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/*
* Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
* or more contributor license agreements. Licensed under the Elastic License
* 2.0 and the Server Side Public License, v 1; you may not use this file except
* in compliance with, at your election, the Elastic License 2.0 or the Server
* Side Public License, v 1.
*/
package org.elasticsearch.common.util.concurrent;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.elasticsearch.action.support.ContextPreservingActionListener;
import org.elasticsearch.client.OriginSettingClient;
import org.elasticsearch.common.collect.MapBuilder;
import org.elasticsearch.common.collect.Tuple;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.io.stream.Writeable;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.http.HttpTransportSettings;
import org.elasticsearch.tasks.Task;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Stream;
import static org.elasticsearch.http.HttpTransportSettings.SETTING_HTTP_MAX_WARNING_HEADER_COUNT;
import static org.elasticsearch.http.HttpTransportSettings.SETTING_HTTP_MAX_WARNING_HEADER_SIZE;
/**
* A ThreadContext is a map of string headers and a transient map of keyed objects that are associated with
* a thread. It allows to store and retrieve header information across method calls, network calls as well as threads spawned from a
* thread that has a {@link ThreadContext} associated with. Threads spawned from a {@link org.elasticsearch.threadpool.ThreadPool}
* have out of the box support for {@link ThreadContext} and all threads spawned will inherit the {@link ThreadContext} from the thread
* that it is forking from.". Network calls will also preserve the senders headers automatically.
*
* Consumers of ThreadContext usually don't need to interact with adding or stashing contexts. Every elasticsearch thread is managed by
* a thread pool or executor being responsible for stashing and restoring the threads context. For instance if a network request is
* received, all headers are deserialized from the network and directly added as the headers of the threads {@link ThreadContext}
* (see {@link #readHeaders(StreamInput)}. In order to not modify the context that is currently active on this thread the network code
* uses a try/with pattern to stash it's current context, read headers into a fresh one and once the request is handled or a handler thread
* is forked (which in turn inherits the context) it restores the previous context. For instance:
*
*
* // current context is stashed and replaced with a default context
* try (StoredContext context = threadContext.stashContext()) {
* threadContext.readHeaders(in); // read headers into current context
* if (fork) {
* threadPool.execute(() -> request.handle()); // inherits context
* } else {
* request.handle();
* }
* }
* // previous context is restored on StoredContext#close()
*
*
*/
public final class ThreadContext implements Writeable {
public static final String PREFIX = "request.headers";
public static final Setting DEFAULT_HEADERS_SETTING = Setting.groupSetting(PREFIX + ".", Property.NodeScope);
/**
* Name for the {@link #stashWithOrigin origin} attribute.
*/
public static final String ACTION_ORIGIN_TRANSIENT_NAME = "action.origin";
private static final Logger logger = LogManager.getLogger(ThreadContext.class);
private static final ThreadContextStruct DEFAULT_CONTEXT = new ThreadContextStruct();
private final Map defaultHeader;
private final ThreadLocal threadLocal;
private final int maxWarningHeaderCount;
private final long maxWarningHeaderSize;
/**
* Creates a new ThreadContext instance
* @param settings the settings to read the default request headers from
*/
public ThreadContext(Settings settings) {
this.defaultHeader = buildDefaultHeaders(settings);
this.threadLocal = ThreadLocal.withInitial(() -> DEFAULT_CONTEXT);
this.maxWarningHeaderCount = SETTING_HTTP_MAX_WARNING_HEADER_COUNT.get(settings);
this.maxWarningHeaderSize = SETTING_HTTP_MAX_WARNING_HEADER_SIZE.get(settings).getBytes();
}
/**
* Removes the current context and resets a default context. The removed context can be
* restored by closing the returned {@link StoredContext}.
*/
public StoredContext stashContext() {
final ThreadContextStruct context = threadLocal.get();
/**
* X-Opaque-ID should be preserved in a threadContext in order to propagate this across threads.
* This is needed so the DeprecationLogger in another thread can see the value of X-Opaque-ID provided by a user.
* Otherwise when context is stash, it should be empty.
*/
if (context.requestHeaders.containsKey(Task.X_OPAQUE_ID)) {
ThreadContextStruct threadContextStruct =
DEFAULT_CONTEXT.putHeaders(MapBuilder.newMapBuilder()
.put(Task.X_OPAQUE_ID, context.requestHeaders.get(Task.X_OPAQUE_ID))
.immutableMap());
threadLocal.set(threadContextStruct);
} else {
threadLocal.set(DEFAULT_CONTEXT);
}
return () -> {
// If the node and thus the threadLocal get closed while this task
// is still executing, we don't want this runnable to fail with an
// uncaught exception
threadLocal.set(context);
};
}
/**
* Captures the current thread context as writeable, allowing it to be serialized out later
*/
public Writeable captureAsWriteable() {
final ThreadContextStruct context = threadLocal.get();
return out -> context.writeTo(out, defaultHeader);
}
/**
* Removes the current context and resets a default context marked with as
* originating from the supplied string. The removed context can be
* restored by closing the returned {@link StoredContext}. Callers should
* be careful to save the current context before calling this method and
* restore it any listeners, likely with
* {@link ContextPreservingActionListener}. Use {@link OriginSettingClient}
* which can be used to do this automatically.
*
* Without security the origin is ignored, but security uses it to authorize
* actions that are made up of many sub-actions. These actions call
* {@link #stashWithOrigin} before performing on behalf of a user that
* should be allowed even if the user doesn't have permission to perform
* those actions on their own.
*
* For example, a user might not have permission to GET from the tasks index
* but the tasks API will perform a get on their behalf using this method
* if it can't find the task in memory.
*/
public StoredContext stashWithOrigin(String origin) {
final ThreadContext.StoredContext storedContext = stashContext();
putTransient(ACTION_ORIGIN_TRANSIENT_NAME, origin);
return storedContext;
}
/**
* Removes the current context and resets a new context that contains a merge of the current headers and the given headers.
* The removed context can be restored when closing the returned {@link StoredContext}. The merge strategy is that headers
* that are already existing are preserved unless they are defaults.
*/
public StoredContext stashAndMergeHeaders(Map headers) {
final ThreadContextStruct context = threadLocal.get();
Map newHeader = new HashMap<>(headers);
newHeader.putAll(context.requestHeaders);
threadLocal.set(DEFAULT_CONTEXT.putHeaders(newHeader));
return () -> threadLocal.set(context);
}
/**
* Just like {@link #stashContext()} but no default context is set.
* @param preserveResponseHeaders if set to true the response headers of the restore thread will be preserved.
*/
public StoredContext newStoredContext(boolean preserveResponseHeaders) {
return newStoredContext(preserveResponseHeaders, Collections.emptyList());
}
/**
* Just like {@link #stashContext()} but no default context is set. Instead, the {@code transientHeadersToClear} argument can be used
* to clear specific transient headers in the new context. All headers (with the possible exception of {@code responseHeaders}) are
* restored by closing the returned {@link StoredContext}.
*
* @param preserveResponseHeaders if set to true the response headers of the restore thread will be preserved.
*/
public StoredContext newStoredContext(boolean preserveResponseHeaders, Collection transientHeadersToClear) {
final ThreadContextStruct originalContext = threadLocal.get();
// clear specific transient headers from the current context
Map newTransientHeaders = null;
for (String transientHeaderToClear : transientHeadersToClear) {
if (originalContext.transientHeaders.containsKey(transientHeaderToClear)) {
if (newTransientHeaders == null) {
newTransientHeaders = new HashMap<>(originalContext.transientHeaders);
}
newTransientHeaders.remove(transientHeaderToClear);
}
}
if (newTransientHeaders != null) {
ThreadContextStruct threadContextStruct = new ThreadContextStruct(originalContext.requestHeaders,
originalContext.responseHeaders, newTransientHeaders, originalContext.isSystemContext,
originalContext.warningHeadersSize);
threadLocal.set(threadContextStruct);
}
// this is the context when this method returns
final ThreadContextStruct newContext = threadLocal.get();
return () -> {
if (preserveResponseHeaders && threadLocal.get() != newContext) {
threadLocal.set(originalContext.putResponseHeaders(threadLocal.get().responseHeaders));
} else {
threadLocal.set(originalContext);
}
};
}
/**
* Returns a supplier that gathers a {@link #newStoredContext(boolean)} and restores it once the
* returned supplier is invoked. The context returned from the supplier is a stored version of the
* suppliers callers context that should be restored once the originally gathered context is not needed anymore.
* For instance this method should be used like this:
*
*
* Supplier<ThreadContext.StoredContext> restorable = context.newRestorableContext(true);
* new Thread() {
* public void run() {
* try (ThreadContext.StoredContext ctx = restorable.get()) {
* // execute with the parents context and restore the threads context afterwards
* }
* }
*
* }.start();
*
*
* @param preserveResponseHeaders if set to true the response headers of the restore thread will be preserved.
* @return a restorable context supplier
*/
public Supplier newRestorableContext(boolean preserveResponseHeaders) {
return wrapRestorable(newStoredContext(preserveResponseHeaders));
}
/**
* Same as {@link #newRestorableContext(boolean)} but wraps an existing context to restore.
* @param storedContext the context to restore
*/
public Supplier wrapRestorable(StoredContext storedContext) {
return () -> {
StoredContext context = newStoredContext(false);
storedContext.restore();
return context;
};
}
@Override
public void writeTo(StreamOutput out) throws IOException {
threadLocal.get().writeTo(out, defaultHeader);
}
/**
* Reads the headers from the stream into the current context
*/
public void readHeaders(StreamInput in) throws IOException {
setHeaders(readHeadersFromStream(in));
}
public void setHeaders(Tuple, Map>> headerTuple) {
final Map requestHeaders = headerTuple.v1();
final Map> responseHeaders = headerTuple.v2();
final ThreadContextStruct struct;
if (requestHeaders.isEmpty() && responseHeaders.isEmpty()) {
struct = ThreadContextStruct.EMPTY;
} else {
struct = new ThreadContextStruct(requestHeaders, responseHeaders, Collections.emptyMap(), false);
}
threadLocal.set(struct);
}
public static Tuple, Map>> readHeadersFromStream(StreamInput in) throws IOException {
final Map requestHeaders = in.readMap(StreamInput::readString, StreamInput::readString);
final Map> responseHeaders = in.readMap(StreamInput::readString, input -> {
final int size = input.readVInt();
if (size == 0) {
return Collections.emptySet();
} else if (size == 1) {
return Collections.singleton(input.readString());
} else {
// use a linked hash set to preserve order
final LinkedHashSet values = new LinkedHashSet<>(size);
for (int i = 0; i < size; i++) {
final String value = input.readString();
final boolean added = values.add(value);
assert added : value;
}
return values;
}
});
return new Tuple<>(requestHeaders, responseHeaders);
}
/**
* Returns the header for the given key or null if not present
*/
public String getHeader(String key) {
String value = threadLocal.get().requestHeaders.get(key);
if (value == null) {
return defaultHeader.get(key);
}
return value;
}
/**
* Returns all of the request headers from the thread's context.
* Be advised, headers might contain credentials.
* In order to avoid storing, and erroneously exposing, such headers,
* it is recommended to instead store security headers that prove
* the credentials have been verified successfully, and which are
* internal to the system, in the sense that they cannot be sent
* by the clients.
*/
public Map getHeaders() {
HashMap map = new HashMap<>(defaultHeader);
map.putAll(threadLocal.get().requestHeaders);
return Collections.unmodifiableMap(map);
}
/**
* Returns the request headers, without the default headers
*/
public Map getRequestHeadersOnly() {
return Collections.unmodifiableMap(new HashMap<>(threadLocal.get().requestHeaders));
}
/**
* Get a copy of all response headers.
*
* @return Never {@code null}.
*/
public Map> getResponseHeaders() {
Map> responseHeaders = threadLocal.get().responseHeaders;
HashMap> map = new HashMap<>(responseHeaders.size());
for (Map.Entry> entry : responseHeaders.entrySet()) {
map.put(entry.getKey(), Collections.unmodifiableList(new ArrayList<>(entry.getValue())));
}
return Collections.unmodifiableMap(map);
}
/**
* Copies all header key, value pairs into the current context
*/
public void copyHeaders(Iterable> headers) {
threadLocal.set(threadLocal.get().copyHeaders(headers));
}
/**
* Puts a header into the context
*/
public void putHeader(String key, String value) {
threadLocal.set(threadLocal.get().putRequest(key, value));
}
/**
* Puts all of the given headers into this context
*/
public void putHeader(Map header) {
threadLocal.set(threadLocal.get().putHeaders(header));
}
/**
* Puts a transient header object into this context
*/
public void putTransient(String key, Object value) {
threadLocal.set(threadLocal.get().putTransient(key, value));
}
/**
* Returns a transient header object or null if there is no header for the given key
*/
@SuppressWarnings("unchecked") // (T)object
public T getTransient(String key) {
return (T) threadLocal.get().transientHeaders.get(key);
}
/**
* Add the {@code value} for the specified {@code key} Any duplicate {@code value} is ignored.
*
* @param key the header name
* @param value the header value
*/
public void addResponseHeader(final String key, final String value) {
addResponseHeader(key, value, v -> v);
}
/**
* Add the {@code value} for the specified {@code key} with the specified {@code uniqueValue} used for de-duplication. Any duplicate
* {@code value} after applying {@code uniqueValue} is ignored.
*
* @param key the header name
* @param value the header value
* @param uniqueValue the function that produces de-duplication values
*/
public void addResponseHeader(final String key, final String value, final Function uniqueValue) {
threadLocal.set(threadLocal.get().putResponse(key, value, uniqueValue, maxWarningHeaderCount, maxWarningHeaderSize));
}
/**
* Saves the current thread context and wraps command in a Runnable that restores that context before running command. If
* command has already been passed through this method then it is returned unaltered rather than wrapped twice.
*/
public Runnable preserveContext(Runnable command) {
if (command instanceof ContextPreservingAbstractRunnable) {
return command;
}
if (command instanceof ContextPreservingRunnable) {
return command;
}
if (command instanceof AbstractRunnable) {
return new ContextPreservingAbstractRunnable((AbstractRunnable) command);
}
return new ContextPreservingRunnable(command);
}
/**
* Unwraps a command that was previously wrapped by {@link #preserveContext(Runnable)}.
*/
public Runnable unwrap(Runnable command) {
if (command instanceof WrappedRunnable) {
return ((WrappedRunnable) command).unwrap();
}
return command;
}
/**
* Returns true if the current context is the default context.
*/
boolean isDefaultContext() {
return threadLocal.get() == DEFAULT_CONTEXT;
}
/**
* Marks this thread context as an internal system context. This signals that actions in this context are issued
* by the system itself rather than by a user action.
*/
public void markAsSystemContext() {
threadLocal.set(threadLocal.get().setSystemContext());
}
/**
* Returns true iff this context is a system context
*/
public boolean isSystemContext() {
return threadLocal.get().isSystemContext;
}
@FunctionalInterface
public interface StoredContext extends AutoCloseable {
@Override
void close();
default void restore() {
close();
}
}
public static Map buildDefaultHeaders(Settings settings) {
Settings headers = DEFAULT_HEADERS_SETTING.get(settings);
if (headers == null) {
return Collections.emptyMap();
} else {
Map defaultHeader = new HashMap<>();
for (String key : headers.names()) {
defaultHeader.put(key, headers.get(key));
}
return Collections.unmodifiableMap(defaultHeader);
}
}
private static final class ThreadContextStruct {
private static final ThreadContextStruct EMPTY =
new ThreadContextStruct(Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), false);
private final Map requestHeaders;
private final Map transientHeaders;
private final Map> responseHeaders;
private final boolean isSystemContext;
//saving current warning headers' size not to recalculate the size with every new warning header
private final long warningHeadersSize;
private ThreadContextStruct setSystemContext() {
if (isSystemContext) {
return this;
}
return new ThreadContextStruct(requestHeaders, responseHeaders, transientHeaders, true);
}
private ThreadContextStruct(Map requestHeaders,
Map> responseHeaders,
Map transientHeaders, boolean isSystemContext) {
this.requestHeaders = requestHeaders;
this.responseHeaders = responseHeaders;
this.transientHeaders = transientHeaders;
this.isSystemContext = isSystemContext;
this.warningHeadersSize = 0L;
}
private ThreadContextStruct(Map requestHeaders,
Map> responseHeaders,
Map transientHeaders, boolean isSystemContext,
long warningHeadersSize) {
this.requestHeaders = requestHeaders;
this.responseHeaders = responseHeaders;
this.transientHeaders = transientHeaders;
this.isSystemContext = isSystemContext;
this.warningHeadersSize = warningHeadersSize;
}
/**
* This represents the default context and it should only ever be called by {@link #DEFAULT_CONTEXT}.
*/
private ThreadContextStruct() {
this(Collections.emptyMap(), Collections.emptyMap(), Collections.emptyMap(), false);
}
private ThreadContextStruct putRequest(String key, String value) {
Map newRequestHeaders = new HashMap<>(this.requestHeaders);
putSingleHeader(key, value, newRequestHeaders);
return new ThreadContextStruct(newRequestHeaders, responseHeaders, transientHeaders, isSystemContext);
}
private static void putSingleHeader(String key, T value, Map newHeaders) {
if (newHeaders.putIfAbsent(key, value) != null) {
throw new IllegalArgumentException("value for key [" + key + "] already present");
}
}
private ThreadContextStruct putHeaders(Map headers) {
if (headers.isEmpty()) {
return this;
} else {
final Map newHeaders = new HashMap<>(this.requestHeaders);
for (Map.Entry entry : headers.entrySet()) {
putSingleHeader(entry.getKey(), entry.getValue(), newHeaders);
}
return new ThreadContextStruct(newHeaders, responseHeaders, transientHeaders, isSystemContext);
}
}
private ThreadContextStruct putResponseHeaders(Map> headers) {
assert headers != null;
if (headers.isEmpty()) {
return this;
}
final Map> newResponseHeaders = new HashMap<>(this.responseHeaders);
for (Map.Entry> entry : headers.entrySet()) {
String key = entry.getKey();
final Set existingValues = newResponseHeaders.get(key);
if (existingValues != null) {
final Set newValues =
Stream.concat(entry.getValue().stream(), existingValues.stream()).collect(LINKED_HASH_SET_COLLECTOR);
newResponseHeaders.put(key, Collections.unmodifiableSet(newValues));
} else {
newResponseHeaders.put(key, entry.getValue());
}
}
return new ThreadContextStruct(requestHeaders, newResponseHeaders, transientHeaders, isSystemContext);
}
private ThreadContextStruct putResponse(final String key, final String value, final Function uniqueValue,
final int maxWarningHeaderCount, final long maxWarningHeaderSize) {
assert value != null;
long newWarningHeaderSize = warningHeadersSize;
//check if we can add another warning header - if max size within limits
if (key.equals("Warning") && (maxWarningHeaderSize != -1)) { //if size is NOT unbounded, check its limits
if (warningHeadersSize > maxWarningHeaderSize) { // if max size has already been reached before
logger.warn("Dropping a warning header, as their total size reached the maximum allowed of ["
+ maxWarningHeaderSize + "] bytes set in ["
+ HttpTransportSettings.SETTING_HTTP_MAX_WARNING_HEADER_SIZE.getKey() + "]!");
return this;
}
newWarningHeaderSize += "Warning".getBytes(StandardCharsets.UTF_8).length + value.getBytes(StandardCharsets.UTF_8).length;
if (newWarningHeaderSize > maxWarningHeaderSize) {
logger.warn("Dropping a warning header, as their total size reached the maximum allowed of ["
+ maxWarningHeaderSize + "] bytes set in ["
+ HttpTransportSettings.SETTING_HTTP_MAX_WARNING_HEADER_SIZE.getKey() + "]!");
return new ThreadContextStruct(requestHeaders, responseHeaders,
transientHeaders, isSystemContext, newWarningHeaderSize);
}
}
final Map> newResponseHeaders;
final Set existingValues = responseHeaders.get(key);
if (existingValues != null) {
if (existingValues.contains(uniqueValue.apply(value))) {
return this;
}
// preserve insertion order
final Set newValues = Stream.concat(existingValues.stream(), Stream.of(value)).collect(LINKED_HASH_SET_COLLECTOR);
newResponseHeaders = new HashMap<>(responseHeaders);
newResponseHeaders.put(key, Collections.unmodifiableSet(newValues));
} else {
newResponseHeaders = new HashMap<>(responseHeaders);
newResponseHeaders.put(key, Collections.singleton(value));
}
//check if we can add another warning header - if max count within limits
if ((key.equals("Warning")) && (maxWarningHeaderCount != -1)) { //if count is NOT unbounded, check its limits
final int warningHeaderCount = newResponseHeaders.containsKey("Warning") ? newResponseHeaders.get("Warning").size() : 0;
if (warningHeaderCount > maxWarningHeaderCount) {
logger.warn("Dropping a warning header, as their total count reached the maximum allowed of ["
+ maxWarningHeaderCount + "] set in ["
+ HttpTransportSettings.SETTING_HTTP_MAX_WARNING_HEADER_COUNT.getKey() + "]!");
return this;
}
}
return new ThreadContextStruct(requestHeaders, newResponseHeaders, transientHeaders, isSystemContext, newWarningHeaderSize);
}
private ThreadContextStruct putTransient(String key, Object value) {
Map newTransient = new HashMap<>(this.transientHeaders);
putSingleHeader(key, value, newTransient);
return new ThreadContextStruct(requestHeaders, responseHeaders, newTransient, isSystemContext);
}
private ThreadContextStruct copyHeaders(Iterable> headers) {
Map newHeaders = new HashMap<>();
for (Map.Entry header : headers) {
newHeaders.put(header.getKey(), header.getValue());
}
return putHeaders(newHeaders);
}
private void writeTo(StreamOutput out, Map defaultHeaders) throws IOException {
final Map requestHeaders;
if (defaultHeaders.isEmpty()) {
requestHeaders = this.requestHeaders;
} else {
requestHeaders = new HashMap<>(defaultHeaders);
requestHeaders.putAll(this.requestHeaders);
}
out.writeVInt(requestHeaders.size());
for (Map.Entry entry : requestHeaders.entrySet()) {
out.writeString(entry.getKey());
out.writeString(entry.getValue());
}
out.writeMap(responseHeaders, StreamOutput::writeString, StreamOutput::writeStringCollection);
}
}
/**
* Wraps a Runnable to preserve the thread context.
*/
private class ContextPreservingRunnable implements WrappedRunnable {
private final Runnable in;
private final ThreadContext.StoredContext ctx;
private ContextPreservingRunnable(Runnable in) {
ctx = newStoredContext(false);
this.in = in;
}
@Override
public void run() {
try (ThreadContext.StoredContext ignore = stashContext()){
ctx.restore();
in.run();
}
}
@Override
public String toString() {
return in.toString();
}
@Override
public Runnable unwrap() {
return in;
}
}
/**
* Wraps an AbstractRunnable to preserve the thread context.
*/
private class ContextPreservingAbstractRunnable extends AbstractRunnable implements WrappedRunnable {
private final AbstractRunnable in;
private final ThreadContext.StoredContext creatorsContext;
private ThreadContext.StoredContext threadsOriginalContext = null;
private ContextPreservingAbstractRunnable(AbstractRunnable in) {
creatorsContext = newStoredContext(false);
this.in = in;
}
@Override
public boolean isForceExecution() {
return in.isForceExecution();
}
@Override
public void onAfter() {
try {
in.onAfter();
} finally {
if (threadsOriginalContext != null) {
threadsOriginalContext.restore();
}
}
}
@Override
public void onFailure(Exception e) {
in.onFailure(e);
}
@Override
public void onRejection(Exception e) {
in.onRejection(e);
}
@Override
protected void doRun() throws Exception {
threadsOriginalContext = stashContext();
creatorsContext.restore();
in.doRun();
}
@Override
public String toString() {
return in.toString();
}
@Override
public AbstractRunnable unwrap() {
return in;
}
}
private static final Collector, Set> LINKED_HASH_SET_COLLECTOR = new LinkedHashSetCollector<>();
private static class LinkedHashSetCollector implements Collector, Set> {
@Override
public Supplier> supplier() {
return LinkedHashSet::new;
}
@Override
public BiConsumer, T> accumulator() {
return Set::add;
}
@Override
public BinaryOperator> combiner() {
return (left, right) -> {
left.addAll(right);
return left;
};
}
@Override
public Function, Set> finisher() {
return Function.identity();
}
private static final Set CHARACTERISTICS =
Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.IDENTITY_FINISH));
@Override
public Set characteristics() {
return CHARACTERISTICS;
}
}
}