container/Sources/ContainerizationOS/Reaper.swift

//===----------------------------------------------------------------------===//
// Copyright © 2025 Apple Inc. and the containerization project authors. All rights reserved.
//
// 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
//
//   https://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.
//===----------------------------------------------------------------------===//

import Foundation

/// A process reaper that returns exited processes along
/// with their exit status.
public struct Reaper {
    /// Process's pid and exit status.
    typealias Exit = (pid: Int32, status: Int32)

    /// Reap all pending processes and return the pid and exit status.
    public static func reap() -> [Int32: Int32] {
        var reaped = [Int32: Int32]()
        while true {
            guard let exit = wait() else {
                return reaped
            }
            reaped[exit.pid] = exit.status
        }
        return reaped
    }

    /// Returns the exit status of the last process that exited.
    /// nil is returned when no pending processes exist.
    private static func wait() -> Exit? {
        var rus = rusage()
        var ws = Int32()

        let pid = wait4(-1, &ws, WNOHANG, &rus)
        if pid <= 0 {
            return nil
        }
        return (pid: pid, status: Command.toExitStatus(ws))
    }
}