public final class SelectClaim
extends ObjectThe single-winner state of one selection: the arbiter through which a group of competing offers (the branches of a ChannelSelect, or a lone channel operation) commits exactly one outcome between them.
A claim is a three-state machine: OPEN, PENDING, or COMMITTED. PENDING is a revertible reservation held while a two-party pairing (a send offer meeting a receive offer, each belonging to a different selection) verifies that both sides still stand; the reservation always resolves promptly — its holder does only lock-free work, never completes a future and never takes a lock while holding it — so competitors may spin on it. When two claims must be reserved together they are taken in ascending id order, which keeps every waits-for chain strictly increasing and therefore cycle-free: the shared-memory form of the commit protocol for generalized (input and output) guards of Buckley & Silberschatz (TOPLAS 1983).
A committed claim records the winning party — the completion of the branch that won, or the cancelled marker — so cancellation can distinguish "this branch won, refuse the cancel: its delivery is imminent or done" from "a sibling won, this loser may unpark freely".
| Type Params | Return Type | Name and description |
|---|---|---|
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public boolean |
allowCancel(Object future)Gate for cancelling the given parked completion. |
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public void |
commit(Object token, Object winner)Commits a reservation made with pend; cannot fail while the token is held. |
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public boolean |
isCommitted()Whether the claim has reached a terminal state (a reservation in flight is not terminal). |
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public Object |
pend()Reserves this claim, waiting out any other party's reservation. |
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public static int |
pendBoth(SelectClaim a, SelectClaim b, Object[] tokens)Reserves two parties' claims, in ascending id order regardless of argument order, reverting the first if the second turns out committed. |
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public void |
revert(Object token)Reverts a reservation made with pend, reopening the claim. |
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public boolean |
tryCommit(Object winner)Commits in one step when no partner needs verifying: a value provably present under the channel lock, or a send into free buffer space. |
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public boolean |
tryCommitCancel()Commits to cancellation: once this succeeds, no branch can deliver. |
Gate for cancelling the given parked completion. A still-open claim is committed to the cancel and the future may die; a claim committed to a sibling lets this loser unpark freely; but the committed winner itself is refused — its delivery is imminent or done and must reach the caller.
future - the completion being cancelledCommits a reservation made with pend; cannot fail while the token is held.
token - the reservation tokenwinner - the completion of the branch that wonWhether the claim has reached a terminal state (a reservation in flight is not terminal).
Reserves this claim, waiting out any other party's reservation.
Reserves two parties' claims, in ascending id order regardless of argument order, reverting the first if the second turns out committed.
a - the first party's claim; its token lands in tokens[0]b - the second party's claim; its token lands in tokens[1]tokens - receives the two reservation tokens on successa is already
committed, 2 if b isReverts a reservation made with pend, reopening the claim.
token - the reservation tokenCommits in one step when no partner needs verifying: a value provably present under the channel lock, or a send into free buffer space.
winner - the completion of the branch that wonfalse if the claim was already committed elsewhereCommits to cancellation: once this succeeds, no branch can deliver.
false if a branch had already won