// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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..

//! Platform-independent platform abstraction
//!
//! This is the platform-independent portion of the standard library's
//! platform abstraction layer, whereas `std::sys` is the
//! platform-specific portion.
//!
//! The relationship between `std::sys_common`, `std::sys` and the
//! rest of `std` is complex, with dependencies going in all
//! directions: `std` depending on `sys_common`, `sys_common`
//! depending on `sys`, and `sys` depending on `sys_common` and `std`.
//! This is because `sys_common` not only contains platform-independent code,
//! but also code that is shared between the different platforms in `sys`.
//! Ideally all that shared code should be moved to `sys::common`,
//! and the dependencies between `std`, `sys_common` and `sys` all would form a dag.
//! Progress on this is tracked in #84187.

#![allow(missing_docs)]
#![allow(missing_debug_implementations)]

pub mod at_exit_imp;
#[cfg(feature = "backtrace")]
pub mod backtrace;
pub mod condvar;
pub mod fs;
#[cfg(feature = "backtrace")]
pub mod gnu;
pub mod io;
pub mod lazy_box;
pub mod memchr;
pub mod mutex;
pub mod once;
#[cfg(feature = "net")]
pub mod net;
pub mod remutex;
pub mod rwlock;
#[cfg(feature = "thread")]
pub mod thread;
pub mod thread_info;
#[cfg(feature = "thread")]
pub mod thread_local_dtor;
#[cfg(feature = "thread")]
pub mod thread_local_key;
pub mod thread_parker;
pub mod wtf8;

/// A trait for viewing representations from std types
#[doc(hidden)]
pub trait AsInner<Inner: ?Sized> {
    fn as_inner(&self) -> &Inner;
}

/// A trait for viewing representations from std types
#[doc(hidden)]
pub trait AsInnerMut<Inner: ?Sized> {
    fn as_inner_mut(&mut self) -> &mut Inner;
}

/// A trait for extracting representations from std types
#[doc(hidden)]
pub trait IntoInner<Inner> {
    fn into_inner(self) -> Inner;
}

/// A trait for creating std types from internal representations
#[doc(hidden)]
pub trait FromInner<Inner> {
    fn from_inner(inner: Inner) -> Self;
}

/// Enqueues a procedure to run when the main thread exits.
///
/// Currently these closures are only run once the main *Rust* thread exits.
/// Once the `at_exit` handlers begin running, more may be enqueued, but not
/// infinitely so. Eventually a handler registration will be forced to fail.
///
/// Returns `Ok` if the handler was successfully registered, meaning that the
/// closure will be run once the main thread exits. Returns `Err` to indicate
/// that the closure could not be registered, meaning that it is not scheduled
/// to be run.
#[allow(clippy::result_unit_err)]
pub fn at_exit<F: FnOnce() + Send + 'static>(f: F) -> Result<(), ()> {
    if at_exit_imp::push(Box::new(f)) { Ok(()) } else { Err(()) }
}

// Computes (value*numer)/denom without overflow, as long as both
// (numer*denom) and the overall result fit into i64 (which is the case
// for our time conversions).
#[allow(dead_code)] // not used on all platforms
pub fn mul_div_u64(value: u64, numer: u64, denom: u64) -> u64 {
    let q = value / denom;
    let r = value % denom;
    // Decompose value as (value/denom*denom + value%denom),
    // substitute into (value*numer)/denom and simplify.
    // r < denom, so (denom*numer) is the upper bound of (r*numer)
    q * numer + r * numer / denom
}
