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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! Global style data
use crate::context::StyleSystemOptions;
#[cfg(feature = "gecko")]
use crate::gecko_bindings::bindings;
use crate::parallel::STYLE_THREAD_STACK_SIZE_KB;
use crate::shared_lock::SharedRwLock;
use crate::thread_state;
use gecko_profiler;
use parking_lot::{Mutex, RwLock, RwLockReadGuard};
use rayon;
#[cfg(unix)]
use std::os::unix::thread::{JoinHandleExt, RawPthread};
#[cfg(windows)]
use std::os::windows::{io::AsRawHandle, prelude::RawHandle};
use std::{io, thread};
use thin_vec::ThinVec;
/// Platform-specific handle to a thread.
#[cfg(unix)]
pub type PlatformThreadHandle = RawPthread;
/// Platform-specific handle to a thread.
#[cfg(windows)]
pub type PlatformThreadHandle = RawHandle;
/// Global style data
pub struct GlobalStyleData {
/// Shared RWLock for CSSOM objects
pub shared_lock: SharedRwLock,
/// Global style system options determined by env vars.
pub options: StyleSystemOptions,
}
/// Global thread pool.
pub struct StyleThreadPool {
/// How many threads parallel styling can use. If not using a thread pool, this is set to `None`.
pub num_threads: Option<usize>,
/// The parallel styling thread pool.
///
/// For leak-checking purposes, we want to terminate the thread-pool, which
/// waits for all the async jobs to complete. Thus the RwLock.
style_thread_pool: RwLock<Option<rayon::ThreadPool>>,
}
fn thread_name(index: usize) -> String {
format!("StyleThread#{}", index)
}
lazy_static! {
/// JoinHandles for spawned style threads. These will be joined during
/// StyleThreadPool::shutdown() after exiting the thread pool.
///
/// This would be quite inefficient if rayon destroyed and re-created
/// threads regularly during threadpool operation in response to demand,
/// however rayon actually never destroys its threads until the entire
/// thread pool is shut-down, so the size of this list is bounded.
static ref STYLE_THREAD_JOIN_HANDLES: Mutex<Vec<thread::JoinHandle<()>>> =
Mutex::new(Vec::new());
}
fn thread_spawn(options: rayon::ThreadBuilder) -> io::Result<()> {
let mut b = thread::Builder::new();
if let Some(name) = options.name() {
b = b.name(name.to_owned());
}
if let Some(stack_size) = options.stack_size() {
b = b.stack_size(stack_size);
}
let join_handle = b.spawn(|| options.run())?;
STYLE_THREAD_JOIN_HANDLES.lock().push(join_handle);
Ok(())
}
fn thread_startup(_index: usize) {
thread_state::initialize_layout_worker_thread();
#[cfg(feature = "gecko")]
unsafe {
bindings::Gecko_SetJemallocThreadLocalArena(true);
let name = thread_name(_index);
gecko_profiler::register_thread(&name);
}
}
fn thread_shutdown(_: usize) {
#[cfg(feature = "gecko")]
unsafe {
gecko_profiler::unregister_thread();
bindings::Gecko_SetJemallocThreadLocalArena(false);
}
}
impl StyleThreadPool {
/// Shuts down the thread pool, waiting for all work to complete.
pub fn shutdown() {
if STYLE_THREAD_JOIN_HANDLES.lock().is_empty() {
return;
}
{
// Drop the pool.
let _ = STYLE_THREAD_POOL.style_thread_pool.write().take();
}
// Join spawned threads until all of the threads have been joined. This
// will usually be pretty fast, as on shutdown there should be basically
// no threads left running.
while let Some(join_handle) = STYLE_THREAD_JOIN_HANDLES.lock().pop() {
let _ = join_handle.join();
}
}
/// Returns a reference to the thread pool.
///
/// We only really want to give read-only access to the pool, except
/// for shutdown().
pub fn pool(&self) -> RwLockReadGuard<Option<rayon::ThreadPool>> {
self.style_thread_pool.read()
}
/// Returns a list of the pool's platform-specific thread handles.
pub fn get_thread_handles(handles: &mut ThinVec<PlatformThreadHandle>) {
// Force the lazy initialization of STYLE_THREAD_POOL so that the threads get spawned and
// their join handles are added to STYLE_THREAD_JOIN_HANDLES.
lazy_static::initialize(&STYLE_THREAD_POOL);
for join_handle in STYLE_THREAD_JOIN_HANDLES.lock().iter() {
#[cfg(unix)]
let handle = join_handle.as_pthread_t();
#[cfg(windows)]
let handle = join_handle.as_raw_handle();
handles.push(handle);
}
}
}
#[cfg(feature = "servo")]
fn stylo_threads_pref() -> i32 {
pref!(layout.threads)
}
#[cfg(feature = "gecko")]
fn stylo_threads_pref() -> i32 {
static_prefs::pref!("layout.css.stylo-threads")
}
/// The performance benefit of additional threads seems to level off at around six, so we cap it
/// there on many-core machines (see bug 1431285 comment 14).
pub(crate) const STYLO_MAX_THREADS: usize = 6;
lazy_static! {
/// Global thread pool
pub static ref STYLE_THREAD_POOL: StyleThreadPool = {
use std::cmp;
// We always set this pref on startup, before layout or script have had a chance of
// accessing (and thus creating) the thread-pool.
let threads_pref: i32 = stylo_threads_pref();
let num_threads = if threads_pref >= 0 {
threads_pref as usize
} else {
// Gecko may wish to override the default number of threads, for example on
// systems with heterogeneous CPUs.
#[cfg(feature = "gecko")]
let num_threads = unsafe { bindings::Gecko_GetNumStyleThreads() };
#[cfg(not(feature = "gecko"))]
let num_threads = -1;
if num_threads >= 0 {
num_threads as usize
} else {
use num_cpus;
// The default heuristic is num_virtual_cores * .75. This gives us three threads on a
// hyper-threaded dual core, and six threads on a hyper-threaded quad core.
cmp::max(num_cpus::get() * 3 / 4, 1)
}
};
let num_threads = cmp::min(num_threads, STYLO_MAX_THREADS);
// Since the main-thread is also part of the pool, having one thread or less doesn't make
// sense.
let (pool, num_threads) = if num_threads <= 1 {
(None, None)
} else {
let workers = rayon::ThreadPoolBuilder::new()
.spawn_handler(thread_spawn)
.use_current_thread()
.num_threads(num_threads)
.thread_name(thread_name)
.start_handler(thread_startup)
.exit_handler(thread_shutdown)
.stack_size(STYLE_THREAD_STACK_SIZE_KB * 1024)
.build();
(workers.ok(), Some(num_threads))
};
StyleThreadPool {
num_threads,
style_thread_pool: RwLock::new(pool),
}
};
/// Global style data
pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = GlobalStyleData {
shared_lock: SharedRwLock::new_leaked(),
options: StyleSystemOptions::default(),
};
}