Merge pull request #3489 from sfc-gh-tclinkenbeard/dont-throw-deque-relocate

Add exception-safety to Deque::grow

flow/Deque.cpp

@@ -79,4 +79,41 @@ TEST_CASE("/flow/Deque/max_size") {
 	return Void();
 }
 
+struct RandomlyThrows {
+	int data = 0;
+	RandomlyThrows() = default;
+	explicit RandomlyThrows(int data) : data(data) {}
+	~RandomlyThrows() = default;
+	RandomlyThrows(const RandomlyThrows& other) : data(other.data) { randomlyThrow(); }
+	RandomlyThrows& operator=(const RandomlyThrows& other) {
+		data = other.data;
+		randomlyThrow();
+		return *this;
+	}
+
+private:
+	void randomlyThrow() {
+		if (deterministicRandom()->random01() < 0.1) {
+			throw success();
+		}
+	}
+};
+
+TEST_CASE("/flow/Deque/grow_exception_safety") {
+	Deque<RandomlyThrows> q;
+	for (int i = 0; i < 100; ++i) {
+		loop {
+			try {
+				q.push_back(RandomlyThrows{ i });
+				break;
+			} catch (Error& e) {
+			}
+		}
+	}
+	for (int i = 0; i < 100; ++i) {
+		ASSERT(q[i].data == i);
+	}
+	return Void();
+}
+
 void forceLinkDequeTests() {}

flow/Deque.h

@@ -168,10 +168,18 @@ private:
 		if (newSize > max_size()) throw std::bad_alloc();
 		//printf("Growing to %lld (%u-%u mask %u)\n", (long long)newSize, begin, end, mask);
 		T* newArr = (T*)aligned_alloc(std::max(__alignof(T), sizeof(void*)),
-		                              newSize * sizeof(T)); // SOMEDAY: FastAllocator, exception safety
+		                              newSize * sizeof(T)); // SOMEDAY: FastAllocator
 		ASSERT(newArr != nullptr);
 		for (int i = begin; i != end; i++) {
-			new (&newArr[i - begin]) T(std::move(arr[i&mask]));
+			try {
+				new (&newArr[i - begin]) T(std::move_if_noexcept(arr[i & mask]));
+			} catch (...) {
+				cleanup(newArr, i-begin);
+				throw;
+			}
+		}
+		for (int i = begin; i != end; i++) {
+			static_assert(std::is_nothrow_destructible_v<T>);
 			arr[i&mask].~T();
 		}
 		aligned_free(arr);
@@ -181,7 +189,14 @@ private:
 		mask = uint32_t(newSize - 1);
 	}
 
-	void cleanup() {
+	static void cleanup(T *data, size_t size) noexcept {
+		for (int i = 0; i < size; ++i) {
+			data[i].~T();
+		}
+		aligned_free(data);
+	}
+
+	void cleanup() noexcept {
 		for (int i = begin; i != end; i++)
 			arr[i&mask].~T();
 		if(arr)