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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.nativeaccess;

import java.nio.file.Path;
import java.util.Optional;
import java.util.OptionalLong;

/**
 * Provides access to native functionality needed by Elastisearch.
 */
public interface NativeAccess {

    /**
     * Get the one and only instance of {@link NativeAccess} which is specific to the running platform and JVM.
     */
    static NativeAccess instance() {
        return NativeAccessHolder.INSTANCE;
    }

    /**
     * Determine whether this JVM is running as the root user.
     *
     * @return true if running as root, or false if unsure
     */
    boolean definitelyRunningAsRoot();

    /**
     * Return limits for the current process.
     */
    ProcessLimits getProcessLimits();

    /**
     * Attempt to lock this process's virtual memory address space into physical RAM.
     */
    void tryLockMemory();

    /**
     * Return whether locking memory was successful, or false otherwise.
     */
    boolean isMemoryLocked();

    /**
     * Attempts to install a system call filter to block process execution.
     */
    void tryInstallExecSandbox();

    /**
     * Return whether installing the exec system call filters was successful, and to what degree.
     */
    ExecSandboxState getExecSandboxState();

    Systemd systemd();

    /**
     * Returns an accessor to zstd compression functions.
     * @return an object used to compress and decompress bytes using zstd
     */
    Zstd getZstd();

    /**
     * Retrieves the actual number of bytes of disk storage used to store a specified file.
     *
     * @param path the path to the file
     * @return an {@link OptionalLong} that contains the number of allocated bytes on disk for the file, or empty if the size is invalid
     */
    OptionalLong allocatedSizeInBytes(Path path);

    void tryPreallocate(Path file, long size);

    /**
     * Returns an accessor for native functions only available on Windows, or {@code null} if not on Windows.
     */
    default WindowsFunctions getWindowsFunctions() {
        return null;
    }

    /*
     * Returns the vector similarity functions, or an empty optional.
     */
    Optional getVectorSimilarityFunctions();

    /**
     * Creates a new {@link CloseableByteBuffer}. The buffer must be used within the same thread
     * that it is created.
     * @param len the number of bytes the buffer should allocate
     * @return the buffer
     */
    CloseableByteBuffer newBuffer(int len);

    /**
     * Possible stats for execution filtering.
     */
    enum ExecSandboxState {
        /** No execution filtering */
        NONE,
        /** Exec is blocked for threads that were already created */
        EXISTING_THREADS,
        /** Exec is blocked for all current and future threads */
        ALL_THREADS
    }
}