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package kotlinx.atomicfu.locks
import platform.posix.*
import interop.*
import kotlinx.cinterop.*
import kotlin.native.concurrent.*
import kotlin.native.internal.NativePtr
import kotlinx.atomicfu.locks.SynchronizedObject.Status.*
public actual open class SynchronizedObject {
protected val lock = AtomicReference(LockState(UNLOCKED, 0, 0))
public fun lock() {
val currentThreadId = pthread_self()!!
while (true) {
val state = lock.value
when (state.status) {
UNLOCKED -> {
val thinLock = LockState(THIN, 1, 0, currentThreadId)
if (lock.compareAndSet(state, thinLock))
return
}
THIN -> {
if (currentThreadId == state.ownerThreadId) {
// reentrant lock
val thinNested = LockState(THIN, state.nestedLocks + 1, state.waiters, currentThreadId)
if (lock.compareAndSet(state, thinNested))
return
} else {
// another thread is trying to take this lock -> allocate native mutex
val mutex = mutexPool.allocate()
mutex.lock()
val fatLock = LockState(FAT, state.nestedLocks, state.waiters + 1, state.ownerThreadId, mutex)
if (lock.compareAndSet(state, fatLock)) {
//block the current thread waiting for the owner thread to release the permit
mutex.lock()
tryLockAfterResume(currentThreadId)
return
} else {
// return permit taken for the owner thread and release mutex back to the pool
mutex.unlock()
mutexPool.release(mutex)
}
}
}
FAT -> {
if (currentThreadId == state.ownerThreadId) {
// reentrant lock
val nestedFatLock = LockState(FAT, state.nestedLocks + 1, state.waiters, state.ownerThreadId, state.mutex)
if (lock.compareAndSet(state, nestedFatLock)) return
} else if (state.ownerThreadId != null) {
val fatLock = LockState(FAT, state.nestedLocks, state.waiters + 1, state.ownerThreadId, state.mutex)
if (lock.compareAndSet(state, fatLock)) {
fatLock.mutex!!.lock()
tryLockAfterResume(currentThreadId)
return
}
}
}
}
}
}
public fun tryLock(): Boolean {
val currentThreadId = pthread_self()!!
while (true) {
val state = lock.value
if (state.status == UNLOCKED) {
val thinLock = LockState(THIN, 1, 0, currentThreadId)
if (lock.compareAndSet(state, thinLock))
return true
} else {
if (currentThreadId == state.ownerThreadId) {
val nestedLock = LockState(state.status, state.nestedLocks + 1, state.waiters, currentThreadId, state.mutex)
if (lock.compareAndSet(state, nestedLock))
return true
} else {
return false
}
}
}
}
public fun unlock() {
val currentThreadId = pthread_self()!!
while (true) {
val state = lock.value
require(currentThreadId == state.ownerThreadId) { "Thin lock may be only released by the owner thread, expected: ${state.ownerThreadId}, real: $currentThreadId" }
when (state.status) {
THIN -> {
// nested unlock
if (state.nestedLocks == 1) {
val unlocked = LockState(UNLOCKED, 0, 0)
if (lock.compareAndSet(state, unlocked))
return
} else {
val releasedNestedLock =
LockState(THIN, state.nestedLocks - 1, state.waiters, state.ownerThreadId)
if (lock.compareAndSet(state, releasedNestedLock))
return
}
}
FAT -> {
if (state.nestedLocks == 1) {
// last nested unlock -> release completely, resume some waiter
val releasedLock = LockState(FAT, 0, state.waiters - 1, null, state.mutex)
if (lock.compareAndSet(state, releasedLock)) {
releasedLock.mutex!!.unlock()
return
}
} else {
// lock is still owned by the current thread
val releasedLock =
LockState(FAT, state.nestedLocks - 1, state.waiters, state.ownerThreadId, state.mutex)
if (lock.compareAndSet(state, releasedLock))
return
}
}
else -> error("It is not possible to unlock the mutex that is not obtained")
}
}
}
private fun tryLockAfterResume(threadId: pthread_t) {
while (true) {
val state = lock.value
val newState = if (state.waiters == 0) // deflate
LockState(THIN, 1, 0, threadId)
else
LockState(FAT, 1, state.waiters, threadId, state.mutex)
if (lock.compareAndSet(state, newState)) {
if (state.waiters == 0) {
state.mutex!!.unlock()
mutexPool.release(state.mutex)
}
return
}
}
}
protected class LockState(
val status: Status,
val nestedLocks: Int,
val waiters: Int,
val ownerThreadId: pthread_t? = null,
val mutex: CPointer<mutex_node_t>? = null
) {
init { freeze() }
}
protected enum class Status { UNLOCKED, THIN, FAT }
private fun CPointer<mutex_node_t>.lock() = lock(this.pointed.mutex)
private fun CPointer<mutex_node_t>.unlock() = unlock(this.pointed.mutex)
}
public actual fun reentrantLock() = ReentrantLock()
public actual typealias ReentrantLock = SynchronizedObject
public actual inline fun <T> ReentrantLock.withLock(block: () -> T): T {
lock()
try {
return block()
} finally {
unlock()
}
}
public actual inline fun <T> synchronized(lock: SynchronizedObject, block: () -> T): T {
lock.lock()
try {
return block()
} finally {
lock.unlock()
}
}
private const val INITIAL_POOL_CAPACITY = 64
@SharedImmutable
private val mutexPool by lazy { MutexPool(INITIAL_POOL_CAPACITY) }
class MutexPool(capacity: Int) {
private val top = AtomicNativePtr(NativePtr.NULL)
private val mutexes = nativeHeap.allocArray<mutex_node_t>(capacity) { mutex_node_init(ptr) }
init {
for (i in 0 until capacity) {
release(interpretCPointer<mutex_node_t>(mutexes.rawValue.plus(i * mutex_node_t.size))!!)
}
}
private fun allocMutexNode() = nativeHeap.alloc<mutex_node_t> { mutex_node_init(ptr) }.ptr
fun allocate(): CPointer<mutex_node_t> = pop() ?: allocMutexNode()
fun release(mutexNode: CPointer<mutex_node_t>) {
while (true) {
val oldTop = interpretCPointer<mutex_node_t>(top.value)
mutexNode.pointed.next = oldTop
if (top.compareAndSet(oldTop.rawValue, mutexNode.rawValue))
return
}
}
private fun pop(): CPointer<mutex_node_t>? {
while (true) {
val oldTop = interpretCPointer<mutex_node_t>(top.value)
if (oldTop.rawValue === NativePtr.NULL)
return null
val newHead = oldTop!!.pointed.next
if (top.compareAndSet(oldTop.rawValue, newHead.rawValue))
return oldTop
}
}
}
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