currentTimeMillis()
val r = code
(r, (System.currentTimeMillis() - t1))
}
}
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/instrumentation/TestHelper.scala deleted 100644 → 0
View file @ 2396bbb9
package m20.instrumentation
import scala.util.Random
import scala.collection.mutable.{Map => MutableMap}
import Stats._
object TestHelper {
val noOfSchedules = 10000 // set this to 100k during deployment
val readWritesPerThread = 20 // maximum number of read/writes possible in one thread
val contextSwitchBound = 10
val testTimeout = 150 // the total time out for a test in seconds
val schedTimeout = 15 // the total time out for execution of a schedule in secs
// Helpers
/*def testManySchedules(op1: => Any): Unit = testManySchedules(List(() => op1))
def testManySchedules(op1: => Any, op2: => Any): Unit = testManySchedules(List(() => op1, () => op2))
def testManySchedules(op1: => Any, op2: => Any, op3: => Any): Unit = testManySchedules(List(() => op1, () => op2, () => op3))
def testManySchedules(op1: => Any, op2: => Any, op3: => Any, op4: => Any): Unit = testManySchedules(List(() => op1, () => op2, () => op3, () => op4))*/
def testSequential[T](ops: Scheduler => Any)(assertions: T => (Boolean, String)) =
testManySchedules(1,
(sched: Scheduler) => {
(List(() => ops(sched)),
(res: List[Any]) => assertions(res.head.asInstanceOf[T]))
})
/**
* @numThreads number of threads
* @ops operations to be executed, one per thread
* @assertion as condition that will executed after all threads have completed (without exceptions)
* the arguments are the results of the threads
*/
def testManySchedules(numThreads: Int,
ops: Scheduler =>
(List[() => Any], // Threads
List[Any] => (Boolean, String)) // Assertion
) = {
var timeout = testTimeout * 1000L
val threadIds = (1 to numThreads)
//(1 to scheduleLength).flatMap(_ => threadIds).toList.permutations.take(noOfSchedules).foreach {
val schedules = (new ScheduleGenerator(numThreads)).schedules()
var schedsExplored = 0
schedules.takeWhile(_ => schedsExplored <= noOfSchedules && timeout > 0).foreach {
//case _ if timeout <= 0 => // break
case schedule =>
schedsExplored += 1
val schedr = new Scheduler(schedule)
//println("Exploring Sched: "+schedule)
val (threadOps, assertion) = ops(schedr)
if (threadOps.size != numThreads)
throw new IllegalStateException(s"Number of threads: $numThreads, do not match operations of threads: $threadOps")
timed { schedr.runInParallel(schedTimeout * 1000, threadOps) } { t => timeout -= t } match {
case Timeout(msg) =>
throw new java.lang.AssertionError("assertion failed\n"+"The schedule took too long to complete. A possible deadlock! \n"+msg)
case Except(msg, stkTrace) =>
val traceStr = "Thread Stack trace: \n"+stkTrace.map(" at "+_.toString).mkString("\n")
throw new java.lang.AssertionError("assertion failed\n"+msg+"\n"+traceStr)
case RetVal(threadRes) =>
// check the assertion
val (success, custom_msg) = assertion(threadRes)
if (!success) {
val msg = "The following schedule resulted in wrong results: \n" + custom_msg + "\n" + schedr.getOperationLog().mkString("\n")
throw new java.lang.AssertionError("Assertion failed: "+msg)
}
}
}
if (timeout <= 0) {
throw new java.lang.AssertionError("Test took too long to complete! Cannot check all schedules as your code is too slow!")
}
}
/**
* A schedule generator that is based on the context bound
*/
class ScheduleGenerator(numThreads: Int) {
val scheduleLength = readWritesPerThread * numThreads
val rands = (1 to scheduleLength).map(i => new Random(0xcafe * i)) // random numbers for choosing a thread at each position
def schedules(): LazyList[List[Int]] = {
var contextSwitches = 0
var contexts = List[Int]() // a stack of thread ids in the order of context-switches
val remainingOps = MutableMap[Int, Int]()
remainingOps ++= (1 to numThreads).map(i => (i, readWritesPerThread)) // num ops remaining in each thread
val liveThreads = (1 to numThreads).toSeq.toBuffer
/**
* Updates remainingOps and liveThreads once a thread is chosen for a position in the schedule
*/
def updateState(tid: Int): Unit = {
val remOps = remainingOps(tid)
if (remOps == 0) {
liveThreads -= tid
} else {
remainingOps += (tid -> (remOps - 1))
}
}
val schedule = rands.foldLeft(List[Int]()) {
case (acc, r) if contextSwitches < contextSwitchBound =>
val tid = liveThreads(r.nextInt(liveThreads.size))
contexts match {
case prev :: tail if prev != tid => // we have a new context switch here
contexts +:= tid
contextSwitches += 1
case prev :: tail =>
case _ => // init case
contexts +:= tid
}
updateState(tid)
acc :+ tid
case (acc, _) => // here context-bound has been reached so complete the schedule without any more context switches
if (!contexts.isEmpty) {
contexts = contexts.dropWhile(remainingOps(_) == 0)
}
val tid = contexts match {
case top :: tail => top
case _ => liveThreads(0) // here, there has to be threads that have not even started
}
updateState(tid)
acc :+ tid
}
schedule #:: schedules()
}
}
}
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/instrumentation/TestUtils.scala deleted 100644 → 0
View file @ 2396bbb9
package m20.instrumentation
import scala.concurrent._
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global
object TestUtils {
def failsOrTimesOut[T](action: => T): Boolean = {
val asyncAction = Future {
action
}
try {
Await.result(asyncAction, 2000.millisecond)
} catch {
case _: Throwable => return true
}
return false
}
}
previous-exams/2021-midterm-solutions/m20/src/test/scala/m20/overrides.scala deleted 100644 → 0
View file @ 2396bbb9
package m20
import instrumentation._
import scala.annotation.tailrec
import java.util.concurrent.atomic._
class SchedulableAtomicVariable[T](initial: T, scheduler: Scheduler, name: String) extends AbstractAtomicVariable[T]:
private val proxied: AtomicVariable[T] = new AtomicVariable[T](initial)
override def get: T = scheduler.exec {
proxied.get
} (s"", Some(res => s"$name: get $res"))
override def set(value: T): Unit = scheduler.exec {
proxied.set(value)
} (s"$name: set $value", None)
override def compareAndSet(expected: T, newValue: T): Boolean = {
scheduler.exec {
proxied.compareAndSet(expected, newValue)
} (s"$name: compareAndSet(expected = $expected, newValue = $newValue)", Some(res => s"$name: Did it set? $res") )
}
end SchedulableAtomicVariable
class SchedulableSeqCount(val scheduler: Scheduler) extends SeqCount with LockFreeMonitor:
override def generation: Int = scheduler.exec {
super.generation
} ("", Some(res => s"generation is $res"))
override def setGeneration(newGeneration: Int): Unit = scheduler.exec {
super.setGeneration(newGeneration)
} ( s"setGeneration($newGeneration)", None )
override def x: Int = scheduler.exec {
super.x
} ("", Some(res => s"x is $res"))
override def setX(newX: Int): Unit = scheduler.exec {
super.setX(newX)
} (s"setX($newX)", None)
override def y: Int = scheduler.exec {
super.y
} ("", Some(res => s"y is $res"))
override def setY(newY: Int): Unit = scheduler.exec {
super.setY(newY)
} (s"setY($newY)", None)
end SchedulableSeqCount
class SchedulableMultiWriterSeqCount(val scheduler: Scheduler) extends MultiWriterSeqCount with LockFreeMonitor:
override protected val myGeneration: AbstractAtomicVariable[Int] = new SchedulableAtomicVariable(0, scheduler, "myGeneration")
override def x: Int = scheduler.exec {
super.x
} ("", Some(res => s"x is $res"))
override def setX(newX: Int): Unit = scheduler.exec {
super.setX(newX)
} (s"setX($newX)", None)
override def y: Int = scheduler.exec {
super.y
} ("", Some(res => s"y is $res"))
override def setY(newY: Int): Unit = scheduler.exec {
super.setY(newY)
} (s"setY($newY)", None)
end SchedulableMultiWriterSeqCount
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Use the following commands to make a fresh clone of your repository:
```
git clone -b m21 git@gitlab.epfl.ch:lamp/student-repositories-s21/cs206-GASPAR.git m21
```
## Useful links
* [A guide to the Scala parallel collections](https://docs.scala-lang.org/overviews/parallel-collections/overview.html)
* [The API documentation of the Scala parallel collections](https://www.javadoc.io/doc/org.scala-lang.modules/scala-parallel-collections_2.13/latest/scala/collection/index.html)
* [The API documentation of the Scala standard library](https://www.scala-lang.org/files/archive/api/2.13.4)
* [The API documentation of the Java standard library](https://docs.oracle.com/en/java/javase/15/docs/api/index.html)
**If you have issues with the IDE, try [reimporting the
build](https://gitlab.epfl.ch/lamp/cs206/-/blob/master/labs/example-lab.md#ide-features-like-type-on-hover-or-go-to-definition-do-not-work),
if you still have problems, use `compile` in sbt instead.**
## Exercise
In this question, you will complete the definition of two concurrent data
structures **without using `synchronized`**: `SeqCount` and `MultiWriterSeqCount`.
## Part 1: SeqCount (defined in `SeqCount.scala`)
An instance of this class stores two integers (initially set to 1), the stored
values can be updated using `write` and retrieved using `copy`. Only one thread
at a time is allowed to call `write` but multiple threads can call `copy` at
once.
Your task in this part is to implement `copy` such that this method never
returns _partially updated values_, for example given two threads operating
concurrently on a `SeqCount` `sc`:
```scala
// Thread 1
sc.write(1, 2)
```
```scala
// Thread 2
val result = sc.copy()
```
`result` must either be `(0, 0)` (since the initial values are 0) or `(1, 2)`,
but it must not be `(1, 0)`, `(0, 2)` or any other value.
To successfully implement this method you will need to use `generation`: this
method returns the current value of a volatile variable which is initially set
to 1, gets incremented by one at the beginning of `write`, and incremented by
one again at the end of `write`.
**You are not allowed to use `synchronized` or directly call any of
`myGeneration`, `myX` or `myY` (use the pre-defined getters and setters
instead).**
Hints:
- Remember that a write to a volatile field _happens-before_ every subsequent
read of that field.
- `generation` will always be odd when a write has completed and always
even when a write is in progress.
- `copy` can be implemented as a tail-recursive method.
## Part 2: MultiWriterSeqCount (defined in `MultiWriterSeqCount.scala`)
Like `SeqCount`, this class stores two integers updated using `write` and
retrieved using `copy`, but unlike `SeqCount` multiple threads are allowed to
call `write` at the same time: these writes will all succeed but they are
allowed to complete in any order, for example given three threads operating
concurrently on a `MultiWriterSeqCount` `msc`:
```scala
// Thread 1
msc.write(1, 2)
```
```scala
// Thread 2
msc.write(10, 20)
```
```scala
// Thread 3
val result = msc.copy()
```
`result` must either be `(0, 0)`, `(1, 2)` or `(10, 20)`.
In this class, the generation is stored in an atomic variable instead of a
volatible field therefore it's important to note that:
- a `set` on an atomic variable _happens-before_ every subsequent `get` of that
variable.
- A call to `compareAndSet` both gets and set an atomic variable.
Your task in this part is to implement both `copy` and `write`.
**You are not allowed to use `synchronized` or directly call any of
`myGeneration`, `myX` or `myY` (use the pre-defined getters and setters
instead).**
Hints:
- you should be able to just copy-paste the implementation of `copy` you
implemented in Part 1
- you will need to make use of `compareAndSetGeneration` in `write`
- `write` can be implemented as a tail-recursive method.
previous-exams/2021-midterm-solutions/m21/.gitignore deleted 100644 → 0
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# General
*.DS_Store
*.swp
*~
# Dotty
*.class
*.tasty
*.hasTasty
# sbt
target/
# IDE
.bsp
.bloop
.metals
.vscode
# datasets
stackoverflow-grading.csv
wikipedia-grading.dat
previous-exams/2021-midterm-solutions/m21/assignment.sbt deleted 100644 → 0
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// Student tasks (i.e. submit, packageSubmission)
enablePlugins(StudentTasks)
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course := "midterm"
assignment := "m21"
scalaVersion := "3.0.0-RC1"
scalacOptions ++= Seq("-language:implicitConversions", "-deprecation")
libraryDependencies += "org.scalameta" %% "munit" % "0.7.22"
val MUnitFramework = new TestFramework("munit.Framework")
testFrameworks += MUnitFramework
// Decode Scala names
testOptions += Tests.Argument(MUnitFramework, "-s")
testSuite := "m21.M21Suite"
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File deleted
previous-exams/2021-midterm-solutions/m21/project/FilteringReporterPlugin.scala deleted 100644 → 0
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package sbt // To access the private[sbt] compilerReporter key
package filteringReporterPlugin
import Keys._
import ch.epfl.lamp._
object FilteringReporterPlugin extends AutoPlugin {
override lazy val projectSettings = Seq(
// Turn off warning coming from scalameter that we cannot fix without changing scalameter
compilerReporter in (Compile, compile) ~= { reporter => new FilteringReporter(reporter) }
)
}
class FilteringReporter(reporter: xsbti.Reporter) extends xsbti.Reporter {
def reset(): Unit = reporter.reset()
def hasErrors: Boolean = reporter.hasErrors
def hasWarnings: Boolean = reporter.hasWarnings
def printSummary(): Unit = reporter.printSummary()
def problems: Array[xsbti.Problem] = reporter.problems
def log(problem: xsbti.Problem): Unit = {
if (!problem.message.contains("An existential type that came from a Scala-2 classfile cannot be"))
reporter.log(problem)
}
def comment(pos: xsbti.Position, msg: String): Unit =
reporter.comment(pos, msg)
override def toString = s"CollectingReporter($reporter)"
}
previous-exams/2021-midterm-solutions/m21/project/MOOCSettings.scala deleted 100644 → 0
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package ch.epfl.lamp
import sbt._
import sbt.Keys._
/**
* Coursera uses two versions of each assignment. They both have the same assignment key and part id but have
* different item ids.
*
* @param key Assignment key
* @param partId Assignment partId
* @param itemId Item id of the non premium version
* @param premiumItemId Item id of the premium version (`None` if the assignment is optional)
*/
case class CourseraId(key: String, partId: String, itemId: String, premiumItemId: Option[String])
/**
* Settings shared by all assignments, reused in various tasks.
*/
object MOOCSettings extends AutoPlugin {
override def requires = super.requires && filteringReporterPlugin.FilteringReporterPlugin
object autoImport {
val course = SettingKey[String]("course")
val assignment = SettingKey[String]("assignment")
val options = SettingKey[Map[String, Map[String, String]]]("options")
val courseraId = settingKey[CourseraId]("Coursera-specific information identifying the assignment")
val testSuite = settingKey[String]("Fully qualified name of the test suite of this assignment")
.withRank(KeyRanks.Invisible)
// Convenient alias
type CourseraId = ch.epfl.lamp.CourseraId
val CourseraId = ch.epfl.lamp.CourseraId
}
import autoImport._
override val globalSettings: Seq[Def.Setting[_]] = Seq(
// supershell is verbose, buggy and useless.
useSuperShell := false
)
override val projectSettings: Seq[Def.Setting[_]] = Seq(
parallelExecution in Test := false,
// Report test result after each test instead of waiting for every test to finish
logBuffered in Test := false,
name := s"${course.value}-${assignment.value}"
)
}
previous-exams/2021-midterm-solutions/m21/project/StudentTasks.scala deleted 100644 → 0
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package ch.epfl.lamp
import sbt._
import Keys._
// import scalaj.http._
import java.io.{File, FileInputStream, IOException}
import org.apache.commons.codec.binary.Base64
// import play.api.libs.json.{Json, JsObject, JsPath}
import scala.util.{Failure, Success, Try}
/**
* Provides tasks for submitting the assignment
*/
object StudentTasks extends AutoPlugin {
override def requires = super.requires && MOOCSettings
object autoImport {
val packageSourcesOnly = TaskKey[File]("packageSourcesOnly", "Package the sources of the project")
val packageBinWithoutResources = TaskKey[File]("packageBinWithoutResources", "Like packageBin, but without the resources")
val packageSubmissionZip = TaskKey[File]("packageSubmissionZip")
val packageSubmission = inputKey[Unit]("package solution as an archive file")
lazy val Grading = config("grading") extend(Runtime)
}
import autoImport._
import MOOCSettings.autoImport._
override lazy val projectSettings = Seq(
packageSubmissionSetting,
fork := true,
connectInput in run := true,
outputStrategy := Some(StdoutOutput),
) ++
packageSubmissionZipSettings ++
inConfig(Grading)(Defaults.testSettings ++ Seq(
unmanagedJars += file("grading-tests.jar"),
definedTests := (definedTests in Test).value,
internalDependencyClasspath := (internalDependencyClasspath in Test).value
))
/** **********************************************************
* SUBMITTING A SOLUTION TO COURSERA
*/
val packageSubmissionZipSettings = Seq(
packageSubmissionZip := {
val submission = crossTarget.value / "submission.zip"
val sources = (packageSourcesOnly in Compile).value
val binaries = (packageBinWithoutResources in Compile).value
IO.zip(Seq(sources -> "sources.zip", binaries -> "binaries.jar"), submission, None)
submission
},
artifactClassifier in packageSourcesOnly := Some("sources"),
artifact in (Compile, packageBinWithoutResources) ~= (art => art.withName(art.name + "-without-resources"))
) ++
inConfig(Compile)(
Defaults.packageTaskSettings(packageSourcesOnly, Defaults.sourceMappings) ++
Defaults.packageTaskSettings(packageBinWithoutResources, Def.task {
val relativePaths =
(unmanagedResources in Compile).value.flatMap(Path.relativeTo((unmanagedResourceDirectories in Compile).value)(_))
(mappings in (Compile, packageBin)).value.filterNot { case (_, path) => relativePaths.contains(path) }
})
)
val maxSubmitFileSize = {
val mb = 1024 * 1024
10 * mb
}
/** Check that the jar exists, isn't empty, isn't crazy big, and can be read
* If so, encode jar as base64 so we can send it to Coursera
*/
def prepareJar(jar: File, s: TaskStreams): String = {
val errPrefix = "Error submitting assignment jar: "
val fileLength = jar.length()
if (!jar.exists()) {
s.log.error(errPrefix + "jar archive does not exist\n" + jar.getAbsolutePath)
failSubmit()
} else if (fileLength == 0L) {
s.log.error(errPrefix + "jar archive is empty\n" + jar.getAbsolutePath)
failSubmit()
} else if (fileLength > maxSubmitFileSize) {
s.log.error(errPrefix + "jar archive is too big. Allowed size: " +
maxSubmitFileSize + " bytes, found " + fileLength + " bytes.\n" +
jar.getAbsolutePath)
failSubmit()
} else {
val bytes = new Array[Byte](fileLength.toInt)
val sizeRead = try {
val is = new FileInputStream(jar)
val read = is.read(bytes)
is.close()
read
} catch {
case ex: IOException =>
s.log.error(errPrefix + "failed to read sources jar archive\n" + ex.toString)
failSubmit()
}
if (sizeRead != bytes.length) {
s.log.error(errPrefix + "failed to read the sources jar archive, size read: " + sizeRead)
failSubmit()
} else encodeBase64(bytes)
}
}
/** Task to package solution to a given file path */
lazy val packageSubmissionSetting = packageSubmission := {
val args: Seq[String] = Def.spaceDelimited("[path]").parsed
val s: TaskStreams = streams.value // for logging
val jar = (packageSubmissionZip in Compile).value
val base64Jar = prepareJar(jar, s)
val path = args.headOption.getOrElse((baseDirectory.value / "submission.jar").absolutePath)
scala.tools.nsc.io.File(path).writeAll(base64Jar)
}
/*
/** Task to submit a solution to coursera */
val submit = inputKey[Unit]("submit solution to Coursera")
lazy val submitSetting = submit := {
// Fail if scalafix linting does not pass.
scalafixLinting.value
val args: Seq[String] = Def.spaceDelimited("<arg>").parsed
val s: TaskStreams = streams.value // for logging
val jar = (packageSubmissionZip in Compile).value
val assignmentDetails =
courseraId.?.value.getOrElse(throw new MessageOnlyException("This assignment can not be submitted to Coursera because the `courseraId` setting is undefined"))
val assignmentKey = assignmentDetails.key
val courseName =
course.value match {
case "capstone" => "scala-capstone"
case "bigdata" => "scala-spark-big-data"
case other => other
}
val partId = assignmentDetails.partId
val itemId = assignmentDetails.itemId
val premiumItemId = assignmentDetails.premiumItemId
val (email, secret) = args match {
case email :: secret :: Nil =>
(email, secret)
case _ =>
val inputErr =
s"""|Invalid input to `submit`. The required syntax for `submit` is:
|submit <email-address> <submit-token>
|
|The submit token is NOT YOUR LOGIN PASSWORD.
|It can be obtained from the assignment page:
|https://www.coursera.org/learn/$courseName/programming/$itemId
|${
premiumItemId.fold("") { id =>
s"""or (for premium learners):
|https://www.coursera.org/learn/$courseName/programming/$id
""".stripMargin
}
}
""".stripMargin
s.log.error(inputErr)
failSubmit()
}
val base64Jar = prepareJar(jar, s)
val json =
s"""|{
| "assignmentKey":"$assignmentKey",
| "submitterEmail":"$email",
| "secret":"$secret",
| "parts":{
| "$partId":{
| "output":"$base64Jar"
| }
| }
|}""".stripMargin
def postSubmission[T](data: String): Try[HttpResponse[String]] = {
val http = Http("https://www.coursera.org/api/onDemandProgrammingScriptSubmissions.v1")
val hs = List(
("Cache-Control", "no-cache"),
("Content-Type", "application/json")
)
s.log.info("Connecting to Coursera...")
val response = Try(http.postData(data)
.headers(hs)
.option(HttpOptions.connTimeout(10000)) // scalaj default timeout is only 100ms, changing that to 10s
.asString) // kick off HTTP POST
response
}
val connectMsg =
s"""|Attempting to submit "${assignment.value}" assignment in "$courseName" course
|Using:
|- email: $email
|- submit token: $secret""".stripMargin
s.log.info(connectMsg)
def reportCourseraResponse(response: HttpResponse[String]): Unit = {
val code = response.code
val respBody = response.body
/* Sample JSON response from Coursera
{
"message": "Invalid email or token.",
"details": {
"learnerMessage": "Invalid email or token."
}
}
*/
// Success, Coursera responds with 2xx HTTP status code
if (response.is2xx) {
val successfulSubmitMsg =
s"""|Successfully connected to Coursera. (Status $code)
|
|Assignment submitted successfully!
|
|You can see how you scored by going to:
|https://www.coursera.org/learn/$courseName/programming/$itemId/
|${
premiumItemId.fold("") { id =>
s"""or (for premium learners):
|https://www.coursera.org/learn/$courseName/programming/$id
""".stripMargin
}
}
|and clicking on "My Submission".""".stripMargin
s.log.info(successfulSubmitMsg)
}
// Failure, Coursera responds with 4xx HTTP status code (client-side failure)
else if (response.is4xx) {
val result = Try(Json.parse(respBody)).toOption
val learnerMsg = result match {
case Some(resp: JsObject) =>
(JsPath \ "details" \ "learnerMessage").read[String].reads(resp).get
case Some(x) => // shouldn't happen
"Could not parse Coursera's response:\n" + x
case None =>
"Could not parse Coursera's response:\n" + respBody
}
val failedSubmitMsg =
s"""|Submission failed.
|There was something wrong while attempting to submit.
|Coursera says:
|$learnerMsg (Status $code)""".stripMargin
s.log.error(failedSubmitMsg)
}
// Failure, Coursera responds with 5xx HTTP status code (server-side failure)
else if (response.is5xx) {
val failedSubmitMsg =
s"""|Submission failed.
|Coursera seems to be unavailable at the moment (Status $code)
|Check https://status.coursera.org/ and try again in a few minutes.
""".stripMargin
s.log.error(failedSubmitMsg)
}
// Failure, Coursera repsonds with an unexpected status code
else {
val failedSubmitMsg =
s"""|Submission failed.
|Coursera replied with an unexpected code (Status $code)
""".stripMargin
s.log.error(failedSubmitMsg)
}
}
// kick it all off, actually make request
postSubmission(json) match {
case Success(resp) => reportCourseraResponse(resp)
case Failure(e) =>
val failedConnectMsg =
s"""|Connection to Coursera failed.
|There was something wrong while attempting to connect to Coursera.
|Check your internet connection.
|${e.toString}""".stripMargin
s.log.error(failedConnectMsg)
}
}
*/
def failSubmit(): Nothing = {
sys.error("Submission failed")
}
/**
* *****************
* DEALING WITH JARS
*/
def encodeBase64(bytes: Array[Byte]): String =
new String(Base64.encodeBase64(bytes))
}
previous-exams/2021-midterm-solutions/m21/project/build.properties deleted 100644 → 0
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sbt.version=1.4.7
previous-exams/2021-midterm-solutions/m21/project/buildSettings.sbt deleted 100644 → 0
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// Used for Coursera submission (StudentPlugin)
// libraryDependencies += "org.scalaj" %% "scalaj-http" % "2.4.2"
// libraryDependencies += "com.typesafe.play" %% "play-json" % "2.7.4"
// Used for Base64 (StudentPlugin)
libraryDependencies += "commons-codec" % "commons-codec" % "1.10"
previous-exams/2021-midterm-solutions/m21/project/plugins.sbt deleted 100644 → 0
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// addSbtPlugin("org.scala-js" % "sbt-scalajs" % "0.6.28")
addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.5.3")
previous-exams/2021-midterm-solutions/m21/src/main/scala/m21/MultiWriterSeqCount.scala deleted 100644 → 0
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package m21
import instrumentation._
import scala.annotation.tailrec
/** Multi-writer, multi-reader data structure containing a pair of integers. */
class MultiWriterSeqCount extends Monitor:
/** Do not directly use this variable, use `generation`, `setGeneration` and
* `compareAndSetGeneration` instead.
*/
protected val myGeneration: AbstractAtomicVariable[Int] = new AtomicVariable(1)
protected def generation: Int = myGeneration.get
protected def setGeneration(newGeneration: Int): Unit =
myGeneration.set(newGeneration)
protected def compareAndSetGeneration(expected: Int, newValue: Int): Boolean =
myGeneration.compareAndSet(expected, newValue)
/** Do not directly use this variable, use `x` and `setX` instead. */
protected var myX: Int = 0
protected def x: Int = myX
protected def setX(newX: Int): Unit =
myX = newX
/** Do not directly use this variable, use `y` and `setY` instead. */
protected var myY: Int = 0
protected def y: Int = myY
protected def setY(newY: Int): Unit =
myY = newY
/** Write new values into this data structure.
* This method is always safe to call.
* The implementation of this method is not allowed to call `synchronized`.
*/
@tailrec
final def write(newX: Int, newY: Int): Unit =
val old = generation
if old % 2 != 1 then
write(newX, newY)
else
if !compareAndSetGeneration(old, old + 1) then
write(newX, newY)
else
setX(newX)
setY(newY)
setGeneration(old + 2)
/** Copy the values previously written into this data structure into a tuple.
* This method is always safe to call.
* The implementation of this method is not allowed to call `synchronized`.
*/
@tailrec
final def copy(): (Int, Int) =
val old = generation
if old % 2 != 1 then
copy()
else
val result = (x, y)
if generation != old then
copy()
else
result
end MultiWriterSeqCount
previous-exams/2021-midterm-solutions/m21/src/main/scala/m21/SeqCount.scala deleted 100644 → 0
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package m21
import instrumentation._
import scala.annotation.tailrec
/** Single-writer, multi-reader data structure containing a pair of integers. */
class SeqCount extends Monitor:
/** Do not directly use this variable, use `generation` and `setGeneration` instead. */
@volatile protected var myGeneration: Int = 1
protected def generation: Int = myGeneration
protected def setGeneration(newGeneration: Int): Unit =
myGeneration = newGeneration
/** Do not directly use this variable, use `x` and `setX` instead. */
protected var myX: Int = 0
protected def x: Int = myX
protected def setX(newX: Int): Unit =
myX = newX
/** Do not directly use this variable, use `y` and `setY` instead. */
protected var myY: Int = 0
protected def y: Int = myY
protected def setY(newY: Int): Unit =
myY = newY
/** Write new values into this data structure.
* This method must only be called from one thread at a time.
*/
final def write(newX: Int, newY: Int): Unit =
setGeneration(generation + 1)
setX(newX)
setY(newY)
setGeneration(generation + 1)
/** Copy the values previously written into this data structure into a tuple.
* This method is always safe to call.
* The implementation of this method is not allowed to call `synchronized`.
*/
@tailrec
final def copy(): (Int, Int) =
val old = generation
if old % 2 != 1 then
copy()
else
val result = (x, y)
if generation != old then
copy()
else
result
end SeqCount