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Use the first call to set_mm_thread_characteristics as the warmup call #28

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Mar 14, 2024
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Use the first call to set_mm_thread_characteristics as the warmup call #28

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57 changes: 22 additions & 35 deletions src/rt_win.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,13 +3,10 @@ use crate::AudioThreadPriorityError;
use log::info;
use std::sync::OnceLock;
use windows_sys::{
core::PCWSTR,
w,
Win32::Foundation::{HANDLE, WIN32_ERROR},
};

const MMCSS_TASK_NAME: PCWSTR = w!("Audio");

#[derive(Debug)]
pub struct RtPriorityHandleInternal {
mmcss_task_index: u32,
Expand Down Expand Up @@ -40,7 +37,7 @@ pub fn promote_current_thread_to_real_time_internal(
_audio_samplerate_hz: u32,
) -> Result<RtPriorityHandleInternal, AudioThreadPriorityError> {
avrt()?
.set_mm_thread_characteristics(MMCSS_TASK_NAME)
.set_mm_thread_characteristics(w!("Audio"))
.map(|(mmcss_task_index, task_handle)| {
info!("task {mmcss_task_index} bumped to real time priority.");
RtPriorityHandleInternal::new(mmcss_task_index, task_handle)
Expand Down Expand Up @@ -72,10 +69,8 @@ pub fn demote_current_thread_from_real_time_internal(
}

mod avrt_lib {
use super::{
win32_utils::{win32_error_if, OwnedLibrary},
MMCSS_TASK_NAME,
};
use super::win32_utils::{win32_error_if, OwnedLibrary};
use std::sync::Once;
use windows_sys::{
core::PCWSTR,
s, w,
Expand Down Expand Up @@ -108,39 +103,31 @@ mod avrt_lib {
module.get_proc(s!("AvRevertMmThreadCharacteristics"))?,
)
};
Ok(Self::new(
Ok(Self {
module,
av_set_mm_thread_characteristics_w,
av_revert_mm_thread_characteristics,
))
})
}

fn new(
module: OwnedLibrary,
av_set_mm_thread_characteristics_w: AvSetMmThreadCharacteristicsWFn,
av_revert_mm_thread_characteristics: AvRevertMmThreadCharacteristicsFn,
) -> Self {
let library = AvRtLibrary {
module,
av_set_mm_thread_characteristics_w,
av_revert_mm_thread_characteristics,
};

// Warmup code to ensure that the MMCSS service will already be active once
// we return from this function.
//
// Note: This warmup code seems necessary to guarantee the thread safety of
// the avrt functions later. Removing this warmup code can result in
// calls to AvSetMmThreadCharacteristicsW failing with an error code of
// ERROR_PATH_NOT_FOUND.
if let Ok((_, handle)) = library.set_mm_thread_characteristics(MMCSS_TASK_NAME) {
let _ = library.revert_mm_thread_characteristics(handle);
}

library
pub(super) fn set_mm_thread_characteristics(
&self,
task_name: PCWSTR,
) -> Result<(u32, HANDLE), WIN32_ERROR> {
// Ensure that the first call never runs in parallel with other calls. This
// seems necessary to guarantee the success of these other calls. We saw them
// fail with an error code of ERROR_PATH_NOT_FOUND in tests, presumably on a
// machine where the MMCSS service was initially inactive.
static FIRST_CALL: Once = Once::new();
let mut first_call_result = None;
FIRST_CALL.call_once(|| {
first_call_result = Some(self.set_mm_thread_characteristics_internal(task_name))
});
first_call_result
.unwrap_or_else(|| self.set_mm_thread_characteristics_internal(task_name))
}

pub(super) fn set_mm_thread_characteristics(
fn set_mm_thread_characteristics_internal(
&self,
task_name: PCWSTR,
) -> Result<(u32, HANDLE), WIN32_ERROR> {
Expand Down Expand Up @@ -186,7 +173,7 @@ mod win32_utils {
pub(super) fn try_new(lib_file_name: PCWSTR) -> Result<Self, WIN32_ERROR> {
let module = unsafe { LoadLibraryW(lib_file_name) };
win32_error_if(module == 0)?;
Ok(OwnedLibrary(module))
Ok(Self(module))
}

fn raw(&self) -> HMODULE {
Expand Down
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