/*
 * Copyright (C) 2011 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.system;

import java.io.FileDescriptor;
import libcore.util.Objects;

/**
 * Used as an in/out parameter to {@link Os#poll}.
 * Corresponds to C's {@code struct pollfd} from {@code <poll.h>}.
 */
public final class StructPollfd {
    /** The file descriptor to poll. */
    public FileDescriptor fd;

    /**
     * The events we're interested in. POLLIN corresponds to being in select(2)'s read fd set,
     * POLLOUT to the write fd set.
     */
    public short events;

    /** The events that actually happened. */
    public short revents;

    /**
     * A non-standard extension that lets callers conveniently map back to the object
     * their fd belongs to. This is used by Selector, for example, to associate each
     * FileDescriptor with the corresponding SelectionKey.
     */
    public Object userData;

    @Override public String toString() {
        return Objects.toString(this);
    }
}
