Fix simulation reaching different states when started from different snaphots.

3 files changed, 155 insertions, 0 deletions

diff --git a/src/data/hashmap.rs b/src/data/hashmap.rs
new file mode 100644
index 0000000..78f9797
--- /dev/null
+++ b/src/data/hashmap.rs
@@ -0,0 +1,137 @@
+//! A hash-map that behaves deterministically when the
+//! `enhanced-determinism` feature is enabled.
+
+#[cfg(all(feature = "enhanced-determinism", feature = "serde-serialize"))]
+use indexmap::IndexMap as StdHashMap;
+#[cfg(all(not(feature = "enhanced-determinism"), feature = "serde-serialize"))]
+use std::collections::HashMap as StdHashMap;
+
+/// Serializes only the capacity of a hash-map instead of its actual content.
+#[cfg(feature = "serde-serialize")]
+pub fn serialize_hashmap_capacity<S: serde::Serializer, K, V, H: std::hash::BuildHasher>(
+    map: &StdHashMap<K, V, H>,
+    s: S,
+) -> Result<S::Ok, S::Error> {
+    s.serialize_u64(map.capacity() as u64)
+}
+
+/// Creates a new hash-map with its capacity deserialized from `d`.
+#[cfg(feature = "serde-serialize")]
+pub fn deserialize_hashmap_capacity<
+    'de,
+    D: serde::Deserializer<'de>,
+    K,
+    V,
+    H: std::hash::BuildHasher + Default,
+>(
+    d: D,
+) -> Result<StdHashMap<K, V, H>, D::Error> {
+    struct CapacityVisitor;
+    impl<'de> serde::de::Visitor<'de> for CapacityVisitor {
+        type Value = u64;
+
+        fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+            write!(formatter, "an integer between 0 and 2^64")
+        }
+
+        fn visit_u64<E: serde::de::Error>(self, val: u64) -> Result<Self::Value, E> {
+            Ok(val)
+        }
+    }
+
+    let capacity = d.deserialize_u64(CapacityVisitor)? as usize;
+    Ok(StdHashMap::with_capacity_and_hasher(
+        capacity,
+        Default::default(),
+    ))
+}
+
+/*
+ * FxHasher taken from rustc_hash, except that it does not depend on the pointer size.
+ */
+#[cfg(feature = "enhanced-determinism")]
+pub type FxHashMap32<K, V> = indexmap::IndexMap<K, V, std::hash::BuildHasherDefault<FxHasher32>>;
+#[cfg(not(feature = "enhanced-determinism"))]
+pub use rustc_hash::{Entry, FxHashMap as HashMap};
+#[cfg(feature = "enhanced-determinism")]
+pub use {self::FxHashMap32 as HashMap, indexmap::map::Entry};
+
+const K: u32 = 0x9e3779b9;
+
+// Same as FxHasher, but with the guarantee that the internal hash is
+// an u32 instead of something that depends on the platform.
+pub struct FxHasher32 {
+    hash: u32,
+}
+
+impl Default for FxHasher32 {
+    #[inline]
+    fn default() -> FxHasher32 {
+        FxHasher32 { hash: 0 }
+    }
+}
+
+impl FxHasher32 {
+    #[inline]
+    fn add_to_hash(&mut self, i: u32) {
+        use std::ops::BitXor;
+        self.hash = self.hash.rotate_left(5).bitxor(i).wrapping_mul(K);
+    }
+}
+
+impl std::hash::Hasher for FxHasher32 {
+    #[inline]
+    fn write(&mut self, mut bytes: &[u8]) {
+        use std::convert::TryInto;
+        let read_u32 = |bytes: &[u8]| u32::from_ne_bytes(bytes[..4].try_into().unwrap());
+        let mut hash = FxHasher32 { hash: self.hash };
+        assert!(std::mem::size_of::<u32>() <= 8);
+        while bytes.len() >= std::mem::size_of::<u32>() {
+            hash.add_to_hash(read_u32(bytes) as u32);
+            bytes = &bytes[std::mem::size_of::<u32>()..];
+        }
+        if (std::mem::size_of::<u32>() > 4) && (bytes.len() >= 4) {
+            hash.add_to_hash(u32::from_ne_bytes(bytes[..4].try_into().unwrap()) as u32);
+            bytes = &bytes[4..];
+        }
+        if (std::mem::size_of::<u32>() > 2) && bytes.len() >= 2 {
+            hash.add_to_hash(u16::from_ne_bytes(bytes[..2].try_into().unwrap()) as u32);
+            bytes = &bytes[2..];
+        }
+        if (std::mem::size_of::<u32>() > 1) && bytes.len() >= 1 {
+            hash.add_to_hash(bytes[0] as u32);
+        }
+        self.hash = hash.hash;
+    }
+
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.add_to_hash(i as u32);
+    }
+
+    #[inline]
+    fn write_u16(&mut self, i: u16) {
+        self.add_to_hash(i as u32);
+    }
+
+    #[inline]
+    fn write_u32(&mut self, i: u32) {
+        self.add_to_hash(i as u32);
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.add_to_hash(i as u32);
+        self.add_to_hash((i >> 32) as u32);
+    }
+
+    #[inline]
+    fn write_usize(&mut self, i: usize) {
+        self.add_to_hash(i as u32);
+    }
+
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.hash as u64
+    }
+}
diff --git a/src/data/maybe_serializable_data.rs b/src/data/maybe_serializable_data.rs
new file mode 100644
index 0000000..db38963
--- /dev/null
+++ b/src/data/maybe_serializable_data.rs
@@ -0,0 +1,14 @@
+use downcast_rs::{impl_downcast, DowncastSync};
+#[cfg(feature = "serde-serialize")]
+use erased_serde::Serialize;
+
+/// Piece of data that may be serializable.
+pub trait MaybeSerializableData: DowncastSync {
+    /// Convert this shape as a serializable entity.
+    #[cfg(feature = "serde-serialize")]
+    fn as_serialize(&self) -> Option<(u32, &dyn Serialize)> {
+        None
+    }
+}
+
+impl_downcast!(sync MaybeSerializableData);
diff --git a/src/data/mod.rs b/src/data/mod.rs
index 5d3efa6..0e0459e 100644
--- a/src/data/mod.rs
+++ b/src/data/mod.rs
@@ -1,5 +1,9 @@
 //! Data structures modified with guaranteed deterministic behavior after deserialization.
 
+pub use self::maybe_serializable_data::MaybeSerializableData;
+
 pub mod arena;
 pub(crate) mod graph;
+pub(crate) mod hashmap;
+mod maybe_serializable_data;
 pub mod pubsub;