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/*
 * Copyright 2016-2022 The OSHI Project Contributors
 * SPDX-License-Identifier: MIT
 */
package oshi.software.os;

import java.util.List;

import oshi.annotation.concurrent.ThreadSafe;

/**
 * The File System is a logical arrangement, usually in a hierarchial tree, where files are placed for storage and
 * retrieval. It may consist of one or more file stores.
 */
@ThreadSafe
public interface FileSystem {

    /**
     * Get file stores on this machine
     *
     * Instantiates a list of {@link oshi.software.os.OSFileStore} objects, representing a storage pool, device,
     * partition, volume, concrete file system or other implementation specific means of file storage.
     *
     * @return A list of {@link oshi.software.os.OSFileStore} objects or an empty array if none are present.
     */
    List getFileStores();

    /**
     * Get file stores on this machine
     *
     * Instantiates a list of {@link oshi.software.os.OSFileStore} objects, representing a storage pool, device,
     * partition, volume, concrete file system or other implementation specific means of file storage.
     *
     * @param localOnly If true, filters the list to only local file stores.
     *
     * @return A list of {@link oshi.software.os.OSFileStore} objects or an empty array if none are present.
     */
    List getFileStores(boolean localOnly);

    /**
     * The current number of open file descriptors. A file descriptor is an abstract handle used to access I/O resources
     * such as files and network connections. On UNIX-based systems there is a system-wide limit on the number of open
     * file descriptors.
     *
     * On Windows systems, this method returns the total number of handles held by Processes. While Windows handles are
     * conceptually similar to file descriptors, they may also refer to a number of non-I/O related objects.
     *
     * @return The number of open file descriptors if available, 0 otherwise.
     */
    long getOpenFileDescriptors();

    /**
     * The maximum number of open file descriptors. A file descriptor is an abstract handle used to access I/O resources
     * such as files and network connections. On UNIX-based systems there is a system-wide limit on the number of open
     * file descriptors.
     *
     * On Windows systems, this method returns the theoretical max number of handles (2^24-2^15 on 32-bit, 2^24-2^16 on
     * 64-bit). There may be a lower per-process limit. While Windows handles are conceptually similar to file
     * descriptors, they may also refer to a number of non-I/O related objects.
     *
     * @return The maximum number of file descriptors if available, 0 otherwise.
     */
    long getMaxFileDescriptors();

    /**
     * The maximum number of open file descriptors per process. This returns the upper limit which applies to each
     * process. The actual limit of a process may be lower if configured.
     *
     * @return The maximum number of file descriptors of each process if available, 0 otherwise.
     */
    long getMaxFileDescriptorsPerProcess();
}