audio_thread_priority 0.35.0

//! # audio_thread_priority
//!
//! Promote the current thread, or another thread (possibly in another process), to real-time
//! priority, suitable for low-latency audio processing.
//!
//! # Example
//!
//! ```rust
//!
//! use audio_thread_priority::{promote_current_thread_to_real_time, demote_current_thread_from_real_time};
//!
//! // ... on a thread that will compute audio and has to be real-time:
//! match promote_current_thread_to_real_time(512, 44100) {
//!   Ok(h) => {
//!     println!("this thread is now bumped to real-time priority.");
//!
//!     // Do some real-time work...
//!
//!     match demote_current_thread_from_real_time(h) {
//!       Ok(_) => {
//!         println!("this thread is now bumped back to normal.")
//!       }
//!       Err(_) => {
//!         println!("Could not bring the thread back to normal priority.")
//!       }
//!     };
//!   }
//!   Err(e) => {
//!     eprintln!("Error promoting thread to real-time: {}", e);
//!   }
//! }
//!
//! ```

#![warn(missing_docs)]

use cfg_if::cfg_if;
use std::error::Error;
use std::fmt;

/// The OS-specific issue is available as `inner`
#[derive(Debug)]
pub struct AudioThreadPriorityError {
    message: String,
    inner: Option<Box<dyn Error + 'static>>,
}

impl AudioThreadPriorityError {
    cfg_if! {
        if #[cfg(all(target_os = "linux", feature = "dbus"))] {
            fn new_with_inner(message: &str, inner: Box<dyn Error>) -> AudioThreadPriorityError {
                AudioThreadPriorityError {
                    message: message.into(),
                    inner: Some(inner),
                }
            }
        }
    }
    fn new(message: &str) -> AudioThreadPriorityError {
        AudioThreadPriorityError {
            message: message.into(),
            inner: None,
        }
    }
}

impl fmt::Display for AudioThreadPriorityError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut rv = write!(f, "AudioThreadPriorityError: {}", &self.message);
        if let Some(inner) = &self.inner {
            rv = write!(f, " ({inner})");
        }
        rv
    }
}

impl Error for AudioThreadPriorityError {
    fn description(&self) -> &str {
        &self.message
    }

    fn source(&self) -> Option<&(dyn Error + 'static)> {
        self.inner.as_ref().map(|e| e.as_ref())
    }
}

cfg_if! {
    if #[cfg(any(target_os = "macos", target_os = "ios"))] {
        mod rt_mach;
        extern crate mach2;
        extern crate libc;
        use rt_mach::promote_current_thread_to_real_time_internal;
        use rt_mach::demote_current_thread_from_real_time_internal;
        use rt_mach::RtPriorityHandleInternal;
    } else if #[cfg(target_os = "windows")] {
        mod rt_win;
        use rt_win::promote_current_thread_to_real_time_internal;
        use rt_win::demote_current_thread_from_real_time_internal;
        use rt_win::RtPriorityHandleInternal;
    } else if #[cfg(all(target_os = "linux", feature = "dbus"))] {
        mod rt_linux;
        extern crate dbus;
        extern crate libc;
        use rt_linux::promote_current_thread_to_real_time_internal;
        use rt_linux::demote_current_thread_from_real_time_internal;
        use rt_linux::set_real_time_hard_limit_internal as set_real_time_hard_limit;
        use rt_linux::get_current_thread_info_internal;
        use rt_linux::promote_thread_to_real_time_internal;
        use rt_linux::demote_thread_from_real_time_internal;
        use rt_linux::RtPriorityThreadInfoInternal;
        use rt_linux::RtPriorityHandleInternal;
        #[no_mangle]
        /// Size of a RtPriorityThreadInfo or atp_thread_info struct, for use in FFI.
        pub static ATP_THREAD_INFO_SIZE: usize = std::mem::size_of::<RtPriorityThreadInfo>();
    } else if #[cfg(target_os = "android")] {
        mod rt_android;
        use rt_android::promote_current_thread_to_real_time_internal;
        use rt_android::demote_current_thread_from_real_time_internal;
        use rt_android::RtPriorityHandleInternal;
    } else {
        // blanket implementations for Android, Linux Desktop without dbus and others
        /// Fallback priority handle that performs no-op operations on unsupported platforms.
        pub struct RtPriorityHandleInternal {}
        #[derive(Clone, Copy, PartialEq)]
        /// Fallback thread information structure for unsupported platforms.
        pub struct RtPriorityThreadInfoInternal {
            _dummy: u8
        }

        cfg_if! {
            if #[cfg(not(target_os = "linux"))] {
                pub type RtPriorityThreadInfo = RtPriorityThreadInfoInternal;
            }
        }

        impl RtPriorityThreadInfo {
            /// Serialize the thread info to a byte array (fallback implementation).
            pub fn serialize(&self) -> [u8; 1] {
                [0]
            }
            /// Deserialize thread info from a byte array (fallback implementation).
            pub fn deserialize(_: [u8; 1]) -> Self {
                RtPriorityThreadInfo{_dummy: 0}
            }
            /// Returns the PID of the process containing the thread (fallback: always -1).
            pub fn pid(&self) -> i32 {
                -1
            }
        }
        /// Fallback implementation that performs no operation for unsupported platforms.
        pub fn promote_current_thread_to_real_time_internal(_: u32, audio_samplerate_hz: u32) -> Result<RtPriorityHandle, AudioThreadPriorityError> {
            if audio_samplerate_hz == 0 {
                return Err(AudioThreadPriorityError{message: "sample rate is zero".to_string(), inner: None});
            }
            // no-op
            Ok(RtPriorityHandle{})
        }
        /// Fallback implementation that performs no operation for unsupported platforms.
        pub fn demote_current_thread_from_real_time_internal(_: RtPriorityHandle) -> Result<(), AudioThreadPriorityError> {
            // no-op
            Ok(())
        }
        /// Fallback implementation that performs no operation for unsupported platforms.
        pub fn set_real_time_hard_limit(
            _: u32,
            _: u32,
        ) -> Result<(), AudioThreadPriorityError> {
            Ok(())
        }
        /// Fallback implementation that returns dummy thread info for unsupported platforms.
        pub fn get_current_thread_info_internal() -> Result<RtPriorityThreadInfo, AudioThreadPriorityError> {
            Ok(RtPriorityThreadInfo{_dummy: 0})
        }
        /// Fallback implementation that performs no operation for unsupported platforms.
        pub fn promote_thread_to_real_time_internal(
            _: RtPriorityThreadInfo,
            _: u32,
            audio_samplerate_hz: u32,
        ) -> Result<RtPriorityHandle, AudioThreadPriorityError> {
            if audio_samplerate_hz == 0 {
                return Err(AudioThreadPriorityError::new("sample rate is zero"));
            }
            Ok(RtPriorityHandle{})
        }

        /// Fallback implementation that performs no operation for unsupported platforms.
        pub fn demote_thread_from_real_time_internal(_: RtPriorityThreadInfo) -> Result<(), AudioThreadPriorityError> {
            Ok(())
        }
        #[no_mangle]
        /// Size of a RtPriorityThreadInfo or atp_thread_info struct, for use in FFI.
        pub static ATP_THREAD_INFO_SIZE: usize = std::mem::size_of::<RtPriorityThreadInfo>();
    }
}

/// Opaque handle to a thread handle structure.
pub type RtPriorityHandle = RtPriorityHandleInternal;

cfg_if! {
    if #[cfg(target_os = "linux")] {
/// Opaque handle to a thread info.
///
/// This can be serialized to raw bytes to be sent via IPC.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
pub type RtPriorityThreadInfo = RtPriorityThreadInfoInternal;


/// Get the calling thread's information, to be able to promote it to real-time from somewhere
/// else, later.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
///
/// # Return value
///
/// Ok in case of success, with an opaque structure containing relevant info for the platform, Err
/// otherwise.
pub fn get_current_thread_info() -> Result<RtPriorityThreadInfo, AudioThreadPriorityError> {
    get_current_thread_info_internal()
}

/// Return a byte buffer containing serialized information about a thread, to promote it to
/// real-time from elsewhere.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
pub fn thread_info_serialize(
    thread_info: RtPriorityThreadInfo,
) -> [u8; std::mem::size_of::<RtPriorityThreadInfo>()] {
    thread_info.serialize()
}

/// From a byte buffer, return a `RtPriorityThreadInfo`.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
///
/// # Arguments
///
/// A byte buffer containing a serializezd `RtPriorityThreadInfo`.
pub fn thread_info_deserialize(
    bytes: [u8; std::mem::size_of::<RtPriorityThreadInfo>()],
) -> RtPriorityThreadInfo {
    RtPriorityThreadInfoInternal::deserialize(bytes)
}

/// Get the calling threads' information, to promote it from another process or thread, with a C
/// API.
///
/// This is intended to call on the thread that will end up being promoted to real time priority,
/// but that cannot do it itself (probably because of sandboxing reasons).
///
/// After use, it MUST be freed by calling `atp_free_thread_info`.
///
/// # Return value
///
/// A pointer to a struct that can be serialized and deserialized, and that can be passed to
/// `atp_promote_thread_to_real_time`, even from another process.
#[no_mangle]
pub extern "C" fn atp_get_current_thread_info() -> *mut atp_thread_info {
    match get_current_thread_info() {
        Ok(thread_info) => Box::into_raw(Box::new(atp_thread_info(thread_info))),
        _ => std::ptr::null_mut(),
    }
}

/// Frees a thread info, with a c api.
///
/// # Arguments
///
/// thread_info: the `atp_thread_info` structure to free.
///
/// # Return value
///
/// 0 in case of success, 1 otherwise (if `thread_info` is NULL).
///
/// # Safety
///
/// This function is safe only and only if the pointer comes from this library, of if is null.
#[no_mangle]
pub unsafe extern "C" fn atp_free_thread_info(thread_info: *mut atp_thread_info) -> i32 {
    if thread_info.is_null() {
        return 1;
    }
    drop(Box::from_raw(thread_info));
    0
}

/// Return a byte buffer containing serialized information about a thread, to promote it to
/// real-time from elsewhere, with a C API.
///
/// `bytes` MUST be `std::mem::size_of<RtPriorityThreadInfo>()` bytes long.
///
/// This is exposed in the C API as `ATP_THREAD_INFO_SIZE`.
///
/// This call is useful on Linux desktop only, when the process is sandboxed, cannot promote itself
/// directly, and the `atp_thread_info` struct must be passed via IPC.
///
/// # Safety
///
/// This function is safe only and only if the first pointer comes from this library, and the
/// second pointer is at least ATP_THREAD_INFO_SIZE bytes long.
#[no_mangle]
pub unsafe extern "C" fn atp_serialize_thread_info(
    thread_info: *mut atp_thread_info,
    bytes: *mut libc::c_void,
) {
    let thread_info = &mut *thread_info;
    let source = thread_info.0.serialize();
    std::ptr::copy(source.as_ptr(), bytes as *mut u8, source.len());
}

/// From a byte buffer, return a `RtPriorityThreadInfo`, with a C API.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
///
/// # Arguments
///
/// A byte buffer containing a serializezd `RtPriorityThreadInfo`.
///
/// # Safety
///
/// This function is safe only and only if pointer is at least ATP_THREAD_INFO_SIZE bytes long.
#[no_mangle]
pub unsafe extern "C" fn atp_deserialize_thread_info(
    in_bytes: *mut u8,
) -> *mut atp_thread_info {
    let bytes = *(in_bytes as *mut [u8; std::mem::size_of::<RtPriorityThreadInfoInternal>()]);
    let thread_info = RtPriorityThreadInfoInternal::deserialize(bytes);
    Box::into_raw(Box::new(atp_thread_info(thread_info)))
}

/// Promote a particular thread thread to real-time priority.
///
/// This call is useful on Linux desktop only, when the process is sandboxed and
/// cannot promote itself directly.
///
/// # Arguments
///
/// * `thread_info` - informations about the thread to promote, gathered using
/// `get_current_thread_info`.
/// * `audio_buffer_frames` - the exact or an upper limit on the number of frames that have to be
/// rendered each callback, or 0 for a sensible default value.
/// * `audio_samplerate_hz` - the sample-rate for this audio stream, in Hz.
///
/// # Return value
///
/// This function returns a `Result<RtPriorityHandle>`, which is an opaque struct to be passed to
/// `demote_current_thread_from_real_time` to revert to the previous thread priority.
pub fn promote_thread_to_real_time(
    thread_info: RtPriorityThreadInfo,
    audio_buffer_frames: u32,
    audio_samplerate_hz: u32,
) -> Result<RtPriorityHandle, AudioThreadPriorityError> {
    if audio_samplerate_hz == 0 {
        return Err(AudioThreadPriorityError::new("sample rate is zero"));
    }
    promote_thread_to_real_time_internal(
        thread_info,
        audio_buffer_frames,
        audio_samplerate_hz,
    )
}

/// Demotes a thread from real-time priority.
///
/// # Arguments
///
/// * `thread_info` - An opaque struct returned from a successful call to
/// `get_current_thread_info`.
///
/// # Return value
///
/// `Ok` in case of success, `Err` otherwise.
pub fn demote_thread_from_real_time(thread_info: RtPriorityThreadInfo) -> Result<(), AudioThreadPriorityError> {
    demote_thread_from_real_time_internal(thread_info)
}

/// Opaque info to a particular thread.
#[allow(non_camel_case_types)]
pub struct atp_thread_info(RtPriorityThreadInfo);

/// Promote a specific thread to real-time, with a C API.
///
/// This is useful when the thread to promote cannot make some system calls necessary to promote
/// it.
///
/// # Arguments
///
/// `thread_info` - the information of the thread to promote to real-time, gather from calling
/// `atp_get_current_thread_info` on the thread to promote.
/// * `audio_buffer_frames` - the exact or an upper limit on the number of frames that have to be
/// rendered each callback, or 0 for a sensible default value.
/// * `audio_samplerate_hz` - the sample-rate for this audio stream, in Hz.
///
/// # Return value
///
/// A pointer to an `atp_handle` in case of success, NULL otherwise.
///
/// # Safety
///
/// This function is safe as long as the first pointer comes from this library.
#[no_mangle]
pub unsafe extern "C" fn atp_promote_thread_to_real_time(
    thread_info: *mut atp_thread_info,
    audio_buffer_frames: u32,
    audio_samplerate_hz: u32,
) -> *mut atp_handle {
    let thread_info = &mut *thread_info;
    match promote_thread_to_real_time(thread_info.0, audio_buffer_frames, audio_samplerate_hz) {
        Ok(handle) => Box::into_raw(Box::new(atp_handle(handle))),
        _ => std::ptr::null_mut(),
    }
}

/// Demote a thread promoted to from real-time, with a C API.
///
/// # Arguments
///
/// `handle` -  an opaque struct received from a promoting function.
///
/// # Return value
///
/// 0 in case of success, non-zero otherwise.
///
/// # Safety
///
/// This function is safe as long as the first pointer comes from this library, or is null.
#[no_mangle]
pub unsafe extern "C" fn atp_demote_thread_from_real_time(thread_info: *mut atp_thread_info) -> i32 {
    if thread_info.is_null() {
        return 1;
    }
    let thread_info = (*thread_info).0;

    match demote_thread_from_real_time(thread_info) {
        Ok(_) => 0,
        _ => 1,
    }
}

/// Set a real-time limit for the calling thread.
///
/// # Arguments
///
/// `audio_buffer_frames` - the number of frames the audio callback has to render each quantum. 0
/// picks a rather high default value.
/// `audio_samplerate_hz` - the sample-rate of the audio stream.
///
/// # Return value
///
/// 0 in case of success, 1 otherwise.
#[no_mangle]
pub extern "C" fn atp_set_real_time_limit(audio_buffer_frames: u32,
                                          audio_samplerate_hz: u32) -> i32 {
    let r = set_real_time_hard_limit(audio_buffer_frames, audio_samplerate_hz);
    if r.is_err() {
        return 1;
    }
    0
}

}
}

/// Promote the calling thread thread to real-time priority.
///
/// # Arguments
///
/// * `audio_buffer_frames` - the exact or an upper limit on the number of frames that have to be
///   rendered each callback, or 0 for a sensible default value.
/// * `audio_samplerate_hz` - the sample-rate for this audio stream, in Hz.
///
/// # Return value
///
/// This function returns a `Result<RtPriorityHandle>`, which is an opaque struct to be passed to
/// `demote_current_thread_from_real_time` to revert to the previous thread priority.
pub fn promote_current_thread_to_real_time(
    audio_buffer_frames: u32,
    audio_samplerate_hz: u32,
) -> Result<RtPriorityHandle, AudioThreadPriorityError> {
    if audio_samplerate_hz == 0 {
        return Err(AudioThreadPriorityError::new("sample rate is zero"));
    }
    promote_current_thread_to_real_time_internal(audio_buffer_frames, audio_samplerate_hz)
}

/// Demotes the calling thread from real-time priority.
///
/// # Arguments
///
/// * `handle` - An opaque struct returned from a successful call to
///   `promote_current_thread_to_real_time`.
///
/// # Return value
///
/// `Ok` in case of success, `Err` otherwise.
pub fn demote_current_thread_from_real_time(
    handle: RtPriorityHandle,
) -> Result<(), AudioThreadPriorityError> {
    demote_current_thread_from_real_time_internal(handle)
}

/// Opaque handle for the C API
#[allow(non_camel_case_types)]
pub struct atp_handle(RtPriorityHandle);

/// Promote the calling thread thread to real-time priority, with a C API.
///
/// # Arguments
///
/// * `audio_buffer_frames` - the exact or an upper limit on the number of frames that have to be
///   rendered each callback, or 0 for a sensible default value.
/// * `audio_samplerate_hz` - the sample-rate for this audio stream, in Hz.
///
/// # Return value
///
/// This function returns `NULL` in case of error: if it couldn't bump the thread, or if the
/// `audio_samplerate_hz` is zero. It returns an opaque handle, to be passed to
/// `atp_demote_current_thread_from_real_time` to demote the thread.
///
/// Additionaly, NULL can be returned in sandboxed processes on Linux, when DBUS cannot be used in
/// the process (for example because the socket to DBUS cannot be created). If this is the case,
/// it's necessary to get the information from the thread to promote and ask another process to
/// promote it (maybe via another privileged process).
#[no_mangle]
pub extern "C" fn atp_promote_current_thread_to_real_time(
    audio_buffer_frames: u32,
    audio_samplerate_hz: u32,
) -> *mut atp_handle {
    match promote_current_thread_to_real_time(audio_buffer_frames, audio_samplerate_hz) {
        Ok(handle) => Box::into_raw(Box::new(atp_handle(handle))),
        _ => std::ptr::null_mut(),
    }
}
/// Demotes the calling thread from real-time priority, with a C API.
///
/// # Arguments
///
/// * `atp_handle` - An opaque struct returned from a successful call to
///   `atp_promote_current_thread_to_real_time`.
///
/// # Return value
///
/// 0 in case of success, non-zero in case of error.
///
/// # Safety
///
/// Only to be used with a valid pointer from this library -- not after having released it via
/// atp_free_handle.
#[no_mangle]
pub unsafe extern "C" fn atp_demote_current_thread_from_real_time(handle: *mut atp_handle) -> i32 {
    assert!(!handle.is_null());
    let handle = Box::from_raw(handle);

    match demote_current_thread_from_real_time(handle.0) {
        Ok(_) => 0,
        _ => 1,
    }
}

/// Frees a handle, with a C API.
///
/// This is useful when it impractical to call `atp_demote_current_thread_from_real_time` on the
/// right thread. Access to the handle must be synchronized externaly, or the thread that was
/// promoted to real-time priority must have exited.
///
/// # Arguments
///
/// * `atp_handle` - An opaque struct returned from a successful call to
///   `atp_promote_current_thread_to_real_time`.
///
/// # Return value
///
/// 0 in case of success, non-zero in case of error.
///
/// # Safety
///
/// Should only be called to free something from this crate.
#[no_mangle]
pub unsafe extern "C" fn atp_free_handle(handle: *mut atp_handle) -> i32 {
    if handle.is_null() {
        return 1;
    }
    let _handle = Box::from_raw(handle);
    0
}

#[cfg(test)]
mod tests {
    use super::*;
    #[cfg(feature = "terminal-logging")]
    use simple_logger;
    #[test]
    fn it_works() {
        #[cfg(feature = "terminal-logging")]
        simple_logger::init().unwrap();
        {
            assert!(promote_current_thread_to_real_time(0, 0).is_err());
        }
        {
            match promote_current_thread_to_real_time(0, 44100) {
                Ok(rt_prio_handle) => {
                    let rv = demote_current_thread_from_real_time(rt_prio_handle);
                    assert!(rv.is_ok());
                }
                Err(e) => {
                    panic!("{}", e);
                }
            }
        }
        {
            match promote_current_thread_to_real_time(512, 44100) {
                Ok(rt_prio_handle) => {
                    let rv = demote_current_thread_from_real_time(rt_prio_handle);
                    assert!(rv.is_ok());
                }
                Err(e) => {
                    panic!("{}", e);
                }
            }
        }
        {
            // Try larger values to test https://github.com/mozilla/audio_thread_priority/pull/23
            match promote_current_thread_to_real_time(0, 192000) {
                Ok(rt_prio_handle) => {
                    let rv = demote_current_thread_from_real_time(rt_prio_handle);
                    assert!(rv.is_ok());
                }
                Err(e) => {
                    panic!("{}", e);
                }
            }
        }
        {
            // Try larger values to test https://github.com/mozilla/audio_thread_priority/pull/23
            match promote_current_thread_to_real_time(8192, 48000) {
                Ok(rt_prio_handle) => {
                    let rv = demote_current_thread_from_real_time(rt_prio_handle);
                    assert!(rv.is_ok());
                }
                Err(e) => {
                    panic!("{}", e);
                }
            }
        }
        {
            match promote_current_thread_to_real_time(512, 44100) {
                Ok(_) => {}
                Err(e) => {
                    panic!("{}", e);
                }
            }
            // automatically deallocated, but not demoted until the thread exits.
        }
    }

    #[test]
    fn it_works_in_different_threads() {
        let handles: Vec<_> = (0..32).map(|_| std::thread::spawn(it_works)).collect();
        for handle in handles {
            handle.join().unwrap()
        }
    }

    cfg_if! {
        if #[cfg(target_os = "linux")] {
            use nix::unistd::*;
            use nix::sys::signal::*;

            #[test]
            fn test_linux_api() {
                {
                    let info = get_current_thread_info().unwrap();
                    match promote_thread_to_real_time(info, 512, 44100) {
                        Ok(_) => { }
                        Err(e) => {
                          panic!("{}", e);
                        }
                    }
                }
                {
                    let info = get_current_thread_info().unwrap();
                    let bytes = info.serialize();
                    let info2 = RtPriorityThreadInfo::deserialize(bytes);
                    assert!(info == info2);
                }
                {
                    let info = get_current_thread_info().unwrap();
                    let bytes = thread_info_serialize(info);
                    let info2 = thread_info_deserialize(bytes);
                    assert!(info == info2);
                }
            }
            #[test]
            fn test_remote_promotion() {
                let (rd, wr) = pipe().unwrap();

                match unsafe { fork().expect("fork failed") } {
                    ForkResult::Parent{ child } => {
                        eprintln!("Parent PID: {}", getpid());
                        let mut bytes = [0_u8; std::mem::size_of::<RtPriorityThreadInfo>()];
                        match read(rd, &mut bytes) {
                             Ok(_) => {
                                let info = RtPriorityThreadInfo::deserialize(bytes);
                                match promote_thread_to_real_time(info, 0, 44100) {
                                    Ok(_) => {
                                        eprintln!("thread promotion in the child from the parent succeeded");
                                    }
                                    Err(e) => {
                                        kill(child, SIGKILL).expect("Could not kill the child?");
                                        panic!("{}", e);
                                    }
                                }
                            }
                            Err(e) => {
                                eprintln!("could not read from the pipe: {}", e);
                            }
                        }
                        kill(child, SIGKILL).expect("Could not kill the child?");
                    }
                    ForkResult::Child => {
                        let r = set_real_time_hard_limit(0, 44100);
                        if r.is_err() {
                            eprintln!("Could not set RT limit, the test will fail.");
                        }
                        eprintln!("Child pid: {}", getpid());
                        let info = get_current_thread_info().unwrap();
                        let bytes = info.serialize();
                        match write(wr, &bytes) {
                            Ok(_) => {
                                loop {
                                    std::thread::sleep(std::time::Duration::from_millis(1000));
                                    eprintln!("child sleeping, waiting to be promoted...");
                                }
                            }
                            Err(_) => {
                                eprintln!("write error on the pipe.");
                            }
                        }
                    }
                }
            }
        }
    }
}