1 files changed, 112 insertions, 0 deletions
diff --git a/vendor/string_cache/src/dynamic_set.rs b/vendor/string_cache/src/dynamic_set.rs
new file mode 100644
index 00000000..4442b4da
--- /dev/null
+++ b/vendor/string_cache/src/dynamic_set.rs
@@ -0,0 +1,112 @@
+// Copyright 2014 The Servo Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use parking_lot::Mutex;
+use std::borrow::Cow;
+use std::mem;
+use std::ptr::NonNull;
+use std::sync::atomic::AtomicIsize;
+use std::sync::atomic::Ordering::SeqCst;
+use std::sync::OnceLock;
+
+const NB_BUCKETS: usize = 1 << 12; // 4096
+const BUCKET_MASK: u32 = (1 << 12) - 1;
+
+pub(crate) struct Set {
+    buckets: Box<[Mutex<Option<Box<Entry>>>]>,
+}
+
+pub(crate) struct Entry {
+    pub(crate) string: Box<str>,
+    pub(crate) hash: u32,
+    pub(crate) ref_count: AtomicIsize,
+    next_in_bucket: Option<Box<Entry>>,
+}
+
+// Addresses are a multiples of this,
+// and therefore have have TAG_MASK bits unset, available for tagging.
+pub(crate) const ENTRY_ALIGNMENT: usize = 4;
+
+#[test]
+fn entry_alignment_is_sufficient() {
+    assert!(mem::align_of::<Entry>() >= ENTRY_ALIGNMENT);
+}
+
+pub(crate) fn dynamic_set() -> &'static Set {
+    // NOTE: Using const initialization for buckets breaks the small-stack test.
+    // ```
+    // // buckets: [Mutex<Option<Box<Entry>>>; NB_BUCKETS],
+    // const MUTEX: Mutex<Option<Box<Entry>>> = Mutex::new(None);
+    // let buckets = Box::new([MUTEX; NB_BUCKETS]);
+    // ```
+    static DYNAMIC_SET: OnceLock<Set> = OnceLock::new();
+
+    DYNAMIC_SET.get_or_init(|| {
+        let buckets = (0..NB_BUCKETS).map(|_| Mutex::new(None)).collect();
+        Set { buckets }
+    })
+}
+
+impl Set {
+    pub(crate) fn insert(&self, string: Cow<str>, hash: u32) -> NonNull<Entry> {
+        let bucket_index = (hash & BUCKET_MASK) as usize;
+        let mut linked_list = self.buckets[bucket_index].lock();
+
+        {
+            let mut ptr: Option<&mut Box<Entry>> = linked_list.as_mut();
+
+            while let Some(entry) = ptr.take() {
+                if entry.hash == hash && *entry.string == *string {
+                    if entry.ref_count.fetch_add(1, SeqCst) > 0 {
+                        return NonNull::from(&mut **entry);
+                    }
+                    // Uh-oh. The pointer's reference count was zero, which means someone may try
+                    // to free it. (Naive attempts to defend against this, for example having the
+                    // destructor check to see whether the reference count is indeed zero, don't
+                    // work due to ABA.) Thus we need to temporarily add a duplicate string to the
+                    // list.
+                    entry.ref_count.fetch_sub(1, SeqCst);
+                    break;
+                }
+                ptr = entry.next_in_bucket.as_mut();
+            }
+        }
+        debug_assert!(mem::align_of::<Entry>() >= ENTRY_ALIGNMENT);
+        let string = string.into_owned();
+        let mut entry = Box::new(Entry {
+            next_in_bucket: linked_list.take(),
+            hash,
+            ref_count: AtomicIsize::new(1),
+            string: string.into_boxed_str(),
+        });
+        let ptr = NonNull::from(&mut *entry);
+        *linked_list = Some(entry);
+        ptr
+    }
+
+    pub(crate) fn remove(&self, ptr: *mut Entry) {
+        let value: &Entry = unsafe { &*ptr };
+        let bucket_index = (value.hash & BUCKET_MASK) as usize;
+
+        let mut linked_list = self.buckets[bucket_index].lock();
+        debug_assert!(value.ref_count.load(SeqCst) == 0);
+        let mut current: &mut Option<Box<Entry>> = &mut linked_list;
+
+        while let Some(entry_ptr) = current.as_mut() {
+            let entry_ptr: *mut Entry = &mut **entry_ptr;
+            if entry_ptr == ptr {
+                mem::drop(mem::replace(current, unsafe {
+                    (*entry_ptr).next_in_bucket.take()
+                }));
+                break;
+            }
+            current = unsafe { &mut (*entry_ptr).next_in_bucket };
+        }
+    }
+}