Class RoleStateBuilder

java.lang.Object
io.krabka.streams.coordination.RoleStateBuilder
public final class RoleStateBuilder extends Object
Folds the records of one role into a RoleState.

The builder keeps the record of the highest offset for every key, which is what log compaction keeps. A later registration for a member replaces the earlier one and moves the member to the tail of the roster. A registration tombstone removes the member. A lease tombstone clears the lease.

The builder drops a record of another role, so a caller folds a partition that holds several roles and needs no filter of its own.

The key carries the identity, because the key is the compaction key. The builder takes the member and the record kind from the key, and it takes neither from the value.

One builder is not safe for concurrent use. Confine it to one thread.

Example

RoleStateBuilder builder = new RoleStateBuilder(Role.of("controller"));
for (CoordinationEntry entry : transport.readRoleRecords(builder.role())) {
    builder.apply(entry);
}
RoleState state = builder.build();

  • Constructor Details

    • RoleStateBuilder

      public RoleStateBuilder(Role role)
      Creates an empty fold for one role.
      Parameters:
      role - the role to collect
      Throws:
      NullPointerException - if the role is null

  • Method Details

    • role

      public Role role()
      Returns the role that this fold collects.
      Returns:
      the role the builder was created for

    • apply

      public RoleStateBuilder apply(CoordinationEntry entry)
      Applies one record of the coordination partition.

      The builder drops a record of another role, and it drops a value whose kind does not match the kind of its key. CoordinationCodec reads the kind from the key, so a decoder cannot produce such a pair.

      Parameters:
      entry - the decoded record and the offset it sits at
      Returns:
      this builder, so a caller chains calls
      Throws:
      NullPointerException - if the entry is null

    • build

      public RoleState build()
      Builds the role state, with the roster in offset order.
      Returns:
      the folded state of the role