auto merge of #10312 : thestinger/rust/thread_local, r=alexcritchton

This provides a building block for fast thread-local storage. It does
not change the safety semantics of `static mut`.

Closes #10310

Author: bors

doc/rust.md

@@ -1754,6 +1754,8 @@ names are effectively reserved. Some significant attributes include:
 * The `deriving` attribute, for automatically generating
   implementations of certain traits.
 * The `static_assert` attribute, for asserting that a static bool is true at compiletime
+* The `thread_local` attribute, for defining a `static mut` as a thread-local. Note that this is
+  only a low-level building block, and is not local to a *task*, nor does it provide safety.
 
 Other attributes may be added or removed during development of the language.
 

src/librustc/front/feature_gate.rs

@@ -38,6 +38,7 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
     ("asm", Active),
     ("managed_boxes", Active),
     ("non_ascii_idents", Active),
+    ("thread_local", Active),
 
     // These are used to test this portion of the compiler, they don't actually
     // mean anything
@@ -107,6 +108,17 @@ impl Visitor<()> for Context {
     }
 
     fn visit_item(&mut self, i: @ast::item, _:()) {
+        // NOTE: uncomment after snapshot
+        /*
+        for attr in i.attrs.iter() {
+            if "thread_local" == attr.name() {
+                self.gate_feature("thread_local", i.span,
+                                  "`#[thread_local]` is an experimental feature, and does not \
+                                  currently handle destructors. There is no corresponding \
+                                  `#[task_local]` mapping to the task model");
+            }
+        }
+        */
         match i.node {
             ast::item_enum(ref def, _) => {
                 for variant in def.variants.iter() {
@@ -152,8 +164,8 @@ impl Visitor<()> for Context {
             },
             ast::ty_box(_) => {
                 self.gate_feature("managed_boxes", t.span,
-                                  "The managed box syntax is being replaced by the `std::gc::Gc`
-                                  and `std::rc::Rc` types. Equivalent functionality to managed
+                                  "The managed box syntax is being replaced by the `std::gc::Gc` \
+                                  and `std::rc::Rc` types. Equivalent functionality to managed \
                                   trait objects will be implemented but is currently missing.");
             }
             _ => {}

src/librustc/lib/llvm.rs

@@ -1749,6 +1749,12 @@ pub fn SetUnnamedAddr(Global: ValueRef, Unnamed: bool) {
     }
 }
 
+pub fn set_thread_local(global: ValueRef, is_thread_local: bool) {
+    unsafe {
+        llvm::LLVMSetThreadLocal(global, is_thread_local as Bool);
+    }
+}
+
 pub fn ConstICmp(Pred: IntPredicate, V1: ValueRef, V2: ValueRef) -> ValueRef {
     unsafe {
         llvm::LLVMConstICmp(Pred as c_ushort, V1, V2)

src/librustc/middle/lint.rs

@@ -816,6 +816,7 @@ static obsolete_attrs: &'static [(&'static str, &'static str)] = &[
 static other_attrs: &'static [&'static str] = &[
     // item-level
     "address_insignificant", // can be crate-level too
+    "thread_local", // for statics
     "allow", "deny", "forbid", "warn", // lint options
     "deprecated", "experimental", "unstable", "stable", "locked", "frozen", //item stability
     "crate_map", "cfg", "doc", "export_name", "link_section", "no_freeze",

src/librustc/middle/trans/base.rs

@@ -2544,6 +2544,10 @@ pub fn get_item_val(ccx: @mut CrateContext, id: ast::NodeId) -> ValueRef {
                                     inlineable = true;
                                 }
 
+                                if attr::contains_name(i.attrs, "thread_local") {
+                                    lib::llvm::set_thread_local(g, true);
+                                }
+
                                 if !inlineable {
                                     debug!("{} not inlined", sym);
                                     ccx.non_inlineable_statics.insert(id);

src/libstd/rt/local_ptr.rs

@@ -17,16 +17,35 @@
 
 use libc::c_void;
 use cast;
+#[cfg(stage0)]
+#[cfg(windows)]
 use ptr;
 use cell::Cell;
 use option::{Option, Some, None};
 use unstable::finally::Finally;
+#[cfg(stage0)]
+#[cfg(windows)]
 use unstable::mutex::{Mutex, MUTEX_INIT};
+#[cfg(stage0)]
+#[cfg(windows)]
 use tls = rt::thread_local_storage;
 
+#[cfg(not(stage0), not(windows), test)]
+#[thread_local]
+pub use realstd::rt::shouldnt_be_public::RT_TLS_PTR;
+
+#[cfg(not(stage0), not(windows), not(test))]
+#[thread_local]
+pub static mut RT_TLS_PTR: *mut c_void = 0 as *mut c_void;
+
+#[cfg(stage0)]
+#[cfg(windows)]
 static mut RT_TLS_KEY: tls::Key = -1;
 
 /// Initialize the TLS key. Other ops will fail if this isn't executed first.
+#[inline(never)]
+#[cfg(stage0)]
+#[cfg(windows)]
 pub fn init_tls_key() {
     static mut lock: Mutex = MUTEX_INIT;
     static mut initialized: bool = false;
@@ -41,24 +60,42 @@ pub fn init_tls_key() {
     }
 }
 
+#[cfg(not(stage0), not(windows))]
+pub fn init_tls_key() {}
+
 /// Give a pointer to thread-local storage.
 ///
 /// # Safety note
 ///
 /// Does not validate the pointer type.
 #[inline]
+#[cfg(stage0)]
+#[cfg(windows)]
 pub unsafe fn put<T>(sched: ~T) {
     let key = tls_key();
     let void_ptr: *mut c_void = cast::transmute(sched);
     tls::set(key, void_ptr);
 }
 
+/// Give a pointer to thread-local storage.
+///
+/// # Safety note
+///
+/// Does not validate the pointer type.
+#[inline]
+#[cfg(not(stage0), not(windows))]
+pub unsafe fn put<T>(sched: ~T) {
+    RT_TLS_PTR = cast::transmute(sched)
+}
+
 /// Take ownership of a pointer from thread-local storage.
 ///
 /// # Safety note
 ///
 /// Does not validate the pointer type.
 #[inline]
+#[cfg(stage0)]
+#[cfg(windows)]
 pub unsafe fn take<T>() -> ~T {
     let key = tls_key();
     let void_ptr: *mut c_void = tls::get(key);
@@ -70,13 +107,28 @@ pub unsafe fn take<T>() -> ~T {
     return ptr;
 }
 
+/// Take ownership of a pointer from thread-local storage.
+///
+/// # Safety note
+///
+/// Does not validate the pointer type.
+#[inline]
+#[cfg(not(stage0), not(windows))]
+pub unsafe fn take<T>() -> ~T {
+    let ptr: ~T = cast::transmute(RT_TLS_PTR);
+    RT_TLS_PTR = cast::transmute(0); // can't use `as`, due to type not matching with `cfg(test)`
+    ptr
+}
+
 /// Take ownership of a pointer from thread-local storage.
 ///
 /// # Safety note
 ///
 /// Does not validate the pointer type.
 /// Leaves the old pointer in TLS for speed.
 #[inline]
+#[cfg(stage0)]
+#[cfg(windows)]
 pub unsafe fn unsafe_take<T>() -> ~T {
     let key = tls_key();
     let void_ptr: *mut c_void = tls::get(key);
@@ -87,7 +139,21 @@ pub unsafe fn unsafe_take<T>() -> ~T {
     return ptr;
 }
 
+/// Take ownership of a pointer from thread-local storage.
+///
+/// # Safety note
+///
+/// Does not validate the pointer type.
+/// Leaves the old pointer in TLS for speed.
+#[inline]
+#[cfg(not(stage0), not(windows))]
+pub unsafe fn unsafe_take<T>() -> ~T {
+    cast::transmute(RT_TLS_PTR)
+}
+
 /// Check whether there is a thread-local pointer installed.
+#[cfg(stage0)]
+#[cfg(windows)]
 pub fn exists() -> bool {
     unsafe {
         match maybe_tls_key() {
@@ -97,6 +163,14 @@ pub fn exists() -> bool {
     }
 }
 
+/// Check whether there is a thread-local pointer installed.
+#[cfg(not(stage0), not(windows))]
+pub fn exists() -> bool {
+    unsafe {
+        RT_TLS_PTR.is_not_null()
+    }
+}
+
 /// Borrow the thread-local value from thread-local storage.
 /// While the value is borrowed it is not available in TLS.
 ///
@@ -119,6 +193,8 @@ pub unsafe fn borrow<T>(f: |&mut T|) {
 ///
 /// Because this leaves the value in thread-local storage it is possible
 /// For the Scheduler pointer to be aliased
+#[cfg(stage0)]
+#[cfg(windows)]
 pub unsafe fn unsafe_borrow<T>() -> *mut T {
     let key = tls_key();
     let void_ptr = tls::get(key);
@@ -128,6 +204,16 @@ pub unsafe fn unsafe_borrow<T>() -> *mut T {
     void_ptr as *mut T
 }
 
+#[cfg(not(stage0), not(windows))]
+pub unsafe fn unsafe_borrow<T>() -> *mut T {
+    if RT_TLS_PTR.is_null() {
+        rtabort!("thread-local pointer is null. bogus!");
+    }
+    RT_TLS_PTR as *mut T
+}
+
+#[cfg(stage0)]
+#[cfg(windows)]
 pub unsafe fn try_unsafe_borrow<T>() -> Option<*mut T> {
     match maybe_tls_key() {
         Some(key) => {
@@ -142,7 +228,18 @@ pub unsafe fn try_unsafe_borrow<T>() -> Option<*mut T> {
     }
 }
 
+#[cfg(not(stage0), not(windows))]
+pub unsafe fn try_unsafe_borrow<T>() -> Option<*mut T> {
+    if RT_TLS_PTR.is_null() {
+        None
+    } else {
+        Some(RT_TLS_PTR as *mut T)
+    }
+}
+
 #[inline]
+#[cfg(stage0)]
+#[cfg(windows)]
 fn tls_key() -> tls::Key {
     match maybe_tls_key() {
         Some(key) => key,
@@ -151,7 +248,8 @@ fn tls_key() -> tls::Key {
 }
 
 #[inline]
-#[cfg(not(test))]
+#[cfg(not(test), stage0)]
+#[cfg(not(test), windows)]
 pub fn maybe_tls_key() -> Option<tls::Key> {
     unsafe {
         // NB: This is a little racy because, while the key is
@@ -172,11 +270,9 @@ pub fn maybe_tls_key() -> Option<tls::Key> {
     }
 }
 
-// XXX: The boundary between the running runtime and the testing runtime
-// seems to be fuzzy at the moment, and trying to use two different keys
-// results in disaster. This should not be necessary.
 #[inline]
-#[cfg(test)]
+#[cfg(test, stage0)]
+#[cfg(test, windows)]
 pub fn maybe_tls_key() -> Option<tls::Key> {
     unsafe { ::cast::transmute(::realstd::rt::shouldnt_be_public::maybe_tls_key()) }
 }

src/libstd/rt/mod.rs

@@ -95,7 +95,11 @@ pub use self::kill::BlockedTask;
 pub mod shouldnt_be_public {
     pub use super::select::SelectInner;
     pub use super::select::{SelectInner, SelectPortInner};
+    #[cfg(stage0)]
+    #[cfg(windows)]
     pub use super::local_ptr::maybe_tls_key;
+    #[cfg(not(stage0), not(windows))]
+    pub use super::local_ptr::RT_TLS_PTR;
 }
 
 // Internal macros used by the runtime.