From efb0104adcdebcc08dc9d5579d9490ea538b5da2 Mon Sep 17 00:00:00 2001
From: Richard Feldman <oss@rtfeldman.com>
Date: Wed, 18 Dec 2019 07:28:36 -0500
Subject: [PATCH 1/3] Use spawn_blocking for load_module

---
 Cargo.toml      |  2 +-
 src/load/mod.rs | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 115ab140ea..33c7de49f9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,7 +10,7 @@ petgraph = { version = "0.4.5", optional = true }
 im = "14.0.0"    # im and im-rc should always have the same version!
 im-rc = "14.0.0" # im and im-rc should always have the same version!
 wyhash = "0.3"
-tokio = { version = "0.2", features = ["fs", "sync", "rt-threaded"] }
+tokio = { version = "0.2", features = ["blocking", "fs", "sync", "rt-threaded"] }
 bumpalo = "2.6"
 # NOTE: Breaking API changes get pushed directly to this Inkwell branch, so be
 # very careful when running `cargo update` to get a new revision into Cargo.lock.
diff --git a/src/load/mod.rs b/src/load/mod.rs
index 9e4d786ff9..3c9c236c93 100644
--- a/src/load/mod.rs
+++ b/src/load/mod.rs
@@ -16,11 +16,12 @@ use crate::types::Constraint;
 use crate::unify::Problems;
 use bumpalo::Bump;
 use futures::future::join_all;
+use std::fs::read_to_string;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
-use tokio::fs::read_to_string;
 use tokio::sync::mpsc::{self, Receiver, Sender};
+use tokio::task::spawn_blocking;
 
 #[derive(Debug)]
 pub struct Loaded {
@@ -90,8 +91,7 @@ pub async fn load<'a>(
     let main_tx = tx.clone();
     let arc_var_store = Arc::new(VarStore::new(vars_created));
     let var_store = Arc::clone(&arc_var_store);
-    let handle =
-        tokio::spawn(async move { load_filename(&env, filename, main_tx, &var_store).await });
+    let handle = tokio::spawn(async move { load_filename(&env, filename, main_tx, &var_store) });
 
     let requested_module = handle
         .await
@@ -118,7 +118,10 @@ pub async fn load<'a>(
             let tx = tx.clone();
             let var_store = Arc::clone(&arc_var_store);
 
-            tokio::spawn(async move { load_module(&env, dep, tx, &var_store).await })
+            // Use spawn_blocking here because we're canonicalizing these in
+            // parallel, and canonicalization can potentially block the
+            // executor for awhile.
+            spawn_blocking(move || load_module(&env, dep, tx, &var_store))
         }))
         .await;
 
@@ -142,7 +145,7 @@ pub async fn load<'a>(
     }
 }
 
-async fn load_module(
+fn load_module(
     env: &Env,
     module_name: Box<str>,
     tx: Sender<DepNames>,
@@ -160,16 +163,16 @@ async fn load_module(
     // End with .roc
     filename.set_extension("roc");
 
-    load_filename(env, filename, tx, var_store).await
+    load_filename(env, filename, tx, var_store)
 }
 
-async fn load_filename(
+fn load_filename(
     env: &Env,
     filename: PathBuf,
     tx: Sender<DepNames>,
     var_store: &VarStore,
 ) -> LoadedModule {
-    match read_to_string(&filename).await {
+    match read_to_string(&filename) {
         Ok(src) => {
             let arena = Bump::new();
             // TODO instead of env.arena.alloc(src), we should create a new buffer

From d398f715d64e26c043d163c28ba5be5685c544ce Mon Sep 17 00:00:00 2001
From: Richard Feldman <oss@rtfeldman.com>
Date: Wed, 18 Dec 2019 07:33:10 -0500
Subject: [PATCH 2/3] Follow clippy's advice

---
 src/load/mod.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/load/mod.rs b/src/load/mod.rs
index 3c9c236c93..97d11c7934 100644
--- a/src/load/mod.rs
+++ b/src/load/mod.rs
@@ -121,7 +121,7 @@ pub async fn load<'a>(
             // Use spawn_blocking here because we're canonicalizing these in
             // parallel, and canonicalization can potentially block the
             // executor for awhile.
-            spawn_blocking(move || load_module(&env, dep, tx, &var_store))
+            spawn_blocking(move || load_module(&env, &dep, tx, &var_store))
         }))
         .await;
 
@@ -147,7 +147,7 @@ pub async fn load<'a>(
 
 fn load_module(
     env: &Env,
-    module_name: Box<str>,
+    module_name: &str,
     tx: Sender<DepNames>,
     var_store: &VarStore,
 ) -> LoadedModule {

From 12cd440284d628110a63658893d28273b43d68bc Mon Sep 17 00:00:00 2001
From: Richard Feldman <oss@rtfeldman.com>
Date: Wed, 18 Dec 2019 07:40:25 -0500
Subject: [PATCH 3/3] Use spawn_blocking for load()

---
 src/load/mod.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/load/mod.rs b/src/load/mod.rs
index 97d11c7934..97956f191e 100644
--- a/src/load/mod.rs
+++ b/src/load/mod.rs
@@ -91,8 +91,10 @@ pub async fn load<'a>(
     let main_tx = tx.clone();
     let arc_var_store = Arc::new(VarStore::new(vars_created));
     let var_store = Arc::clone(&arc_var_store);
-    let handle = tokio::spawn(async move { load_filename(&env, filename, main_tx, &var_store) });
 
+    // Use spawn_blocking here so that we can proceed to the recv() loop
+    // while this is doing blocking work like reading and parsing the file.
+    let handle = spawn_blocking(move || load_filename(&env, filename, main_tx, &var_store));
     let requested_module = handle
         .await
         .unwrap_or_else(|err| panic!("Unable to load requested module: {:?}", err));