org.apache.nifi.controller.repository.claim

Interface ResourceClaimManager

public interface ResourceClaimManager

Responsible for managing all ResourceClaims that are used in the application

Method Summary

Methods

Modifier and Type	Method and Description
int	decrementClaimantCount(ResourceClaim claim) Decreases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count
void	drainDestructableClaims(Collection<ResourceClaim> destination, int maxElements) Drains up to maxElements Content Claims from the internal queue of destructable content claims to the given destination so that they can be destroyed.
void	drainDestructableClaims(Collection<ResourceClaim> destination, int maxElements, long timeout, TimeUnit unit) Drains up to maxElements Content Claims from the internal queue of destructable content claims to the given destination so that they can be destroyed.
int	getClaimantCount(ResourceClaim claim)
int	incrementClaimantCount(ResourceClaim claim) Increases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count
int	incrementClaimantCount(ResourceClaim claim, boolean newClaim) Increases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count.
void	markDestructable(ResourceClaim claim) Indicates that the given ResourceClaim can now be destroyed by the appropriate Content Repository.
ResourceClaim	newResourceClaim(String container, String section, String id, boolean lossTolerant) Creates a new Resource Claim with the given id, container, section, and loss tolerance.
void	purge() Clears the manager's memory of any and all ResourceClaims that it knows about

Method Detail

newResourceClaim

ResourceClaim newResourceClaim(String container,
                             String section,
                             String id,
                             boolean lossTolerant)

Creates a new Resource Claim with the given id, container, section, and loss tolerance.

Parameters:

id - of claim

container - of claim

section - of claim

lossTolerant - of claim

Returns:

new claim

getClaimantCount

int getClaimantCount(ResourceClaim claim)

Parameters:

claim - to obtain reference count for

Returns:

the number of FlowFiles that hold a claim to a particular piece of FlowFile content

decrementClaimantCount

int decrementClaimantCount(ResourceClaim claim)

Decreases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count

Parameters:

claim - to decrement claimants on

Returns:

new claimaint count

incrementClaimantCount

int incrementClaimantCount(ResourceClaim claim)

Increases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count

Parameters:

claim - to increment claims on

Returns:

new claimant count

incrementClaimantCount

int incrementClaimantCount(ResourceClaim claim,
                         boolean newClaim)

Increases by 1 the count of how many FlowFiles hold a claim to a particular piece of FlowFile content and returns the new count. If it is known that the Content Claim whose count is being incremented is a newly created ResourceClaim, this method should be called with a value of true as the second argument, as it may allow the manager to optimize its tasks, knowing that the Content Claim cannot be referenced by any other component

Parameters:

claim - to increment

newClaim - provides a hint that no other process can have access to this claim right now

Returns:

new claim count

markDestructable

void markDestructable(ResourceClaim claim)

Indicates that the given ResourceClaim can now be destroyed by the appropriate Content Repository. This should be done only after it is guaranteed that the FlowFile Repository has been synchronized with its underlying storage component. This way, we avoid the following sequence of events:

• FlowFile Repository is updated to indicate that FlowFile F no longer depends on ResourceClaim C
• ResourceClaim C is no longer needed and is destroyed
• The Operating System crashes or there is a power failure
• Upon restart, the FlowFile Repository was not synchronized with its underlying storage mechanism and as such indicates that FlowFile F needs ResourceClaim C.
• Since ResourceClaim C has already been destroyed, it is inaccessible, and FlowFile F's Content is not found, so the FlowFile is removed, resulting in data loss.

Using this method of marking the ResourceClaim as destructable only when the FlowFile repository has been synced with the underlying storage mechanism, we can ensure that on restart, we will not point to this unneeded claim. As such, it is now safe to destroy the contents.

Parameters:

claim - to mark as now destructable

drainDestructableClaims

void drainDestructableClaims(Collection<ResourceClaim> destination,
                           int maxElements)

Drains up to maxElements Content Claims from the internal queue of destructable content claims to the given destination so that they can be destroyed.

Parameters:

destination - to drain to

maxElements - max items to drain

drainDestructableClaims

void drainDestructableClaims(Collection<ResourceClaim> destination,
                           int maxElements,
                           long timeout,
                           TimeUnit unit)

Drains up to maxElements Content Claims from the internal queue of destructable content claims to the given destination so that they can be destroyed. If no ResourceClaim is ready to be destroyed at this time, will wait up to the specified amount of time before returning. If, after the specified amount of time, there is still no ResourceClaim ready to be destroyed, the method will return without having added anything to the given destination.

Parameters:

destination - to drain to

maxElements - max items to drain

timeout - maximum time to wait

unit - unit of time to wait

purge

void purge()

Clears the manager's memory of any and all ResourceClaims that it knows about