servo/components/style/gecko/global_style_data.rs

/* 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 http://mozilla.org/MPL/2.0/. */

//! Global style data

use context::StyleSystemOptions;
use gecko_bindings::bindings::{Gecko_RegisterProfilerThread, Gecko_UnregisterProfilerThread};
use gecko_bindings::bindings::Gecko_SetJemallocThreadLocalArena;
use num_cpus;
use parallel::STYLE_THREAD_STACK_SIZE_KB;
use rayon;
use shared_lock::SharedRwLock;
use std::cmp;
use std::env;
use std::ffi::CString;
use thread_state;

/// 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.
    pub style_thread_pool: Option<rayon::ThreadPool>,
}

fn thread_name(index: usize) -> String {
    format!("StyleThread#{}", index)
}

fn thread_startup(index: usize) {
    thread_state::initialize_layout_worker_thread();
    unsafe {
        Gecko_SetJemallocThreadLocalArena(true);
    }
    let name = thread_name(index);
    let name = CString::new(name).unwrap();
    unsafe {
        // Gecko_RegisterProfilerThread copies the passed name here.
        Gecko_RegisterProfilerThread(name.as_ptr());
    }
}

fn thread_shutdown(_: usize) {
    unsafe {
        Gecko_UnregisterProfilerThread();
        Gecko_SetJemallocThreadLocalArena(false);
    }
}

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,
            _ => cmp::max(num_cpus::get() * 3 / 4, 1),
        };

        // 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)
                // Enable a breadth-first rayon traversal. This causes the work
                // queue to be always FIFO, rather than FIFO for stealers and
                // FILO for the owner (which is what rayon does by default). This
                // ensures that we process all the elements at a given depth before
                // proceeding to the next depth, which is important for style sharing.
                .breadth_first()
                .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: num_threads,
            style_thread_pool: pool,
        }
    };
    /// Global style data
    pub static ref GLOBAL_STYLE_DATA: GlobalStyleData = GlobalStyleData {
        shared_lock: SharedRwLock::new(),
        options: StyleSystemOptions::default(),
    };
}