序
本文主要研究下reactor-netty的PoolResources的两种模式elastic及fixed。
LoopResources与PoolResources
TcpResources是个工具类，可以用来创建loopResources和poolResources。
loopResources
主要是创建NioEventLoopGroup，以及该group下面的workerCount个NioEventLoop(这里涉及两个参数，一个是worker thread count，一个是selector thread count)
- DEFAULT_IO_WORKER_COUNT：如果环境变量有设置reactor.ipc.netty.workerCount，则用该值；没有设置则取Math.max(Runtime.getRuntime().availableProcessors(), 4)))
- DEFAULT_IO_SELECT_COUNT：如果环境变量有设置reactor.ipc.netty.selectCount，则用该值；没有设置则取-1，表示没有selector thread
- DEFAULT_MAX_PENDING_TASKS: 指定NioEventLoop的taskQueue的大小，Math.max(16,SystemPropertyUtil.getInt("io.netty.eventLoop.maxPendingTasks", Integer.MAX_VALUE))
- NioEventLoop继承了SingleThreadEventLoop，而SingleThreadEventLoop则继承SingleThreadEventExecutor，而其代理的executor是ThreadPerTaskExecutor，rejectHandler是RejectedExecutionHandlers.reject()，默认的taskQueue是LinkedBlockingQueue，其大小为Integer.MAX_VALUE
poolResources
主要是创建channelPools，类型是ConcurrentMap
DefaultPoolResources
reactor-netty-0.7.5.RELEASE-sources.jar!/reactor/ipc/netty/resources/DefaultPoolResources.java
它实现了netty-transport-4.1.22.Final-sources.jar!/io/netty/channel/pool/ChannelPool.java的接口，重点看如下的几个方法：
@Override
public Future acquire() {
return acquire(defaultGroup.next().newPromise());
}
@Override
public Future acquire(Promise promise) {
return pool.acquire(promise).addListener(this);
}
@Override
public Future release(Channel channel) {
return pool.release(channel);
}
@Override
public Future release(Channel channel, Promise promise) {
return pool.release(channel, promise);
}
@Override
public void close() {
if(compareAndSet(false, true)) {
pool.close();
}
}
复制代码 这里的几个接口基本是委托为具体的pool来进行操作，其实现主要有SimpleChannelPool及FixedChannelPool。
PoolResources.elastic(SimpleChannelPool)
reactor-netty-0.7.5.RELEASE-sources.jar!/reactor/ipc/netty/resources/PoolResources.java
/**
* Create an uncapped {@link PoolResources} to provide automatically for {@link
* ChannelPool}.
* An elastic {@link PoolResources} will never wait before opening a new
* connection. The reuse window is limited but it cannot starve an undetermined volume
* of clients using it.
*
* @param name the channel pool map name
*
* @return a new {@link PoolResources} to provide automatically for {@link
* ChannelPool}
*/
static PoolResources elastic(String name) {
return new DefaultPoolResources(name, SimpleChannelPool::new);
}
复制代码
这个是TcpClient.create过程中，默认使用的方法，默认使用的是SimpleChannelPool，创建的是DefaultPoolResources
reactor-netty-0.7.5.RELEASE-sources.jar!/reactor/ipc/netty/tcp/TcpResources.java
static T create(T previous,
LoopResources loops,
PoolResources pools,
String name,
BiFunction onNew) {
if (previous == null) {
loops = loops == null ? LoopResources.create("reactor-" + name) : loops;
pools = pools == null ? PoolResources.elastic(name) : pools;
}
else {
loops = loops == null ? previous.defaultLoops : loops;
pools = pools == null ? previous.defaultPools : pools;
}
return onNew.apply(loops, pools);
}
复制代码 SimpleChannelPool
netty-transport-4.1.22.Final-sources.jar!/io/netty/channel/pool/SimpleChannelPool.java
/**
* Simple {@link ChannelPool} implementation which will create new {@link Channel}s if someone tries to acquire
* a {@link Channel} but none is in the pool atm. No limit on the maximal concurrent {@link Channel}s is enforced.
*
* This implementation uses LIFO order for {@link Channel}s in the {@link ChannelPool}.
*
*/
public class SimpleChannelPool implements ChannelPool {
@Override
public final Future acquire() {
return acquire(bootstrap.config().group().next().newPromise());
}
@Override
public Future acquire(final Promise promise) {
checkNotNull(promise, "promise");
return acquireHealthyFromPoolOrNew(promise);
}
/**
* Tries to retrieve healthy channel from the pool if any or creates a new channel otherwise.
* @param promise the promise to provide acquire result.
* @return future for acquiring a channel.
*/
private Future acquireHealthyFromPoolOrNew(final Promise promise) {
try {
final Channel ch = pollChannel();
if (ch == null) {
// No Channel left in the pool bootstrap a new Channel
Bootstrap bs = bootstrap.clone();
bs.attr(POOL_KEY, this);
ChannelFuture f = connectChannel(bs);
if (f.isDone()) {
notifyConnect(f, promise);
} else {
f.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
notifyConnect(future, promise);
}
});
}
return promise;
}
EventLoop loop = ch.eventLoop();
if (loop.inEventLoop()) {
doHealthCheck(ch, promise);
} else {
loop.execute(new Runnable() {
@Override
public void run() {
doHealthCheck(ch, promise);
}
});
}
} catch (Throwable cause) {
promise.tryFailure(cause);
}
return promise;
}
@Override
public final Future release(Channel channel) {
return release(channel, channel.eventLoop().newPromise());
}
@Override
public Future release(final Channel channel, final Promise promise) {
checkNotNull(channel, "channel");
checkNotNull(promise, "promise");
try {
EventLoop loop = channel.eventLoop();
if (loop.inEventLoop()) {
doReleaseChannel(channel, promise);
} else {
loop.execute(new Runnable() {
@Override
public void run() {
doReleaseChannel(channel, promise);
}
});
}
} catch (Throwable cause) {
closeAndFail(channel, cause, promise);
}
return promise;
}
@Override
public void close() {
for (;;) {
Channel channel = pollChannel();
if (channel == null) {
break;
}
channel.close();
}
}
//......
}
复制代码 这个连接池的实现如果没有连接则会创建一个(
没有限制)，取出连接(连接池使用一个LIFO的Deque来维护Channel)的时候会检测连接的有效性。
PoolResources.fixed(FixedChannelPool)
reactor-netty-0.7.5.RELEASE-sources.jar!/reactor/ipc/netty/resources/PoolResources.java
/**
* Default max connection, if -1 will never wait to acquire before opening new
* connection in an unbounded fashion. Fallback to
* available number of processors.
*/
int DEFAULT_POOL_MAX_CONNECTION =
Integer.parseInt(System.getProperty("reactor.ipc.netty.pool.maxConnections",
"" + Math.max(Runtime.getRuntime()
.availableProcessors(), 8) * 2));
/**
* Default acquisition timeout before error. If -1 will never wait to
* acquire before opening new
* connection in an unbounded fashion. Fallback to
* available number of processors.
*/
long DEFAULT_POOL_ACQUIRE_TIMEOUT = Long.parseLong(System.getProperty(
"reactor.ipc.netty.pool.acquireTimeout",
"" + 45000));
/**
* Create a capped {@link PoolResources} to provide automatically for {@link
* ChannelPool}.
* A Fixed {@link PoolResources} will open up to the given max number of
* processors observed by this jvm (minimum 4).
* Further connections will be pending acquisition indefinitely.
*
* @param name the channel pool map name
*
* @return a new {@link PoolResources} to provide automatically for {@link
* ChannelPool}
*/
static PoolResources fixed(String name) {
return fixed(name, DEFAULT_POOL_MAX_CONNECTION);
}
/**
* Create a capped {@link PoolResources} to provide automatically for {@link
* ChannelPool}.
*
A Fixed {@link PoolResources} will open up to the given max connection value.
* Further connections will be pending acquisition indefinitely.
*
* @param name the channel pool map name
* @param maxConnections the maximum number of connections before starting pending
* acquisition on existing ones
*
* @return a new {@link PoolResources} to provide automatically for {@link
* ChannelPool}
*/
static PoolResources fixed(String name, int maxConnections) {
return fixed(name, maxConnections, DEFAULT_POOL_ACQUIRE_TIMEOUT);
}
/**
* Create a capped {@link PoolResources} to provide automatically for {@link
* ChannelPool}.
*
A Fixed {@link PoolResources} will open up to the given max connection value.
* Further connections will be pending acquisition indefinitely.
*
* @param name the channel pool map name
* @param maxConnections the maximum number of connections before starting pending
* @param acquireTimeout the maximum time in millis to wait for aquiring
*
* @return a new {@link PoolResources} to provide automatically for {@link
* ChannelPool}
*/
static PoolResources fixed(String name, int maxConnections, long acquireTimeout) {
if (maxConnections == -1) {
return elastic(name);
}
if (maxConnections <= 0) {
throw new IllegalArgumentException("Max Connections value must be strictly " + "positive");
}
if (acquireTimeout != -1L && acquireTimeout < 0) {
throw new IllegalArgumentException("Acquire Timeout value must " + "be " + "positive");
}
return new DefaultPoolResources(name,
(bootstrap, handler, checker) -> new FixedChannelPool(bootstrap,
handler,
checker,
FixedChannelPool.AcquireTimeoutAction.FAIL,
acquireTimeout,
maxConnections,
Integer.MAX_VALUE
));
}
复制代码
最后调用的fixed方法有三个参数，一个是name，一个是maxConnections，一个是acquireTimeout。可以看到这里创建的是FixedChannelPool。
FixedChannelPool
netty-transport-4.1.22.Final-sources.jar!/io/netty/channel/pool/FixedChannelPool.java
/**
* {@link ChannelPool} implementation that takes another {@link ChannelPool} implementation and enforce a maximum
* number of concurrent connections.
*/
public class FixedChannelPool extends SimpleChannelPool {
@Override
public Future acquire(final Promise promise) {
try {
if (executor.inEventLoop()) {
acquire0(promise);
} else {
executor.execute(new Runnable() {
@Override
public void run() {
acquire0(promise);
}
});
}
} catch (Throwable cause) {
promise.setFailure(cause);
}
return promise;
}
private void acquire0(final Promise promise) {
assert executor.inEventLoop();
if (closed) {
promise.setFailure(POOL_CLOSED_ON_ACQUIRE_EXCEPTION);
return;
}
if (acquiredChannelCount < maxConnections) {
assert acquiredChannelCount >= 0;
// We need to create a new promise as we need to ensure the AcquireListener runs in the correct
// EventLoop
Promise p = executor.newPromise();
AcquireListener l = new AcquireListener(promise);
l.acquired();
p.addListener(l);
super.acquire(p);
} else {
if (pendingAcquireCount >= maxPendingAcquires) {
promise.setFailure(FULL_EXCEPTION);
} else {
AcquireTask task = new AcquireTask(promise);
if (pendingAcquireQueue.offer(task)) {
++pendingAcquireCount;
if (timeoutTask != null) {
task.timeoutFuture = executor.schedule(timeoutTask, acquireTimeoutNanos, TimeUnit.NANOSECONDS);
}
} else {
promise.setFailure(FULL_EXCEPTION);
}
}
assert pendingAcquireCount > 0;
}
}
@Override
public Future release(final Channel channel, final Promise promise) {
ObjectUtil.checkNotNull(promise, "promise");
final Promise p = executor.newPromise();
super.release(channel, p.addListener(new FutureListener() {
@Override
public void operationComplete(Future future) throws Exception {
assert executor.inEventLoop();
if (closed) {
// Since the pool is closed, we have no choice but to close the channel
channel.close();
promise.setFailure(POOL_CLOSED_ON_RELEASE_EXCEPTION);
return;
}
if (future.isSuccess()) {
decrementAndRunTaskQueue();
promise.setSuccess(null);
} else {
Throwable cause = future.cause();
// Check if the exception was not because of we passed the Channel to the wrong pool.
if (!(cause instanceof IllegalArgumentException)) {
decrementAndRunTaskQueue();
}
promise.setFailure(future.cause());
}
}
}));
return promise;
}
@Override
public void close() {
executor.execute(new Runnable() {
@Override
public void run() {
if (!closed) {
closed = true;
for (;;) {
AcquireTask task = pendingAcquireQueue.poll();
if (task == null) {
break;
}
ScheduledFuture f = task.timeoutFuture;
if (f != null) {
f.cancel(false);
}
task.promise.setFailure(new ClosedChannelException());
}
acquiredChannelCount = 0;
pendingAcquireCount = 0;
FixedChannelPool.super.close();
}
}
});
}
//......
}
复制代码 这里的acquire，如果当前线程不是在eventLoop中，则放入队列中等待执行acquire0，这里可能撑爆eventLoop的taskQueue，不过其队列大小的值取Math.max(16,SystemPropertyUtil.getInt("io.netty.eventLoop.maxPendingTasks", Integer.MAX_VALUE))，默认是Integer.MAX_VALUE。
FixedChannelPool继承了SimpleChannelPool，并重写了acquire、release、close方法。它对获取连接进行了限制，主要有如下几个参数：
-
maxConnections 该值先从系统变量reactor.ipc.netty.pool.maxConnections取(
如果设置为-1，表示无限制，回到elastic模式)，如果没有设置，则取Math.max(Runtime.getRuntime().availableProcessors(), 8) * 2，即核数与8的最大值的2倍。 -
acquireTimeout 该值先从系统变量reactor.ipc.netty.pool.acquireTimeout取(
如果设置为-1，表示立即执行不等待)，如果没有设置，则为45000毫秒 -
maxPendingAcquires 这里设置的是Integer.MAX_VALUE
-
AcquireTimeoutAction 这里设置为FixedChannelPool.AcquireTimeoutAction.FAIL，即timeoutTask为
timeoutTask = new TimeoutTask() {
@Override
public void onTimeout(AcquireTask task) {
// Fail the promise as we timed out.
task.promise.setFailure(TIMEOUT_EXCEPTION);
}
};
复制代码如果当前连接超过maxConnections，则进入pendingAcquireQueue等待获取连接，而在进入pendingAcquireQueue之前，如果当前等待数量超过了maxPendingAcquires，则返回FULL_EXCEPTION(
Too many outstanding acquire operations)，这里设置的是Integer.MAX_VALUE，所以不会有这个异常。进入pendingAcquireQueue之后，还有一个acquireTimeout参数，即进入pendingAcquireQueue等待acquireTimeout时间，如果还没有获取到连接则返回TIMEOUT_EXCEPTION(Acquire operation took longer then configured maximum time)。
小结
默认TcpClient创建的PoolResources使用的是elastic模式，即连接池的实现是SimpleChannelPool，默认使用一个LIFO的Deque来维护Channel，如果从连接池取不到连接则会创建新的连接，上限应该是系统设置的能够打开的文件资源数量，超过则报SocketException: Too many open files。PoolResources还提供了FixedChannelPool实现，使用的是fixed模式，即限定了连接池最大连接数及最大等待超时，避免连接创建数量过多撑爆内存或者报SocketException: Too many open files异常。
注意，对于fixed模式，如果reactor.ipc.netty.pool.maxConnections设置为-1，则回退到elastic模式。
doc
- Netty 连接池的使用姿势
- Netty连接池ChannelPool,FixedChannelPool应用
- 教你正确地利用Netty建立连接池
- reactor-netty中TcpClient的create过程
- reactor-netty中TcpClient的newHandler过程
- Too many files open
- linux服务器报Too many open files的解决方法