/// <summary>
/// Inits the guard with the action to be performed once
/// disposal takes place.
/// </summary>
/// <param name="item">Encapsulates the locking information.</param>
/// <param name="repository">The repository that issued the lock.</param>
/// <exception cref="ArgumentNullException">If any of the parameters
/// is a null reference.</exception>
public ResourceLockGuard(LockItem item, IResourceLockRepository repository)
{
Ensure.ArgumentNotNull(item, "item");
Ensure.ArgumentNotNull(repository, "repository");
Item = item;
Repository = repository;
}
/// <summary>
/// Inits the guard with the action to be performed once
/// disposal takes place.
/// </summary>
/// <param name="item">Encapsulates the locking information.</param>
/// <param name="repository">The repository that issued the lock.</param>
/// <exception cref="ArgumentNullException">If any of the parameters
/// is a null reference.</exception>
public ResourceLockGuard(LockItem item, IResourceLockRepository repository)
{
Ensure.ArgumentNotNull(item, "item");
Ensure.ArgumentNotNull(repository, "repository");
Item = item;
Repository = repository;
}
/// <summary>
/// Tries to acquire an exclusive write
/// for the resource, and specifies a timeout for the lock. If this operation
/// succeeds, the lock must be released as soon
/// as possible through the <see cref="ReleaseWriteLock"/>
/// method.
/// </summary>
/// <param name="timeout">The timeout of the lock.
/// A value of null requests a lock that doesn't time out.</param>
/// <returns>A lock that corresponds to the request. If the lock was denied, the
/// returned item's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
/// <exception cref="ArgumentOutOfRangeException">In case of a negative
/// timeout.</exception>
public LockItem TryGetWriteLock(TimeSpan?timeout)
{
lock (this)
{
if (HasWriteLock || HasReadLocks)
{
return(LockItem.CreateDenied(ResourceId));
}
activeWriteLock = LockItem.CreateWrite(ResourceId, timeout);
return(activeWriteLock);
}
}
/// <summary>
/// Releases a previously acquired write lock.
/// </summary>
/// <param name="lockId">The <see cref="LockItem.LockId"/>
/// which identifies the lock to be released.</param>
/// <returns>True if a matching lock was found and released.
/// If no lock was found, false.</returns>
public bool ReleaseWriteLock(string lockId)
{
lock (this)
{
if (activeWriteLock != null && activeWriteLock.LockId == lockId)
{
//don't check whether lock has expired - invoking party is happy
activeWriteLock = null;
return(true);
}
return(false);
}
}
/// <summary>
/// Removes expired locks.
/// </summary>
private void Cleanup()
{
cleanUpCounter++;
if (cleanUpCounter % 100 == 0)
{
//TODO audit/log expired locks?
readLocks.RemoveAll(li => li.Expiration.IsExpired());
if (activeWriteLock != null && activeWriteLock.Expiration.IsExpired())
{
activeWriteLock = null;
}
cleanUpCounter = 1;
}
}
/// <summary>
/// Releases a previously acquired lock for a given
/// resource.
/// </summary>
/// <param name="item">The lock to be released.</param>
/// <returns>True if the lock was released. False in case
/// of an unknown (e.g. automatically removed) lock, or if
/// the lock is ignored because it's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
public bool ReleaseLock(LockItem item)
{
switch (item.LockType)
{
case ResourceLockType.Read:
return(ReleaseReadLock(item.ResourceId, item.LockId));
case ResourceLockType.Write:
return(ReleaseWriteLock(item.ResourceId, item.LockId));
case ResourceLockType.Denied:
return(false);
default:
throw new ArgumentOutOfRangeException("Unsupported lock type: " + item.LockType);
}
}
/// <summary>
/// Tries to acquire a shared read lock
/// for the resource, and specifies a timeout for the lock. If this operation
/// succeeds, the lock must be released as soon
/// as possible through the <see cref="ReleaseReadLock"/>
/// method.
/// </summary>
/// <returns>A lock that corresponds to the request. If the lock was denied, the
/// returned item's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
/// <param name="timeout">The timeout of the lock.
/// A null value requests a lock that doesn't time out.</param>
/// <returns>True if the lock was granted.</returns>
/// <exception cref="ArgumentOutOfRangeException">In case of a negative
/// timeout.</exception>
public LockItem TryGetReadLock(TimeSpan?timeout)
{
lock (this)
{
if (HasWriteLock)
{
return(LockItem.CreateDenied(ResourceId));
}
//clean up inactive locks from time to time
Cleanup();
var item = LockItem.CreateRead(ResourceId, timeout);
readLocks.Add(item);
return(item);
}
}
/// <summary>
/// Releases a previously acquired read lock.
/// </summary>
/// <param name="lockId">The <see cref="LockItem.LockId"/>
/// which identifies the lock to be released.</param>
/// <returns>True if a matching lock was found and released.
/// If no lock was found, false.</returns>
public bool ReleaseReadLock(string lockId)
{
lock (this)
{
for (int i = 0; i < readLocks.Count; i++)
{
LockItem lockItem = readLocks[i];
if (lockItem.LockId == lockId)
{
readLocks.RemoveAt(i);
//don't check whether lock has expired - invoking party is happy
return(true);
}
}
return(false);
}
}
/// <summary>
/// Gets a read lock on all parent folders of a given resource, and rolls back the resources
/// if the locking fails.
/// </summary>
/// <param name="repository">The repository that manages locked resources.</param>
/// <param name="resourceId">The resource to be locked.</param>
/// <param name="isWriteLock">Whether to acquire a read or write lock for the resource itself.</param>
/// <param name="parentFolderIds">Ids of the resource's parent folders, which are being locked one
/// by one. The list should be ordered, with the first item being the immediate parent of the locked
/// resource, and the last one the topmost folder to be locked.</param>
/// <returns>A guard which releases the resource and all folders once it is being disposed.</returns>
public static ResourceLockGuard GetResourceChainLock(this IResourceLockRepository repository, string resourceId,
bool isWriteLock, List <string> parentFolderIds)
{
LockItem lockItem = isWriteLock ? repository.TryGetWriteLock(resourceId) : repository.TryGetReadLock(resourceId);
//we couldn't get a lock on the resource itself
if (!lockItem.IsEnabled)
{
return(new ResourceLockGuard(lockItem, repository));
}
//get read locks for all parent folders
List <LockItem> folderLocks = new List <LockItem>();
LockItem folderLock = null;
foreach (string folderId in parentFolderIds)
{
//lock parent folders, one by one for read access (prevents deletion)
folderLock = repository.TryGetReadLock(folderId);
if (!folderLock.IsEnabled)
{
break;
}
folderLocks.Add(folderLock);
}
if (folderLock != null && !folderLock.IsEnabled)
{
//roll back all locks...
repository.ReleaseLock(lockItem);
folderLocks.ForEach(li => repository.ReleaseLock(li));
//...and return a dummy lock
return(new ResourceLockGuard(LockItem.CreateDenied(resourceId), repository));
}
return(new ResourceLockGuard(lockItem, repository)
{
SecondaryLocks = folderLocks
});
}
/// <summary>
/// Gets a guard that can be used with a <c>using</c>
/// statement, which tries to get a read lock and
/// ensures the lock is being released as soon as
/// the using block is being exited. Check the
/// guard's <see cref="ResourceLockGuard.IsLockEnabled"/>
/// property to verify whether the lock was granted
/// or not.
/// </summary>
/// <returns>A guard that handles management of the
/// acquired read lock.</returns>
public ResourceLockGuard GetReadGuard(string resourceId)
{
return(new ResourceLockGuard(LockItem.CreateRead(resourceId, null), this));
}
/// <summary>
/// Removes expired locks.
/// </summary>
private void Cleanup()
{
cleanUpCounter++;
if (cleanUpCounter % 100 == 0)
{
//TODO audit/log expired locks?
readLocks.RemoveAll(li => li.Expiration.IsExpired());
if (activeWriteLock != null && activeWriteLock.Expiration.IsExpired())
{
activeWriteLock = null;
}
cleanUpCounter = 1;
}
}
/// <summary>
/// Releases a previously acquired lock for a given
/// resource.
/// </summary>
/// <param name="item">The lock to be released.</param>
/// <returns>True if the lock was released. False in case
/// of an unknown (e.g. automatically removed) lock, or if
/// the lock is ignored because it's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
public bool ReleaseLock(LockItem item)
{
return true;
}
/// <summary>
/// Tries to acquire an exclusive write lock for the resource
/// which expires after a given while in order not to block
/// the resource indefinitely.
/// If this operation succeeds, the lock must be released as soon
/// as possible through the <see cref="IResourceLockRepository.ReleaseWriteLock"/>
/// method.
/// </summary>
/// <param name="resourceId">Identifies the locked resource.</param>
/// <param name="timeout">The specified expiration timeout from now.
/// Allowed values are null for indefinite locking, or any positive value.</param>
/// <returns>True if the lock was granted.</returns>
/// <exception cref="ArgumentOutOfRangeException">In case of a negative
/// timeout.</exception>sitive value.</param>
/// <returns>True if the lock was granted.</returns>
public LockItem TryGetWriteLock(string resourceId, TimeSpan?timeout)
{
return(LockItem.CreateWrite(resourceId, timeout));
}
/// <summary>
/// Tries to acquire an exclusive write lock for the resource
/// which expires after a given time span in order not to block
/// the resource indefinitely.
/// If this operation succeeds, the lock must be released as soon
/// as possible through the <see cref="IResourceLockRepository.ReleaseReadLock"/>
/// method.
/// </summary>
/// <param name="resourceId">Identifies the locked resource.</param>
/// <param name="timeout">The specified expiration timeout from now.
/// Allowed values are null for indefinite locking, or any positive value.</param>
/// <returns>True if the lock was granted.</returns>
/// <exception cref="ArgumentOutOfRangeException">In case of a negative
/// timeout.</exception>
public LockItem TryGetReadLock(string resourceId, TimeSpan?timeout)
{
return(LockItem.CreateRead(resourceId, timeout));
}
/// <summary>
/// Gets a guard that can be used with a <c>using</c>
/// statement, which tries to get a write lock and
/// ensures the lock is being released as soon as
/// the using block is being exited. Check the
/// guard's <see cref="ResourceLockGuard.IsLockEnabled"/>
/// property to verify whether the lock was granted
/// or not.
/// </summary>
/// <returns>A guard that handles management of the
/// acquired write lock.</returns>
public ResourceLockGuard GetWriteGuard(string resourceId)
{
return(new ResourceLockGuard(LockItem.CreateWrite(resourceId, null), this));
}
/// <summary>
/// Tries to acquire a shared read lock for a given resource
/// which never expires.
/// If this operation succeeds, the lock must be released as soon
/// as possible through the <see cref="IResourceLockRepository.ReleaseReadLock"/>
/// method.
/// </summary>
/// <returns>A <see cref="LockItem"/> instance which represents
/// the acquired lock, if any. If no lock was granted, the
/// returned item's <see cref="LockItem.LockType"/> property
/// returns <see cref="ResourceLockType.Denied"/>.</returns>
public LockItem TryGetReadLock(string resourceId)
{
return(LockItem.CreateRead(resourceId, null));
}
/// <summary>
/// Releases a previously acquired lock for a given
/// resource.
/// </summary>
/// <param name="item">The lock to be released.</param>
/// <returns>True if the lock was released. False in case
/// of an unknown (e.g. automatically removed) lock, or if
/// the lock is ignored because it's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
public bool ReleaseLock(LockItem item)
{
switch (item.LockType)
{
case ResourceLockType.Read:
return ReleaseReadLock(item.ResourceId, item.LockId);
case ResourceLockType.Write:
return ReleaseWriteLock(item.ResourceId, item.LockId);
case ResourceLockType.Denied:
return false;
default:
throw new ArgumentOutOfRangeException("Unsupported lock type: " + item.LockType);
}
}
/// <summary>
/// Tries to acquire an exclusive write lock for a given resource
/// which never expires.
/// If this operation succeeds, the lock must be released as soon
/// as possible through the <see cref="IResourceLockRepository.ReleaseWriteLock"/>
/// method.
/// </summary>
/// <returns>A <see cref="LockItem"/> instance which represents
/// the acquired lock, if any. If no lock was granted, the
/// returned item's <see cref="LockItem.LockType"/> property
/// returns <see cref="ResourceLockType.Denied"/>.</returns>
public LockItem TryGetWriteLock(string resourceId)
{
return(LockItem.CreateWrite(resourceId, null));
}
/// <summary>
/// Tries to acquire an exclusive write
/// for the resource, and specifies a timeout for the lock. If this operation
/// succeeds, the lock must be released as soon
/// as possible through the <see cref="ReleaseWriteLock"/>
/// method.
/// </summary>
/// <param name="timeout">The timeout of the lock.
/// A value of null requests a lock that doesn't time out.</param>
/// <returns>A lock that corresponds to the request. If the lock was denied, the
/// returned item's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
/// <exception cref="ArgumentOutOfRangeException">In case of a negative
/// timeout.</exception>
public LockItem TryGetWriteLock(TimeSpan? timeout)
{
lock (this)
{
if (HasWriteLock || HasReadLocks)
{
return LockItem.CreateDenied(ResourceId);
}
activeWriteLock = LockItem.CreateWrite(ResourceId, timeout);
return activeWriteLock;
}
}
/// <summary>
/// Releases a previously acquired lock for a given
/// resource.
/// </summary>
/// <param name="item">The lock to be released.</param>
/// <returns>True if the lock was released. False in case
/// of an unknown (e.g. automatically removed) lock, or if
/// the lock is ignored because it's <see cref="LockItem.LockType"/>
/// is <see cref="ResourceLockType.Denied"/>.</returns>
public bool ReleaseLock(LockItem item)
{
return(true);
}
/// <summary>
/// Releases a previously acquired write lock.
/// </summary>
/// <param name="lockId">The <see cref="LockItem.LockId"/>
/// which identifies the lock to be released.</param>
/// <returns>True if a matching lock was found and released.
/// If no lock was found, false.</returns>
public bool ReleaseWriteLock(string lockId)
{
lock (this)
{
if(activeWriteLock != null && activeWriteLock.LockId == lockId)
{
//don't check whether lock has expired - invoking party is happy
activeWriteLock = null;
return true;
}
return false;
}
}