Auto merge of #111713 - Zoxc:lock-switch, r=nnethercote

Use conditional synchronization for Lock

This changes `Lock` to use synchronization only if `mode::is_dyn_thread_safe` could be true. This reduces overhead for the parallel compiler running with 1 thread.

The emitters are changed to use `DynSend` instead of `Send` so they can still use `Lock`.

A Rayon thread pool is not used with 1 thread anymore, as session globals contains `Lock`s which are no longer `Sync`.

Performance improvement with 1 thread and `cfg(parallel_compiler)`:
<table><tr><td rowspan="2">Benchmark</td><td colspan="1"><b>Before</b></th><td colspan="2"><b>After</b></th></tr><tr><td align="right">Time</td><td align="right">Time</td><td align="right">%</th></tr><tr><td>🟣 <b>clap</b>:check</td><td align="right">1.7665s</td><td align="right">1.7336s</td><td align="right">💚  -1.86%</td></tr><tr><td>🟣 <b>hyper</b>:check</td><td align="right">0.2780s</td><td align="right">0.2736s</td><td align="right">💚  -1.61%</td></tr><tr><td>🟣 <b>regex</b>:check</td><td align="right">0.9994s</td><td align="right">0.9824s</td><td align="right">💚  -1.70%</td></tr><tr><td>🟣 <b>syn</b>:check</td><td align="right">1.5875s</td><td align="right">1.5656s</td><td align="right">💚  -1.38%</td></tr><tr><td>🟣 <b>syntex_syntax</b>:check</td><td align="right">6.0682s</td><td align="right">5.9532s</td><td align="right">💚  -1.90%</td></tr><tr><td>Total</td><td align="right">10.6997s</td><td align="right">10.5083s</td><td align="right">💚  -1.79%</td></tr><tr><td>Summary</td><td align="right">1.0000s</td><td align="right">0.9831s</td><td align="right">💚  -1.69%</td></tr></table>

cc `@SparrowLii`

3 files changed, 14 insertions, 12 deletions

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 0cae06881b1..1811738c011 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -24,7 +24,7 @@ use rustc_lint_defs::pluralize;
 
 use derive_setters::Setters;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
-use rustc_data_structures::sync::Lrc;
+use rustc_data_structures::sync::{DynSend, IntoDynSyncSend, Lrc};
 use rustc_error_messages::{FluentArgs, SpanLabel};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use std::borrow::Cow;
@@ -188,6 +188,8 @@ impl Margin {
 
 const ANONYMIZED_LINE_NUM: &str = "LL";
 
+pub type DynEmitter = dyn Emitter + DynSend;
+
 /// Emitter trait for emitting errors.
 pub trait Emitter: Translate {
     /// Emit a structured diagnostic.
@@ -625,7 +627,7 @@ impl ColorConfig {
 #[derive(Setters)]
 pub struct EmitterWriter {
     #[setters(skip)]
-    dst: Destination,
+    dst: IntoDynSyncSend<Destination>,
     sm: Option<Lrc<SourceMap>>,
     fluent_bundle: Option<Lrc<FluentBundle>>,
     #[setters(skip)]
@@ -655,7 +657,7 @@ impl EmitterWriter {
 
     fn create(dst: Destination, fallback_bundle: LazyFallbackBundle) -> EmitterWriter {
         EmitterWriter {
-            dst,
+            dst: IntoDynSyncSend(dst),
             sm: None,
             fluent_bundle: None,
             fallback_bundle,
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index b8f58e3057c..390bf28df09 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -22,7 +22,7 @@ use crate::{
 };
 use rustc_lint_defs::Applicability;
 
-use rustc_data_structures::sync::Lrc;
+use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
 use rustc_error_messages::FluentArgs;
 use rustc_span::hygiene::ExpnData;
 use rustc_span::Span;
@@ -38,7 +38,7 @@ use serde::Serialize;
 mod tests;
 
 pub struct JsonEmitter {
-    dst: Box<dyn Write + Send>,
+    dst: IntoDynSyncSend<Box<dyn Write + Send>>,
     registry: Option<Registry>,
     sm: Lrc<SourceMap>,
     fluent_bundle: Option<Lrc<FluentBundle>>,
@@ -66,7 +66,7 @@ impl JsonEmitter {
         terminal_url: TerminalUrl,
     ) -> JsonEmitter {
         JsonEmitter {
-            dst: Box::new(io::BufWriter::new(io::stderr())),
+            dst: IntoDynSyncSend(Box::new(io::BufWriter::new(io::stderr()))),
             registry,
             sm: source_map,
             fluent_bundle,
@@ -120,7 +120,7 @@ impl JsonEmitter {
         terminal_url: TerminalUrl,
     ) -> JsonEmitter {
         JsonEmitter {
-            dst,
+            dst: IntoDynSyncSend(dst),
             registry,
             sm: source_map,
             fluent_bundle,
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index b7e1b0c8ad1..39f440e31e0 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -30,11 +30,11 @@ pub use emitter::ColorConfig;
 use rustc_lint_defs::LintExpectationId;
 use Level::*;
 
-use emitter::{is_case_difference, Emitter, EmitterWriter};
+use emitter::{is_case_difference, DynEmitter, Emitter, EmitterWriter};
 use registry::Registry;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
-use rustc_data_structures::sync::{self, IntoDynSyncSend, Lock, Lrc};
+use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_data_structures::AtomicRef;
 pub use rustc_error_messages::{
     fallback_fluent_bundle, fluent_bundle, DelayDm, DiagnosticMessage, FluentBundle,
@@ -428,7 +428,7 @@ struct HandlerInner {
     err_count: usize,
     warn_count: usize,
     deduplicated_err_count: usize,
-    emitter: IntoDynSyncSend<Box<dyn Emitter + sync::Send>>,
+    emitter: Box<DynEmitter>,
     delayed_span_bugs: Vec<DelayedDiagnostic>,
     delayed_good_path_bugs: Vec<DelayedDiagnostic>,
     /// This flag indicates that an expected diagnostic was emitted and suppressed.
@@ -594,7 +594,7 @@ impl Handler {
         self
     }
 
-    pub fn with_emitter(emitter: Box<dyn Emitter + sync::Send>) -> Self {
+    pub fn with_emitter(emitter: Box<DynEmitter>) -> Self {
         Self {
             inner: Lock::new(HandlerInner {
                 flags: HandlerFlags { can_emit_warnings: true, ..Default::default() },
@@ -603,7 +603,7 @@ impl Handler {
                 warn_count: 0,
                 deduplicated_err_count: 0,
                 deduplicated_warn_count: 0,
-                emitter: IntoDynSyncSend(emitter),
+                emitter,
                 delayed_span_bugs: Vec::new(),
                 delayed_good_path_bugs: Vec::new(),
                 suppressed_expected_diag: false,