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HostnameCache.java
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package io.sentry;
import io.sentry.util.Objects;
import java.net.InetAddress;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
/**
* Time sensitive cache in charge of keeping track of the hostname. The {@code
* InetAddress.getLocalHost().getCanonicalHostName()} call can be quite expensive and could be
* called for the creation of each {@link SentryEvent}. This system will prevent unnecessary costs
* by keeping track of the hostname for a period defined during the construction. For performance
* purposes, the operation of retrieving the hostname will automatically fail after a period of time
* defined by {@link #GET_HOSTNAME_TIMEOUT} without result.
*/
final class HostnameCache {
private static final long HOSTNAME_CACHE_DURATION = TimeUnit.HOURS.toMillis(5);
/** Time before the get hostname operation times out (in ms). */
private static final long GET_HOSTNAME_TIMEOUT = TimeUnit.SECONDS.toMillis(1);
/** Time for which the cache is kept. */
private final long cacheDuration;
/** Current value for hostname (might change over time). */
@Nullable private volatile String hostname;
/** Time at which the cache should expire. */
private volatile long expirationTimestamp;
/** Whether a cache update thread is currently running or not. */
private final @NotNull AtomicBoolean updateRunning = new AtomicBoolean(false);
private final @NotNull Callable<InetAddress> getLocalhost;
private final @NotNull ExecutorService executorService =
Executors.newSingleThreadExecutor(new HostnameCacheThreadFactory());
public HostnameCache() {
this(HOSTNAME_CACHE_DURATION);
}
HostnameCache(long cacheDuration) {
this(cacheDuration, () -> InetAddress.getLocalHost());
}
/**
* Sets up a cache for the hostname.
*
* @param cacheDuration cache duration in milliseconds.
* @param getLocalhost a callback to obtain the localhost address - this is mostly here because of
* testability
*/
HostnameCache(long cacheDuration, final @NotNull Callable<InetAddress> getLocalhost) {
this.cacheDuration = cacheDuration;
this.getLocalhost = Objects.requireNonNull(getLocalhost, "getLocalhost is required");
updateCache();
}
/**
* Gets the hostname of the current machine.
*
* <p>Gets the value from the cache if possible otherwise calls {@link #updateCache()}.
*
* @return the hostname of the current machine.
*/
@Nullable
String getHostname() {
if (expirationTimestamp < System.currentTimeMillis()
&& updateRunning.compareAndSet(false, true)) {
updateCache();
}
return hostname;
}
/** Force an update of the cache to get the current value of the hostname. */
private void updateCache() {
final Callable<Void> hostRetriever =
() -> {
try {
hostname = getLocalhost.call().getCanonicalHostName();
expirationTimestamp = System.currentTimeMillis() + cacheDuration;
} finally {
updateRunning.set(false);
}
return null;
};
try {
final Future<Void> futureTask = executorService.submit(hostRetriever);
futureTask.get(GET_HOSTNAME_TIMEOUT, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
handleCacheUpdateFailure();
} catch (ExecutionException | TimeoutException | RuntimeException e) {
handleCacheUpdateFailure();
}
}
private void handleCacheUpdateFailure() {
expirationTimestamp = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(1);
}
private static final class HostnameCacheThreadFactory implements ThreadFactory {
private int cnt;
@Override
public @NotNull Thread newThread(final @NotNull Runnable r) {
final Thread ret = new Thread(r, "SentryHostnameCache-" + cnt++);
ret.setDaemon(true);
return ret;
}
}
}