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Reduce the memory consumption slightly
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In exchange, now, removal is linear in the size of number of
registered handlers instead of being amortized constant.
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@dkhalanskyjb
dkhalanskyjb committed Apr 11, 2024
1 parent 9b9148c commit 03a42b9
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Showing 3 changed files with 65 additions and 74 deletions.
55 changes: 36 additions & 19 deletions kotlinx-coroutines-core/common/src/JobSupport.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -357,7 +357,7 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren

private fun notifyHandlers(list: NodeList, permissionBitmask: Byte, cause: Throwable?, predicate: (JobNode) -> Boolean) {
var exception: Throwable? = null
list.forEach(forbidBitmask = permissionBitmask) { node ->
list.forEach(forbidBitmask = permissionBitmask) { node, _, _ ->
if (node is JobNode && predicate(node)) {
try {
node.invoke(cause)
Expand Down Expand Up @@ -558,7 +558,10 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren

private fun promoteSingleToNodeList(state: JobNode) {
// try to promote it to list (SINGLE+ state)
_state.compareAndSet(state, state.attachToList(NodeList()))
val list = NodeList()
val address = list.addLastWithoutModifying(state, permissionsBitmask = 0)
assert { address == 0L }
_state.compareAndSet(state, list)
}

public final override suspend fun join() {
Expand Down Expand Up @@ -621,7 +624,7 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren
}
is Incomplete -> { // may have a list of completion handlers
// remove node from the list if there is a list
if (state.list != null) node.remove()
state.list?.remove(node)
return
}
else -> return // it is complete and does not have any completion handlers
Expand Down Expand Up @@ -932,39 +935,52 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren
private val Any?.exceptionOrNull: Throwable?
get() = (this as? CompletedExceptionally)?.cause

private fun shouldWaitForChildren(state: Finishing, proposedUpdate: Any?, suggestedStart: ChildHandleNode? = null): Boolean {
private fun shouldWaitForChildren(
state: Finishing,
proposedUpdate: Any?,
suggestedStartSegment: LockFreeLinkedListSegment? = null,
suggestedStartIndex: Int? = null
): Boolean {
val list = state.list
fun tryFindChildren(suggestedStart: ChildHandleNode?, closeList: Boolean): Boolean {
var startAfter: ChildHandleNode? = suggestedStart
fun tryFindChildren(
closeList: Boolean,
suggestedStartSegment: LockFreeLinkedListSegment? = null,
suggestedStartIndex: Int? = null,
): Boolean {
var startSegment = suggestedStartSegment
var startIndex = suggestedStartIndex
while (true) {
val child = run {
list.forEach(forbidBitmask = if (closeList) LIST_CHILD_PERMISSION else 0, startAfter = startAfter) {
if (it is ChildHandleNode) return@run it
list.forEach(forbidBitmask = if (closeList) LIST_CHILD_PERMISSION else 0, startInSegment = startSegment, startAfterIndex = startIndex) { node, segment, indexInSegment ->
if (node is ChildHandleNode) {
startSegment = segment
startIndex = indexInSegment
return@run node
}
}
null
} ?: break
val handle = child.childJob.invokeOnCompletion(
invokeImmediately = false,
handler = ChildCompletion(this, state, child, proposedUpdate)
handler = ChildCompletion(this, state, startSegment!!, startIndex!!, proposedUpdate)
)
if (handle !== NonDisposableHandle) return true // child is not complete and we've started waiting for it
startAfter = child
}
return false
}
// Look for children that are currently in the list after the suggested start node.
if (tryFindChildren(suggestedStart = suggestedStart, closeList = false)) return true
if (tryFindChildren(suggestedStartSegment = suggestedStartSegment, suggestedStartIndex = suggestedStartIndex, closeList = false)) return true
// We didn't find anyone in the list after the suggested start node. Let's check the beginning now.
if (suggestedStart != null && tryFindChildren(suggestedStart = null, closeList = false)) return true
if (suggestedStartSegment != null && tryFindChildren(closeList = false)) return true
// Now we know that, at the moment this function started, there were no more children.
// We can close the list for the new children, and if we still don't find any, we can be sure there are none.
return tryFindChildren(suggestedStart = null, closeList = true)
return tryFindChildren(closeList = true)
}

// ## IMPORTANT INVARIANT: Only one thread can be concurrently invoking this method.
private fun continueCompleting(state: Finishing, lastChild: ChildHandleNode, proposedUpdate: Any?) {
private fun continueCompleting(state: Finishing, proposedUpdate: Any?, lastSegment: LockFreeLinkedListSegment, lastIndexInSegment: Int) {
assert { this.state === state } // consistency check -- it cannot change while we are waiting for children
if (shouldWaitForChildren(state, proposedUpdate, suggestedStart = lastChild)) return // waiting for the next child
if (shouldWaitForChildren(state, proposedUpdate, suggestedStartSegment = lastSegment, suggestedStartIndex = lastIndexInSegment)) return // waiting for the next child
// no more children, now we are sure; try to update the state
val finalState = finalizeFinishingState(state, proposedUpdate)
afterCompletion(finalState)
Expand All @@ -974,7 +990,7 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren
when (val state = this@JobSupport.state) {
is ChildHandleNode -> yield(state.childJob)
is Incomplete -> state.list?.let { list ->
list.forEach { if (it is ChildHandleNode) yield(it.childJob) }
list.forEach { it, _, _ -> if (it is ChildHandleNode) yield(it.childJob) }
}
}
}
Expand Down Expand Up @@ -1232,11 +1248,12 @@ public open class JobSupport constructor(active: Boolean) : Job, ChildJob, Paren
private class ChildCompletion(
private val parent: JobSupport,
private val state: Finishing,
private val child: ChildHandleNode,
private val segment: LockFreeLinkedListSegment,
private val indexInSegment: Int,
private val proposedUpdate: Any?
) : JobNode() {
override fun invoke(cause: Throwable?) {
parent.continueCompleting(state, child, proposedUpdate)
parent.continueCompleting(state, proposedUpdate, lastSegment = segment, lastIndexInSegment = indexInSegment)
}
override val onCancelling: Boolean get() = false
}
Expand Down Expand Up @@ -1477,7 +1494,7 @@ internal class NodeList : LockFreeLinkedListHead(), Incomplete {
append(state)
append("}[")
var first = true
this@NodeList.forEach { node ->
this@NodeList.forEach { node, _, _ ->
if (node is JobNode) {
if (first) first = false else append(", ")
append(node)
Expand Down
76 changes: 25 additions & 51 deletions kotlinx-coroutines-core/common/src/internal/LockFreeLinkedList.common.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,38 +11,10 @@ import kotlin.jvm.*
/** @suppress **This is unstable API and it is subject to change.** */
internal open class LockFreeLinkedListNode {
/**
* Try putting this node into a list.
*
* Returns:
* - The new head of the list if the operation succeeded.
* - The head of the list if someone else concurrently added this node to the list,
* but no other modifications to the list were made.
*/
fun attachToList(head: LockFreeLinkedListHead): LockFreeLinkedListHead {
val newAddress = head.addLastWithoutModifying(this, permissionsBitmask = 0)
assert { newAddress != null }
return if (_address.compareAndSet(null, newAddress)) {
head
} else {
_address.value!!.segment.head
}
}

/**
* Remove this node from the list.
* The default value of 0 means that either the node is not in any list or [LockFreeLinkedListHead.addLast] wasn't
* yet called on it.
*/
open fun remove() {
_address.value?.let {
val segment = it.segment
segment.clearSlot(it.index)
}
}

private val _address = atomic<Address?>(null)

val address: Address get() = _address.value!!

internal fun trySetAddress(address: Address) = this._address.compareAndSet(null, address)
var address: Long = 0
}

/** @suppress **This is unstable API and it is subject to change.** */
Expand All @@ -66,13 +38,13 @@ internal open class LockFreeLinkedListHead: LockFreeLinkedListSegment(
*/
inline fun forEach(
forbidBitmask: Byte = 0,
startAfter: LockFreeLinkedListNode? = null,
block: (LockFreeLinkedListNode) -> Unit
startInSegment: LockFreeLinkedListSegment? = null,
startAfterIndex: Int? = null,
block: (LockFreeLinkedListNode, LockFreeLinkedListSegment, Int) -> Unit
) {
forbiddenBits.update { it or forbidBitmask.toInt() }
val startAddress = startAfter?.address
var segment: LockFreeLinkedListSegment? = startAddress?.segment ?: head
var startIndex: Int = startAddress?.index?.let { it + 1 } ?: 0
var segment: LockFreeLinkedListSegment? = startInSegment ?: this
var startIndex: Int = startAfterIndex?.let { it + 1 } ?: 0
while (segment != null) {
segment.forEach(forbidBitmask = forbidBitmask, startIndex = startIndex, block = block)
segment = segment.next
Expand All @@ -85,17 +57,15 @@ internal open class LockFreeLinkedListHead: LockFreeLinkedListSegment(
* and then sets the [node]'s address to the new address.
*/
fun addLast(node: LockFreeLinkedListNode, permissionsBitmask: Byte): Boolean {
val address = addLastWithoutModifying(node, permissionsBitmask) ?: return false
val success = node.trySetAddress(address)
assert { success }
node.address = addLastWithoutModifying(node, permissionsBitmask) ?: return false
return true
}

/**
* Adds the [node] to the end of the list if every bit in [permissionsBitmask] is still allowed in the list.
* As opposed to [addLast], doesn't modify the [node]'s address.
*/
fun addLastWithoutModifying(node: LockFreeLinkedListNode, permissionsBitmask: Byte): Address? {
fun addLastWithoutModifying(node: LockFreeLinkedListNode, permissionsBitmask: Byte): Long? {
/** First, avoid modifying the list at all if it was already closed for elements like ours. */
if (permissionsBitmask and forbiddenBits.value.toByte() != 0.toByte()) return null
/** Obtain the place from which the desired segment will certainly be reachable. */
Expand All @@ -115,13 +85,21 @@ internal open class LockFreeLinkedListHead: LockFreeLinkedListSegment(
* to observe the new segment and either break the cell where [node] wants to arrive or process the [node].
* In any case, we have linearizable behavior. */
return if (segment.tryAdd(node, permissionsBitmask = permissionsBitmask, indexInSegment = indexInSegment)) {
Address(segment, indexInSegment)
index
} else {
null
}
}

override val head: LockFreeLinkedListHead get() = this
fun remove(node: LockFreeLinkedListNode) {
val address = node.address
val id = address / SEGMENT_SIZE
var segment: LockFreeLinkedListSegment = this
while (segment.id < id) { segment = segment.next!! }
if (segment.id == id) {
segment.clearSlot((address % SEGMENT_SIZE).toInt(), node)
}
}
}

internal open class LockFreeLinkedListSegment(
Expand All @@ -135,15 +113,15 @@ internal open class LockFreeLinkedListSegment(

override val numberOfSlots: Int get() = SEGMENT_SIZE

fun clearSlot(index: Int) {
cells[index].value = null
onSlotCleaned()
fun clearSlot(index: Int, node: LockFreeLinkedListNode) {
if (cells[index].compareAndSet(node, null))
onSlotCleaned()
}

inline fun forEach(forbidBitmask: Byte, startIndex: Int, block: (LockFreeLinkedListNode) -> Unit) {
inline fun forEach(forbidBitmask: Byte, startIndex: Int, block: (LockFreeLinkedListNode, LockFreeLinkedListSegment, Int) -> Unit) {
for (i in startIndex until SEGMENT_SIZE) {
val node = breakCellOrGetValue(forbidBitmask, i)
if (node != null) block(node)
if (node != null) block(node, this, i)
}
}

Expand Down Expand Up @@ -183,12 +161,8 @@ internal open class LockFreeLinkedListSegment(
override fun onCancellation(index: Int, cause: Throwable?, context: CoroutineContext) {
throw UnsupportedOperationException("Cancellation is not supported on LockFreeLinkedList")
}

open val head: LockFreeLinkedListHead get() = prev!!.head
}

internal class Address(@JvmField val segment: LockFreeLinkedListSegment, @JvmField val index: Int)

private fun createSegment(id: Long, prev: LockFreeLinkedListSegment): LockFreeLinkedListSegment =
LockFreeLinkedListSegment(
id = id,
Expand Down
8 changes: 4 additions & 4 deletions kotlinx-coroutines-core/jvm/test/MemoryFootprintTest.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,10 @@ class MemoryFootprintTest : TestBase(true) {

@Test
fun testJobSize() {
assertTotalSize(jobWithChildren(1), 112)
assertTotalSize(jobWithChildren(2), 336) // originally: 192
assertTotalSize(jobWithChildren(3), 416) // originally: 248
assertTotalSize(jobWithChildren(4), 496) // originally: 304
assertTotalSize(jobWithChildren(1), 120) // originally: 112
assertTotalSize(jobWithChildren(2), 304) // originally: 192
assertTotalSize(jobWithChildren(3), 368) // originally: 248
assertTotalSize(jobWithChildren(4), 432) // originally: 304
}

private fun jobWithChildren(numberOfChildren: Int): Job {
Expand Down

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