switch threadpool back from rayon to threadpool

rayon does not replenish the pool when the thread panics, but we must
be reselient to bugs.

Cargo.lock

@@ -697,6 +697,7 @@ dependencies = [
  "tempdir 0.3.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "test_utils 0.1.0",
  "text_unit 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "threadpool 1.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "url_serde 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 2.2.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1103,6 +1104,14 @@ dependencies = [
  "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "threadpool"
+version = "1.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "num_cpus 1.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "time"
 version = "0.1.40"
@@ -1414,6 +1423,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum text_unit 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)" = "8009d7bdbd896a7e09b595f8f9325a19047fc708653e60d0895202b82135048f"
 "checksum textwrap 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "307686869c93e71f94da64286f9a9524c0f308a9e1c87a583de8e9c9039ad3f6"
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
+"checksum threadpool 1.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e2f0c90a5f3459330ac8bc0d2f879c693bb7a2f59689c1083fc4ef83834da865"
 "checksum time 0.1.40 (registry+https://github.com/rust-lang/crates.io-index)" = "d825be0eb33fda1a7e68012d51e9c7f451dc1a69391e7fdc197060bb8c56667b"
 "checksum typenum 1.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "612d636f949607bdf9b123b4a6f6d966dedf3ff669f7f045890d3a4a73948169"
 "checksum ucd-trie 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "71a9c5b1fe77426cf144cc30e49e955270f5086e31a6441dfa8b32efc09b9d77"

crates/ra_lsp_server/Cargo.toml

@@ -6,6 +6,7 @@ authors = ["Aleksey Kladov <aleksey.kladov@gmail.com>"]
 
 [dependencies]
 rayon = "1.0.2"
+threadpool = "1.7.1"
 relative-path = "0.4.0"
 failure = "0.1.2"
 failure_derive = "0.1.2"

crates/ra_lsp_server/src/main_loop.rs

@@ -9,7 +9,8 @@ use gen_lsp_server::{
 };
 use languageserver_types::NumberOrString;
 use ra_analysis::{Canceled, FileId, LibraryData};
-use rayon::{self, ThreadPool};
+use rayon;
+use threadpool::ThreadPool;
 use rustc_hash::FxHashSet;
 use serde::{de::DeserializeOwned, Serialize};
 use failure::{format_err, bail};
@@ -54,11 +55,7 @@ pub fn main_loop(
     msg_receiver: &Receiver<RawMessage>,
     msg_sender: &Sender<RawMessage>,
 ) -> Result<()> {
-    let pool = rayon::ThreadPoolBuilder::new()
+    let pool = ThreadPool::new(8);
-        .num_threads(4)
-        .panic_handler(|_| log::error!("thread panicked :("))
-        .build()
-        .unwrap();
     let (task_sender, task_receiver) = unbounded::<Task>();
     let (fs_worker, fs_watcher) = vfs::roots_loader();
     let (ws_worker, ws_watcher) = workspace_loader();
@@ -155,7 +152,7 @@ fn main_loop_inner(
                 } else {
                     let (files, resolver) = state.events_to_files(events);
                     let sender = libdata_sender.clone();
-                    pool.spawn(move || {
+                    pool.execute(move || {
                         let start = ::std::time::Instant::now();
                         log::info!("indexing {} ... ", root.display());
                         let data = LibraryData::prepare(files, resolver);
@@ -402,7 +399,7 @@ impl<'a> PoolDispatcher<'a> {
             Ok((id, params)) => {
                 let world = self.world.snapshot();
                 let sender = self.sender.clone();
-                self.pool.spawn(move || {
+                self.pool.execute(move || {
                     let resp = match f(world, params) {
                         Ok(resp) => RawResponse::ok::<R>(id, &resp),
                         Err(e) => match e.downcast::<LspError>() {
@@ -452,7 +449,7 @@ fn update_file_notifications_on_threadpool(
     sender: Sender<Task>,
     subscriptions: Vec<FileId>,
 ) {
-    pool.spawn(move || {
+    pool.execute(move || {
         for file_id in subscriptions {
             match handlers::publish_diagnostics(&world, file_id) {
                 Err(e) => {