Package com.axelor.db

Class ClaimLease

java.lang.Object

com.axelor.db.ClaimLease

public final class ClaimLease
extends Object

The three columns that say a row is being worked on, and by whom.

A row claimed for work carries owner, claimToken and claimedAt: who holds it, which claim this is, and since when. The last is what makes the claim a lease rather than a flag -- a node that dies holding a row does not take the work with it, because the row can be told from its timestamp to have been abandoned and handed to somebody else.

Only the columns live here, not the policy. What predicate wins the row, what status it moves through, how long a lease may run and what happens when one expires all differ per table and belong with the table's own code. What must not differ is the shape, so a table that grows a lease copies a name rather than a convention.

The maps are meant to be handed to GuardedUpdate.setAll(java.util.Map<java.lang.String, java.lang.Object>) alongside whatever else the caller is writing -- the claim and the status change are one statement, or they are not atomic.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	CLAIM_TOKEN
static final String	CLAIMED_AT
static final String	LEASE_SECONDS	The parameter OUTLIVED reads its lease from.
static final String	OUTLIVED	True when a claim has outlived a lease of LEASE_SECONDS seconds, measured by the database.
static final String	OWNER	Column names, for callers writing their own predicates over them.

Method Summary

Modifier and Type	Method	Description
static long	leaseSeconds(Duration lease)	The lease OUTLIVED measures against, in seconds.
static Map<String,Object>	released()	Let the row go, so the next caller to try may have it.
static Map<String,Object>	renewed()	Say the holder is still alive, without changing whose claim it is.
static Map<String,Object>	taken(String owner)	Take the row for owner, stamped now, under a claim of its own.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

OUTLIVED

public static final String OUTLIVED

True when a claim has outlived a lease of LEASE_SECONDS seconds, measured by the database. Says nothing about an unclaimed row: whether a null claimedAt counts as available differs per table, so each predicate keeps its own answer to that.

See Also:

• Constant Field Values

LEASE_SECONDS

public static final String LEASE_SECONDS

The parameter OUTLIVED reads its lease from.

See Also:

• Constant Field Values

OWNER

public static final String OWNER

Column names, for callers writing their own predicates over them.

See Also:

• Constant Field Values

CLAIM_TOKEN

public static final String CLAIM_TOKEN

See Also:

• Constant Field Values

CLAIMED_AT

public static final String CLAIMED_AT

See Also:

• Constant Field Values

Method Details

taken

public static Map<String,Object> taken(String owner)

Take the row for owner, stamped now, under a claim of its own.

renewed

public static Map<String,Object> renewed()

Say the holder is still alive, without changing whose claim it is.

A lease measured from when the row was claimed expires on work that simply takes longer than the lease -- and the row is then handed to somebody else while the first holder is still going. Renewing moves the clock forward so the lease measures liveness rather than duration.

released

public static Map<String,Object> released()

Let the row go, so the next caller to try may have it.

leaseSeconds

public static long leaseSeconds(Duration lease)

The lease OUTLIVED measures against, in seconds.

Measured from when the row was claimed, never from when the work became due: a row claimed a moment ago but overdue by a day -- a backlog after downtime -- is being worked on, not abandoned, and reaping it would take it away from the node that holds it.