/*
* Copyright (C) 2014 Square, Inc.
*
* Licensed 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 okio;
import java.io.IOException;
import java.io.InterruptedIOException;
/**
* This timeout uses a background thread to take action exactly when the timeout
* occurs. Use this to implement timeouts where they aren't supported natively,
* such as to sockets that are blocked on writing.
*
* <p>Subclasses should override {@link #timedOut} to take action when a timeout
* occurs. This method will be invoked by the shared watchdog thread so it
* should not do any long-running operations. Otherwise we risk starving other
* timeouts from being triggered.
*
* <p>Use {@link #sink} and {@link #source} to apply this timeout to a stream.
* The returned value will apply the timeout to each operation on the wrapped
* stream.
*
* <p>Callers should call {@link #enter} before doing work that is subject to
* timeouts, and {@link #exit} afterwards. The return value of {@link #exit}
* indicates whether a timeout was triggered. Note that the call to {@link
* #timedOut} is asynchronous, and may be called after {@link #exit}.
*/
public class AsyncTimeout extends Timeout {
/**
* The watchdog thread processes a linked list of pending timeouts, sorted in
* the order to be triggered. This class synchronizes on AsyncTimeout.class.
* This lock guards the queue.
*
* <p>Head's 'next' points to the first element of the linked list. The first
* element is the next node to time out, or null if the queue is empty. The
* head is null until the watchdog thread is started.
*/
private static AsyncTimeout head;
/** True if this node is currently in the queue. */
private boolean inQueue;
/** The next node in the linked list. */
private AsyncTimeout next;
/** If scheduled, this is the time that the watchdog should time this out. */
private long timeoutAt;
public final void enter() {
if (inQueue) throw new IllegalStateException("Unbalanced enter/exit");
long timeoutNanos = timeoutNanos();
boolean hasDeadline = hasDeadline();
if (timeoutNanos == 0 && !hasDeadline) {
return; // No timeout and no deadline? Don't bother with the queue.
}
inQueue = true;
scheduleTimeout(this, timeoutNanos, hasDeadline);
}
private static synchronized void scheduleTimeout(
AsyncTimeout node, long timeoutNanos, boolean hasDeadline) {
// Start the watchdog thread and create the head node when the first timeout is scheduled.
if (head == null) {
head = new AsyncTimeout();
new Watchdog().start();
}
long now = System.nanoTime();
if (timeoutNanos != 0 && hasDeadline) {
// Compute the earliest event; either timeout or deadline. Because nanoTime can wrap around,
// Math.min() is undefined for absolute values, but meaningful for relative ones.
node.timeoutAt = now + Math.min(timeoutNanos, node.deadlineNanoTime() - now);
} else if (timeoutNanos != 0) {
node.timeoutAt = now + timeoutNanos;
} else if (hasDeadline) {
node.timeoutAt = node.deadlineNanoTime();
} else {
throw new AssertionError();
}
// Insert the node in sorted order.
long remainingNanos = node.remainingNanos(now);
for (AsyncTimeout prev = head; true; prev = prev.next) {
if (prev.next == null || remainingNanos < prev.next.remainingNanos(now)) {
node.next = prev.next;
prev.next = node;
if (prev == head) {
AsyncTimeout.class.notify(); // Wake up the watchdog when inserting at the front.
}
break;
}
}
}
/** Returns true if the timeout occurred. */
public final boolean exit() {
if (!inQueue) return false;
inQueue = false;
return cancelScheduledTimeout(this);
}
/** Returns true if the timeout occurred. */
private static synchronized boolean cancelScheduledTimeout(AsyncTimeout node) {
// Remove the node from the linked list.
for (AsyncTimeout prev = head; prev != null; prev = prev.next) {
if (prev.next == node) {
prev.next = node.next;
node.next = null;
return false;
}
}
// The node wasn't found in the linked list: it must have timed out!
return true;
}
/**
* Returns the amount of time left until the time out. This will be negative
* if the timeout has elapsed and the timeout should occur immediately.
*/
private long remainingNanos(long now) {
return timeoutAt - now;
}
/**
* Invoked by the watchdog thread when the time between calls to {@link
* #enter()} and {@link #exit()} has exceeded the timeout.
*/
protected void timedOut() {
}
/**
* Returns a new sink that delegates to {@code sink}, using this to implement
* timeouts. This works best if {@link #timedOut} is overridden to interrupt
* {@code sink}'s current operation.
*/
public final Sink sink(final Sink sink) {
return new Sink() {
@Override public void write(Buffer source, long byteCount) throws IOException {
boolean throwOnTimeout = false;
enter();
try {
sink.write(source, byteCount);
throwOnTimeout = true;
} catch (IOException e) {
throw exit(e);
} finally {
exit(throwOnTimeout);
}
}
@Override public void flush() throws IOException {
boolean throwOnTimeout = false;
enter();
try {
sink.flush();
throwOnTimeout = true;
} catch (IOException e) {
throw exit(e);
} finally {
exit(throwOnTimeout);
}
}
@Override public void close() throws IOException {
boolean throwOnTimeout = false;
enter();
try {
sink.close();
throwOnTimeout = true;
} catch (IOException e) {
throw exit(e);
} finally {
exit(throwOnTimeout);
}
}
@Override public Timeout timeout() {
return AsyncTimeout.this;
}
@Override public String toString() {
return "AsyncTimeout.sink(" + sink + ")";
}
};
}
/**
* Returns a new source that delegates to {@code source}, using this to
* implement timeouts. This works best if {@link #timedOut} is overridden to
* interrupt {@code sink}'s current operation.
*/
public final Source source(final Source source) {
return new Source() {
@Override public long read(Buffer sink, long byteCount) throws IOException {
boolean throwOnTimeout = false;
enter();
try {
long result = source.read(sink, byteCount);
throwOnTimeout = true;
return result;
} catch (IOException e) {
throw exit(e);
} finally {
exit(throwOnTimeout);
}
}
@Override public void close() throws IOException {
boolean throwOnTimeout = false;
try {
source.close();
throwOnTimeout = true;
} catch (IOException e) {
throw exit(e);
} finally {
exit(throwOnTimeout);
}
}
@Override public Timeout timeout() {
return AsyncTimeout.this;
}
@Override public String toString() {
return "AsyncTimeout.source(" + source + ")";
}
};
}
/**
* Throws an IOException if {@code throwOnTimeout} is {@code true} and a
* timeout occurred. See {@link #newTimeoutException(java.io.IOException)}
* for the type of exception thrown.
*/
final void exit(boolean throwOnTimeout) throws IOException {
boolean timedOut = exit();
if (timedOut && throwOnTimeout) throw newTimeoutException(null);
}
/**
* Returns either {@code cause} or an IOException that's caused by
* {@code cause} if a timeout occurred. See
* {@link #newTimeoutException(java.io.IOException)} for the type of
* exception returned.
*/
final IOException exit(IOException cause) throws IOException {
if (!exit()) return cause;
return newTimeoutException(cause);
}
/**
* Returns an {@link IOException} to represent a timeout. By default this method returns
* {@link java.io.InterruptedIOException}. If {@code cause} is non-null it is set as the cause of
* the returned exception.
*/
protected IOException newTimeoutException(IOException cause) {
InterruptedIOException e = new InterruptedIOException("timeout");
if (cause != null) {
e.initCause(cause);
}
return e;
}
private static final class Watchdog extends Thread {
public Watchdog() {
super("Okio Watchdog");
setDaemon(true);
}
public void run() {
while (true) {
try {
AsyncTimeout timedOut = awaitTimeout();
// Didn't find a node to interrupt. Try again.
if (timedOut == null) continue;
// Close the timed out node.
timedOut.timedOut();
} catch (InterruptedException ignored) {
}
}
}
}
/**
* Removes and returns the node at the head of the list, waiting for it to
* time out if necessary. Returns null if the situation changes while waiting:
* either a newer node is inserted at the head, or the node being waited on
* has been removed.
*/
private static synchronized AsyncTimeout awaitTimeout() throws InterruptedException {
// Get the next eligible node.
AsyncTimeout node = head.next;
// The queue is empty. Wait for something to be enqueued.
if (node == null) {
AsyncTimeout.class.wait();
return null;
}
long waitNanos = node.remainingNanos(System.nanoTime());
// The head of the queue hasn't timed out yet. Await that.
if (waitNanos > 0) {
// Waiting is made complicated by the fact that we work in nanoseconds,
// but the API wants (millis, nanos) in two arguments.
long waitMillis = waitNanos / 1000000L;
waitNanos -= (waitMillis * 1000000L);
AsyncTimeout.class.wait(waitMillis, (int) waitNanos);
return null;
}
// The head of the queue has timed out. Remove it.
head.next = node.next;
node.next = null;
return node;
}
}