Rollup merge of #74263 - RalfJung:thread-local, r=Mark-Simulacrum

Slight reorganization of sys/(fast_)thread_local

I was long confused by the `thread_local` and `fast_thread_local` modules in the `sys(_common)` part of libstd. The names make it *sound* like `fast_thread_local` is just a faster version of `thread_local`, but really these are totally different APIs: one provides thread-local "keys", which are non-addressable pointer-sized pieces of local storage with an associated destructor; the other (the "fast" one) provides just a destructor.

So I propose we rename `fast_thread_local` to `thread_local_dtor`, and `thread_local` to `thread_local_key`. That's what this PR does.

Author: Manishearth

src/libstd/sys/cloudabi/mod.rs

@@ -16,8 +16,8 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-#[path = "../unix/thread_local.rs"]
-pub mod thread_local;
+#[path = "../unix/thread_local_key.rs"]
+pub mod thread_local_key;
 pub mod time;
 
 pub use crate::sys_common::os_str_bytes as os_str;

src/libstd/sys/hermit/mod.rs

@@ -22,7 +22,6 @@ pub mod cmath;
 pub mod condvar;
 pub mod env;
 pub mod ext;
-pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;
 pub mod io;
@@ -37,7 +36,8 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod time;
 
 use crate::io::ErrorKind;

src/libstd/sys/hermit/fast_thread_local.rs src/libstd/sys/hermit/thread_local_dtor.rs

@@ -2,25 +2,25 @@ pub type Key = usize;
 
 #[inline]
 pub unsafe fn create(_dtor: Option<unsafe extern "C" fn(*mut u8)>) -> Key {
-    panic!("should not be used on the wasm target");
+    panic!("should not be used on the hermit target");
 }
 
 #[inline]
 pub unsafe fn set(_key: Key, _value: *mut u8) {
-    panic!("should not be used on the wasm target");
+    panic!("should not be used on the hermit target");
 }
 
 #[inline]
 pub unsafe fn get(_key: Key) -> *mut u8 {
-    panic!("should not be used on the wasm target");
+    panic!("should not be used on the hermit target");
 }
 
 #[inline]
 pub unsafe fn destroy(_key: Key) {
-    panic!("should not be used on the wasm target");
+    panic!("should not be used on the hermit target");
 }
 
 #[inline]
 pub fn requires_synchronized_create() -> bool {
-    panic!("should not be used on the wasm target");
+    panic!("should not be used on the hermit target");
 }

src/libstd/sys/wasm/thread_local.rs src/libstd/sys/hermit/thread_local_key.rs

@@ -30,7 +30,7 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_key;
 pub mod time;
 
 pub use crate::sys_common::os_str_bytes as os_str;

src/libstd/sys/sgx/mod.rs

@@ -47,7 +47,6 @@ pub mod cmath;
 pub mod condvar;
 pub mod env;
 pub mod ext;
-pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;
 pub mod io;
@@ -68,7 +67,8 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod time;
 
 pub use crate::sys_common::os_str_bytes as os_str;

src/libstd/sys/sgx/thread_local.rs src/libstd/sys/sgx/thread_local_key.rs

@@ -1,6 +1,9 @@
 #![cfg(target_thread_local)]
 #![unstable(feature = "thread_local_internals", issue = "none")]
 
+//! Provides thread-local destructors without an associated "key", which
+//! can be more efficient.
+
 // Since what appears to be glibc 2.18 this symbol has been shipped which
 // GCC and clang both use to invoke destructors in thread_local globals, so
 // let's do the same!
@@ -16,7 +19,7 @@
 ))]
 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::mem;
-    use crate::sys_common::thread_local::register_dtor_fallback;
+    use crate::sys_common::thread_local_dtor::register_dtor_fallback;
 
     extern "C" {
         #[linkage = "extern_weak"]

src/libstd/sys/unix/mod.rs

@@ -13,7 +13,6 @@ pub mod cmath;
 pub mod condvar;
 pub mod env;
 pub mod ext;
-pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;
 pub mod io;
@@ -29,7 +28,8 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod time;
 
 pub use crate::sys_common::os_str_bytes as os_str;

src/libstd/sys/unix/fast_thread_local.rs src/libstd/sys/unix/thread_local_dtor.rs

@@ -5,7 +5,3 @@ pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
     use crate::sys_common::thread_local::register_dtor_fallback;
     register_dtor_fallback(t, dtor);
 }
-
-pub fn requires_move_before_drop() -> bool {
-    false
-}

src/libstd/sys/unix/thread_local.rs src/libstd/sys/unix/thread_local_key.rs

@@ -36,8 +36,6 @@ pub mod net;
 pub mod os;
 pub use crate::sys_common::os_str_bytes as os_str;
 pub mod ext;
-#[path = "../wasm/fast_thread_local.rs"]
-pub mod fast_thread_local;
 pub mod path;
 pub mod pipe;
 pub mod process;
@@ -47,8 +45,10 @@ pub mod rwlock;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-#[path = "../wasm/thread_local.rs"]
-pub mod thread_local;
+#[path = "../wasm/thread_local_dtor.rs"]
+pub mod thread_local_dtor;
+#[path = "../wasm/thread_local_key.rs"]
+pub mod thread_local_key;
 pub mod time;
 
 #[cfg(not(test))]

src/libstd/sys/vxworks/mod.rs

@@ -20,7 +20,6 @@ pub mod alloc;
 pub mod args;
 pub mod cmath;
 pub mod env;
-pub mod fast_thread_local;
 pub mod fs;
 pub mod io;
 pub mod memchr;
@@ -32,7 +31,8 @@ pub mod process;
 pub mod stack_overflow;
 pub mod stdio;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod time;
 
 pub use crate::sys_common::os_str_bytes as os_str;

src/libstd/sys/vxworks/fast_thread_local.rs src/libstd/sys/vxworks/thread_local_dtor.rs

@@ -20,7 +20,6 @@ pub mod cmath;
 pub mod condvar;
 pub mod env;
 pub mod ext;
-pub mod fast_thread_local;
 pub mod fs;
 pub mod handle;
 pub mod io;
@@ -35,7 +34,8 @@ pub mod process;
 pub mod rand;
 pub mod rwlock;
 pub mod thread;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod time;
 cfg_if::cfg_if! {
     if #[cfg(not(target_vendor = "uwp"))] {

src/libstd/sys/vxworks/thread_local.rs src/libstd/sys/vxworks/thread_local_key.rs

@@ -1,4 +1,4 @@
 #![unstable(feature = "thread_local_internals", issue = "none")]
 #![cfg(target_thread_local)]
 
-pub use crate::sys_common::thread_local::register_dtor_fallback as register_dtor;
+pub use crate::sys_common::thread_local_dtor::register_dtor_fallback as register_dtor;

src/libstd/sys/wasi/mod.rs

@@ -65,7 +65,8 @@ pub mod remutex;
 pub mod rwlock;
 pub mod thread;
 pub mod thread_info;
-pub mod thread_local;
+pub mod thread_local_dtor;
+pub mod thread_local_key;
 pub mod util;
 pub mod wtf8;
 

src/libstd/sys/wasm/mod.rs

@@ -0,0 +1,49 @@
+//! Thread-local destructor
+//!
+//! Besides thread-local "keys" (pointer-sized non-adressable thread-local store
+//! with an associated destructor), many platforms also provide thread-local
+//! destructors that are not associated with any particular data. These are
+//! often more efficient.
+//!
+//! This module provides a fallback implementation for that interface, based
+//! on the less efficient thread-local "keys". Each platform provides
+//! a `thread_local_dtor` module which will either re-export the fallback,
+//! or implement something more efficient.
+
+#![unstable(feature = "thread_local_internals", issue = "none")]
+#![allow(dead_code)] // sys isn't exported yet
+
+use crate::ptr;
+use crate::sys_common::thread_local_key::StaticKey;
+
+pub unsafe fn register_dtor_fallback(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
+    // The fallback implementation uses a vanilla OS-based TLS key to track
+    // the list of destructors that need to be run for this thread. The key
+    // then has its own destructor which runs all the other destructors.
+    //
+    // The destructor for DTORS is a little special in that it has a `while`
+    // loop to continuously drain the list of registered destructors. It
+    // *should* be the case that this loop always terminates because we
+    // provide the guarantee that a TLS key cannot be set after it is
+    // flagged for destruction.
+
+    static DTORS: StaticKey = StaticKey::new(Some(run_dtors));
+    type List = Vec<(*mut u8, unsafe extern "C" fn(*mut u8))>;
+    if DTORS.get().is_null() {
+        let v: Box<List> = box Vec::new();
+        DTORS.set(Box::into_raw(v) as *mut u8);
+    }
+    let list: &mut List = &mut *(DTORS.get() as *mut List);
+    list.push((t, dtor));
+
+    unsafe extern "C" fn run_dtors(mut ptr: *mut u8) {
+        while !ptr.is_null() {
+            let list: Box<List> = Box::from_raw(ptr as *mut List);
+            for (ptr, dtor) in list.into_iter() {
+                dtor(ptr);
+            }
+            ptr = DTORS.get();
+            DTORS.set(ptr::null_mut());
+        }
+    }
+}

src/libstd/sys/wasm/fast_thread_local.rs src/libstd/sys/wasm/thread_local_dtor.rs

@@ -4,7 +4,7 @@
 //! using the native OS-provided facilities (think `TlsAlloc` or
 //! `pthread_setspecific`). The interface of this differs from the other types
 //! of thread-local-storage provided in this crate in that OS-based TLS can only
-//! get/set pointers,
+//! get/set pointer-sized data, possibly with an associated destructor.
 //!
 //! This module also provides two flavors of TLS. One is intended for static
 //! initialization, and does not contain a `Drop` implementation to deallocate
@@ -14,7 +14,7 @@
 //! # Usage
 //!
 //! This module should likely not be used directly unless other primitives are
-//! being built on. types such as `thread_local::spawn::Key` are likely much
+//! being built on. Types such as `thread_local::spawn::Key` are likely much
 //! more useful in practice than this OS-based version which likely requires
 //! unsafe code to interoperate with.
 //!
@@ -48,9 +48,8 @@
 #![unstable(feature = "thread_local_internals", issue = "none")]
 #![allow(dead_code)] // sys isn't exported yet
 
-use crate::ptr;
 use crate::sync::atomic::{self, AtomicUsize, Ordering};
-use crate::sys::thread_local as imp;
+use crate::sys::thread_local_key as imp;
 use crate::sys_common::mutex::Mutex;
 
 /// A type for TLS keys that are statically allocated.
@@ -233,38 +232,6 @@ impl Drop for Key {
     }
 }
 
-pub unsafe fn register_dtor_fallback(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
-    // The fallback implementation uses a vanilla OS-based TLS key to track
-    // the list of destructors that need to be run for this thread. The key
-    // then has its own destructor which runs all the other destructors.
-    //
-    // The destructor for DTORS is a little special in that it has a `while`
-    // loop to continuously drain the list of registered destructors. It
-    // *should* be the case that this loop always terminates because we
-    // provide the guarantee that a TLS key cannot be set after it is
-    // flagged for destruction.
-
-    static DTORS: StaticKey = StaticKey::new(Some(run_dtors));
-    type List = Vec<(*mut u8, unsafe extern "C" fn(*mut u8))>;
-    if DTORS.get().is_null() {
-        let v: Box<List> = box Vec::new();
-        DTORS.set(Box::into_raw(v) as *mut u8);
-    }
-    let list: &mut List = &mut *(DTORS.get() as *mut List);
-    list.push((t, dtor));
-
-    unsafe extern "C" fn run_dtors(mut ptr: *mut u8) {
-        while !ptr.is_null() {
-            let list: Box<List> = Box::from_raw(ptr as *mut List);
-            for (ptr, dtor) in list.into_iter() {
-                dtor(ptr);
-            }
-            ptr = DTORS.get();
-            DTORS.set(ptr::null_mut());
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::{Key, StaticKey};

src/libstd/sys/hermit/thread_local.rs src/libstd/sys/wasm/thread_local_key.rs

@@ -363,7 +363,7 @@ pub mod fast {
     use crate::cell::Cell;
     use crate::fmt;
     use crate::mem;
-    use crate::sys::fast_thread_local::register_dtor;
+    use crate::sys::thread_local_dtor::register_dtor;
 
     #[derive(Copy, Clone)]
     enum DtorState {
@@ -468,7 +468,7 @@ pub mod os {
     use crate::fmt;
     use crate::marker;
     use crate::ptr;
-    use crate::sys_common::thread_local::StaticKey as OsStaticKey;
+    use crate::sys_common::thread_local_key::StaticKey as OsStaticKey;
 
     pub struct Key<T> {
         // OS-TLS key that we'll use to key off.