Auto merge of #118069 - onur-ozkan:bypass_bootstrap_lock, r=Mark-Simulacrum

allow bypassing the build directory lock
As bootstrap locks its entire build directory, parallel bootstrapping for anything becomes impossible. This change enables developers to bypass the locking mechanism (with `--bypass-bootstrap-lock` flag) when it is unnecessary for their specific use case.
more context: https://rust-lang.zulipchat.com/#narrow/stream/326414-t-infra.2Fbootstrap/topic/Build.20.28miri.3F.29.20sysroots.20in.20parallel
cc `@saethlin`

Author: bors

src/bootstrap/src/bin/main.rs

@@ -26,35 +26,40 @@ fn main() {
 letmut build_lock;
 #[cfg(all(any(unix, windows), not(target_os = "solaris")))]
 let _build_lock_guard;
-#[cfg(all(any(unix, windows), not(target_os = "solaris")))]
-// Display PID of process holding the lock
-// PID will be stored in a lock file
-{
-let path = config.out.join("lock");
-let pid = match fs::read_to_string(&path){
-Ok(contents) => contents,
-Err(_) => String::new(),
-};
-
- build_lock =
- fd_lock::RwLock::new(t!(fs::OpenOptions::new().write(true).create(true).open(&path)));
- _build_lock_guard = match build_lock.try_write(){
-Ok(mut lock) => {
-t!(lock.write(&process::id().to_string().as_ref()));
- lock
-}
- err => {
-drop(err);
-println!("WARNING: build directory locked by process {pid}, waiting for lock");
-letmut lock = t!(build_lock.write());
-t!(lock.write(&process::id().to_string().as_ref()));
- lock
-}
-};
-}
 
-#[cfg(any(not(any(unix, windows)), target_os = "solaris"))]
-println!("WARNING: file locking not supported for target, not locking build directory");
+if !config.bypass_bootstrap_lock{
+// Display PID of process holding the lock
+// PID will be stored in a lock file
+#[cfg(all(any(unix, windows), not(target_os = "solaris")))]
+{
+let path = config.out.join("lock");
+let pid = match fs::read_to_string(&path){
+Ok(contents) => contents,
+Err(_) => String::new(),
+};
+
+ build_lock = fd_lock::RwLock::new(t!(fs::OpenOptions::new()
+.write(true)
+.create(true)
+.open(&path)));
+ _build_lock_guard = match build_lock.try_write(){
+Ok(mut lock) => {
+t!(lock.write(&process::id().to_string().as_ref()));
+ lock
+}
+ err => {
+drop(err);
+println!("WARNING: build directory locked by process {pid}, waiting for lock");
+letmut lock = t!(build_lock.write());
+t!(lock.write(&process::id().to_string().as_ref()));
+ lock
+}
+};
+}
+
+#[cfg(any(not(any(unix, windows)), target_os = "solaris"))]
+println!("WARNING: file locking not supported for target, not locking build directory");
+}
 
 // check_version warnings are not printed during setup
 let changelog_suggestion =

src/bootstrap/src/core/config/config.rs

@@ -117,6 +117,7 @@ impl Display for DebuginfoLevel {
 pubstructConfig{
 pubchangelog_seen:Option<usize>,// FIXME: Deprecated field. Remove it at 2024.
 pubchange_id:Option<usize>,
+pubbypass_bootstrap_lock:bool,
 pubccache:Option<String>,
 /// Call Build::ninja() instead of this.
 pubninja_in_file:bool,
@@ -1059,6 +1060,7 @@ define_config! {
 implConfig{
 pubfndefault_opts() -> Config{
 letmut config = Config::default();
+ config.bypass_bootstrap_lock = false;
  config.llvm_optimize = true;
  config.ninja_in_file = true;
  config.llvm_static_stdcpp = false;
@@ -1137,6 +1139,7 @@ impl Config {
  config.llvm_profile_use = flags.llvm_profile_use;
  config.llvm_profile_generate = flags.llvm_profile_generate;
  config.enable_bolt_settings = flags.enable_bolt_settings;
+ config.bypass_bootstrap_lock = flags.bypass_bootstrap_lock;
 
 // Infer the rest of the configuration.
 

src/bootstrap/src/core/config/flags.rs

@@ -133,6 +133,13 @@ pub struct Flags {
 /// whether to use color in cargo and rustc output
 pubcolor:Color,
 
+#[arg(global(true), long)]
+/// Bootstrap uses this value to decide whether it should bypass locking the build process.
+/// This is rarely needed (e.g., compiling the std library for different targets in parallel).
+///
+/// Unless you know exactly what you are doing, you probably don't need this.
+pubbypass_bootstrap_lock:bool,
+
 /// whether rebuilding llvm should be skipped, overriding `skip-rebuld` in config.toml
 #[arg(global(true), long, value_name = "VALUE")]
 publlvm_skip_rebuild:Option<bool>,