Add prefs to limit threadpool sizes (#34478)

* Add prefs to limit threadpool sizes

Add preferences to control the size of threadpools,
so that we can easily reduce the amount of runtime
threads and test which pools benefit from more
threads.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

* Add pref for Webrender threadpool

Add a preference to limit the size of the webrender threadpool.
Note: WebRender by default calls hooks which register the threads with
a profiler instance that the embedder can register with webrender.
Servo currently doesn't register such a profiler with webrender,
but in the future we might also want to profile the
webrender threadpool.

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

---------

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

1 files changed, 26 insertions, 4 deletions

diff --git a/components/net/async_runtime.rs b/components/net/async_runtime.rs
index 144f4262835..7d1fb9daeaa 100644
--- a/components/net/async_runtime.rs
+++ b/components/net/async_runtime.rs
@@ -1,10 +1,32 @@
 /* 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/. */
-
+use std::cmp::Ord;
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{LazyLock, Mutex};
+use std::thread;
 
-use tokio::runtime::Runtime;
+use tokio::runtime::{Builder, Runtime};
 
-pub static HANDLE: LazyLock<Mutex<Option<Runtime>>> =
-    LazyLock::new(|| Mutex::new(Some(Runtime::new().unwrap())));
+pub static HANDLE: LazyLock<Mutex<Option<Runtime>>> = LazyLock::new(|| {
+    Mutex::new(Some(
+        Builder::new_multi_thread()
+            .thread_name_fn(|| {
+                static ATOMIC_ID: AtomicUsize = AtomicUsize::new(0);
+                let id = ATOMIC_ID.fetch_add(1, Ordering::Relaxed);
+                format!("tokio-runtime-{}", id)
+            })
+            .worker_threads(
+                thread::available_parallelism()
+                    .map(|i| i.get())
+                    .unwrap_or(servo_config::pref!(threadpools.fallback_worker_num) as usize)
+                    .min(
+                        servo_config::pref!(threadpools.async_runtime_workers.max).max(1) as usize,
+                    ),
+            )
+            .enable_io()
+            .enable_time()
+            .build()
+            .unwrap(),
+    ))
+});