Add fallible HashMap APIs

src/hash_map.rs

@@ -25,6 +25,8 @@ use super::table::BucketState::{Empty, Full};
 
 const MIN_NONZERO_RAW_CAPACITY: usize = 32;     // must be a power of two
 
+static OOM_STR: &str = "out of memory whilst allocating hashmap"; 
+
 /// The default behavior of HashMap implements a maximum load factor of 90.9%.
 #[derive(Clone)]
 struct DefaultResizePolicy;
@@ -610,6 +612,11 @@ impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
     pub fn with_capacity(capacity: usize) -> HashMap<K, V, RandomState> {
         HashMap::with_capacity_and_hasher(capacity, Default::default())
     }
+
+    #[inline]
+    pub fn with_capacity_fallible(capacity: usize) -> Result<HashMap<K, V, RandomState>, ()> {
+        HashMap::with_capacity_and_hasher_fallible(capacity, Default::default())
+    }
 }
 
 impl<K, V, S> HashMap<K, V, S>
@@ -637,12 +644,17 @@ impl<K, V, S> HashMap<K, V, S>
     /// map.insert(1, 2);
     /// ```
     #[inline]
-        pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
-        HashMap {
+    pub fn with_hasher_fallible(hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
+        Ok(HashMap {
             hash_builder,
             resize_policy: DefaultResizePolicy::new(),
-            table: RawTable::new(0),
+            table: RawTable::new(0)?,
+        })
     }
+
+    #[inline]
+    pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
+        Self::with_hasher_fallible(hash_builder).expect(OOM_STR)
     }
 
     /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
@@ -667,14 +679,18 @@ impl<K, V, S> HashMap<K, V, S>
     /// map.insert(1, 2);
     /// ```
     #[inline]
-        pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
+    pub fn with_capacity_and_hasher_fallible(capacity: usize, hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
         let resize_policy = DefaultResizePolicy::new();
         let raw_cap = resize_policy.raw_capacity(capacity);
-        HashMap {
+        Ok(HashMap {
             hash_builder,
             resize_policy,
-            table: RawTable::new(raw_cap),
+            table: RawTable::new(raw_cap)?,
+        })
     }
+
+    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> HashMap<K, V, S> {
+        Self::with_capacity_and_hasher_fallible(capacity, hash_builder).expect(OOM_STR)
     }
 
     /// Returns a reference to the map's [`BuildHasher`].
@@ -725,35 +741,37 @@ impl<K, V, S> HashMap<K, V, S>
     /// map.reserve(10);
     /// ```
     pub fn reserve(&mut self, additional: usize) {
+        self.reserve_fallible(additional).expect(OOM_STR);
+    }
+
+
+    #[inline]
+    pub fn reserve_fallible(&mut self, additional: usize) -> Result<(), ()> {
         let remaining = self.capacity() - self.len(); // this can't overflow
         if remaining < additional {
             let min_cap = self.len().checked_add(additional).expect("reserve overflow");
             let raw_cap = self.resize_policy.raw_capacity(min_cap);
-            self.resize(raw_cap);
+            self.resize_fallible(raw_cap)?;
         } else if self.table.tag() && remaining <= self.len() {
             // Probe sequence is too long and table is half full,
             // resize early to reduce probing length.
             let new_capacity = self.table.capacity() * 2;
-            self.resize(new_capacity);
+            self.resize_fallible(new_capacity)?;
         }
+        Ok(())
     }
 
-    /// Resizes the internal vectors to a new capacity. It's your
-    /// responsibility to:
-    ///   1) Ensure `new_raw_cap` is enough for all the elements, accounting
-    ///      for the load factor.
-    ///   2) Ensure `new_raw_cap` is a power of two or zero.
-    #[inline(never)]
     #[cold]
-    fn resize(&mut self, new_raw_cap: usize) {
+    #[inline(never)]
+    fn resize_fallible(&mut self, new_raw_cap: usize) -> Result<(), ()> {
         assert!(self.table.size() <= new_raw_cap);
         assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
 
-        let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
+        let mut old_table = replace(&mut self.table, RawTable::new(new_raw_cap)?);
         let old_size = old_table.size();
 
         if old_table.size() == 0 {
-            return;
+            return Ok(());
         }
 
         let mut bucket = Bucket::head_bucket(&mut old_table);
@@ -788,6 +806,7 @@ impl<K, V, S> HashMap<K, V, S>
         }
 
         assert_eq!(self.table.size(), old_size);
+        Ok(())
     }
 
     /// Shrinks the capacity of the map as much as possible. It will drop
@@ -807,9 +826,13 @@ impl<K, V, S> HashMap<K, V, S>
     /// assert!(map.capacity() >= 2);
     /// ```
     pub fn shrink_to_fit(&mut self) {
+        self.shrink_to_fit_fallible().expect(OOM_STR);
+    }
+
+    pub fn shrink_to_fit_fallible(&mut self) -> Result<(), ()> {
         let new_raw_cap = self.resize_policy.raw_capacity(self.len());
         if self.raw_capacity() != new_raw_cap {
-            let old_table = replace(&mut self.table, RawTable::new(new_raw_cap));
+            let old_table = replace(&mut self.table, RawTable::new(new_raw_cap)?);
             let old_size = old_table.size();
 
             // Shrink the table. Naive algorithm for resizing:
@@ -819,6 +842,7 @@ impl<K, V, S> HashMap<K, V, S>
 
             debug_assert_eq!(self.table.size(), old_size);
         }
+        Ok(())
     }
 
     /// Insert a pre-hashed key-value pair, without first checking
@@ -975,11 +999,15 @@ impl<K, V, S> HashMap<K, V, S>
     /// assert_eq!(letters.get(&'y'), None);
     /// ```
     pub fn entry(&mut self, key: K) -> Entry<K, V> {
+        self.entry_fallible(key).expect(OOM_STR)
+    }
+
+    pub fn entry_fallible(&mut self, key: K) -> Result<Entry<K, V>, ()> {
         // Gotta resize now.
-        self.reserve(1);
+        self.reserve_fallible(1)?;
         let hash = self.make_hash(&key);
-        search_hashed(&mut self.table, hash, |q| q.eq(&key))
-            .into_entry(key).expect("unreachable")
+        Ok(search_hashed(&mut self.table, hash, |q| q.eq(&key))
+            .into_entry(key).expect("unreachable"))
     }
 
     /// Returns the number of elements in the map.
@@ -1163,9 +1191,14 @@ impl<K, V, S> HashMap<K, V, S>
     /// assert_eq!(map[&37], "c");
     /// ```
     pub fn insert(&mut self, k: K, v: V) -> Option<V> {
+        self.insert_fallible(k, v).expect(OOM_STR)
+    }
+
+    #[inline]
+    pub fn insert_fallible(&mut self, k: K, v: V) -> Result<Option<V>, ()> {
         let hash = self.make_hash(&k);
-        self.reserve(1);
-        self.insert_hashed_nocheck(hash, k, v)
+        self.reserve_fallible(1)?;
+        Ok(self.insert_hashed_nocheck(hash, k, v))
     }
 
     /// Removes a key from the map, returning the value at the key if the key

src/table.rs

@@ -802,11 +802,11 @@ impl<K, V> RawTable<K, V> {
 
     /// Creates a new raw table from a given capacity. All buckets are
     /// initially empty.
-    pub fn new(capacity: usize) -> RawTable<K, V> {
+    pub fn new(capacity: usize) -> Result<RawTable<K, V>, ()> {
         unsafe {
-            let ret = RawTable::new_uninitialized(capacity);
+            let ret = RawTable::new_uninitialized_fallible(capacity)?;
             ptr::write_bytes(ret.hashes.ptr(), 0, capacity);
-            ret
+            Ok(ret)
         }
     }