org.jgroups.raft.blocks.CounterService Maven / Gradle / Ivy
package org.jgroups.raft.blocks;
import org.jgroups.JChannel;
import org.jgroups.blocks.atomic.Counter;
import org.jgroups.protocols.raft.InternalCommand;
import org.jgroups.protocols.raft.RAFT;
import org.jgroups.protocols.raft.Role;
import org.jgroups.protocols.raft.StateMachine;
import org.jgroups.raft.RaftHandle;
import org.jgroups.util.*;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
/**
* Provides a consensus based distributed counter (similar to AtomicLong) which can be atomically updated across a cluster.
* @author Bela Ban
* @since 0.2
*/
public class CounterService implements StateMachine, RAFT.RoleChange {
protected JChannel ch;
protected RaftHandle raft;
protected long repl_timeout=20000; // timeout (ms) to wait for a majority to ack a write
/** If true, reads can return the local counter value directly. Else, reads have to go through the leader */
protected boolean allow_dirty_reads=true;
// keys: counter names, values: counter values
protected final Map counters=new HashMap<>();
protected enum Command {create, delete, get, set, compareAndSet, incrementAndGet, decrementAndGet, addAndGet}
public CounterService(JChannel ch) {
setChannel(ch);
}
public void setChannel(JChannel ch) {
this.ch=ch;
this.raft=new RaftHandle(this.ch, this);
raft.addRoleListener(this);
}
public void addRoleChangeListener(RAFT.RoleChange listener) {raft.addRoleListener(listener);}
public long replTimeout() {return repl_timeout;}
public CounterService replTimeout(long timeout) {this.repl_timeout=timeout; return this;}
public boolean allowDirtyReads() {return allow_dirty_reads;}
public CounterService allowDirtyReads(boolean flag) {allow_dirty_reads=flag; return this;}
public int lastApplied() {return raft.lastApplied();}
public int commitIndex() {return raft.commitIndex();}
public void snapshot() throws Exception {raft.snapshot();}
public int logSize() {return raft.logSizeInBytes();}
public String raftId() {return raft.raftId();}
public CounterService raftId(String id) {raft.raftId(id); return this;}
/**
* Returns an instance of the counter. This is local operation which never fails and don't create a record in the
* log. For cluster-wide operation call getOrCreateCounter(name, initial_value).
* @param name Name of the counter, different counters have to have different names
* @return The counter instance
*/
public Counter counter(String name) {
return new CounterImpl(name, this);
}
/**
* Returns an existing counter, or creates a new one if none exists. This is a cluster-wide operation which would
* fail if no leader is elected.
* @param name Name of the counter, different counters have to have different names
* @param initial_value The initial value of a new counter if there is no existing counter. Ignored
* if the counter already exists
* @return The counter implementation
*/
public Counter getOrCreateCounter(String name, long initial_value) throws Exception {
invoke(Command.create, name, false, initial_value);
return new CounterImpl(name, this);
}
/**
* Deletes a counter instance (on the coordinator)
* @param name The name of the counter. No-op if the counter doesn't exist
*/
public void deleteCounter(String name) throws Exception {
invoke(Command.delete, name, true);
}
public String printCounters() {
return counters.entrySet()
.stream().collect(StringBuilder::new,
(sb,entry) -> sb.append(entry.getKey()).append(" = ").append(entry.getValue()).append("\n"),
(l,r) -> {}).toString();
}
public long get(String name) throws Exception {
Object retval=allow_dirty_reads? _get(name) : invoke(Command.get, name, false);
return (long)retval;
}
public void set(String name, long new_value) throws Exception {
invoke(Command.set, name, true, new_value);
}
public boolean compareAndSet(String name, long expect, long update) throws Exception {
Object retval=invoke(Command.compareAndSet, name, false, expect, update);
return (boolean)retval;
}
public long incrementAndGet(String name) throws Exception {
Object retval=invoke(Command.incrementAndGet, name, false);
return (long)retval;
}
public long decrementAndGet(String name) throws Exception {
Object retval=invoke(Command.decrementAndGet, name, false);
return (long)retval;
}
public long addAndGet(String name, long delta) throws Exception {
Object retval=invoke(Command.addAndGet, name, false, delta);
return (long)retval;
}
@Override
public byte[] apply(byte[] data, int offset, int length) throws Exception {
ByteArrayDataInputStream in=new ByteArrayDataInputStream(data, offset, length);
Command command=Command.values()[in.readByte()];
String name=Bits.readAsciiString(in).toString();
long v1, v2, retval;
switch(command) {
case create:
v1=Bits.readLongCompressed(in);
retval=_create(name, v1);
return Util.objectToByteBuffer(retval);
case delete:
_delete(name);
break;
case get:
retval=_get(name);
return Util.objectToByteBuffer(retval);
case set:
v1=Bits.readLongCompressed(in);
_set(name, v1);
break;
case compareAndSet:
v1=Bits.readLongCompressed(in);
v2=Bits.readLongCompressed(in);
boolean success=_cas(name, v1, v2);
return Util.objectToByteBuffer(success);
case incrementAndGet:
retval=_add(name, +1L);
return Util.objectToByteBuffer(retval);
case decrementAndGet:
retval=_add(name, -1L);
return Util.objectToByteBuffer(retval);
case addAndGet:
v1=Bits.readLongCompressed(in);
retval=_add(name, v1);
return Util.objectToByteBuffer(retval);
default:
throw new IllegalArgumentException("command " + command + " is unknown");
}
return Util.objectToByteBuffer(null);
}
@Override
public void writeContentTo(DataOutput out) throws Exception {
synchronized(counters) {
int size=counters.size();
out.writeInt(size);
for(Map.Entry entry: counters.entrySet()) {
AsciiString name=new AsciiString(entry.getKey());
Long value=entry.getValue();
Bits.writeAsciiString(name, out);
Bits.writeLongCompressed(value, out);
}
}
}
@Override
public void readContentFrom(DataInput in) throws Exception {
int size=in.readInt();
for(int i=0; i < size; i++) {
AsciiString name=Bits.readAsciiString(in);
Long value=Bits.readLongCompressed(in);
counters.put(name.toString(), value);
}
}
public void dumpLog() {
raft.logEntries((entry, index) -> {
StringBuilder sb=new StringBuilder().append(index).append(" (").append(entry.term()).append("): ");
if(entry.command() == null) {
sb.append("");
System.out.println(sb);
return;
}
if(entry.internal()) {
try {
InternalCommand cmd=Util.streamableFromByteBuffer(InternalCommand.class,
entry.command(), entry.offset(), entry.length());
sb.append("[internal] ").append(cmd);
}
catch(Exception ex) {
sb.append("[failure reading internal cmd] ").append(ex);
}
System.out.println(sb);
return;
}
ByteArrayDataInputStream in=new ByteArrayDataInputStream(entry.command(), entry.offset(), entry.length());
try {
Command cmd=Command.values()[in.readByte()];
String name=Bits.readAsciiString(in).toString();
switch(cmd) {
case create:
case set:
case addAndGet:
sb.append(print(cmd, name, 1, in));
break;
case delete:
case get:
case incrementAndGet:
case decrementAndGet:
sb.append(print(cmd, name, 0, in));
break;
case compareAndSet:
sb.append(print(cmd, name, 2, in));
break;
default:
throw new IllegalArgumentException("command " + cmd + " is unknown");
}
}
catch(Throwable t) {
sb.append(t);
}
System.out.println(sb);
});
}
@Override
public void roleChanged(Role role) {
System.out.println("-- changed role to " + role);
}
protected Object invoke(Command command, String name, boolean ignore_return_value, long ... values) throws Exception {
ByteArrayDataOutputStream out=new ByteArrayDataOutputStream(256);
try {
out.writeByte(command.ordinal());
Bits.writeAsciiString(new AsciiString(name), out);
for(long val: values)
Bits.writeLongCompressed(val, out);
}
catch(Exception ex) {
throw new Exception("serialization failure (cmd=" + command + ", name=" + name + "): " + ex);
}
byte[] buf=out.buffer();
byte[] rsp=raft.set(buf, 0, out.position(), repl_timeout, TimeUnit.MILLISECONDS);
return ignore_return_value? null: Util.objectFromByteBuffer(rsp);
}
protected static String print(Command command, String name, int num_args, DataInput in) {
StringBuilder sb=new StringBuilder(command.toString()).append("(").append(name);
for(int i=0; i < num_args; i++) {
try {
long val=Bits.readLongCompressed(in);
sb.append(", ").append(val);
}
catch(IOException ignored) {
break;
}
}
sb.append(")");
return sb.toString();
}
protected long _create(String name, long initial_value) {
synchronized(counters) {
Long val=counters.get(name);
if(val != null)
return val;
counters.put(name, initial_value);
return initial_value;
}
}
protected void _delete(String name) {
synchronized(counters) {
counters.remove(name);
}
}
protected long _get(String name) {
synchronized(counters) {
Long retval=counters.get(name);
return retval != null? (long)retval : 0;
}
}
protected void _set(String name, long new_val) {
synchronized(counters) {
counters.put(name, new_val);
}
}
protected boolean _cas(String name, long expected, long value) {
synchronized(counters) {
Long existing_value=counters.get(name);
if(existing_value == null) return false;
if(existing_value == expected) {
counters.put(name, value);
return true;
}
return false;
}
}
protected long _add(String name, long delta) {
synchronized(counters) {
Long val=counters.get(name);
if(val == null)
val=(long)0;
counters.put(name, val+delta);
return val+delta;
}
}
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