From d3fd30960969807b3c08aec80a0d298a009924d1 Mon Sep 17 00:00:00 2001
From: akwizgran <michael@briarproject.org>
Date: Fri, 8 May 2020 14:35:50 +0100
Subject: [PATCH] Only check timeouts when we have some streams to monitor.

---
 .../bramble/io/TimeoutMonitorImpl.java        | 47 ++++++++++++++-----
 1 file changed, 36 insertions(+), 11 deletions(-)

diff --git a/bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java b/bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java
index 0411e9c19..25ea97869 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java
@@ -7,12 +7,14 @@ import org.briarproject.bramble.api.system.Scheduler;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.Executor;
+import java.util.concurrent.Future;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -28,35 +30,58 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 
 	private static final long CHECK_INTERVAL_MS = SECONDS.toMillis(10);
 
+	private final ScheduledExecutorService scheduler;
 	private final Executor ioExecutor;
 	private final Clock clock;
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final List<TimeoutInputStream> streams = new ArrayList<>();
 
-	private final List<TimeoutInputStream> streams =
-			new CopyOnWriteArrayList<>();
+	@GuardedBy("lock")
+	private Future<?> task = null;
 
 	@Inject
-	TimeoutMonitorImpl(@IoExecutor Executor ioExecutor, Clock clock,
-			@Scheduler ScheduledExecutorService scheduler) {
+	TimeoutMonitorImpl(@Scheduler ScheduledExecutorService scheduler,
+			@IoExecutor Executor ioExecutor, Clock clock) {
+		this.scheduler = scheduler;
 		this.ioExecutor = ioExecutor;
 		this.clock = clock;
-		scheduler.scheduleWithFixedDelay(this::checkTimeouts,
-				CHECK_INTERVAL_MS, CHECK_INTERVAL_MS, MILLISECONDS);
 	}
 
 	@Override
 	public InputStream createTimeoutInputStream(InputStream in,
 			long timeoutMs) {
 		TimeoutInputStream stream = new TimeoutInputStream(clock, in,
-				timeoutMs * 1_000_000, streams::remove);
-		streams.add(stream);
+				timeoutMs * 1_000_000, this::removeStream);
+		synchronized (lock) {
+			if (streams.isEmpty()) {
+				task = scheduler.scheduleWithFixedDelay(this::checkTimeouts,
+						CHECK_INTERVAL_MS, CHECK_INTERVAL_MS, MILLISECONDS);
+			}
+			streams.add(stream);
+		}
 		return stream;
 	}
 
+	private void removeStream(TimeoutInputStream stream) {
+		Future<?> toCancel = null;
+		synchronized (lock) {
+			if (streams.remove(stream) && streams.isEmpty()) {
+				toCancel = task;
+				task = null;
+			}
+		}
+		if (toCancel != null) toCancel.cancel(false);
+	}
+
 	@Scheduler
 	private void checkTimeouts() {
 		ioExecutor.execute(() -> {
-			LOG.info("Checking input stream timeouts");
-			for (TimeoutInputStream stream : streams) {
+			List<TimeoutInputStream> snapshot;
+			synchronized (lock) {
+				snapshot = new ArrayList<>(streams);
+			}
+			for (TimeoutInputStream stream : snapshot) {
 				if (stream.hasTimedOut()) {
 					LOG.info("Input stream has timed out");
 					try {