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package org.aoju.bus.health.builtin.hardware;

import org.aoju.bus.core.annotation.ThreadSafe;

/**
 * The VirtuallMemory class tracks information about the use of a computer's
 * virtual memory (swap file) which temporarily moves rarely accessed
 * information to a disk or other storage device.
 *
 * @author Kimi Liu
 * @since Java 17+
 */
@ThreadSafe
public interface VirtualMemory {

    /**
     * The current size of the paging/swap file(s), in bytes. If the paging/swap
     * file can be extended, this is a soft limit.
     *
     * @return Total swap in bytes.
     */
    long getSwapTotal();

    /**
     * The current memory committed to the paging/swap file(s), in bytes
     *
     * @return Swap used in bytes
     */
    long getSwapUsed();

    /**
     * The maximum memory that can be committed by the system without extending the
     * paging file(s), in bytes. Also called the Commit Limit. If the paging/swap
     * file can be extended, this is a soft limit. This is generally equal to the
     * sum of the sizes of physical memory and paging/swap file(s).
     * <p>
     * On Linux, represents the total amount of memory currently available to be
     * allocated on the system based on the overcommit ratio, identified as
     * {@code CommitLimit}. This may be higher or lower than the total size of
     * physical and swap memory depending on system configuration.
     *
     * @return Max Virtual Memory in bytes
     */
    long getVirtualMax();

    /**
     * The memory currently committed by the system, in bytes. Also called the
     * Commit Total. This is generally equal to the sum of the bytes used of
     * physical memory and paging/swap file(s).
     * <p>
     * On Windows, committing pages changes this value immediately; however, the
     * physical memory is not charged until the pages are accessed, so this value
     * may exceed the sum of used physical and paging/swap file memory.
     *
     * @return Swap used in bytes
     */
    long getVirtualInUse();

    /**
     * Number of pages read from paging/swap file(s) to resolve hard page faults.
     * (Hard page faults occur when a process requires code or data that is not in
     * its working set or elsewhere in physical memory, and must be retrieved from
     * disk.) This property was designed as a primary indicator of the kinds of
     * faults that cause system-wide delays. It includes pages retrieved to satisfy
     * faults in the file system cache (usually requested by applications) and in
     * non-cached mapped memory files.
     *
     * @return Pages swapped in
     */
    long getSwapPagesIn();

    /**
     * Number of pages written to paging/swap file(s) to free up space in physical
     * memory. Pages are written back to disk only if they are changed in physical
     * memory, so they are likely to hold data, not code. A high rate of pages
     * output might indicate a memory shortage. The operating system writes more
     * pages back to disk to free up space when physical memory is in short supply.
     *
     * @return Pages swapped out
     */
    long getSwapPagesOut();

}
