Suwayomi-Server/AndroidCompat/src/main/java/android/os/MessageQueue.java

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * 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 android.os;

import android.annotation.IntDef;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.annotation.SuppressLint;
import android.annotation.TestApi;
import android.os.shadows.ShadowPausedMessageQueue;
import android.util.Log;
import android.util.SparseArray;
import java.io.FileDescriptor;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.ArrayList;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Low-level class holding the list of messages to be dispatched by a
 * {@link Looper}.  Messages are not added directly to a MessageQueue,
 * but rather through {@link Handler} objects associated with the Looper.
 *
 * <p>You can retrieve the MessageQueue for the current thread with
 * {@link Looper#myQueue() Looper.myQueue()}.
 */
public final class MessageQueue {
    private static final String TAG = "MessageQueue";
    private static final boolean DEBUG = false;
    private static final boolean TRACE = false;

    // True if the message queue can be quit.
    private final boolean mQuitAllowed;

    @SuppressWarnings("unused")
    private long mPtr; // used by native code

    Message mMessages;
    private Message mLast;
    private final ArrayList<IdleHandler> mIdleHandlers = new ArrayList<IdleHandler>();
    private SparseArray<FileDescriptorRecord> mFileDescriptorRecords;
    private IdleHandler[] mPendingIdleHandlers;
    private boolean mQuitting;

    // Indicates whether next() is blocked waiting in pollOnce() with a non-zero timeout.
    private boolean mBlocked;

    // Tracks the number of async message. We use this in enqueueMessage() to avoid searching the
    // queue for async messages when inserting a message at the tail.
    private int mAsyncMessageCount;

    // The next barrier token.
    // Barriers are indicated by messages with a null target whose arg1 field carries the token.
    private int mNextBarrierToken;

    MessageQueue(boolean quitAllowed) {
        mQuitAllowed = quitAllowed;
        mPtr = ShadowPausedMessageQueue.nativeInit();
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            dispose();
        } finally {
            super.finalize();
        }
    }

    // Disposes of the underlying message queue.
    // Must only be called on the looper thread or the finalizer.
    private void dispose() {
        if (mPtr != 0) {
            ShadowPausedMessageQueue.nativeDestroy(mPtr);
            mPtr = 0;
        }
    }

    static boolean getUseConcurrent() {
        return false;
    }

    /**
     * Returns true if the looper has no pending messages which are due to be processed
     * and is not blocked on sync barrier.
     *
     * <p>This method is safe to call from any thread.
     *
     * @return True if the looper is idle.
     */
    public boolean isIdle() {
        synchronized (this) {
            final long now = SystemClock.uptimeMillis();
            return mMessages == null || now < mMessages.when;
        }
    }

    /**
     * Add a new {@link IdleHandler} to this message queue.  This may be
     * removed automatically for you by returning false from
     * {@link IdleHandler#queueIdle IdleHandler.queueIdle()} when it is
     * invoked, or explicitly removing it with {@link #removeIdleHandler}.
     *
     * <p>This method is safe to call from any thread.
     *
     * @param handler The IdleHandler to be added.
     */
    public void addIdleHandler(@NonNull IdleHandler handler) {
        if (handler == null) {
            throw new NullPointerException("Can't add a null IdleHandler");
        }
        synchronized (this) {
            mIdleHandlers.add(handler);
        }
    }

    /**
     * Remove an {@link IdleHandler} from the queue that was previously added
     * with {@link #addIdleHandler}.  If the given object is not currently
     * in the idle list, nothing is done.
     *
     * <p>This method is safe to call from any thread.
     *
     * @param handler The IdleHandler to be removed.
     */
    public void removeIdleHandler(@NonNull IdleHandler handler) {
        synchronized (this) {
            mIdleHandlers.remove(handler);
        }
    }

    /**
     * Returns whether this looper's thread is currently polling for more work to do.
     * This is a good signal that the loop is still alive rather than being stuck
     * handling a callback.  Note that this method is intrinsically racy, since the
     * state of the loop can change before you get the result back.
     *
     * <p>This method is safe to call from any thread.
     *
     * @return True if the looper is currently polling for events.
     * @hide
     */
    public boolean isPolling() {
        synchronized (this) {
            return isPollingLocked();
        }
    }

    private boolean isPollingLocked() {
        // If the loop is quitting then it must not be idling.
        // We can assume mPtr != 0 when mQuitting is false.
        return !mQuitting && ShadowPausedMessageQueue.nativeIsPolling(mPtr);
    }

    /**
     * Adds a file descriptor listener to receive notification when file descriptor
     * related events occur.
     * <p>
     * If the file descriptor has already been registered, the specified events
     * and listener will replace any that were previously associated with it.
     * It is not possible to set more than one listener per file descriptor.
     * </p><p>
     * It is important to always unregister the listener when the file descriptor
     * is no longer of use.
     * </p>
     *
     * @param fd The file descriptor for which a listener will be registered.
     * @param events The set of events to receive: a combination of the
     * {@link OnFileDescriptorEventListener#EVENT_INPUT},
     * {@link OnFileDescriptorEventListener#EVENT_OUTPUT}, and
     * {@link OnFileDescriptorEventListener#EVENT_ERROR} event masks.  If the requested
     * set of events is zero, then the listener is unregistered.
     * @param listener The listener to invoke when file descriptor events occur.
     *
     * @see OnFileDescriptorEventListener
     * @see #removeOnFileDescriptorEventListener
     */
    public void addOnFileDescriptorEventListener(@NonNull FileDescriptor fd,
            @OnFileDescriptorEventListener.Events int events,
            @NonNull OnFileDescriptorEventListener listener) {
        if (fd == null) {
            throw new IllegalArgumentException("fd must not be null");
        }
        if (listener == null) {
            throw new IllegalArgumentException("listener must not be null");
        }

        synchronized (this) {
            updateOnFileDescriptorEventListenerLocked(fd, events, listener);
        }
    }

    /**
     * Removes a file descriptor listener.
     * <p>
     * This method does nothing if no listener has been registered for the
     * specified file descriptor.
     * </p>
     *
     * @param fd The file descriptor whose listener will be unregistered.
     *
     * @see OnFileDescriptorEventListener
     * @see #addOnFileDescriptorEventListener
     */
    public void removeOnFileDescriptorEventListener(@NonNull FileDescriptor fd) {
        if (fd == null) {
            throw new IllegalArgumentException("fd must not be null");
        }

        synchronized (this) {
            updateOnFileDescriptorEventListenerLocked(fd, 0, null);
        }
    }

    private void updateOnFileDescriptorEventListenerLocked(FileDescriptor fd, int events,
            OnFileDescriptorEventListener listener) {
        throw new RuntimeException("Stub!");
//        final int fdNum = fd.getInt$();
//
//        int index = -1;
//        FileDescriptorRecord record = null;
//        if (mFileDescriptorRecords != null) {
//            index = mFileDescriptorRecords.indexOfKey(fdNum);
//            if (index >= 0) {
//                record = mFileDescriptorRecords.valueAt(index);
//                if (record != null && record.mEvents == events) {
//                    return;
//                }
//            }
//        }
//
//        if (events != 0) {
//            events |= OnFileDescriptorEventListener.EVENT_ERROR;
//            if (record == null) {
//                if (mFileDescriptorRecords == null) {
//                    mFileDescriptorRecords = new SparseArray<FileDescriptorRecord>();
//                }
//                record = new FileDescriptorRecord(fd, events, listener);
//                mFileDescriptorRecords.put(fdNum, record);
//            } else {
//                record.mListener = listener;
//                record.mEvents = events;
//                record.mSeq += 1;
//            }
//            nativeSetFileDescriptorEvents(mPtr, fdNum, events);
//        } else if (record != null) {
//            record.mEvents = 0;
//            mFileDescriptorRecords.removeAt(index);
//            nativeSetFileDescriptorEvents(mPtr, fdNum, 0);
//        }
    }

    private static final AtomicLong mMessagesDelivered = new AtomicLong();

    Message next() {
        // Return here if the message loop has already quit and been disposed.
        // This can happen if the application tries to restart a looper after quit
        // which is not supported.
        final long ptr = mPtr;
        if (ptr == 0) {
            return null;
        }

        int pendingIdleHandlerCount = -1; // -1 only during first iteration
        int nextPollTimeoutMillis = 0;
        for (;;) {
            if (nextPollTimeoutMillis != 0) {
//                Binder.flushPendingCommands();
            }

            ShadowPausedMessageQueue.nativePollOnce(ptr, nextPollTimeoutMillis);

            synchronized (this) {
                // Try to retrieve the next message.  Return if found.
                final long now = SystemClock.uptimeMillis();
                Message prevMsg = null;
                Message msg = mMessages;
                if (msg != null && msg.target == null) {
                    // Stalled by a barrier.  Find the next asynchronous message in the queue.
                    do {
                        prevMsg = msg;
                        msg = msg.next;
                    } while (msg != null && !msg.isAsynchronous());
                }
                if (msg != null) {
                    if (now < msg.when) {
                        // Next message is not ready.  Set a timeout to wake up when it is ready.
                        nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
                    } else {
                        // Got a message.
                        mBlocked = false;
                        if (prevMsg != null) {
                            prevMsg.next = msg.next;
                            if (prevMsg.next == null) {
                                mLast = prevMsg;
                            }
                        } else {
                            mMessages = msg.next;
                            if (msg.next == null) {
                                mLast = null;
                            }
                        }
                        msg.next = null;
                        if (DEBUG) Log.v(TAG, "Returning message: " + msg);
                        msg.markInUse();
                        if (msg.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        if (TRACE) {
                            Trace.setCounter("MQ.Delivered", mMessagesDelivered.incrementAndGet());
                        }
                        return msg;
                    }
                } else {
                    // No more messages.
                    nextPollTimeoutMillis = -1;
                }

                // Process the quit message now that all pending messages have been handled.
                if (mQuitting) {
                    dispose();
                    return null;
                }

                // If first time idle, then get the number of idlers to run.
                // Idle handles only run if the queue is empty or if the first message
                // in the queue (possibly a barrier) is due to be handled in the future.
                if (pendingIdleHandlerCount < 0
                        && (mMessages == null || now < mMessages.when)) {
                    pendingIdleHandlerCount = mIdleHandlers.size();
                }
                if (pendingIdleHandlerCount <= 0) {
                    // No idle handlers to run.  Loop and wait some more.
                    mBlocked = true;
                    continue;
                }

                if (mPendingIdleHandlers == null) {
                    mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
                }
                mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
            }

            // Run the idle handlers.
            // We only ever reach this code block during the first iteration.
            for (int i = 0; i < pendingIdleHandlerCount; i++) {
                final IdleHandler idler = mPendingIdleHandlers[i];
                mPendingIdleHandlers[i] = null; // release the reference to the handler

                boolean keep = false;
                try {
                    keep = idler.queueIdle();
                } catch (Throwable t) {
                    Log.wtf(TAG, "IdleHandler threw exception", t);
                }

                if (!keep) {
                    synchronized (this) {
                        mIdleHandlers.remove(idler);
                    }
                }
            }

            // Reset the idle handler count to 0 so we do not run them again.
            pendingIdleHandlerCount = 0;

            // While calling an idle handler, a new message could have been delivered
            // so go back and look again for a pending message without waiting.
            nextPollTimeoutMillis = 0;
        }
    }

    /**
     * Returns the last message in the queue in execution order.
     *
     * Caller must ensure that this doesn't race 'next' from the Looper thread.
     * @hide
     */
    public @Nullable Message peekLastMessageForTest() {
        synchronized (this) {
            Message lastMsg = null;

            Message current = mMessages;
            while (current != null) {
                if (current.target != null && (lastMsg == null || lastMsg.when <= current.when)) {
                    lastMsg = current;
                }
                current = current.next;
            }

            return lastMsg;
        }
    }

    /**
     * Resets this queue's state and allows it to continue being used.
     *
     * @hide
     */
    public void resetForTest() {
        synchronized (this) {
            // This queue is already quitting, so we can't reset its state and continue using it.
            if (mQuitting) {
                return;
            }
            mIdleHandlers.clear();
            removeAllFdRecords();
            removeAllMessagesLocked();
            // We reset the sync barrier tokens to reflect the queue's state reset. This helps
            // ensure that the queue's behavior is deterministic in both individual tests and in a
            // test suite.
            resetSyncBarrierTokens();
            ShadowPausedMessageQueue.nativeWake(mPtr);
        }
    }

    private void removeAllFdRecords() {
        if (mFileDescriptorRecords != null) {
            while (mFileDescriptorRecords.size() > 0) {
                removeOnFileDescriptorEventListener(mFileDescriptorRecords.valueAt(0).mDescriptor);
            }
        }
    }

    private void resetSyncBarrierTokens() {
        // Legacy MQ doesn't use an atomic integer for barrier tokens.
        // mNextBarrierTokenAtomic.set(1);
        mNextBarrierToken = 0;
    }

    void quit(boolean safe) {
        if (!mQuitAllowed) {
            throw new IllegalStateException("Main thread not allowed to quit.");
        }

        synchronized (this) {
            if (mQuitting) {
                return;
            }
            mQuitting = true;

            if (safe) {
                removeAllFutureMessagesLocked();
            } else {
                removeAllMessagesLocked();
            }

            // We can assume mPtr != 0 because mQuitting was previously false.
            ShadowPausedMessageQueue.nativeWake(mPtr);
        }
    }

    /**
     * Posts a synchronization barrier to the Looper's message queue.
     *
     * Message processing occurs as usual until the message queue encounters the
     * synchronization barrier that has been posted.  When the barrier is encountered,
     * later synchronous messages in the queue are stalled (prevented from being executed)
     * until the barrier is released by calling {@link #removeSyncBarrier} and specifying
     * the token that identifies the synchronization barrier.
     *
     * This method is used to immediately postpone execution of all subsequently posted
     * synchronous messages until a condition is met that releases the barrier.
     * Asynchronous messages (see {@link Message#isAsynchronous} are exempt from the barrier
     * and continue to be processed as usual.
     *
     * This call must be always matched by a call to {@link #removeSyncBarrier} with
     * the same token to ensure that the message queue resumes normal operation.
     * Otherwise the application will probably hang!
     *
     * @return A token that uniquely identifies the barrier.  This token must be
     * passed to {@link #removeSyncBarrier} to release the barrier.
     *
     * @hide
     */
    @TestApi
    public int postSyncBarrier() {
        return postSyncBarrier(SystemClock.uptimeMillis());
    }

    private int postSyncBarrier(long when) {
        // Enqueue a new sync barrier token.
        // We don't need to wake the queue because the purpose of a barrier is to stall it.
        synchronized (this) {
            final int token = mNextBarrierToken++;
            final Message msg = Message.obtain();
            msg.markInUse();
            msg.when = when;
            msg.arg1 = token;

            if (mLast != null && mLast.when <= when) {
                /* Message goes to tail of list */
                mLast.next = msg;
                mLast = msg;
                msg.next = null;
                return token;
            }

            Message prev = null;
            Message p = mMessages;
            if (when != 0) {
                while (p != null && p.when <= when) {
                    prev = p;
                    p = p.next;
                }
            }

            if (p == null) {
                /* We reached the tail of the list, or list is empty. */
                mLast = msg;
            }

            if (prev != null) { // invariant: p == prev.next
                msg.next = p;
                prev.next = msg;
            } else {
                msg.next = p;
                mMessages = msg;
            }
            return token;
        }
    }

    /**
     * Removes a synchronization barrier.
     *
     * @param token The synchronization barrier token that was returned by
     * {@link #postSyncBarrier}.
     *
     * @throws IllegalStateException if the barrier was not found.
     *
     * @hide
     */
    @TestApi
    public void removeSyncBarrier(int token) {
        // Remove a sync barrier token from the queue.
        // If the queue is no longer stalled by a barrier then wake it.
        synchronized (this) {
            Message prev = null;
            Message p = mMessages;
            while (p != null && (p.target != null || p.arg1 != token)) {
                prev = p;
                p = p.next;
            }
            if (p == null) {
                throw new IllegalStateException("The specified message queue synchronization "
                        + " barrier token has not been posted or has already been removed.");
            }
            final boolean needWake;
            if (prev != null) {
                prev.next = p.next;
                if (prev.next == null) {
                    mLast = prev;
                }
                needWake = false;
            } else {
                mMessages = p.next;
                if (mMessages == null) {
                    mLast = null;
                }
                needWake = mMessages == null || mMessages.target != null;
            }
            p.recycleUnchecked();

            // If the loop is quitting then it is already awake.
            // We can assume mPtr != 0 when mQuitting is false.
            if (needWake && !mQuitting) {
                ShadowPausedMessageQueue.nativeWake(mPtr);
            }
        }
    }

    boolean enqueueMessage(Message msg, long when) {
        if (msg.target == null) {
            throw new IllegalArgumentException("Message must have a target.");
        }

        synchronized (this) {
            if (msg.isInUse()) {
                throw new IllegalStateException(msg + " This message is already in use.");
            }

            if (mQuitting) {
                IllegalStateException e = new IllegalStateException(
                        msg.target + " sending message to a Handler on a dead thread");
                Log.w(TAG, e.getMessage(), e);
                msg.recycle();
                return false;
            }

            msg.markInUse();
            msg.when = when;
            Message p = mMessages;
            boolean needWake;
            if (p == null || when == 0 || when < p.when) {
                // New head, wake up the event queue if blocked.
                msg.next = p;
                mMessages = msg;
                needWake = mBlocked;
                if (p == null) {
                    mLast = mMessages;
                }
            } else {
                // Message is to be inserted at tail or middle of queue. Usually we don't have to
                // wake up the event queue unless there is a barrier at the head of the queue and
                // the message is the earliest asynchronous message in the queue.
                needWake = mBlocked && p.target == null && msg.isAsynchronous();

                if (when >= mLast.when) {
                    needWake = needWake && mAsyncMessageCount == 0;
                    msg.next = null;
                    mLast.next = msg;
                    mLast = msg;
                } else {
                    // Inserted within the middle of the queue.
                    Message prev;
                    for (;;) {
                        prev = p;
                        p = p.next;
                        if (p == null || when < p.when) {
                            break;
                        }
                        if (needWake && p.isAsynchronous()) {
                            needWake = false;
                        }
                    }
                    if (p == null) {
                        /* Inserting at tail of queue */
                        mLast = msg;
                    }
                    msg.next = p; // invariant: p == prev.next
                    prev.next = msg;
                }
            }

            if (msg.isAsynchronous()) {
                mAsyncMessageCount++;
            }

            // We can assume mPtr != 0 because mQuitting is false.
            if (needWake) {
                ShadowPausedMessageQueue.nativeWake(mPtr);
            }
        }
        return true;
    }

    private Message legacyPeekOrPoll(boolean peek) {
        synchronized (this) {
            // Try to retrieve the next message.  Return if found.
            final long now = SystemClock.uptimeMillis();
            Message prevMsg = null;
            Message msg = mMessages;
            if (msg != null && msg.target == null) {
                // Stalled by a barrier.  Find the next asynchronous message in the queue.
                do {
                    prevMsg = msg;
                    msg = msg.next;
                } while (msg != null && !msg.isAsynchronous());
            }
            if (msg != null) {
                if (peek) {
                    return msg;
                }
                if (now >= msg.when) {
                    // Got a message.
                    mBlocked = false;
                }
                if (prevMsg != null) {
                    prevMsg.next = msg.next;
                    if (prevMsg.next == null) {
                        mLast = prevMsg;
                    }
                } else {
                    mMessages = msg.next;
                    if (msg.next == null) {
                        mLast = null;
                    }
                }
                msg.next = null;
                msg.markInUse();
                if (msg.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                if (TRACE) {
                    Trace.setCounter("MQ.Delivered", mMessagesDelivered.incrementAndGet());
                }
                return msg;
            }
        }
        return null;
    }

    /**
     * Get the timestamp of the next message in our priority queue.
     * Returns null if there are no messages in the queue.
     *
     * Caller must ensure that this doesn't race 'next' from the Looper thread.
     */
    @SuppressLint("VisiblySynchronized") // Legacy MessageQueue synchronizes on this
    Long peekWhenForTest() {
        Message ret = legacyPeekOrPoll(true);
        return ret != null ? ret.when : null;
    }

    /**
     * Return the next message in our priority queue.
     * Returns null if there are no messages in the queue.
     *
     * Caller must ensure that this doesn't race 'next' from the Looper thread.
     */
    @SuppressLint("VisiblySynchronized") // Legacy MessageQueue synchronizes on this
    @Nullable
    Message pollForTest() {
        return legacyPeekOrPoll(false);
    }

    /**
     * @return true if we are blocked on a sync barrier
     *
     * Calls to this method must not be allowed to race with `next`.
     * Specifically, the Looper thread must be paused before calling this method,
     * and may not be resumed until after returning from this method.
     */
    boolean isBlockedOnSyncBarrier() {
        synchronized (this) {
            Message msg = mMessages;
            return msg != null && msg.target == null;
        }
    }

    boolean hasMessages(Handler h, int what, Object object) {
        if (h == null) {
            return false;
        }

        synchronized (this) {
            Message p = mMessages;
            while (p != null) {
                if (p.target == h && p.what == what && (object == null || p.obj == object)) {
                    return true;
                }
                p = p.next;
            }
            return false;
        }
    }

    boolean hasEqualMessages(Handler h, int what, Object object) {
        if (h == null) {
            return false;
        }

        synchronized (this) {
            Message p = mMessages;
            while (p != null) {
                if (p.target == h && p.what == what && (object == null || object.equals(p.obj))) {
                    return true;
                }
                p = p.next;
            }
            return false;
        }
    }

    boolean hasMessages(Handler h, Runnable r, Object object) {
        if (h == null) {
            return false;
        }

        synchronized (this) {
            Message p = mMessages;
            while (p != null) {
                if (p.target == h && p.callback == r && (object == null || p.obj == object)) {
                    return true;
                }
                p = p.next;
            }
            return false;
        }
    }

    boolean hasMessages(Handler h) {
        if (h == null) {
            return false;
        }

        synchronized (this) {
            Message p = mMessages;
            while (p != null) {
                if (p.target == h) {
                    return true;
                }
                p = p.next;
            }
            return false;
        }
    }

    void removeMessages(Handler h, int what, Object object) {
        if (h == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h && p.what == what
                   && (object == null || p.obj == object)) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.what == what
                            && (object == null || n.obj == object)) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    void removeEqualMessages(Handler h, int what, Object object) {
        if (h == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h && p.what == what
                   && (object == null || object.equals(p.obj))) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.what == what
                            && (object == null || object.equals(n.obj))) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    void removeMessages(Handler h, Runnable r, Object object) {
        if (h == null || r == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h && p.callback == r
                   && (object == null || p.obj == object)) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.callback == r
                            && (object == null || n.obj == object)) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    void removeEqualMessages(Handler h, Runnable r, Object object) {
        if (h == null || r == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h && p.callback == r
                   && (object == null || object.equals(p.obj))) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && n.callback == r
                            && (object == null || object.equals(n.obj))) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }


    void removeCallbacksAndMessages(Handler h, Object object) {
        if (h == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h
                    && (object == null || p.obj == object)) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && (object == null || n.obj == object)) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    void removeCallbacksAndEqualMessages(Handler h, Object object) {
        if (h == null) {
            return;
        }

        synchronized (this) {
            Message p = mMessages;

            // Remove all messages at front.
            while (p != null && p.target == h
                    && (object == null || object.equals(p.obj))) {
                Message n = p.next;
                mMessages = n;
                if (p.isAsynchronous()) {
                    mAsyncMessageCount--;
                }
                p.recycleUnchecked();
                p = n;
            }

            if (p == null) {
                mLast = mMessages;
            }

            // Remove all messages after front.
            while (p != null) {
                Message n = p.next;
                if (n != null) {
                    if (n.target == h && (object == null || object.equals(n.obj))) {
                        Message nn = n.next;
                        if (n.isAsynchronous()) {
                            mAsyncMessageCount--;
                        }
                        n.recycleUnchecked();
                        p.next = nn;
                        if (p.next == null) {
                            mLast = p;
                        }
                        continue;
                    }
                }
                p = n;
            }
        }
    }

    private void removeAllMessagesLocked() {
        Message p = mMessages;
        while (p != null) {
            Message n = p.next;
            p.recycleUnchecked();
            p = n;
        }
        mMessages = null;
        mLast = null;
        mAsyncMessageCount = 0;
    }

    private void removeAllFutureMessagesLocked() {
        final long now = SystemClock.uptimeMillis();
        Message p = mMessages;
        if (p != null) {
            if (p.when > now) {
                removeAllMessagesLocked();
            } else {
                Message n;
                for (;;) {
                    n = p.next;
                    if (n == null) {
                        return;
                    }
                    if (n.when > now) {
                        break;
                    }
                    p = n;
                }
                p.next = null;
                mLast = p;

                do {
                    p = n;
                    n = p.next;
                    if (p.isAsynchronous()) {
                        mAsyncMessageCount--;
                    }
                    p.recycleUnchecked();
                } while (n != null);
            }
        }
    }

    /**
     * Callback interface for discovering when a thread is going to block
     * waiting for more messages.
     */
    public static interface IdleHandler {
        /**
         * Called when the message queue has run out of messages and will now
         * wait for more.  Return true to keep your idle handler active, false
         * to have it removed.  This may be called if there are still messages
         * pending in the queue, but they are all scheduled to be dispatched
         * after the current time.
         */
        boolean queueIdle();
    }

    /**
     * A listener which is invoked when file descriptor related events occur.
     */
    public interface OnFileDescriptorEventListener {
        /**
         * File descriptor event: Indicates that the file descriptor is ready for input
         * operations, such as reading.
         * <p>
         * The listener should read all available data from the file descriptor
         * then return <code>true</code> to keep the listener active or <code>false</code>
         * to remove the listener.
         * </p><p>
         * In the case of a socket, this event may be generated to indicate
         * that there is at least one incoming connection that the listener
         * should accept.
         * </p><p>
         * This event will only be generated if the {@link #EVENT_INPUT} event mask was
         * specified when the listener was added.
         * </p>
         */
        public static final int EVENT_INPUT = 1 << 0;

        /**
         * File descriptor event: Indicates that the file descriptor is ready for output
         * operations, such as writing.
         * <p>
         * The listener should write as much data as it needs.  If it could not
         * write everything at once, then it should return <code>true</code> to
         * keep the listener active.  Otherwise, it should return <code>false</code>
         * to remove the listener then re-register it later when it needs to write
         * something else.
         * </p><p>
         * This event will only be generated if the {@link #EVENT_OUTPUT} event mask was
         * specified when the listener was added.
         * </p>
         */
        public static final int EVENT_OUTPUT = 1 << 1;

        /**
         * File descriptor event: Indicates that the file descriptor encountered a
         * fatal error.
         * <p>
         * File descriptor errors can occur for various reasons.  One common error
         * is when the remote peer of a socket or pipe closes its end of the connection.
         * </p><p>
         * This event may be generated at any time regardless of whether the
         * {@link #EVENT_ERROR} event mask was specified when the listener was added.
         * </p>
         */
        public static final int EVENT_ERROR = 1 << 2;

        /** @hide */
        @Retention(RetentionPolicy.SOURCE)
        @IntDef(flag = true, prefix = { "EVENT_" }, value = {
                EVENT_INPUT,
                EVENT_OUTPUT,
                EVENT_ERROR
        })
        public @interface Events {}

        /**
         * Called when a file descriptor receives events.
         *
         * @param fd The file descriptor.
         * @param events The set of events that occurred: a combination of the
         * {@link #EVENT_INPUT}, {@link #EVENT_OUTPUT}, and {@link #EVENT_ERROR} event masks.
         * @return The new set of events to watch, or 0 to unregister the listener.
         *
         * @see #EVENT_INPUT
         * @see #EVENT_OUTPUT
         * @see #EVENT_ERROR
         */
        @Events int onFileDescriptorEvents(@NonNull FileDescriptor fd, @Events int events);
    }

    private static final class FileDescriptorRecord {
        public final FileDescriptor mDescriptor;
        public int mEvents;
        public OnFileDescriptorEventListener mListener;
        public int mSeq;

        public FileDescriptorRecord(FileDescriptor descriptor,
                int events, OnFileDescriptorEventListener listener) {
            mDescriptor = descriptor;
            mEvents = events;
            mListener = listener;
        }
    }
}