Merge #36

36: Delete boehm specific code r=ltratt a=jacob-hughes

This is now being served from the softdev/boehm_allocator crate, which
contains code needed for both rboehm and rustc_boehm.

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

.buildbot.sh

@@ -12,7 +12,7 @@ sh rustup.sh --default-host x86_64-unknown-linux-gnu \
     --profile minimal \
     -y
 export PATH=`pwd`/.cargo/bin/:$PATH
-cargo check --features use_boehm
+cargo check
 
 rustup toolchain install nightly --allow-downgrade --component rustfmt
 cargo +nightly fmt --all -- --check

Cargo.toml

@@ -1,27 +1,21 @@
 [package]
-name = "rboehm"
+name = "libgc"
 version = "0.1.0"
 authors = ["Jacob Hughes <jh@jakehughes.uk>"]
 edition = "2018"
 
-[workspace]
-members = ["boehm"]
-
 [features]
 # Enable this feature to turn on additional GC optimizations that are only
-# possible with the rustc_boehm fork of the compiler.
-rustc_boehm = []
+# possible with the rustgc fork of the compiler.
+rustgc = []
 
 # Enable various GC based statistics. Stats are disabled by default as they have
 # a run-time cost and are expected to only be used for profiling purposes.
 gc_stats = []
 
-# Use boehm as a backend
-use_boehm = ["boehm"]
-
 [dependencies]
 libc = "*"
-boehm = { path = "boehm", optional = true }
+libgc_internal = { git = "https://github.com/softdevteam/libgc_internal" }
 
 [build-dependencies]
 rerun_except = "0.1"

README.md

@@ -1,2 +1,32 @@
-# rboehm
-A Rust API for the Boehm-Demers-Weiser garbage collector
+# libgc
+
+libgc is a garbage collector for Rust. It works by providing a garbage-collected
+`Gc<T>` smart pointer in the style of `Rc<T>`.
+
+# Structure
+
+There are three repositories which make up the gc infrastructure:
+    - **libgc** the main library which provides the `Gc<T>` smart pointer and its
+      API.
+    - **libgc_internal** contains the gc allocation and collector logic. This is
+      collector specific, and can be conditionally compiled to support different
+      implementations. At the moment, it only supports a single collector
+      implementation: the Boehm-Demers-Weiser GC. Users should never interact
+      directly with this crate. Instead, any relevant APIs are re-exported
+      through libgc.
+    - **rustgc** a fork of rustc with GC-aware optimisations. This can be used to
+      compile user programs which use `libgc`, giving them better GC
+      performance. Use of rustgc is not mandated, but it enables further
+      optimisations for programs which use `libgc`.
+
+This seperation between libgc and rustgc exists so that a stripped-down form of
+garbage collection can be used without compiler support. The further split
+between libgc and libgc_core exists to make linkage easier when the rustgc
+compiler is used.
+
+rustgc needs access to the GC's `Allocator` implementation. This exists in the
+libgc_internal crate so that it can be linked to the target binary either as
+part of libgc, or as part of the rust standard library (if compiled with
+rustgc). libgc contains code which would not compile if it was packaged as part
+of rustgc. To prevent duplication, the libgc_interal crate will link correctly
+as either a standard cargo crate, or as part of the rust core library.

src/gc.rs

@@ -205,13 +205,27 @@ impl<T> GcBox<T> {
         #[cfg(feature = "gc_stats")]
         crate::stats::NUM_REGISTERED_FINALIZERS.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
 
-        #[cfg(feature = "boehm")]
-        boehm::register_finalizer(self as *mut _ as *mut T);
+        if !needs_finalizer::<T>() {
+            return;
+        }
+
+        unsafe extern "C" fn fshim<T>(obj: *mut u8, _meta: *mut u8) {
+            ManuallyDrop::drop(&mut *(obj as *mut ManuallyDrop<T>));
+        }
+
+        unsafe {
+            GC_ALLOCATOR.register_finalizer(
+                self as *mut _ as *mut u8,
+                Some(fshim::<T>),
+                ::std::ptr::null_mut(),
+                ::std::ptr::null_mut(),
+                ::std::ptr::null_mut(),
+            )
+        }
     }
 
     fn unregister_finalizer(&mut self) {
-        #[cfg(feature = "boehm")]
-        boehm::unregister_finalizer(self as *mut _ as *mut u8);
+        unsafe { GC_ALLOCATOR.unregister_finalizer(self as *mut _ as *mut u8) };
     }
 }
 

src/lib.rs

@@ -19,10 +19,8 @@ pub mod stats;
 
 pub use gc::Gc;
 
-#[cfg(feature = "use_boehm")]
-pub use boehm::force_gc;
+use libgc_internal::GcAllocator;
+pub use libgc_internal::GlobalAllocator;
 
-pub use boehm::allocator::BoehmAllocator;
-use boehm::allocator::BoehmGcAllocator;
-
-static mut GC_ALLOCATOR: BoehmGcAllocator = BoehmGcAllocator;
+static GC_ALLOCATOR: GcAllocator = GcAllocator;
+pub static GLOBAL_ALLOCATOR: GlobalAllocator = GlobalAllocator;

src/stats.rs

@@ -1,30 +1,3 @@
 use std::sync::atomic::{AtomicUsize, Ordering};
 
 pub static NUM_REGISTERED_FINALIZERS: AtomicUsize = AtomicUsize::new(0);
-
-#[derive(Debug)]
-pub struct GcStats {
-    total_gc_time: usize, // In milliseconds.
-    num_collections: usize,
-    finalizers_registered: usize,
-    total_freed: usize,   // In bytes
-    total_alloced: usize, // In bytes
-}
-
-#[cfg(feature = "gc_stats")]
-impl From<boehm::BoehmStats> for GcStats {
-    fn from(item: boehm::BoehmStats) -> Self {
-        GcStats {
-            total_gc_time: item.total_gc_time,
-            num_collections: item.num_collections,
-            finalizers_registered: NUM_REGISTERED_FINALIZERS.load(Ordering::Relaxed),
-            total_freed: item.total_freed,
-            total_alloced: item.total_alloced,
-        }
-    }
-}
-
-#[cfg(feature = "gc_stats")]
-pub fn get_stats() -> GcStats {
-    GcStats::from(boehm::BoehmStats::gen())
-}