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Remove ZK candidate dep (linkerd#2361)
The artifact for com.twitter.common.zookeeper" % "candidate" % "0.0.84" on maven.twttr.com is not present anymore. Therefore we need to cpy the bits that we use from it and have it in our sourcecode. Fixes linkerd#2360 Signed-off-by: Zahari Dichev <zaharidichev@gmail.com>
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namer/zk-leader/src/main/java/com/twitter/common/zookeeper/Candidate.java
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| // ================================================================================================= | ||
| // Copyright 2011 Twitter, Inc. | ||
| // ------------------------------------------------------------------------------------------------- | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this work except in compliance with the License. | ||
| // You may obtain a copy of the License in the LICENSE file, or at: | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // ================================================================================================= | ||
|
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| package com.twitter.common.zookeeper; | ||
|
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| import com.google.common.base.Optional; | ||
| import com.google.common.base.Supplier; | ||
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| import com.twitter.finagle.common.zookeeper.Group.JoinException; | ||
| import com.twitter.finagle.common.zookeeper.Group.WatchException; | ||
| import com.twitter.finagle.common.zookeeper.ZooKeeperClient.ZooKeeperConnectionException; | ||
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| import org.apache.zookeeper.KeeperException; | ||
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| /** | ||
| * Interface definition for becoming or querying for a ZooKeeper-based group leader. | ||
| */ | ||
| public interface Candidate { | ||
|
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| /** | ||
| * Returns the current group leader by querying ZooKeeper synchronously. | ||
| * | ||
| * @return the current group leader's identifying data or {@link Optional#absent()} if there is | ||
| * no leader | ||
| * @throws ZooKeeperConnectionException if there was a problem connecting to ZooKeeper | ||
| * @throws KeeperException if there was a problem reading the leader information | ||
| * @throws InterruptedException if this thread is interrupted getting the leader | ||
| */ | ||
| public Optional<byte[]> getLeaderData() | ||
| throws ZooKeeperConnectionException, KeeperException, InterruptedException; | ||
|
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| /** | ||
| * Encapsulates a leader that can be elected and subsequently defeated. | ||
| */ | ||
| interface Leader { | ||
|
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| /** | ||
| * Called when this leader has been elected. | ||
| * | ||
| * @param abdicate a command that can be used to abdicate leadership and force a new election | ||
| */ | ||
| void onElected(ExceptionalCommand<JoinException> abdicate); | ||
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| /** | ||
| * Called when the leader has been ousted. Can occur either if the leader abdicates or if an | ||
| * external event causes the leader to lose its leadership role (session expiration). | ||
| */ | ||
| void onDefeated(); | ||
| } | ||
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| /** | ||
| * Offers this candidate in leadership elections for as long as the current jvm process is alive. | ||
| * Upon election, the {@code onElected} callback will be executed and a command that can be used | ||
| * to abdicate leadership will be passed in. If the elected leader jvm process dies or the | ||
| * elected leader successfully abdicates then a new leader will be elected. Leaders that | ||
| * successfully abdicate are removed from the group and will not be eligible for leadership | ||
| * election unless {@link #offerLeadership(Leader)} is called again. | ||
| * | ||
| * @param leader the leader to notify of election and defeat events | ||
| * @throws JoinException if there was a problem joining the group | ||
| * @throws WatchException if there is a problem generating the 1st group membership list | ||
| * @throws InterruptedException if interrupted waiting to join the group and determine initial | ||
| * election results | ||
| * @return a supplier that can be queried to find out if this leader is currently elected | ||
| */ | ||
| public Supplier<Boolean> offerLeadership(Leader leader) | ||
| throws JoinException, WatchException, InterruptedException; | ||
| } |
177 changes: 177 additions & 0 deletions
177
namer/zk-leader/src/main/java/com/twitter/common/zookeeper/CandidateImpl.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,177 @@ | ||
| // ================================================================================================= | ||
| // Copyright 2011 Twitter, Inc. | ||
| // ------------------------------------------------------------------------------------------------- | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this work except in compliance with the License. | ||
| // You may obtain a copy of the License in the LICENSE file, or at: | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // ================================================================================================= | ||
|
|
||
| package com.twitter.common.zookeeper; | ||
|
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| import java.net.InetAddress; | ||
| import java.net.UnknownHostException; | ||
| import java.util.concurrent.atomic.AtomicBoolean; | ||
| import java.util.logging.Level; | ||
| import java.util.logging.Logger; | ||
|
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| import javax.annotation.Nullable; | ||
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| import com.google.common.base.Charsets; | ||
| import com.google.common.base.Function; | ||
| import com.google.common.base.Optional; | ||
| import com.google.common.base.Preconditions; | ||
| import com.google.common.base.Supplier; | ||
| import com.google.common.collect.Iterables; | ||
| import com.google.common.collect.Ordering; | ||
| import org.apache.zookeeper.KeeperException; | ||
| import com.twitter.finagle.common.zookeeper.Group; | ||
| import com.twitter.finagle.common.zookeeper.Group.JoinException; | ||
| import com.twitter.finagle.common.zookeeper.Group.GroupChangeListener; | ||
| import com.twitter.finagle.common.zookeeper.Group.Membership; | ||
| import com.twitter.finagle.common.zookeeper.Group.WatchException; | ||
| import com.twitter.finagle.common.zookeeper.ZooKeeperClient.ZooKeeperConnectionException; | ||
|
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| /** | ||
| * Implements leader election for small groups of candidates. This implementation is subject to the | ||
| * <a href="http://hadoop.apache.org/zookeeper/docs/r3.2.1/recipes.html#sc_leaderElection"> | ||
| * herd effect</a> for a given group and should only be used for small (~10 member) candidate pools. | ||
| */ | ||
| public class CandidateImpl implements Candidate { | ||
| private static final Logger LOG = Logger.getLogger(CandidateImpl.class.getName()); | ||
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| private static final byte[] UNKNOWN_CANDIDATE_DATA = "<unknown>".getBytes(Charsets.UTF_8); | ||
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| private static final Supplier<byte[]> IP_ADDRESS_DATA_SUPPLIER = new Supplier<byte[]>() { | ||
| @Override public byte[] get() { | ||
| try { | ||
| return InetAddress.getLocalHost().getHostAddress().getBytes(); | ||
| } catch (UnknownHostException e) { | ||
| LOG.log(Level.WARNING, "Failed to determine local address!", e); | ||
| return UNKNOWN_CANDIDATE_DATA; | ||
| } | ||
| } | ||
| }; | ||
|
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| private static final Function<Iterable<String>, String> MOST_RECENT_JUDGE = | ||
| new Function<Iterable<String>, String>() { | ||
| @Override public String apply(Iterable<String> candidates) { | ||
| return Ordering.natural().min(candidates); | ||
| } | ||
| }; | ||
|
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| private final Group group; | ||
| private final Function<Iterable<String>, String> judge; | ||
| private final Supplier<byte[]> dataSupplier; | ||
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| /** | ||
| * Equivalent to {@link #CandidateImpl(Group, com.google.common.base.Function, Supplier)} using a | ||
| * judge that always picks the lowest numbered candidate ephemeral node - by proxy the oldest or | ||
| * 1st candidate and a default supplier that provides the ip address of this host according to | ||
| * {@link java.net.InetAddress#getLocalHost()} as the leader identifying data. | ||
| */ | ||
| public CandidateImpl(Group group) { | ||
| this(group, MOST_RECENT_JUDGE, IP_ADDRESS_DATA_SUPPLIER); | ||
| } | ||
|
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| /** | ||
| * Creates a candidate that can be used to offer leadership for the given {@code group} using | ||
| * a judge that always picks the lowest numbered candidate ephemeral node - by proxy the oldest | ||
| * or 1st. The dataSupplier should produce bytes that identify this process as leader. These bytes | ||
| * will become available to all participants via the {@link Candidate#getLeaderData()} method. | ||
| */ | ||
| public CandidateImpl(Group group, Supplier<byte[]> dataSupplier) { | ||
| this(group, MOST_RECENT_JUDGE, dataSupplier); | ||
| } | ||
|
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| /** | ||
| * Creates a candidate that can be used to offer leadership for the given {@code group}. The | ||
| * {@code judge} is used to pick the current leader from all group members whenever the group | ||
| * membership changes. To form a well-behaved election group with one leader, all candidates | ||
| * should use the same judge. The dataSupplier should produce bytes that identify this process | ||
| * as leader. These bytes will become available to all participants via the | ||
| * {@link Candidate#getLeaderData()} method. | ||
| */ | ||
| public CandidateImpl( | ||
| Group group, | ||
| Function<Iterable<String>, String> judge, | ||
| Supplier<byte[]> dataSupplier) { | ||
| this.group = Preconditions.checkNotNull(group); | ||
| this.judge = Preconditions.checkNotNull(judge); | ||
| this.dataSupplier = Preconditions.checkNotNull(dataSupplier); | ||
| } | ||
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| @Override | ||
| public Optional<byte[]> getLeaderData() | ||
| throws ZooKeeperConnectionException, KeeperException, InterruptedException { | ||
|
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| String leaderId = getLeader(group.getMemberIds()); | ||
| return leaderId == null | ||
| ? Optional.<byte[]>absent() | ||
| : Optional.of(group.getMemberData(leaderId)); | ||
| } | ||
|
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| @Override | ||
| public Supplier<Boolean> offerLeadership(final Leader leader) | ||
| throws JoinException, WatchException, InterruptedException { | ||
|
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| final Membership membership = group.join(dataSupplier, () -> leader.onDefeated()); | ||
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| final AtomicBoolean elected = new AtomicBoolean(false); | ||
| final AtomicBoolean abdicated = new AtomicBoolean(false); | ||
| group.watch(new GroupChangeListener() { | ||
| @Override public void onGroupChange(Iterable<String> memberIds) { | ||
| boolean noCandidates = Iterables.isEmpty(memberIds); | ||
| String memberId = membership.getMemberId(); | ||
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| if (noCandidates) { | ||
| LOG.warning("All candidates have temporarily left the group: " + group); | ||
| } else if (!Iterables.contains(memberIds, memberId)) { | ||
| LOG.severe(String.format( | ||
| "Current member ID %s is not a candidate for leader, current voting: %s", | ||
| memberId, memberIds)); | ||
| } else { | ||
| boolean electedLeader = memberId.equals(getLeader(memberIds)); | ||
| boolean previouslyElected = elected.getAndSet(electedLeader); | ||
|
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| if (!previouslyElected && electedLeader) { | ||
| LOG.info(String.format("Candidate %s is now leader of group: %s", | ||
| membership.getMemberPath(), memberIds)); | ||
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| leader.onElected(new ExceptionalCommand<JoinException>() { | ||
| @Override public void execute() throws JoinException { | ||
| membership.cancel(); | ||
| abdicated.set(true); | ||
| } | ||
| }); | ||
| } else if (!electedLeader) { | ||
| if (previouslyElected) { | ||
| leader.onDefeated(); | ||
| } | ||
| LOG.info(String.format( | ||
| "Candidate %s waiting for the next leader election, current voting: %s", | ||
| membership.getMemberPath(), memberIds)); | ||
| } | ||
| } | ||
| } | ||
| }); | ||
|
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| return new Supplier<Boolean>() { | ||
| @Override public Boolean get() { | ||
| return !abdicated.get() && elected.get(); | ||
| } | ||
| }; | ||
| } | ||
|
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| @Nullable | ||
| private String getLeader(Iterable<String> memberIds) { | ||
| return Iterables.isEmpty(memberIds) ? null : judge.apply(memberIds); | ||
| } | ||
| } |
34 changes: 34 additions & 0 deletions
34
namer/zk-leader/src/main/java/com/twitter/common/zookeeper/ExceptionalCommand.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,34 @@ | ||
| // ================================================================================================= | ||
| // Copyright 2011 Twitter, Inc. | ||
| // ------------------------------------------------------------------------------------------------- | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this work except in compliance with the License. | ||
| // You may obtain a copy of the License in the LICENSE file, or at: | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
| // ================================================================================================= | ||
|
|
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| package com.twitter.common.zookeeper; | ||
|
|
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| /** | ||
| * An interface that captures a unit of work. | ||
| * | ||
| * @param <E> The type of exception that the command throws. | ||
| * | ||
| * @author John Sirois | ||
| */ | ||
| public interface ExceptionalCommand<E extends Exception> { | ||
|
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| /** | ||
| * Performs a unit of work, possibly throwing {@code E} in the process. | ||
| * | ||
| * @throws E if there was a problem performing the work | ||
| */ | ||
| void execute() throws E; | ||
| } |
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