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* Find roots when running GC Attempt to address the issue #2773. The existing implementation had an expensive overhead of managing root counts, especially for mutable borrow of GcRefCell. Instead of managing the root counts, this change counts the number of Gc/WeakGc handles located in Gc heap objects and total number of them. Then, we can find whether there is a root by comparing those numbers. * Fix clippy errors * Keep reference counts in Box * Addressing comment * Fix clippy errors * Fix typo * non_root_count includes mark bit * give a spacepull/3176/head
Choongwoo Han
1 year ago
committed by
GitHub
16 changed files with 238 additions and 440 deletions
@ -1,87 +0,0 @@
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use std::ptr::{self, addr_of_mut, NonNull}; |
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/// A [`NonNull`] pointer with a `rooted` tag.
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///
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/// This pointer can be created only from pointers that are 2-byte aligned. In other words,
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/// the pointer must point to an address that is a multiple of 2.
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pub(crate) struct Rootable<T: ?Sized> { |
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ptr: NonNull<T>, |
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} |
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impl<T: ?Sized> Copy for Rootable<T> {} |
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impl<T: ?Sized> Clone for Rootable<T> { |
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fn clone(&self) -> Self { |
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Self { ptr: self.ptr } |
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} |
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} |
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impl<T: ?Sized> std::fmt::Debug for Rootable<T> { |
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { |
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f.debug_struct("Rootable") |
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.field("ptr", &self.as_ptr()) |
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.field("is_rooted", &self.is_rooted()) |
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.finish() |
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} |
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} |
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impl<T: ?Sized> Rootable<T> { |
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/// Creates a new `Rootable` without checking if the [`NonNull`] is properly aligned.
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///
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/// # Safety
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///
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/// `ptr` must be 2-byte aligned.
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pub(crate) const unsafe fn new_unchecked(ptr: NonNull<T>) -> Self { |
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Self { ptr } |
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} |
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/// Returns `true` if the pointer is rooted.
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pub(crate) fn is_rooted(self) -> bool { |
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self.ptr.as_ptr().cast::<u8>() as usize & 1 != 0 |
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} |
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/// Returns a pointer with the same address as `self` but rooted.
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pub(crate) fn rooted(self) -> Self { |
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let ptr = self.ptr.as_ptr(); |
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let data = ptr.cast::<u8>(); |
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let addr = data as isize; |
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let ptr = set_data_ptr(ptr, data.wrapping_offset((addr | 1) - addr)); |
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// SAFETY: ptr must be a non null value.
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unsafe { Self::new_unchecked(NonNull::new_unchecked(ptr)) } |
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} |
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/// Returns a pointer with the same address as `self` but unrooted.
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pub(crate) fn unrooted(self) -> Self { |
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let ptr = self.ptr.as_ptr(); |
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let data = ptr.cast::<u8>(); |
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let addr = data as isize; |
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let ptr = set_data_ptr(ptr, data.wrapping_offset((addr & !1) - addr)); |
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// SAFETY: ptr must be a non null value
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unsafe { Self::new_unchecked(NonNull::new_unchecked(ptr)) } |
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} |
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/// Acquires the underlying `NonNull` pointer.
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pub(crate) fn as_ptr(self) -> NonNull<T> { |
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self.unrooted().ptr |
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} |
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/// Returns a shared reference to the pointee.
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///
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/// # Safety
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///
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/// See [`NonNull::as_ref`].
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pub(crate) unsafe fn as_ref(&self) -> &T { |
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// SAFETY: it is the caller's job to ensure the safety of this operation.
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unsafe { self.as_ptr().as_ref() } |
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} |
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} |
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// Technically, this function is safe, since we're just modifying the address of a pointer without
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// dereferencing it.
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fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T { |
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// SAFETY: this should be safe as ptr must be a valid nonnull
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unsafe { |
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ptr::write(addr_of_mut!(ptr).cast::<*mut u8>(), data.cast::<u8>()); |
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} |
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ptr |
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} |
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