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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 parking_lot::{RwLock, RwLockReadGuard};
use rayon;
use std::env;
use std::sync::atomic::{AtomicUsize, Ordering};
/// 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.
pub num_threads: 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)
}
// A counter so that we can wait for shutdown of all threads. See
// StyleThreadPool::shutdown.
static ALIVE_WORKER_THREADS: AtomicUsize = AtomicUsize::new(0);
fn thread_startup(_index: usize) {
ALIVE_WORKER_THREADS.fetch_add(1, Ordering::Relaxed);
thread_state::initialize_layout_worker_thread();
#[cfg(feature = "gecko")]
unsafe {
use std::ffi::CString;
bindings::Gecko_SetJemallocThreadLocalArena(true);
let name = thread_name(_index);
let name = CString::new(name).unwrap();
// Gecko_RegisterProfilerThread copies the passed name here.
bindings::Gecko_RegisterProfilerThread(name.as_ptr());
}
}
fn thread_shutdown(_: usize) {
#[cfg(feature = "gecko")]
unsafe {
bindings::Gecko_UnregisterProfilerThread();
bindings::Gecko_SetJemallocThreadLocalArena(false);
}
ALIVE_WORKER_THREADS.fetch_sub(1, Ordering::Relaxed);
}
impl StyleThreadPool {
/// Shuts down the thread pool, waiting for all work to complete.
pub fn shutdown() {
if ALIVE_WORKER_THREADS.load(Ordering::Relaxed) == 0 {
return;
}
{
// Drop the pool.
let _ = STYLE_THREAD_POOL.style_thread_pool.write().take();
}
// Spin until all our threads are done. This will usually be pretty
// fast, as on shutdown there should be basically no threads left
// running.
//
// This still _technically_ doesn't give us the guarantee of TLS
// destructors running on the worker threads. For that we'd need help
// from rayon to properly join the threads.
//
// See https://github.com/rayon-rs/rayon/issues/688
//
// So we instead intentionally leak TLS stuff (see BLOOM_KEY and co) for
// now until that's fixed.
while ALIVE_WORKER_THREADS.load(Ordering::Relaxed) != 0 {
std::thread::yield_now();
}
}
/// 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()
}
}
lazy_static! {
/// Global thread pool
pub static ref STYLE_THREAD_POOL: StyleThreadPool = {
let stylo_threads = env::var("STYLO_THREADS")
.map(|s| s.parse::<usize>().expect("invalid STYLO_THREADS value"));
let mut num_threads = match stylo_threads {
Ok(num) => num,
#[cfg(feature = "servo")]
_ => {
use servo_config::pref;
// We always set this pref on startup, before layout or script
// have had a chance of accessing (and thus creating) the
// thread-pool.
pref!(layout.threads) as usize
}
#[cfg(feature = "gecko")]
_ => {
// 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. 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).
use num_cpus;
use std::cmp;
cmp::min(cmp::max(num_cpus::get() * 3 / 4, 1), 6)
}
};
// If num_threads is one, there's no point in creating a thread pool, so
// force it to zero.
//
// We allow developers to force a one-thread pool for testing via a
// special environmental variable.
if num_threads == 1 {
let force_pool = env::var("FORCE_STYLO_THREAD_POOL")
.ok().map_or(false, |s| s.parse::<usize>().expect("invalid FORCE_STYLO_THREAD_POOL value") == 1);
if !force_pool {
num_threads = 0;
}
}
let pool = if num_threads < 1 {
None
} else {
let workers = rayon::ThreadPoolBuilder::new()
.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()
};
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(),
};
}
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