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 when it is unnecessary for their specific use case.
Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/bin/main.rs

@@ -23,35 +23,40 @@ 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,
@@ -1057,6 +1058,7 @@ 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;
@@ -1135,6 +1137,7 @@ 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>,