Spark2.2-Task序列化源码解析

private def clean(
func: AnyRef,
checkSerializable: Boolean,
cleanTransitively: Boolean,
accessedFields: Map[Class[_], Set[String]]): Unit = {

if (!isClosure(func.getClass)) {
logWarning("Expected a closure; got " + func.getClass.getName)
return
}

// TODO: clean all inner closures first. This requires us to find the inner objects.
// TODO: cache outerClasses / innerClasses / accessedFields

if (func == null) {
return
}

logDebug(s"+++ Cleaning closure $func (${func.getClass.getName}) +++")

// A list of classes that represents closures enclosed in the given one
val innerClasses = getInnerClosureClasses(func)

// A list of enclosing objects and their respective classes, from innermost to outermost
// An outer object at a given index is of type outer class at the same index
val (outerClasses, outerObjects) = getOuterClassesAndObjects(func)

// For logging purposes only
val declaredFields = func.getClass.getDeclaredFields
val declaredMethods = func.getClass.getDeclaredMethods

logDebug(" + declared fields: " + declaredFields.size)
declaredFields.foreach { f => logDebug("     " + f) }
logDebug(" + declared methods: " + declaredMethods.size)
declaredMethods.foreach { m => logDebug("     " + m) }
logDebug(" + inner classes: " + innerClasses.size)
innerClasses.foreach { c => logDebug("     " + c.getName) }
logDebug(" + outer classes: " + outerClasses.size)
outerClasses.foreach { c => logDebug("     " + c.getName) }
logDebug(" + outer objects: " + outerObjects.size)
outerObjects.foreach { o => logDebug("     " + o) }

// Fail fast if we detect return statements in closures
getClassReader(func.getClass).accept(new ReturnStatementFinder(), 0)

// If accessed fields is not populated yet, we assume that
// the closure we are trying to clean is the starting one
if (accessedFields.isEmpty) {
logDebug(s" + populating accessed fields because this is the starting closure")
// Initialize accessed fields with the outer classes first
// This step is needed to associate the fields to the correct classes later
for (cls <- outerClasses) {
accessedFields(cls) = Set[String]()
}
// Populate accessed fields by visiting all fields and methods accessed by this and
// all of its inner closures. If transitive cleaning is enabled, this may recursively
// visits methods that
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belong to other classes in search of transitively referenced fields.
for (cls <- func.getClass :: innerClasses) {
getClassReader(cls).accept(new FieldAccessFinder(accessedFields, cleanTransitively), 0)
}
}

logDebug(s" + fields accessed by starting closure: " + accessedFields.size)
accessedFields.foreach { f => logDebug("     " + f) }

// List of outer (class, object) pairs, ordered from outermost to innermost
// Note that all outer objects but the outermost one (first one in this list) must be closures
var outerPairs: List[(Class[_], AnyRef)] = (outerClasses zip outerObjects).reverse
var parent: AnyRef = null
if (outerPairs.size > 0) {
val (outermostClass, outermostObject) = outerPairs.head
if (isClosure(outermostClass)) {
logDebug(s" + outermost object is a closure, so we clone it: ${outerPairs.head}")
} else if (outermostClass.getName.startsWith("$line")) {
// SPARK-14558: if the outermost object is a REPL line object, we should clone and clean it
// as it may carray a lot of unnecessary information, e.g. hadoop conf, spark conf, etc.
logDebug(s" + outermost object is a REPL line object, so we clone it: ${outerPairs.head}")
} else {
// The closure is ultimately nested inside a class; keep the object of that
// class without cloning it since we don't want to clone the user's objects.
// Note that we still need to keep around the outermost object itself because
// we need it to clone its child closure later (see below).
logDebug(" + outermost object is not a closure or REPL line object, so do not clone it: " +
outerPairs.head)
parent = outermostObject // e.g. SparkContext
outerPairs = outerPairs.tail
}
} else {
logDebug(" + there are no enclosing objects!")
}

// Clone the closure objects themselves, nulling out any fields that are not
// used in the closure we're working on or any of its inner closures.
for ((cls, obj) <- outerPairs) {
logDebug(s" + cloning the object $obj of class ${cls.getName}")
// We null out these unused references by cloning each object and then filling in all
// required fields from the original object. We need the parent here because the Java
// language specification requires the first constructor parameter of any closure to be
// its enclosing object.
val clone = instantiateClass(cls, parent)
for (fieldName <- accessedFields(cls)) {
val field = cls.getDeclaredField(fieldName)
field.setAccessible(true)
val value = field.get(obj)
field.set(clone, value)
}
// If transitive cleaning is enabled, we recursively clean any enclosing closure using
// the already populated accessed fields map of the starting closure
if (cleanTransitively && isClosure(clone.getClass)) {
logDebug(s" + cleaning cloned closure $clone recursively (${cls.getName})")
// No need to check serializable here for the outer closures because we're
// only interested in the serializability of the starting closure
clean(clone, checkSerializable = false, cleanTransitively, accessedFields)
}
parent = clone
}

// Update the parent pointer ($outer) of this closure
if (parent != null) {
val field = func.getClass.getDeclaredField("$outer")
field.setAccessible(true)
// If the starting closure doesn't actually need our enclosing object, then just null it out
if (accessedFields.contains(func.getClass) &&
!accessedFields(func.getClass).contains("$outer")) {
logDebug(s" + the starting closure doesn't actually need $parent, so we null it out")
field.set(func, null)
} else {
// Update this closure's parent pointer to point to our enclosing object,
// which could either be a cloned closure or the original user object
field.set(func, parent)
}
}

logDebug(s" +++ closure $func (${func.getClass.getName}) is now cleaned +++")

if (checkSerializable) {
ensureSerializable(func)
}
}