Merge #31

31: Register new threads with the collector r=ltratt a=jacob-hughes



Co-authored-by: Jake Hughes <jh@jakehughes.uk>

.buildbot.sh

@@ -7,4 +7,4 @@ set -e
 # Ensure the build fails if it uses excessive amounts of memory.
 ulimit -d $((1024 * 1024 * 8)) # 8 GiB
 
-./x.py test --stage 1 --exclude rustdoc-json
+./x.py test --stage 1 --exclude rustdoc-json --exclude debuginfo

library/std/src/rt.rs

@@ -25,6 +25,7 @@ fn lang_start_internal(
     argc: isize,
     argv: *const *const u8,
 ) -> isize {
+    use crate::alloc::GcAllocator;
     use crate::panic;
     use crate::sys;
     use crate::sys_common;
@@ -34,6 +35,14 @@ fn lang_start_internal(
     sys::init();
 
     unsafe {
+        // Internally, this registers a SIGSEGV handler to compute the start and
+        // end bounds of the data segment. This means it *MUST* be called before
+        // rustc registers its own SIGSEGV stack overflow handler.
+        //
+        // Rust's stack overflow handler will unregister and return if there is
+        // no stack overflow, allowing the fault to "fall-through" to Boehm's
+        // handler next time. The is not true in the reverse case.
+        GcAllocator::init();
         let main_guard = sys::thread::guard::init();
         sys::stack_overflow::init();
 

library/std/src/sys/unix/thread.rs

@@ -277,7 +277,7 @@ pub mod guard {
         target_os = "netbsd",
         target_os = "l4re"
     ))]
-    unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
+    pub(crate) unsafe fn get_stack_start() -> Option<*mut libc::c_void> {
         let mut ret = None;
         let mut attr: libc::pthread_attr_t = crate::mem::zeroed();
         #[cfg(target_os = "freebsd")]

library/std/src/thread/mod.rs

@@ -148,6 +148,7 @@
 #[cfg(all(test, not(target_os = "emscripten")))]
 mod tests;
 
+use crate::alloc::GcAllocator;
 use crate::any::Any;
 use crate::cell::UnsafeCell;
 use crate::ffi::{CStr, CString};
@@ -464,6 +465,15 @@ impl Builder {
                 imp::Thread::set_name(name);
             }
 
+            // SAFETY: Register the thread with libgc so that its stack can be scanned
+            // for garbage collection.
+            let stack_start = unsafe { imp::guard::get_stack_start().unwrap() };
+            if stack_start != crate::ptr::null_mut() {
+                unsafe {
+                    GcAllocator::register_thread(&stack_start as *const _ as *mut u8);
+                }
+            }
+
             crate::io::set_output_capture(output_capture);
 
             // SAFETY: the stack guard passed is the one for the current thread.
@@ -473,6 +483,12 @@ impl Builder {
             let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
                 crate::sys_common::backtrace::__rust_begin_short_backtrace(f)
             }));
+
+            // SAFETY: The thread has no more work to do, so can be unregisterd.
+            unsafe {
+                GcAllocator::unregister_thread();
+            }
+
             // SAFETY: `their_packet` as been built just above and moved by the
             // closure (it is an Arc<...>) and `my_packet` will be stored in the
             // same `JoinInner` as this closure meaning the mutation will be

src/test/ui/threads-sendsync/thread_registration.rs

@@ -0,0 +1,15 @@
+// run-pass
+// ignore-emscripten no threads support
+#![feature(rustc_private)]
+
+use std::alloc::GcAllocator;
+use std::thread;
+
+pub fn main() {
+    let res = thread::spawn(child).join().unwrap();
+    assert!(res);
+}
+
+fn child() -> bool {
+    GcAllocator::thread_registered()
+}