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Move `fork` from origin to c-scape, and convert it back to using `unsafe extern "C" fn()` hooks instead of safe boxed closures. See bytecodealliance/rustix#137 for discussion. Add an at_thread_exit_raw to origin, which allows thread destructors to be registered without allocating, which is important since Rust will register TLS destructors while threads are being constructed, before parking_lot is prepared for the global allocator to take locks. Update to the latest rustix, and the change from a safe execve to an unsafe raw execveat. This similarly allows it to avoid allocating, which is important as it's primarily called in the child of `fork`. And switch to a branch of parking_lot with changes to allow parking_lot locks to be used from within global allocator implementations. These changes allow us to move the `#[global_allocator]` back to the mustang crate, and restore the wee_alloc allocator option. More generally, origin and c-scape should in theory now work with any global allocator implementation.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,40 @@ | ||
| use std::env::var; | ||
| use std::io::Write; | ||
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| fn main() { | ||
| // Don't rerun this on changes other than build.rs, as we only depend on | ||
| // the rustc version. | ||
| println!("cargo:rerun-if-changed=build.rs"); | ||
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| use_feature_or_nothing("thread_local_const_init"); | ||
| } | ||
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| fn use_feature_or_nothing(feature: &str) { | ||
| if has_feature(feature) { | ||
| use_feature(feature); | ||
| } | ||
| } | ||
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| fn use_feature(feature: &str) { | ||
| println!("cargo:rustc-cfg={}", feature); | ||
| } | ||
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| /// Test whether the rustc at `var("RUSTC")` supports the given feature. | ||
| fn has_feature(feature: &str) -> bool { | ||
| let out_dir = var("OUT_DIR").unwrap(); | ||
| let rustc = var("RUSTC").unwrap(); | ||
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| let mut child = std::process::Command::new(rustc) | ||
| .arg("--crate-type=rlib") // Don't require `main`. | ||
| .arg("--emit=metadata") // Do as little as possible but still parse. | ||
| .arg("--out-dir") | ||
| .arg(out_dir) // Put the output somewhere inconsequential. | ||
| .arg("-") // Read from stdin. | ||
| .stdin(std::process::Stdio::piped()) // Stdin is a pipe. | ||
| .spawn() | ||
| .unwrap(); | ||
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| writeln!(child.stdin.take().unwrap(), "#![feature({})]", feature).unwrap(); | ||
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| child.wait().unwrap().success() | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,73 @@ | ||
| use parking_lot::lock_api::RawMutex as _; | ||
| use parking_lot::{Mutex, RawMutex}; | ||
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| /// Functions registered with `at_fork`. | ||
| static FORK_FUNCS: Mutex<RegisteredForkFuncs> = | ||
| Mutex::const_new(RawMutex::INIT, RegisteredForkFuncs::new()); | ||
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| /// A type for holding `fork` callbacks. | ||
| #[derive(Default)] | ||
| struct RegisteredForkFuncs { | ||
| /// Functions called before calling `fork`. | ||
| pub(crate) prepare: Vec<unsafe extern "C" fn()>, | ||
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| /// Functions called after calling `fork`, in the parent. | ||
| pub(crate) parent: Vec<unsafe extern "C" fn()>, | ||
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| /// Functions called after calling `fork`, in the child. | ||
| pub(crate) child: Vec<unsafe extern "C" fn()>, | ||
| } | ||
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| impl RegisteredForkFuncs { | ||
| pub(crate) const fn new() -> Self { | ||
| Self { | ||
| prepare: Vec::new(), | ||
| parent: Vec::new(), | ||
| child: Vec::new(), | ||
| } | ||
| } | ||
| } | ||
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| /// Register functions to be called when `fork` is called. | ||
| /// | ||
| /// The handlers for each phase are called in the following order: | ||
| /// the prepare handlers are called in reverse order of registration; | ||
| /// the parent and child handlers are called in the order of registration. | ||
| pub(crate) fn at_fork( | ||
| prepare_func: Option<unsafe extern "C" fn()>, | ||
| parent_func: Option<unsafe extern "C" fn()>, | ||
| child_func: Option<unsafe extern "C" fn()>, | ||
| ) { | ||
| let mut funcs = FORK_FUNCS.lock(); | ||
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| // Add the callbacks to the lists. | ||
| funcs.prepare.extend(prepare_func); | ||
| funcs.parent.extend(parent_func); | ||
| funcs.child.extend(child_func); | ||
| } | ||
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| pub(crate) unsafe fn fork() -> rustix::io::Result<Option<rustix::process::Pid>> { | ||
| let funcs = FORK_FUNCS.lock(); | ||
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| // Callbacks before calling `fork`. | ||
| funcs.prepare.iter().rev().for_each(|func| func()); | ||
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| // Call `fork`. | ||
| match rustix::runtime::fork()? { | ||
| None => { | ||
| // The child's thread record is copied from the parent; | ||
| // update it with the child's current-thread-id. | ||
| #[cfg(feature = "threads")] | ||
| origin::set_current_thread_id_after_a_fork(rustix::thread::gettid()); | ||
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| // Callbacks after calling `fork`, in the child. | ||
| funcs.child.iter().for_each(|func| func()); | ||
| Ok(None) | ||
| } | ||
| Some(pid) => { | ||
| // Callbacks after calling `fork`, in the parent. | ||
| funcs.parent.iter().for_each(|func| func()); | ||
| Ok(Some(pid)) | ||
| } | ||
| } | ||
| } |
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