| /* |
| * Copyright 2015 The gRPC Authors |
| * |
| * 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 io.grpc; |
| |
| import io.grpc.Context.CheckReturnValue; |
| import java.io.Closeable; |
| import java.util.ArrayList; |
| import java.util.concurrent.Callable; |
| import java.util.concurrent.Executor; |
| import java.util.concurrent.ScheduledExecutorService; |
| import java.util.concurrent.ScheduledFuture; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.TimeoutException; |
| import java.util.concurrent.atomic.AtomicReference; |
| import java.util.logging.Level; |
| import java.util.logging.Logger; |
| |
| /** |
| * A context propagation mechanism which can carry scoped-values across API boundaries and between |
| * threads. Examples of state propagated via context include: |
| * <ul> |
| * <li>Security principals and credentials.</li> |
| * <li>Local and distributed tracing information.</li> |
| * </ul> |
| * |
| * <p>A Context object can be {@link #attach attached} to the {@link Storage}, which effectively |
| * forms a <b>scope</b> for the context. The scope is bound to the current thread. Within a scope, |
| * its Context is accessible even across API boundaries, through {@link #current}. The scope is |
| * later exited by {@link #detach detaching} the Context. |
| * |
| * <p>Context objects are immutable and inherit state from their parent. To add or overwrite the |
| * current state a new context object must be created and then attached, replacing the previously |
| * bound context. For example: |
| * |
| * <pre> |
| * Context withCredential = Context.current().withValue(CRED_KEY, cred); |
| * withCredential.run(new Runnable() { |
| * public void run() { |
| * readUserRecords(userId, CRED_KEY.get()); |
| * } |
| * }); |
| * </pre> |
| * |
| * <p>Contexts are also used to represent a scoped unit of work. When the unit of work is done the |
| * context can be cancelled. This cancellation will also cascade to all descendant contexts. You can |
| * add a {@link CancellationListener} to a context to be notified when it or one of its ancestors |
| * has been cancelled. Cancellation does not release the state stored by a context and it's |
| * perfectly valid to {@link #attach()} an already cancelled context to make it current. To cancel a |
| * context (and its descendants) you first create a {@link CancellableContext} and when you need to |
| * signal cancellation call {@link CancellableContext#cancel} or {@link |
| * CancellableContext#detachAndCancel}. For example: |
| * <pre> |
| * CancellableContext withCancellation = Context.current().withCancellation(); |
| * try { |
| * withCancellation.run(new Runnable() { |
| * public void run() { |
| * while (waitingForData() && !Context.current().isCancelled()) {} |
| * } |
| * }); |
| * doSomeWork(); |
| * } catch (Throwable t) { |
| * withCancellation.cancel(t); |
| * } |
| * </pre> |
| * |
| * <p>Contexts can also be created with a timeout relative to the system nano clock which will |
| * cause it to automatically cancel at the desired time. |
| * |
| * |
| * <p>Notes and cautions on use: |
| * <ul> |
| * <li>Every {@code attach()} should have a {@code detach()} in the same method. And every |
| * CancellableContext should be cancelled at some point. Breaking these rules may lead to memory |
| * leaks. |
| * <li>While Context objects are immutable they do not place such a restriction on the state |
| * they store.</li> |
| * <li>Context is not intended for passing optional parameters to an API and developers should |
| * take care to avoid excessive dependence on context when designing an API.</li> |
| * <li>Do not mock this class. Use {@link #ROOT} for a non-null instance. |
| * </ul> |
| */ |
| /* @DoNotMock("Use ROOT for a non-null Context") // commented out to avoid dependencies */ |
| @CheckReturnValue |
| public class Context { |
| |
| private static final Logger log = Logger.getLogger(Context.class.getName()); |
| |
| private static final PersistentHashArrayMappedTrie<Key<?>, Object> EMPTY_ENTRIES = |
| new PersistentHashArrayMappedTrie<Key<?>, Object>(); |
| |
| // Long chains of contexts are suspicious and usually indicate a misuse of Context. |
| // The threshold is arbitrarily chosen. |
| // VisibleForTesting |
| static final int CONTEXT_DEPTH_WARN_THRESH = 1000; |
| |
| /** |
| * The logical root context which is the ultimate ancestor of all contexts. This context |
| * is not cancellable and so will not cascade cancellation or retain listeners. |
| * |
| * <p>Never assume this is the default context for new threads, because {@link Storage} may define |
| * a default context that is different from ROOT. |
| */ |
| public static final Context ROOT = new Context(null, EMPTY_ENTRIES); |
| |
| // Lazy-loaded storage. Delaying storage initialization until after class initialization makes it |
| // much easier to avoid circular loading since there can still be references to Context as long as |
| // they don't depend on storage, like key() and currentContextExecutor(). It also makes it easier |
| // to handle exceptions. |
| private static final AtomicReference<Storage> storage = new AtomicReference<Storage>(); |
| |
| // For testing |
| static Storage storage() { |
| Storage tmp = storage.get(); |
| if (tmp == null) { |
| tmp = createStorage(); |
| } |
| return tmp; |
| } |
| |
| private static Storage createStorage() { |
| // Note that this method may be run more than once |
| try { |
| Class<?> clazz = Class.forName("io.grpc.override.ContextStorageOverride"); |
| // The override's constructor is prohibited from triggering any code that can loop back to |
| // Context |
| Storage newStorage = (Storage) clazz.getConstructor().newInstance(); |
| storage.compareAndSet(null, newStorage); |
| } catch (ClassNotFoundException e) { |
| Storage newStorage = new ThreadLocalContextStorage(); |
| // Must set storage before logging, since logging may call Context.current(). |
| if (storage.compareAndSet(null, newStorage)) { |
| // Avoid logging if this thread lost the race, to avoid confusion |
| log.log(Level.FINE, "Storage override doesn't exist. Using default", e); |
| } |
| } catch (Exception e) { |
| throw new RuntimeException("Storage override failed to initialize", e); |
| } |
| // Re-retreive from storage since compareAndSet may have failed (returned false) in case of |
| // race. |
| return storage.get(); |
| } |
| |
| /** |
| * Create a {@link Key} with the given debug name. Multiple different keys may have the same name; |
| * the name is intended for debugging purposes and does not impact behavior. |
| */ |
| public static <T> Key<T> key(String name) { |
| return new Key<T>(name); |
| } |
| |
| /** |
| * Create a {@link Key} with the given debug name and default value. Multiple different keys may |
| * have the same name; the name is intended for debugging purposes and does not impact behavior. |
| */ |
| public static <T> Key<T> keyWithDefault(String name, T defaultValue) { |
| return new Key<T>(name, defaultValue); |
| } |
| |
| /** |
| * Return the context associated with the current scope, will never return {@code null}. |
| * |
| * <p>Will never return {@link CancellableContext} even if one is attached, instead a |
| * {@link Context} is returned with the same properties and lifetime. This is to avoid |
| * code stealing the ability to cancel arbitrarily. |
| */ |
| public static Context current() { |
| Context current = storage().current(); |
| if (current == null) { |
| return ROOT; |
| } |
| return current; |
| } |
| |
| private ArrayList<ExecutableListener> listeners; |
| private CancellationListener parentListener = new ParentListener(); |
| final CancellableContext cancellableAncestor; |
| final PersistentHashArrayMappedTrie<Key<?>, Object> keyValueEntries; |
| // The number parents between this context and the root context. |
| final int generation; |
| |
| /** |
| * Construct a context that cannot be cancelled and will not cascade cancellation from its parent. |
| */ |
| private Context(PersistentHashArrayMappedTrie<Key<?>, Object> keyValueEntries, int generation) { |
| cancellableAncestor = null; |
| this.keyValueEntries = keyValueEntries; |
| this.generation = generation; |
| validateGeneration(generation); |
| } |
| |
| /** |
| * Construct a context that cannot be cancelled but will cascade cancellation from its parent if |
| * it is cancellable. |
| */ |
| private Context(Context parent, PersistentHashArrayMappedTrie<Key<?>, Object> keyValueEntries) { |
| cancellableAncestor = cancellableAncestor(parent); |
| this.keyValueEntries = keyValueEntries; |
| this.generation = parent == null ? 0 : parent.generation + 1; |
| validateGeneration(generation); |
| } |
| |
| /** |
| * Create a new context which is independently cancellable and also cascades cancellation from |
| * its parent. Callers <em>must</em> ensure that either {@link |
| * CancellableContext#cancel(Throwable)} or {@link CancellableContext#detachAndCancel(Context, |
| * Throwable)} are called at a later point, in order to allow this context to be garbage |
| * collected. |
| * |
| * <p>Sample usage: |
| * <pre> |
| * Context.CancellableContext withCancellation = Context.current().withCancellation(); |
| * try { |
| * withCancellation.run(new Runnable() { |
| * public void run() { |
| * Context current = Context.current(); |
| * while (!current.isCancelled()) { |
| * keepWorking(); |
| * } |
| * } |
| * }); |
| * } finally { |
| * withCancellation.cancel(null); |
| * } |
| * </pre> |
| */ |
| public CancellableContext withCancellation() { |
| return new CancellableContext(this); |
| } |
| |
| /** |
| * Create a new context which will cancel itself after the given {@code duration} from now. |
| * The returned context will cascade cancellation of its parent. Callers may explicitly cancel |
| * the returned context prior to the deadline just as for {@link #withCancellation()}. If the unit |
| * of work completes before the deadline, the context should be explicitly cancelled to allow |
| * it to be garbage collected. |
| * |
| * <p>Sample usage: |
| * <pre> |
| * Context.CancellableContext withDeadline = Context.current() |
| * .withDeadlineAfter(5, TimeUnit.SECONDS, scheduler); |
| * try { |
| * withDeadline.run(new Runnable() { |
| * public void run() { |
| * Context current = Context.current(); |
| * while (!current.isCancelled()) { |
| * keepWorking(); |
| * } |
| * } |
| * }); |
| * } finally { |
| * withDeadline.cancel(null); |
| * } |
| * </pre> |
| */ |
| public CancellableContext withDeadlineAfter(long duration, TimeUnit unit, |
| ScheduledExecutorService scheduler) { |
| return withDeadline(Deadline.after(duration, unit), scheduler); |
| } |
| |
| /** |
| * Create a new context which will cancel itself at the given {@link Deadline}. |
| * The returned context will cascade cancellation of its parent. Callers may explicitly cancel |
| * the returned context prior to the deadline just as for {@link #withCancellation()}. If the unit |
| * of work completes before the deadline, the context should be explicitly cancelled to allow |
| * it to be garbage collected. |
| * |
| * <p>Sample usage: |
| * <pre> |
| * Context.CancellableContext withDeadline = Context.current() |
| * .withDeadline(someReceivedDeadline, scheduler); |
| * try { |
| * withDeadline.run(new Runnable() { |
| * public void run() { |
| * Context current = Context.current(); |
| * while (!current.isCancelled() && moreWorkToDo()) { |
| * keepWorking(); |
| * } |
| * } |
| * }); |
| * } finally { |
| * withDeadline.cancel(null); |
| * } |
| * </pre> |
| */ |
| public CancellableContext withDeadline(Deadline deadline, |
| ScheduledExecutorService scheduler) { |
| checkNotNull(deadline, "deadline"); |
| checkNotNull(scheduler, "scheduler"); |
| return new CancellableContext(this, deadline, scheduler); |
| } |
| |
| /** |
| * Create a new context with the given key value set. The new context will cascade cancellation |
| * from its parent. |
| * |
| <pre> |
| * Context withCredential = Context.current().withValue(CRED_KEY, cred); |
| * withCredential.run(new Runnable() { |
| * public void run() { |
| * readUserRecords(userId, CRED_KEY.get()); |
| * } |
| * }); |
| * </pre> |
| * |
| */ |
| public <V> Context withValue(Key<V> k1, V v1) { |
| PersistentHashArrayMappedTrie<Key<?>, Object> newKeyValueEntries = keyValueEntries.put(k1, v1); |
| return new Context(this, newKeyValueEntries); |
| } |
| |
| /** |
| * Create a new context with the given key value set. The new context will cascade cancellation |
| * from its parent. |
| */ |
| public <V1, V2> Context withValues(Key<V1> k1, V1 v1, Key<V2> k2, V2 v2) { |
| PersistentHashArrayMappedTrie<Key<?>, Object> newKeyValueEntries = |
| keyValueEntries.put(k1, v1).put(k2, v2); |
| return new Context(this, newKeyValueEntries); |
| } |
| |
| /** |
| * Create a new context with the given key value set. The new context will cascade cancellation |
| * from its parent. |
| */ |
| public <V1, V2, V3> Context withValues(Key<V1> k1, V1 v1, Key<V2> k2, V2 v2, Key<V3> k3, V3 v3) { |
| PersistentHashArrayMappedTrie<Key<?>, Object> newKeyValueEntries = |
| keyValueEntries.put(k1, v1).put(k2, v2).put(k3, v3); |
| return new Context(this, newKeyValueEntries); |
| } |
| |
| /** |
| * Create a new context with the given key value set. The new context will cascade cancellation |
| * from its parent. |
| */ |
| public <V1, V2, V3, V4> Context withValues(Key<V1> k1, V1 v1, Key<V2> k2, V2 v2, |
| Key<V3> k3, V3 v3, Key<V4> k4, V4 v4) { |
| PersistentHashArrayMappedTrie<Key<?>, Object> newKeyValueEntries = |
| keyValueEntries.put(k1, v1).put(k2, v2).put(k3, v3).put(k4, v4); |
| return new Context(this, newKeyValueEntries); |
| } |
| |
| /** |
| * Create a new context which propagates the values of this context but does not cascade its |
| * cancellation. |
| */ |
| public Context fork() { |
| return new Context(keyValueEntries, generation + 1); |
| } |
| |
| boolean canBeCancelled() { |
| return cancellableAncestor != null; |
| } |
| |
| /** |
| * Attach this context, thus enter a new scope within which this context is {@link #current}. The |
| * previously current context is returned. It is allowed to attach contexts where {@link |
| * #isCancelled()} is {@code true}. |
| * |
| * <p>Instead of using {@code attach()} and {@link #detach(Context)} most use-cases are better |
| * served by using the {@link #run(Runnable)} or {@link #call(java.util.concurrent.Callable)} to |
| * execute work immediately within a context's scope. If work needs to be done in other threads it |
| * is recommended to use the 'wrap' methods or to use a propagating executor. |
| * |
| * <p>All calls to {@code attach()} should have a corresponding {@link #detach(Context)} within |
| * the same method: |
| * <pre>{@code Context previous = someContext.attach(); |
| * try { |
| * // Do work |
| * } finally { |
| * someContext.detach(previous); |
| * }}</pre> |
| */ |
| public Context attach() { |
| Context prev = storage().doAttach(this); |
| if (prev == null) { |
| return ROOT; |
| } |
| return prev; |
| } |
| |
| /** |
| * Reverse an {@code attach()}, restoring the previous context and exiting the current scope. |
| * |
| * <p>This context should be the same context that was previously {@link #attach attached}. The |
| * provided replacement should be what was returned by the same {@link #attach attach()} call. If |
| * an {@code attach()} and a {@code detach()} meet above requirements, they match. |
| * |
| * <p>It is expected that between any pair of matching {@code attach()} and {@code detach()}, all |
| * {@code attach()}es and {@code detach()}es are called in matching pairs. If this method finds |
| * that this context is not {@link #current current}, either you or some code in-between are not |
| * detaching correctly, and a SEVERE message will be logged but the context to attach will still |
| * be bound. <strong>Never</strong> use {@code Context.current().detach()}, as this will |
| * compromise this error-detecting mechanism. |
| */ |
| public void detach(Context toAttach) { |
| checkNotNull(toAttach, "toAttach"); |
| storage().detach(this, toAttach); |
| } |
| |
| // Visible for testing |
| boolean isCurrent() { |
| return current() == this; |
| } |
| |
| /** |
| * Is this context cancelled. |
| */ |
| public boolean isCancelled() { |
| if (cancellableAncestor == null) { |
| return false; |
| } else { |
| return cancellableAncestor.isCancelled(); |
| } |
| } |
| |
| /** |
| * If a context {@link #isCancelled()} then return the cause of the cancellation or |
| * {@code null} if context was cancelled without a cause. If the context is not yet cancelled |
| * will always return {@code null}. |
| * |
| * <p>The cancellation cause is provided for informational purposes only and implementations |
| * should generally assume that it has already been handled and logged properly. |
| */ |
| public Throwable cancellationCause() { |
| if (cancellableAncestor == null) { |
| return null; |
| } else { |
| return cancellableAncestor.cancellationCause(); |
| } |
| } |
| |
| /** |
| * A context may have an associated {@link Deadline} at which it will be automatically cancelled. |
| * @return A {@link io.grpc.Deadline} or {@code null} if no deadline is set. |
| */ |
| public Deadline getDeadline() { |
| if (cancellableAncestor == null) { |
| return null; |
| } |
| return cancellableAncestor.getDeadline(); |
| } |
| |
| /** |
| * Add a listener that will be notified when the context becomes cancelled. |
| */ |
| public void addListener(final CancellationListener cancellationListener, |
| final Executor executor) { |
| checkNotNull(cancellationListener, "cancellationListener"); |
| checkNotNull(executor, "executor"); |
| if (canBeCancelled()) { |
| ExecutableListener executableListener = |
| new ExecutableListener(executor, cancellationListener); |
| synchronized (this) { |
| if (isCancelled()) { |
| executableListener.deliver(); |
| } else { |
| if (listeners == null) { |
| // Now that we have a listener we need to listen to our parent so |
| // we can cascade listener notification. |
| listeners = new ArrayList<>(); |
| listeners.add(executableListener); |
| if (cancellableAncestor != null) { |
| cancellableAncestor.addListener(parentListener, DirectExecutor.INSTANCE); |
| } |
| } else { |
| listeners.add(executableListener); |
| } |
| } |
| } |
| } |
| } |
| |
| /** |
| * Remove a {@link CancellationListener}. |
| */ |
| public void removeListener(CancellationListener cancellationListener) { |
| if (!canBeCancelled()) { |
| return; |
| } |
| synchronized (this) { |
| if (listeners != null) { |
| for (int i = listeners.size() - 1; i >= 0; i--) { |
| if (listeners.get(i).listener == cancellationListener) { |
| listeners.remove(i); |
| // Just remove the first matching listener, given that we allow duplicate |
| // adds we should allow for duplicates after remove. |
| break; |
| } |
| } |
| // We have no listeners so no need to listen to our parent |
| if (listeners.isEmpty()) { |
| if (cancellableAncestor != null) { |
| cancellableAncestor.removeListener(parentListener); |
| } |
| listeners = null; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Notify all listeners that this context has been cancelled and immediately release |
| * any reference to them so that they may be garbage collected. |
| */ |
| void notifyAndClearListeners() { |
| if (!canBeCancelled()) { |
| return; |
| } |
| ArrayList<ExecutableListener> tmpListeners; |
| synchronized (this) { |
| if (listeners == null) { |
| return; |
| } |
| tmpListeners = listeners; |
| listeners = null; |
| } |
| // Deliver events to non-child context listeners before we notify child contexts. We do this |
| // to cancel higher level units of work before child units. This allows for a better error |
| // handling paradigm where the higher level unit of work knows it is cancelled and so can |
| // ignore errors that bubble up as a result of cancellation of lower level units. |
| for (int i = 0; i < tmpListeners.size(); i++) { |
| if (!(tmpListeners.get(i).listener instanceof ParentListener)) { |
| tmpListeners.get(i).deliver(); |
| } |
| } |
| for (int i = 0; i < tmpListeners.size(); i++) { |
| if (tmpListeners.get(i).listener instanceof ParentListener) { |
| tmpListeners.get(i).deliver(); |
| } |
| } |
| if (cancellableAncestor != null) { |
| cancellableAncestor.removeListener(parentListener); |
| } |
| } |
| |
| // Used in tests to ensure that listeners are defined and released when cancellation cascades. |
| // It's very important to ensure that we do not accidentally retain listeners. |
| int listenerCount() { |
| synchronized (this) { |
| return listeners == null ? 0 : listeners.size(); |
| } |
| } |
| |
| /** |
| * Immediately run a {@link Runnable} with this context as the {@link #current} context. |
| * @param r {@link Runnable} to run. |
| */ |
| public void run(Runnable r) { |
| Context previous = attach(); |
| try { |
| r.run(); |
| } finally { |
| detach(previous); |
| } |
| } |
| |
| /** |
| * Immediately call a {@link Callable} with this context as the {@link #current} context. |
| * @param c {@link Callable} to call. |
| * @return result of call. |
| */ |
| @CanIgnoreReturnValue |
| public <V> V call(Callable<V> c) throws Exception { |
| Context previous = attach(); |
| try { |
| return c.call(); |
| } finally { |
| detach(previous); |
| } |
| } |
| |
| /** |
| * Wrap a {@link Runnable} so that it executes with this context as the {@link #current} context. |
| */ |
| public Runnable wrap(final Runnable r) { |
| return new Runnable() { |
| @Override |
| public void run() { |
| Context previous = attach(); |
| try { |
| r.run(); |
| } finally { |
| detach(previous); |
| } |
| } |
| }; |
| } |
| |
| /** |
| * Wrap a {@link Callable} so that it executes with this context as the {@link #current} context. |
| */ |
| public <C> Callable<C> wrap(final Callable<C> c) { |
| return new Callable<C>() { |
| @Override |
| public C call() throws Exception { |
| Context previous = attach(); |
| try { |
| return c.call(); |
| } finally { |
| detach(previous); |
| } |
| } |
| }; |
| } |
| |
| /** |
| * Wrap an {@link Executor} so that it always executes with this context as the {@link #current} |
| * context. It is generally expected that {@link #currentContextExecutor(Executor)} would be |
| * used more commonly than this method. |
| * |
| * <p>One scenario in which this executor may be useful is when a single thread is sharding work |
| * to multiple threads. |
| * |
| * @see #currentContextExecutor(Executor) |
| */ |
| public Executor fixedContextExecutor(final Executor e) { |
| class FixedContextExecutor implements Executor { |
| @Override |
| public void execute(Runnable r) { |
| e.execute(wrap(r)); |
| } |
| } |
| |
| return new FixedContextExecutor(); |
| } |
| |
| /** |
| * Create an executor that propagates the {@link #current} context when {@link Executor#execute} |
| * is called as the {@link #current} context of the {@code Runnable} scheduled. <em>Note that this |
| * is a static method.</em> |
| * |
| * @see #fixedContextExecutor(Executor) |
| */ |
| public static Executor currentContextExecutor(final Executor e) { |
| class CurrentContextExecutor implements Executor { |
| @Override |
| public void execute(Runnable r) { |
| e.execute(Context.current().wrap(r)); |
| } |
| } |
| |
| return new CurrentContextExecutor(); |
| } |
| |
| /** |
| * Lookup the value for a key in the context inheritance chain. |
| */ |
| private Object lookup(Key<?> key) { |
| return keyValueEntries.get(key); |
| } |
| |
| /** |
| * A context which inherits cancellation from its parent but which can also be independently |
| * cancelled and which will propagate cancellation to its descendants. To avoid leaking memory, |
| * every CancellableContext must have a defined lifetime, after which it is guaranteed to be |
| * cancelled. |
| * |
| * <p>This class must be cancelled by either calling {@link #close} or {@link #cancel}. |
| * {@link #close} is equivalent to calling {@code cancel(null)}. It is safe to call the methods |
| * more than once, but only the first call will have any effect. Because it's safe to call the |
| * methods multiple times, users are encouraged to always call {@link #close} at the end of |
| * the operation, and disregard whether {@link #cancel} was already called somewhere else. |
| * |
| * <p>Blocking code can use the try-with-resources idiom: |
| * <pre> |
| * try (CancellableContext c = Context.current() |
| * .withDeadlineAfter(100, TimeUnit.MILLISECONDS, executor)) { |
| * Context toRestore = c.attach(); |
| * try { |
| * // do some blocking work |
| * } finally { |
| * c.detach(toRestore); |
| * } |
| * }</pre> |
| * |
| * <p>Asynchronous code will have to manually track the end of the CancellableContext's lifetime, |
| * and cancel the context at the appropriate time. |
| */ |
| public static final class CancellableContext extends Context implements Closeable { |
| |
| private final Deadline deadline; |
| private final Context uncancellableSurrogate; |
| |
| private boolean cancelled; |
| private Throwable cancellationCause; |
| private ScheduledFuture<?> pendingDeadline; |
| |
| /** |
| * Create a cancellable context that does not have a deadline. |
| */ |
| private CancellableContext(Context parent) { |
| super(parent, parent.keyValueEntries); |
| deadline = parent.getDeadline(); |
| // Create a surrogate that inherits from this to attach so that you cannot retrieve a |
| // cancellable context from Context.current() |
| uncancellableSurrogate = new Context(this, keyValueEntries); |
| } |
| |
| /** |
| * Create a cancellable context that has a deadline. |
| */ |
| private CancellableContext(Context parent, Deadline deadline, |
| ScheduledExecutorService scheduler) { |
| super(parent, parent.keyValueEntries); |
| Deadline parentDeadline = parent.getDeadline(); |
| if (parentDeadline != null && parentDeadline.compareTo(deadline) <= 0) { |
| // The new deadline won't have an effect, so ignore it |
| deadline = parentDeadline; |
| } else { |
| // The new deadline has an effect |
| if (!deadline.isExpired()) { |
| // The parent deadline was after the new deadline so we need to install a listener |
| // on the new earlier deadline to trigger expiration for this context. |
| pendingDeadline = deadline.runOnExpiration(new Runnable() { |
| @Override |
| public void run() { |
| try { |
| cancel(new TimeoutException("context timed out")); |
| } catch (Throwable t) { |
| log.log(Level.SEVERE, "Cancel threw an exception, which should not happen", t); |
| } |
| } |
| }, scheduler); |
| } else { |
| // Cancel immediately if the deadline is already expired. |
| cancel(new TimeoutException("context timed out")); |
| } |
| } |
| this.deadline = deadline; |
| uncancellableSurrogate = new Context(this, keyValueEntries); |
| } |
| |
| |
| @Override |
| public Context attach() { |
| return uncancellableSurrogate.attach(); |
| } |
| |
| @Override |
| public void detach(Context toAttach) { |
| uncancellableSurrogate.detach(toAttach); |
| } |
| |
| /** |
| * Returns true if the Context is the current context. |
| * |
| * @deprecated This method violates some GRPC class encapsulation and should not be used. |
| * If you must know whether a Context is the current context, check whether it is the same |
| * object returned by {@link Context#current()}. |
| */ |
| //TODO(spencerfang): The superclass's method is package-private, so this should really match. |
| @Override |
| @Deprecated |
| public boolean isCurrent() { |
| return uncancellableSurrogate.isCurrent(); |
| } |
| |
| /** |
| * Cancel this context and optionally provide a cause (can be {@code null}) for the |
| * cancellation. This will trigger notification of listeners. It is safe to call this method |
| * multiple times. Only the first call will have any effect. |
| * |
| * <p>Calling {@code cancel(null)} is the same as calling {@link #close}. |
| * |
| * @return {@code true} if this context cancelled the context and notified listeners, |
| * {@code false} if the context was already cancelled. |
| */ |
| @CanIgnoreReturnValue |
| public boolean cancel(Throwable cause) { |
| boolean triggeredCancel = false; |
| synchronized (this) { |
| if (!cancelled) { |
| cancelled = true; |
| if (pendingDeadline != null) { |
| // If we have a scheduled cancellation pending attempt to cancel it. |
| pendingDeadline.cancel(false); |
| pendingDeadline = null; |
| } |
| this.cancellationCause = cause; |
| triggeredCancel = true; |
| } |
| } |
| if (triggeredCancel) { |
| notifyAndClearListeners(); |
| } |
| return triggeredCancel; |
| } |
| |
| /** |
| * Cancel this context and detach it as the current context. |
| * |
| * @param toAttach context to make current. |
| * @param cause of cancellation, can be {@code null}. |
| */ |
| public void detachAndCancel(Context toAttach, Throwable cause) { |
| try { |
| detach(toAttach); |
| } finally { |
| cancel(cause); |
| } |
| } |
| |
| @Override |
| public boolean isCancelled() { |
| synchronized (this) { |
| if (cancelled) { |
| return true; |
| } |
| } |
| // Detect cancellation of parent in the case where we have no listeners and |
| // record it. |
| if (super.isCancelled()) { |
| cancel(super.cancellationCause()); |
| return true; |
| } |
| return false; |
| } |
| |
| @Override |
| public Throwable cancellationCause() { |
| if (isCancelled()) { |
| return cancellationCause; |
| } |
| return null; |
| } |
| |
| @Override |
| public Deadline getDeadline() { |
| return deadline; |
| } |
| |
| @Override |
| boolean canBeCancelled() { |
| return true; |
| } |
| |
| /** |
| * Cleans up this object by calling {@code cancel(null)}. |
| */ |
| @Override |
| public void close() { |
| cancel(null); |
| } |
| } |
| |
| /** |
| * A listener notified on context cancellation. |
| */ |
| public interface CancellationListener { |
| /** |
| * @param context the newly cancelled context. |
| */ |
| public void cancelled(Context context); |
| } |
| |
| /** |
| * Key for indexing values stored in a context. |
| */ |
| public static final class Key<T> { |
| private final String name; |
| private final T defaultValue; |
| |
| Key(String name) { |
| this(name, null); |
| } |
| |
| Key(String name, T defaultValue) { |
| this.name = checkNotNull(name, "name"); |
| this.defaultValue = defaultValue; |
| } |
| |
| /** |
| * Get the value from the {@link #current()} context for this key. |
| */ |
| @SuppressWarnings("unchecked") |
| public T get() { |
| return get(Context.current()); |
| } |
| |
| /** |
| * Get the value from the specified context for this key. |
| */ |
| @SuppressWarnings("unchecked") |
| public T get(Context context) { |
| T value = (T) context.lookup(this); |
| return value == null ? defaultValue : value; |
| } |
| |
| @Override |
| public String toString() { |
| return name; |
| } |
| } |
| |
| /** |
| * Defines the mechanisms for attaching and detaching the "current" context. The constructor for |
| * extending classes <em>must not</em> trigger any activity that can use Context, which includes |
| * logging, otherwise it can trigger an infinite initialization loop. Extending classes must not |
| * assume that only one instance will be created; Context guarantees it will only use one |
| * instance, but it may create multiple and then throw away all but one. |
| * |
| * <p>The default implementation will put the current context in a {@link ThreadLocal}. If an |
| * alternative implementation named {@code io.grpc.override.ContextStorageOverride} exists in the |
| * classpath, it will be used instead of the default implementation. |
| * |
| * <p>This API is <a href="https://github.com/grpc/grpc-java/issues/2462">experimental</a> and |
| * subject to change. |
| */ |
| public abstract static class Storage { |
| /** |
| * @deprecated This is an old API that is no longer used. |
| */ |
| @Deprecated |
| public void attach(Context toAttach) { |
| throw new UnsupportedOperationException("Deprecated. Do not call."); |
| } |
| |
| /** |
| * Implements {@link io.grpc.Context#attach}. |
| * |
| * <p>Caution: {@link Context#attach()} interprets a return value of {@code null} to mean |
| * the same thing as {@link Context#ROOT}. |
| * |
| * <p>See also: {@link #current()}. |
| |
| * @param toAttach the context to be attached |
| * @return A {@link Context} that should be passed back into {@link #detach(Context, Context)} |
| * as the {@code toRestore} parameter. {@code null} is a valid return value, but see |
| * caution note. |
| */ |
| public Context doAttach(Context toAttach) { |
| // This is a default implementation to help migrate existing Storage implementations that |
| // have an attach() method but no doAttach() method. |
| Context current = current(); |
| attach(toAttach); |
| return current; |
| } |
| |
| /** |
| * Implements {@link io.grpc.Context#detach} |
| * |
| * @param toDetach the context to be detached. Should be, or be equivalent to, the current |
| * context of the current scope |
| * @param toRestore the context to be the current. Should be, or be equivalent to, the context |
| * of the outer scope |
| */ |
| public abstract void detach(Context toDetach, Context toRestore); |
| |
| /** |
| * Implements {@link io.grpc.Context#current}. |
| * |
| * <p>Caution: {@link Context} interprets a return value of {@code null} to mean the same |
| * thing as {@code Context{@link #ROOT}}. |
| * |
| * <p>See also {@link #doAttach(Context)}. |
| * |
| * @return The context of the current scope. {@code null} is a valid return value, but see |
| * caution note. |
| */ |
| public abstract Context current(); |
| } |
| |
| /** |
| * Stores listener and executor pair. |
| */ |
| private class ExecutableListener implements Runnable { |
| private final Executor executor; |
| private final CancellationListener listener; |
| |
| private ExecutableListener(Executor executor, CancellationListener listener) { |
| this.executor = executor; |
| this.listener = listener; |
| } |
| |
| private void deliver() { |
| try { |
| executor.execute(this); |
| } catch (Throwable t) { |
| log.log(Level.INFO, "Exception notifying context listener", t); |
| } |
| } |
| |
| @Override |
| public void run() { |
| listener.cancelled(Context.this); |
| } |
| } |
| |
| private class ParentListener implements CancellationListener { |
| @Override |
| public void cancelled(Context context) { |
| if (Context.this instanceof CancellableContext) { |
| // Record cancellation with its cancellationCause. |
| ((CancellableContext) Context.this).cancel(context.cancellationCause()); |
| } else { |
| notifyAndClearListeners(); |
| } |
| } |
| } |
| |
| @CanIgnoreReturnValue |
| private static <T> T checkNotNull(T reference, Object errorMessage) { |
| if (reference == null) { |
| throw new NullPointerException(String.valueOf(errorMessage)); |
| } |
| return reference; |
| } |
| |
| private enum DirectExecutor implements Executor { |
| INSTANCE; |
| |
| @Override |
| public void execute(Runnable command) { |
| command.run(); |
| } |
| |
| @Override |
| public String toString() { |
| return "Context.DirectExecutor"; |
| } |
| } |
| |
| /** |
| * Returns {@code parent} if it is a {@link CancellableContext}, otherwise returns the parent's |
| * {@link #cancellableAncestor}. |
| */ |
| static CancellableContext cancellableAncestor(Context parent) { |
| if (parent == null) { |
| return null; |
| } |
| if (parent instanceof CancellableContext) { |
| return (CancellableContext) parent; |
| } |
| // The parent simply cascades cancellations. |
| // Bypass the parent and reference the ancestor directly (may be null). |
| return parent.cancellableAncestor; |
| } |
| |
| /** |
| * If the ancestry chain length is unreasonably long, then print an error to the log and record |
| * the stack trace. |
| */ |
| private static void validateGeneration(int generation) { |
| if (generation == CONTEXT_DEPTH_WARN_THRESH) { |
| log.log( |
| Level.SEVERE, |
| "Context ancestry chain length is abnormally long. " |
| + "This suggests an error in application code. " |
| + "Length exceeded: " + CONTEXT_DEPTH_WARN_THRESH, |
| new Exception()); |
| } |
| } |
| |
| // Not using the standard com.google.errorprone.annotations.CheckReturnValue because that will |
| // introduce dependencies that some io.grpc.Context API consumers may not want. |
| @interface CheckReturnValue {} |
| |
| @interface CanIgnoreReturnValue {} |
| } |
