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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License 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 org.apache.cassandra.net;
import org.apache.cassandra.exceptions.UnrecoverableIllegalStateException;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
public abstract class ResourceLimits
{
/**
* Represents permits to utilise a resource and ways to allocate and release them.
*
* Two implementations are currently provided:
* 1. {@link Concurrent}, for shared limits, which is thread-safe;
* 2. {@link Basic}, for limits that are not shared between threads, is not thread-safe.
*/
public interface Limit
{
/**
* @return total amount of permits represented by this {@link Limit} - the capacity
*/
long limit();
/**
* Sets the total amount of permits represented by this {@link Limit} - the capacity
*
* If the old limit has been reached and the new limit is large enough to allow for more
* permits to be aqcuired, subsequent calls to {@link #allocate(long)} or {@link #tryAllocate(long)}
* will succeed.
*
* If the new limit is lower than the current amount of allocated permits then subsequent calls
* to {@link #allocate(long)} or {@link #tryAllocate(long)} will block or fail respectively.
*
* @return the old limit
*/
long setLimit(long newLimit);
/**
* @return remaining, unallocated permit amount
*/
long remaining();
/**
* @return amount of permits currently in use
*/
long using();
/**
* Attempts to allocate an amount of permits from this limit. If allocated, MUST eventually
* be released back with {@link #release(long)}.
*
* @return {@code true} if the allocation was successful, {@code false} otherwise
*/
boolean tryAllocate(long amount);
/**
* Allocates an amount independent of permits available from this limit. MUST eventually
* be released back with {@link #release(long)}.
*
*/
void allocate(long amount);
/**
* @param amount return the amount of permits back to this limit
* @return {@code ABOVE_LIMIT} if there aren't enough permits available even after the release, or
* {@code BELOW_LIMIT} if there are enough permits available after the releaese.
*/
Outcome release(long amount);
}
/**
* A thread-safe permit container.
*/
public static class Concurrent implements Limit
{
private volatile long limit;
private static final AtomicLongFieldUpdater limitUpdater =
AtomicLongFieldUpdater.newUpdater(Concurrent.class, "limit");
private volatile long using;
private static final AtomicLongFieldUpdater usingUpdater =
AtomicLongFieldUpdater.newUpdater(Concurrent.class, "using");
public Concurrent(long limit)
{
this.limit = limit;
}
public long limit()
{
return limit;
}
public long setLimit(long newLimit)
{
long oldLimit;
do {
oldLimit = limit;
} while (!limitUpdater.compareAndSet(this, oldLimit, newLimit));
return oldLimit;
}
public long remaining()
{
return limit - using;
}
public long using()
{
return using;
}
public boolean tryAllocate(long amount)
{
long current, next;
do
{
current = using;
next = current + amount;
if (next > limit)
return false;
}
while (!usingUpdater.compareAndSet(this, current, next));
return true;
}
public void allocate(long amount)
{
long current, next;
do
{
current = using;
next = current + amount;
} while (!usingUpdater.compareAndSet(this, current, next));
}
public Outcome release(long amount)
{
assert amount >= 0;
long using = usingUpdater.addAndGet(this, -amount);
if (using < 0L)
{
// Should never be able to release more than was allocated. While recovery is
// possible it would require synchronizing the closing of all outbound connections
// and reinitializing the Concurrent limit before reopening. For such an unlikely path
// (previously this was an assert), it is safer to terminate the JVM and have something external
// restart and get back to a known good state rather than intermittendly crashing on any of
// the connections sharing this limit.
throw new UnrecoverableIllegalStateException(
"Internode messaging byte limits that are shared between connections is invalid (using="+using+")");
}
return using >= limit ? Outcome.ABOVE_LIMIT : Outcome.BELOW_LIMIT;
}
}
/**
* A cheaper, thread-unsafe permit container to be used for unshared limits.
*/
public static class Basic implements Limit
{
private long limit;
private long using;
public Basic(long limit)
{
this.limit = limit;
}
public long limit()
{
return limit;
}
public long setLimit(long newLimit)
{
long oldLimit = limit;
limit = newLimit;
return oldLimit;
}
public long remaining()
{
return limit - using;
}
public long using()
{
return using;
}
public boolean tryAllocate(long amount)
{
if (using + amount > limit)
return false;
using += amount;
return true;
}
public void allocate(long amount)
{
using += amount;
}
public Outcome release(long amount)
{
assert amount >= 0 && amount <= using;
using -= amount;
return using >= limit ? Outcome.ABOVE_LIMIT : Outcome.BELOW_LIMIT;
}
}
/**
* A convenience class that groups a per-endpoint limit with the global one
* to allow allocating/releasing permits from/to both limits as one logical operation.
*/
public static class EndpointAndGlobal
{
final Limit endpoint;
final Limit global;
public EndpointAndGlobal(Limit endpoint, Limit global)
{
this.endpoint = endpoint;
this.global = global;
}
public Limit endpoint()
{
return endpoint;
}
public Limit global()
{
return global;
}
/**
* @return {@code INSUFFICIENT_GLOBAL} if there weren't enough permits in the global limit, or
* {@code INSUFFICIENT_ENDPOINT} if there weren't enough permits in the per-endpoint limit, or
* {@code SUCCESS} if there were enough permits to take from both.
*/
public Outcome tryAllocate(long amount)
{
if (!global.tryAllocate(amount))
return Outcome.INSUFFICIENT_GLOBAL;
if (endpoint.tryAllocate(amount))
return Outcome.SUCCESS;
global.release(amount);
return Outcome.INSUFFICIENT_ENDPOINT;
}
public void allocate(long amount)
{
global.allocate(amount);
endpoint.allocate(amount);
}
public Outcome release(long amount)
{
Outcome endpointReleaseOutcome = endpoint.release(amount);
Outcome globalReleaseOutcome = global.release(amount);
return (endpointReleaseOutcome == Outcome.ABOVE_LIMIT || globalReleaseOutcome == Outcome.ABOVE_LIMIT)
? Outcome.ABOVE_LIMIT : Outcome.BELOW_LIMIT;
}
}
public enum Outcome { SUCCESS, INSUFFICIENT_ENDPOINT, INSUFFICIENT_GLOBAL, BELOW_LIMIT, ABOVE_LIMIT }
}
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