问题：selector在没有结果的情况下，依然被唤醒，导致一直空轮询，cpu100%( nio的epoll bug可以参考)
入口类：NioEventLoop
@Override
protected void run() {
for (;;) {
try {
switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) {
case SelectStrategy.CONTINUE:
continue;
case SelectStrategy.SELECT:
select(wakenUp.getAndSet(false));
if (wakenUp.get()) {
selector.wakeup();
}
// fall through
default:
}
cancelledKeys = 0;
needsToSelectAgain = false;
final int ioRatio = this.ioRatio;
if (ioRatio == 100) {
try {
processSelectedKeys();
} finally {
// Ensure we always run tasks.
runAllTasks();
}
} else {
final long ioStartTime = System.nanoTime();
try {
processSelectedKeys();
} finally {
// Ensure we always run tasks.
final long ioTime = System.nanoTime() - ioStartTime;
runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
}
}
} catch (Throwable t) {
handleLoopException(t);
}
try {
if (isShuttingDown()) {
closeAll();
if (confirmShutdown()) {
return;
}
}
} catch (Throwable t) {
handleLoopException(t);
}
}
}
第二个case:
private void select(boolean oldWakenUp) throws IOException {
Selector selector = this.selector;
try {
int selectCnt = 0;
//当前时间
long currentTimeNanos = System.nanoTime();
//截止时间=当前时间+第一个任务剩余执行时间
long selectDeadLineNanos = currentTimeNanos + delayNanos(currentTimeNanos);
for (;;) {
//执行需要的最少时间
long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L;
if (timeoutMillis <= 0) {
if (selectCnt == 0) {
//非阻塞
selector.selectNow();
selectCnt = 1;
}
break;
}
if (hasTasks() && wakenUp.compareAndSet(false, true)) {
selector.selectNow();
selectCnt = 1;
break;
}
//阻塞轮询
int selectedKeys = selector.select(timeoutMillis);
selectCnt ++;
/*
selectedKeys != 0：已经有轮询到的事件,
oldWakenUp：当前select操作是否需要唤醒,
wakenUp.get()：已经被外部线程唤醒,
hasTasks()：任务队列是否有任务,
hasScheduledTasks()：定时任务队列是否任务
*/
if (selectedKeys != 0 || oldWakenUp || wakenUp.get() || hasTasks() || hasScheduledTasks()) {
break;
}
if (Thread.interrupted()) {
if (logger.isDebugEnabled()) {
logger.debug("Selector.select() returned prematurely because " +
"Thread.currentThread().interrupt() was called. Use " +
"NioEventLoop.shutdownGracefully() to shutdown the NioEventLoop.");
}
selectCnt = 1;
break;
}
//到这一步的系统时间
long time = System.nanoTime();
//当前时间-最少时间>=启动时间表示完成一次阻塞轮询，否则可能空轮询
if (time - TimeUnit.MILLISECONDS.toNanos(timeoutMillis) >= currentTimeNanos) {
selectCnt = 1;
}else if (SELECTOR_AUTO_REBUILD_THRESHOLD > 0 &&
selectCnt >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
//如果空轮询次数过多则进入这里
logger.warn(
"Selector.select() returned prematurely {} times in a row; rebuilding Selector {}.",
selectCnt, selector);
rebuildSelector();
selector = this.selector;
//重构selector
selector.selectNow();
selectCnt = 1;
break;
}
currentTimeNanos = time;
}
if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS) {
if (logger.isDebugEnabled()) {
logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.",
selectCnt - 1, selector);
}
}
} catch (CancelledKeyException e) {
if (logger.isDebugEnabled()) {
logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?",
selector, e);
}
// Harmless exception - log anyway
}
}
public void rebuildSelector() {
if (!inEventLoop()) {
//如果不是本线程发起，封装成任务给NioEventLoop调用
execute(new Runnable() {
@Override
public void run() {
rebuildSelector0();
}
});
return;
}
rebuildSelector0();
}
private void rebuildSelector0() {
final Selector oldSelector = selector;
final SelectorTuple newSelectorTuple;
if (oldSelector == null) {
return;
}
try {
//新建selector
newSelectorTuple = openSelector();
} catch (Exception e) {
logger.warn("Failed to create a new Selector.", e);
return;
}
//把所有的channels注册到新的selector
int nChannels = 0;
for (SelectionKey key: oldSelector.keys()) {
Object a = key.attachment();
try {
if (!key.isValid() || key.channel().keyFor(newSelectorTuple.unwrappedSelector) != null) {
continue;
}
int interestOps = key.interestOps();
key.cancel();
SelectionKey newKey = key.channel().register(newSelectorTuple.unwrappedSelector, interestOps, a);
if (a instanceof AbstractNioChannel) {
//NioChannel重新赋值
((AbstractNioChannel) a).selectionKey = newKey;
}
nChannels ++;
} catch (Exception e) {
logger.warn("Failed to re-register a Channel to the new Selector.", e);
if (a instanceof AbstractNioChannel) {
AbstractNioChannel ch = (AbstractNioChannel) a;
ch.unsafe().close(ch.unsafe().voidPromise());
} else {
@SuppressWarnings("unchecked")
NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
invokeChannelUnregistered(task, key, e);
}
}
}
selector = newSelectorTuple.selector;
unwrappedSelector = newSelectorTuple.unwrappedSelector;
try {
// time to close the old selector as everything else is registered to the new one
oldSelector.close();
} catch (Throwable t) {
if (logger.isWarnEnabled()) {
logger.warn("Failed to close the old Selector.", t);
}
}
logger.info("Migrated " + nChannels + " channel(s) to the new Selector.");
}
