public void Dispose()
{
if (_lockSource.TryRemoveFromQueue())
{
_lockSource = null;
}
}
public Task <IAsyncReaderWriterLockToken> WriterLockAsync(CancellationToken cancellationToken = default(CancellationToken), ReentrancyToken reentrancyToken = default(ReentrancyToken))
{
TaskUtilities.AssertIsOnBackgroundThread();
var task = ReentrantOrCanceled(true, cancellationToken, reentrancyToken);
if (task != null)
{
return(task);
}
var source = new LockSource(this, true);
_queue.AddWriter(source, out var isFirstWriter);
if (isFirstWriter)
{
source.Release();
}
else
{
source.RegisterCancellation(cancellationToken);
}
return(source.Task);
}
/// <summary>
/// Adds a reader item
/// </summary>
/// <remarks>
/// 1. R−→R−→R ―► R−→R−→R−→R
/// ↑ ↑
/// _tail _tail
///
///
/// 2. _wTail _wTail
/// ↓ ↓
/// R−→R−→W ―► R−→R−→W−→R
/// ↑ ↑
/// _tail _tail
///
///
/// 3. _wTail _wTail
/// ↓ ↓
/// R−→W−→W−→R ―► R−→W−→W−→R−→R
/// ↑ ↑
/// _tail _tail
/// </remarks>
/// <param name="item"></param>
/// <param name="isAddedAfterWriter"></param>
public void AddReader(LockSource item, out bool isAddedAfterWriter)
{
lock (this) {
UpdateTail(item);
isAddedAfterWriter = _wTail != null;
}
}
private LockSource[] FilterAndCopyToArray(LockSource start)
{
var count = 0;
var item = start;
while (item != null)
{
if (ReaderCanBeReleased(item))
{
count++;
}
item = item.Next;
}
var items = new LockSource[count];
count = 0;
item = start;
while (item != null)
{
if (ReaderCanBeReleased(item))
{
items[count] = item;
count++;
}
item = item.Next;
}
return(items);
}
private void Remove(LockSource lockSource)
{
var sourcesToRelease = _queue.Remove(lockSource);
foreach (var source in sourcesToRelease)
{
source.Release();
}
}
private bool ReaderCanBeReleased(LockSource source)
{
var erlSource = source as ExclusiveReaderLockSource;
var previousErlSource = source.Previous as ExclusiveReaderLockSource;
return(erlSource == null ||
previousErlSource == null ||
erlSource.ExclusiveReaderLock != previousErlSource.ExclusiveReaderLock);
}
private void UpdateTail(LockSource item)
{
var tail = Interlocked.Exchange(ref _tail, item);
if (tail == null)
{
Interlocked.Exchange(ref _head, item);
}
else
{
Link(tail, item);
}
}
private static void Unlink(LockSource item)
{
if (item.Next != null)
{
Interlocked.Exchange(ref item.Next.Previous, item.Previous);
}
if (item.Previous != null)
{
Interlocked.Exchange(ref item.Previous.Next, item.Next);
}
Interlocked.Exchange(ref item.Next, null);
Interlocked.Exchange(ref item.Previous, null);
}
/// <summary>
/// Adds a writer item
/// </summary>
/// <remarks>
/// 1. _wTail
/// ↓
/// R−→R−→R ―► R−→R−→R−→W
/// ↑ ↑
/// _tail _tail
///
///
/// 2. _wTail _wTail
/// ↓ ↓
/// R−→R−→W ―► R−→R−→W−→W
/// ↑ ↑
/// _tail _tail
///
///
/// 3. _wTail _wTail
/// ↓ ↓
/// R−→W−→W−→R ―► R−→W−→W−→W−→R
/// ↑ ↑
/// _tail _tail
/// </remarks>
/// <param name="item"></param>
/// <param name="isFirstWriter"></param>
public void AddWriter(LockSource item, out bool isFirstWriter)
{
lock (this) {
var wTail = Interlocked.Exchange(ref _wTail, item);
// Case 1. No writers in the queue. Update _wTail and the _tail
// Case 2. No readers in front of a writer, _tail and _wTail point at the same item. Update _wTail.Next, _tail and _wTail
if (wTail == null || wTail == _tail)
{
UpdateTail(item);
}
else
{
Link(item, wTail.Next);
Link(wTail, item);
}
isFirstWriter = _head == item;
}
}
public LockSource[] Remove(LockSource item)
{
lock (this) {
var next = item.Next;
var oldHead = Interlocked.CompareExchange(ref _head, next, item);
var previous = item.Previous;
Interlocked.CompareExchange(ref _tail, previous, item);
Interlocked.CompareExchange(ref _wTail, previous != null && previous.IsWriter ? previous : null, item);
var erLock = (item as ExclusiveReaderLockSource)?.ExclusiveReaderLock;
if (erLock != null)
{
var previousErlSource = previous as ExclusiveReaderLockSource;
Interlocked.CompareExchange(ref erLock.Tail, previousErlSource?.ExclusiveReaderLock == erLock ? previousErlSource : null, item);
}
Unlink(item);
if (_head == null)
{
return(new LockSource[0]);
}
if (_head.IsWriter && item == oldHead)
{
return(new[] { _head });
}
if (_wTail == null && next != null)
{
return(FilterAndCopyToArray(next));
}
if (erLock != null)
{
return(FindFirstExclusiveReader(erLock));
}
return(new LockSource[0]);
}
}
/// <summary>
/// Adds a writer item
/// </summary>
/// <remarks>
/// 1. _wTail
/// ↓
/// R−→R−→R ―► R−→R−→R−→W
/// ↑ ↑
/// _tail _tail
///
///
/// 2. _wTail _wTail
/// ↓ ↓
/// R−→R−→W ―► R−→R−→W−→W
/// ↑ ↑
/// _tail _tail
///
///
/// 3. _wTail _wTail
/// ↓ ↓
/// R−→W−→W−→R ―► R−→W−→W−→W−→R
/// ↑ ↑
/// _tail _tail
/// </remarks>
/// <param name="item"></param>
/// <param name="isFirstWriter"></param>
public void AddWriter(LockSource item, out bool isFirstWriter) {
lock (this) {
var wTail = Interlocked.Exchange(ref _wTail, item);
// Case 1. No writers in the queue. Update _wTail and the _tail
// Case 2. No readers in front of a writer, _tail and _wTail point at the same item. Update _wTail.Next, _tail and _wTail
if (wTail == null || wTail == _tail) {
UpdateTail(item);
} else {
Link(item, wTail.Next);
Link(wTail, item);
}
isFirstWriter = _head == item;
}
}
private static void Link(LockSource previous, LockSource next)
{
Interlocked.Exchange(ref previous.Next, next);
Interlocked.Exchange(ref next.Previous, previous);
}
/// <summary>
/// Adds a reader item
/// </summary>
/// <remarks>
/// 1. R−→R−→R ―► R−→R−→R−→R
/// ↑ ↑
/// _tail _tail
///
///
/// 2. _wTail _wTail
/// ↓ ↓
/// R−→R−→W ―► R−→R−→W−→R
/// ↑ ↑
/// _tail _tail
///
///
/// 3. _wTail _wTail
/// ↓ ↓
/// R−→W−→W−→R ―► R−→W−→W−→R−→R
/// ↑ ↑
/// _tail _tail
/// </remarks>
/// <param name="item"></param>
/// <param name="isAddedAfterWriter"></param>
public void AddReader(LockSource item, out bool isAddedAfterWriter) {
lock (this) {
UpdateTail(item);
isAddedAfterWriter = _wTail != null;
}
}
private static void Unlink(LockSource item) {
if (item.Next != null) {
Interlocked.Exchange(ref item.Next.Previous, item.Previous);
}
if (item.Previous != null) {
Interlocked.Exchange(ref item.Previous.Next, item.Next);
}
Interlocked.Exchange(ref item.Next, null);
Interlocked.Exchange(ref item.Previous, null);
}
private static void Link(LockSource previous, LockSource next) {
Interlocked.Exchange(ref previous.Next, next);
Interlocked.Exchange(ref next.Previous, previous);
}
private bool ReaderCanBeReleased(LockSource source) {
var erlSource = source as ExclusiveReaderLockSource;
var previousErlSource = source.Previous as ExclusiveReaderLockSource;
return erlSource == null
|| previousErlSource == null
|| erlSource.ExclusiveReaderLock != previousErlSource.ExclusiveReaderLock;
}
private LockSource[] FilterAndCopyToArray(LockSource start) {
var count = 0;
var item = start;
while (item != null) {
if (ReaderCanBeReleased(item)) {
count++;
}
item = item.Next;
}
var items = new LockSource[count];
count = 0;
item = start;
while (item != null) {
if (ReaderCanBeReleased(item)) {
items[count] = item;
count++;
}
item = item.Next;
}
return items;
}
private void UpdateTail(LockSource item) {
var tail = Interlocked.Exchange(ref _tail, item);
if (tail == null) {
Interlocked.Exchange(ref _head, item);
} else {
Link(tail, item);
}
}
public LockSource[] Remove(LockSource item) {
lock (this) {
var next = item.Next;
var oldHead = Interlocked.CompareExchange(ref _head, next, item);
var previous = item.Previous;
Interlocked.CompareExchange(ref _tail, previous, item);
Interlocked.CompareExchange(ref _wTail, previous != null && previous.IsWriter ? previous : null, item);
var erLock = (item as ExclusiveReaderLockSource)?.ExclusiveReaderLock;
if (erLock != null) {
var previousErlSource = previous as ExclusiveReaderLockSource;
Interlocked.CompareExchange(ref erLock.Tail, previousErlSource?.ExclusiveReaderLock == erLock ? previousErlSource : null, item);
}
Unlink(item);
if (_head == null) {
return new LockSource[0];
}
if (_head.IsWriter && item == oldHead) {
return new[] { _head };
}
if (_wTail == null && next != null) {
return FilterAndCopyToArray(next);
}
if (erLock != null) {
return FindFirstExclusiveReader(erLock);
}
return new LockSource[0];
}
}
public void Dispose() {
if (_lockSource.TryRemoveFromQueue()) {
_lockSource = null;
}
}
public Token(LockSource lockSource)
{
_lockSource = lockSource;
Reentrancy = LockTokenFactory.Create(lockSource);
}
public Token(LockSource lockSource) {
_lockSource = lockSource;
Reentrancy = LockTokenFactory.Create(lockSource);
}
