feat(imperative/utils): add serval utils

GitOrigin-RevId: f401663ae3

imperative/src/impl/profiler/states.h

@@ -160,7 +160,7 @@ private:
     template <typename TItem>
     void register_converter() {
         m_table[typeid(TItem)] = [](const any_t& input) {
-            return variant_t(*input.as<TItem>());
+            return variant_t(input.cast<TItem>());
         };
     }
 

imperative/src/include/megbrain/imperative/profiler.h

@@ -11,7 +11,6 @@
 
 #pragma once
 
-#include <any>
 #include <bitset>
 #include <chrono>
 #include <deque>
@@ -28,6 +27,7 @@
 
 #include "megbrain/imperative/op_def.h"
 #include "megbrain/imperative/physical_tensor.h"
+#include "megbrain/imperative/utils/any.h"
 
 namespace mgb {
 namespace imperative {
@@ -51,48 +51,6 @@ public:
     static std::shared_ptr<CompNode::Event> record_device(CompNode device);
 };
 
-class AnyPtr {
-public:
-    struct Deleter {
-        void* object;
-        void (*method)(void*, void*);
-        void operator()(void* ptr) { method(object, ptr); }
-    };
-
-private:
-    using holder_t = std::unique_ptr<void, Deleter>;
-
-    const std::type_info* m_type = nullptr;
-    holder_t m_holder = nullptr;
-
-public:
-    AnyPtr() = default;
-    template <
-            typename T,
-            typename = std::enable_if_t<!std::is_same_v<std::decay_t<T>, AnyPtr>>>
-    explicit AnyPtr(T* value, Deleter deleter) {
-        m_type = &typeid(T);
-        m_holder = {value, deleter};
-    }
-    template <typename T>
-    T* as() {
-        mgb_assert(is_exactly<T>(), "type mismatch");
-        return reinterpret_cast<T*>(m_holder.get());
-    }
-    template <typename T>
-    const T* as() const {
-        mgb_assert(is_exactly<T>(), "type mismatch");
-        return reinterpret_cast<const T*>(m_holder.get());
-    }
-    template <typename T>
-    bool is_exactly() const {
-        return std::type_index{typeid(T)} == std::type_index{*m_type};
-    }
-    const std::type_info& type() const { return *m_type; }
-    bool operator==(std::nullptr_t nptr) const { return m_holder == nullptr; }
-    operator bool() const { return m_holder != nullptr; }
-};
-
 class Profiler {
 public:
     struct Record {
@@ -128,7 +86,6 @@ private:
     std::thread::id m_thread_id;
     std::vector<Record> m_records;
     std::atomic<Status> m_status = Running;
-    std::unordered_map<std::type_index, AnyPtr> m_mem_pools;
 
     static std::vector<entry_t> sm_records;
     static options_t sm_profile_options;
@@ -161,42 +118,21 @@ public:
         return *tm_profiler;
     }
 
-    template <typename T>
-    static MemPool<T>& get_mem_pool() {
-        thread_local MemPool<T>* t_pool = nullptr;
-        if (t_pool == nullptr) {
-            auto& pool = get_instance().m_mem_pools[typeid(MemPool<T>)];
-            if (pool == nullptr) {
-                pool =
-                        AnyPtr(new MemPool<T>(),
-                               {nullptr, [](void*, void* ptr) {
-                                    delete reinterpret_cast<MemPool<T>*>(ptr);
-                                }});
-            }
-            t_pool = pool.as<MemPool<T>>();
-        }
-        return *t_pool;
-    }
-
     static uint64_t next_id() { return sm_last_id++; }
 
     template <typename T, typename... TArgs>
     static uint64_t record(TArgs&&... args) {
         auto& profiler = get_instance();
-        auto& mem_pool = get_mem_pool<T>();
+        // auto& mem_pool = get_mem_pool<T>();
         if constexpr (sm_debug) {
             Status expected = Running;
             mgb_assert(profiler.m_status.compare_exchange_strong(expected, Recording));
         }
         uint64_t id = next_id();
         profiler::Time time = sm_timer.record_host();
-        auto deleter = [](void* obj, void* ptr) {
-            reinterpret_cast<MemPool<T>*>(obj)->free(reinterpret_cast<T*>(ptr));
-        };
         profiler.m_records.emplace_back(
                 id, profiler.m_thread_id, time,
-                AnyPtr{mem_pool.alloc(T{std::forward<TArgs>(args)...}),
-                       {&mem_pool, deleter}});
+                AnyPtr::make<T>(T{std::forward<TArgs&&>(args)...}));
         if constexpr (sm_debug) {
             Status expected = Recording;
             mgb_assert(profiler.m_status.compare_exchange_strong(expected, Running));
@@ -241,7 +177,7 @@ public:
         bundle.options = get_options();
         bundle.start_at = sm_start_at;
         bundle.thread_dict = get_thread_dict();
-        return std::move(bundle);
+        return bundle;
     }
 
     static option_t get_option(std::string key, option_t default_val) {

imperative/src/include/megbrain/imperative/utils/allocator.h

@@ -0,0 +1,71 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/allocator.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <typeindex>
+
+#include "megbrain/utils/mempool.h"
+#include "megbrain/utils/metahelper.h"
+
+namespace mgb::imperative {
+
+template <typename T>
+class Allocator {
+public:
+    using pointer = T*;
+    using const_pointer = const T*;
+    using void_pointer = void*;
+    using const_void_pointer = const void*;
+    using value_type = T;
+    using size_type = std::size_t;
+    using diffenence_type = std::ptrdiff_t;
+    using pool_type = MemPoolStorage;
+
+private:
+    pool_type* m_pool = nullptr;
+
+public:
+    Allocator(pool_type* pool) : m_pool(pool) {}
+
+    T* allocate(size_type n) {
+        mgb_assert(n == 1);
+        return m_pool->alloc(sizeof(T));
+    }
+
+    void deallocate(pointer* p, size_type n) {
+        mgb_assert(n == 1);
+        m_pool->free(p);
+    }
+
+    bool operator==(const Allocator& rhs) const { return m_pool == rhs.m_pool; }
+
+    bool operator!=(const Allocator& rhs) const { return m_pool != rhs.m_pool; }
+};
+
+template <typename T>
+class ThreadLocalAllocatorAdapter {
+public:
+    using value_type = T;
+    using size_type = std::size_t;
+    using pointer = T*;
+
+public:
+    T* allocate(size_type n) { mgb_assert(false); }
+
+    void deallocate(pointer* p, size_type n) { mgb_assert(false); }
+
+    bool operator==(const ThreadLocalAllocatorAdapter& rhs) const { return true; }
+
+    bool operator!=(const ThreadLocalAllocatorAdapter& rhs) const { return false; }
+};
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/any.h

@@ -0,0 +1,70 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/any.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <typeindex>
+
+#include "megbrain/imperative/utils/local_ptr.h"
+
+namespace mgb::imperative {
+
+class AnyMixinBase {
+private:
+    const std::type_info* m_type = nullptr;
+
+public:
+    AnyMixinBase() = default;
+
+    const std::type_info& type() const { return *m_type; }
+
+    friend class AnyPtr;
+};
+
+template <typename T>
+class AnyMixin : public AnyMixinBase, public T {
+public:
+    AnyMixin(T&& val) : T(std::move(val)) {}
+};
+
+class AnyPtr {
+public:
+    using storage_t = LocalPtr<AnyMixinBase>;
+
+private:
+    storage_t m_storage;
+
+public:
+    const std::type_info& type() const { return m_storage->type(); }
+    template <typename T>
+    const T& cast() const {
+        mgb_assert(is_exactly<T>(), "type mismatch");
+        return *static_cast<const AnyMixin<T>*>(m_storage.get());
+    }
+    template <typename T>
+    bool is_exactly() const {
+        return std::type_index{typeid(T)} == std::type_index{type()};
+    }
+    bool operator==(std::nullptr_t nptr) const { return m_storage == nullptr; }
+    bool operator!=(std::nullptr_t nptr) const { return m_storage != nullptr; }
+    operator bool() const { return m_storage != nullptr; }
+
+    template <typename T, typename... TArgs>
+    static AnyPtr make(TArgs&&... args) {
+        AnyPtr ret;
+        ret.m_storage = LocalPtr<AnyMixinBase>::make<AnyMixin<T>>(
+                std::forward<TArgs&&>(args)...);
+        ret.m_storage->m_type = &typeid(T);
+        return ret;
+    }
+};
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/box.h

@@ -0,0 +1,96 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/visit.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <chrono>
+#include <future>
+#include <vector>
+
+#include "megbrain/utils/metahelper.h"
+#include "megbrain/utils/small_vector.h"
+
+namespace mgb::imperative {
+
+class BoxBase : public NonCopyableObj {
+public:
+    virtual void reset() = 0;
+    virtual void set_exception(std::exception_ptr exc) = 0;
+    virtual bool try_set_exception(std::exception_ptr exc) = 0;
+};
+
+/**
+ * \brief An reusable promise
+ *
+ * \tparam T type of value
+ */
+template <typename T>
+class Box final : public BoxBase {
+private:
+    std::promise<T> m_promise;
+    std::shared_future<T> m_future;
+    std::mutex m_mutex;
+    bool m_value_set;
+    bool m_exception_set;
+
+public:
+    Box() { reset(); }
+    const T& get_value() { return m_future.get(); }
+    T take_value() {
+        T value = m_future.get();
+        reset();
+        return value;
+    }
+    void set_value(T value) {
+        MGB_LOCK_GUARD(m_mutex);
+        m_promise.set_value(std::move(value));
+        m_value_set = true;
+    }
+    bool try_set_value(T value) {
+        MGB_LOCK_GUARD(m_mutex);
+        if (m_exception_set) {
+            return false;
+        }
+        m_promise.set_value(std::move(value));
+        m_value_set = true;
+        return true;
+    }
+    void set_exception(std::exception_ptr exc) override {
+        MGB_LOCK_GUARD(m_mutex);
+        m_promise.set_exception(exc);
+        m_exception_set = true;
+    }
+    bool try_set_exception(std::exception_ptr exc) override {
+        MGB_LOCK_GUARD(m_mutex);
+        if (m_value_set) {
+            return false;
+        }
+        m_promise.set_exception(exc);
+        m_exception_set = true;
+        return true;
+    }
+    void reset() override {
+        MGB_LOCK_GUARD(m_mutex);
+        m_promise = {};
+        m_future = m_promise.get_future();
+        m_value_set = false;
+        m_exception_set = false;
+    }
+
+    /**
+     * \brief make an empty box
+     *
+     * \return std::shared_ptr<Box>
+     */
+    static std::shared_ptr<Box> make() { return std::make_shared<Box>(); }
+};
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/helper.h

@@ -0,0 +1,40 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/span.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <iomanip>
+#include <memory>
+#include <sstream>
+
+namespace mgb {
+
+namespace imperative {
+
+template <typename T>
+class CleanupGuard {
+private:
+    T m_callback;
+
+public:
+    explicit CleanupGuard(T cb) : m_callback{std::move(cb)} {}
+    ~CleanupGuard() { m_callback(); }
+};
+
+inline std::string quoted(std::string str) {
+    std::stringstream ss;
+    ss << std::quoted(str);
+    return ss.str();
+}
+
+}  // namespace imperative
+
+}  // namespace mgb

imperative/src/include/megbrain/imperative/utils/intrusive_list.h

@@ -0,0 +1,245 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/intrusive_list.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#include "megbrain/utils/metahelper.h"
+
+namespace mgb::imperative::utils::intrusive_list {
+
+// copy policy
+struct after_t {};
+struct before_t {};
+struct disable_t {};
+
+template <typename T>
+struct Tail;
+
+// invariant: next->prev == this
+template <typename T>
+struct Head {
+    Tail<T>* next;
+
+    Head(Tail<T>* node = nullptr) : next(node) {}
+    Head(const Head<T>&) = delete;
+    Head<T>& operator=(const Head<T>&) = delete;
+    Head(Head<T>&& rhs) : next(rhs.next) {
+        rhs.next = nullptr;
+        if (next) {
+            next->prev = this;
+        }
+    }
+    Head<T>& operator=(Head<T>&& rhs) {
+        mgb_assert(!next);
+        next = rhs.next;
+        rhs.next = nullptr;
+        if (next) {
+            next->prev = this;
+        }
+        return *this;
+    }
+    ~Head() {
+        if (next) {
+            next->prev = nullptr;
+        }
+    }
+};
+
+// invariant: prev->next == this
+template <typename T>
+struct Tail {
+    Head<T>* prev;
+
+    Tail(Head<T>* node = nullptr) : prev(node) {}
+    Tail(const Tail<T>&) = delete;
+    Tail<T>& operator=(const Tail<T>&) = delete;
+    Tail(Tail<T>&& rhs) : prev(rhs.prev) {
+        rhs.prev = nullptr;
+        if (prev) {
+            prev->next = this;
+        }
+    }
+    Tail<T>& operator=(Tail<T>&& rhs) {
+        mgb_assert(!prev);
+        prev = rhs.prev;
+        rhs.prev = nullptr;
+        if (prev) {
+            prev->next = this;
+        }
+        return *this;
+    }
+    ~Tail() {
+        if (prev) {
+            prev->next = nullptr;
+        }
+    }
+};
+
+template <typename T, typename policy>
+struct Node;
+
+template <typename T>
+class Iterator {
+    T* ptr;
+
+    void inc() { ptr = static_cast<T*>(ptr->Head<T>::next); }
+    void dec() { ptr = static_cast<T*>(ptr->Head<T>::prev); }
+
+public:
+    Iterator(Head<T>& head) : ptr(static_cast<T*>(head.next)) {}
+    Iterator(Tail<T>& tail) : ptr(static_cast<T*>(tail.prev)) {}
+
+    template <typename policy>
+    Iterator(Node<T, policy>& node) : ptr(static_cast<T*>(&node)) {}
+
+    T& operator*() { return *static_cast<T*>(ptr); }
+    T* operator->() { return static_cast<T*>(ptr); }
+
+    operator bool() { return ptr; }
+    bool operator==(const Iterator<T>& rhs) { return ptr == rhs.ptr; }
+
+    Iterator& operator++() {
+        inc();
+        return *this;
+    }
+    Iterator& operator--() {
+        dec();
+        return *this;
+    }
+    Iterator operator++(int) {
+        auto ret = *this;
+        inc();
+        return ret;
+    }
+    Iterator operator--(int) {
+        auto ret = *this;
+        dec();
+        return ret;
+    }
+};
+
+// Node in a doubly linked list. Unlike std::list, nodes are not owned by a container.
+// Instead, nodes may join or leave a list freely.
+// NOTE: Derived classes have to explicitly declare copy / assignment as default,
+//       otherwise the compiler generated version would use the const T& signature,
+//       which is deleted.
+template <typename T = void, typename policy = disable_t>
+struct Node : Tail<std::conditional_t<std::is_same_v<T, void>, Node<T, policy>, T>>,
+              Head<std::conditional_t<std::is_same_v<T, void>, Node<T, policy>, T>> {
+private:
+    using this_t = Node<T, policy>;
+    using U = std::conditional_t<std::is_same_v<T, void>, this_t, T>;
+
+public:
+    using head_t = Head<U>;
+    using tail_t = Tail<U>;
+    using head_t::next;
+    using tail_t::prev;
+
+    Node() = default;
+    Node(const this_t&) = delete;
+    this_t& operator=(const this_t&) = delete;
+
+    //! constructed node is inserted after the input node
+    Node(after_t, head_t& node) : tail_t(&node), head_t(node.next) {
+        node.next = this;
+        if (next) {
+            next->prev = this;
+        }
+    }
+
+    //! constructed node is inserted before the input node
+    Node(before_t, tail_t& node) : head_t(&node), tail_t(node.prev) {
+        node.prev = this;
+        if (prev) {
+            prev->next = this;
+        }
+    }
+
+    Node(this_t&& rhs) : tail_t(rhs.prev), head_t(rhs.next) {
+        rhs.prev = nullptr;
+        rhs.next = nullptr;
+        if (prev) {
+            prev->next = this;
+        }
+        if (next) {
+            next->prev = this;
+        }
+    }
+
+    Node& operator=(this_t&& rhs) {
+        unlink();
+        prev = rhs.prev;
+        next = rhs.next;
+        rhs.prev = nullptr;
+        rhs.next = nullptr;
+        if (prev) {
+            prev->next = this;
+        }
+        if (next) {
+            next->prev = this;
+        }
+        return *this;
+    }
+
+    template <
+            typename p = policy,
+            typename = std::enable_if_t<
+                    std::is_same_v<p, before_t> || std::is_same_v<p, after_t>, void>>
+    Node(this_t& rhs) : Node(policy{}, rhs) {}
+
+    template <
+            typename p = policy,
+            typename = std::enable_if_t<
+                    std::is_same_v<p, before_t> || std::is_same_v<p, after_t>, void>>
+    this_t& operator=(this_t& rhs) {
+        insert(policy{}, rhs);
+        return *this;
+    }
+
+    void unlink() {
+        if (prev) {
+            prev->next = next;
+        }
+        if (next) {
+            next->prev = prev;
+        }
+        prev = nullptr;
+        next = nullptr;
+    }
+
+    //! this node is unlinked from its list and inserted after the input node
+    void insert(after_t, head_t& node) {
+        unlink();
+        prev = &node;
+        next = node.next;
+        node.next = this;
+        if (next) {
+            next->prev = this;
+        }
+    }
+
+    //! this node is unlinked from its list and inserted before the input node
+    void insert(before_t, tail_t& node) {
+        unlink();
+        next = &node;
+        prev = node.prev;
+        node.prev = this;
+        if (prev) {
+            prev->next = this;
+        }
+    }
+
+    void insert_before(tail_t& node) { insert(before_t{}, node); }
+    void insert_after(head_t& node) { insert(after_t{}, node); }
+
+    ~Node() { unlink(); }
+};
+
+}  // namespace mgb::imperative::utils::intrusive_list

imperative/src/include/megbrain/imperative/utils/local_ptr.h

@@ -0,0 +1,285 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/local_ptr.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <optional>
+
+#include "megbrain/imperative/utils/mempool.h"
+#include "megbrain/utils/metahelper.h"
+
+namespace mgb::imperative {
+
+template <typename T>
+class LocalPtrStorage : public NonCopyableObj {
+private:
+    size_t m_ref_count = 0;
+    size_t m_weak_count = 0;
+    T* m_pointer = nullptr;
+    void (*reset)(LocalPtrStorage*) = nullptr;
+    void (*free)(LocalPtrStorage*) = nullptr;
+
+    void inc_ref() { m_ref_count++; }
+
+    void dec_ref() {
+        m_ref_count--;
+        if (m_ref_count == 0) {
+            reset(this);
+            m_pointer = nullptr;
+            reset = nullptr;
+            if (m_weak_count == 0) {
+                free(this);
+                // dead
+            }
+        }
+    }
+
+    void inc_weak_ref() { m_weak_count++; }
+
+    void dec_weak_ref() {
+        m_weak_count--;
+        if ((m_weak_count + m_ref_count) == 0) {
+            free(this);
+            // dead
+        }
+    }
+
+    template <typename U>
+    friend class LocalPtr;
+
+    template <typename U>
+    friend class LocalWeakPtr;
+
+public:
+};
+
+template <typename T, typename TDerived>
+class LocalPtrStorgeImpl : public LocalPtrStorage<T> {
+private:
+    std::optional<TDerived> m_value;
+    void* m_pool = nullptr;
+
+    template <typename U>
+    friend class LocalPtr;
+
+    template <typename U>
+    friend class LocalWeakPtr;
+};
+
+template <typename T>
+class LocalWeakPtr;
+
+/**
+ * \brief thread-unsafe smart pointer
+ *
+ * \tparam T type of value
+ */
+template <typename T>
+class LocalPtr {
+public:
+    using storage_t = LocalPtrStorage<T>;
+    using pool_t = MemPool<storage_t>;
+    using weak_type = LocalWeakPtr<T>;
+
+private:
+    storage_t* m_storage = nullptr;
+
+    void emplace(storage_t* ptr) {
+        if (ptr) {
+            ptr->inc_ref();
+            m_storage = ptr;
+        }
+    }
+
+    LocalPtr(storage_t* ptr) { emplace(ptr); }
+
+public:
+    LocalPtr() = default;
+    LocalPtr(const LocalPtr& rhs) { (*this) = rhs; }
+    LocalPtr(LocalPtr&& rhs) { (*this) = std::move(rhs); }
+    LocalPtr& operator=(const LocalPtr& rhs) {
+        if (this == &rhs) {
+            return *this;
+        }
+        auto storage = rhs.m_storage;
+        if (storage) {
+            storage->inc_ref();
+        }
+        if (m_storage) {
+            m_storage->dec_ref();
+            // rhs.m_storage may be invalid here
+        }
+        m_storage = storage;
+        return *this;
+    }
+    LocalPtr& operator=(LocalPtr&& rhs) {
+        if (this == &rhs) {
+            return *this;
+        }
+        std::swap(m_storage, rhs.m_storage);
+        rhs.reset();
+        return *this;
+    }
+    bool operator==(const LocalPtr& rhs) const { return m_storage == rhs.m_storage; }
+    bool operator!=(const LocalPtr& rhs) const { return m_storage != rhs.m_storage; }
+    size_t hash() const { return reinterpret_cast<uintptr_t>(m_storage); }
+
+    ~LocalPtr() { reset(); }
+
+    /**
+     * \brief Construct an instance of TDerived and return an LocalPtr
+     *
+     * There is an memory pool for each (T, TDerived) pair
+     *
+     * \tparam TDerived type of concrete instance, should be subclass of T
+     * \tparam TArgs
+     * \param args constructor arguments
+     * \return LocalPtr points to the instance
+     */
+    template <typename TDerived = T, typename... TArgs>
+    static LocalPtr make(TArgs&&... args) {
+        static_assert(std::is_base_of_v<T, TDerived>);
+        using storage_impl_t = LocalPtrStorgeImpl<T, TDerived>;
+        constexpr auto normalize_size = [](size_t size) {
+            size_t normalized_size = 64;
+            while (normalized_size < size) {
+                normalized_size *= 2;
+            }
+            return normalized_size;
+        };
+        using raw_storage_t =
+                std::aligned_storage_t<normalize_size(sizeof(storage_impl_t))>;
+        static_assert(alignof(raw_storage_t) % alignof(storage_impl_t) == 0);
+        static_assert(sizeof(raw_storage_t) >= sizeof(storage_impl_t));
+        using pool_t = MemPool<raw_storage_t>;
+        pool_t& pool = MemPoolUtils<raw_storage_t>::get_thread_local();
+        auto* raw_storage = pool.alloc_raw();
+        auto* storage = reinterpret_cast<storage_impl_t*>(raw_storage);
+        new (storage) storage_impl_t();
+        storage->m_value.emplace(std::forward<TArgs&&>(args)...);
+        storage->m_pointer = &*storage->m_value;
+        storage->reset = [](storage_t* storage) {
+            auto* storage_impl = static_cast<storage_impl_t*>(storage);
+            storage_impl->m_value.reset();
+            storage_impl->m_pointer = nullptr;
+        };
+        storage->free = [](storage_t* storage_base) {
+            auto* storage = static_cast<storage_impl_t*>(storage_base);
+            auto* pool = reinterpret_cast<pool_t*>(storage->m_pool);
+            storage->m_pool = nullptr;
+            storage->~storage_impl_t();
+            auto* raw_storage = reinterpret_cast<raw_storage_t*>(storage);
+            pool->free_raw(raw_storage);
+        };
+        storage->m_pool = &pool;
+        return {(storage_t*)storage};
+    }
+
+    T& operator*() const { return *get(); }
+
+    T* get() const {
+        if ((!m_storage) || !m_storage->m_pointer) {
+            return nullptr;
+        }
+        return m_storage->m_pointer;
+    }
+
+    T* operator->() const { return get(); }
+
+    size_t ref_count() const { return m_storage->m_ref_count; }
+
+    bool unique() const { return ref_count() == 1; }
+
+    void reset() {
+        if (m_storage) {
+            m_storage->dec_ref();
+            m_storage = nullptr;
+        }
+    }
+
+    operator bool() const { return bool(m_storage); }
+    bool operator==(std::nullptr_t nptr) const { return m_storage == nullptr; }
+    bool operator!=(std::nullptr_t nptr) const { return m_storage != nullptr; }
+
+    template <typename U>
+    friend class LocalWeakPtr;
+};
+
+template <typename T>
+class LocalWeakPtr {
+public:
+    using storage_t = LocalPtrStorage<T>;
+
+private:
+    storage_t* m_storage = nullptr;
+
+    void emplace(storage_t* ptr) {
+        if (ptr) {
+            ptr->inc_weak_ref();
+            m_storage = ptr;
+        }
+    }
+
+public:
+    LocalWeakPtr() = default;
+    LocalWeakPtr(const LocalPtr<T>& rhs) { emplace(rhs.m_storage); }
+    LocalWeakPtr(const LocalWeakPtr& rhs) { (*this) = rhs; }
+    LocalWeakPtr(LocalWeakPtr&& rhs) { (*this) = std::move(rhs); }
+    LocalWeakPtr& operator=(const LocalWeakPtr& rhs) {
+        if (this == &rhs) {
+            return *this;
+        }
+        reset();
+        emplace(rhs.m_storage);
+        return *this;
+    }
+    LocalWeakPtr& operator=(LocalWeakPtr&& rhs) {
+        if (this == &rhs) {
+            return *this;
+        }
+        std::swap(m_storage, rhs.m_storage);
+        rhs.reset();
+        return *this;
+    }
+
+    ~LocalWeakPtr() { reset(); }
+
+    void reset() {
+        if (m_storage) {
+            m_storage->dec_weak_ref();
+            m_storage = nullptr;
+        }
+    }
+
+    LocalPtr<T> lock() const {
+        if (m_storage && m_storage->m_ref_count) {
+            return {m_storage};
+        }
+        return {};
+    }
+
+    bool operator==(const LocalWeakPtr& rhs) const {
+        return m_storage == rhs.m_storage;
+    }
+
+    bool operator!=(const LocalWeakPtr& rhs) const {
+        return m_storage != rhs.m_storage;
+    }
+
+    size_t hash() const { return reinterpret_cast<uintptr_t>(m_storage); }
+};
+
+template <typename T, typename TDerived, typename... TArgs>
+LocalPtr<T> make_local(TArgs&&... args) {
+    return LocalPtr<T>::template make<TDerived>(std::forward<TArgs&&>(args)...);
+}
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/map.h

@@ -0,0 +1,157 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/map.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <optional>
+
+#include "megbrain/utils/metahelper.h"
+
+namespace mgb::imperative {
+
+/**
+ * \brief an hash map optimized for weak pointer as key
+ *
+ * Keys were scanned automatically, so values referenced by invalid keys whould be
+ * released soon
+ *
+ * \tparam TKey key type, requires(bool(key.lock()))
+ * \tparam TValue value type
+ */
+template <typename TKey, typename TValue>
+class WeakKeyMap : public NonCopyableObj {
+public:
+    using storage_t = std::unordered_map<TKey, TValue>;
+
+private:
+    storage_t m_storage;
+    typename storage_t::iterator m_cursor = m_storage.begin();
+
+    /**
+     * \brief select a key and verify that whether it is invalid. If yes, erase it
+     *
+     */
+    void _step() {
+        if (m_cursor == m_storage.end()) {
+            m_cursor = m_storage.begin();
+            return;
+        }
+        auto key = m_cursor->first;
+        if (!key.lock()) {
+            m_cursor = m_storage.erase(m_cursor);
+        } else {
+            ++m_cursor;
+        }
+    }
+
+public:
+    size_t count(TKey key) {
+        _step();
+        _step();
+        return m_storage.count(key);
+    }
+
+    TValue& at(TKey key) const { return m_storage.at(key); }
+
+    TValue& at(TKey key) {
+        _step();
+        _step();
+        return m_storage.at(key);
+    }
+
+    TValue& operator[](TKey key) {
+        _step();
+        _step();
+        if (m_storage.count(key)) {
+            return m_storage.at(key);
+        } else {
+            size_t bucket_count = m_storage.bucket_count();
+            TValue& result = m_storage[key];
+            if (bucket_count != m_storage.bucket_count()) {
+                m_cursor = m_storage.begin();
+            }
+            return result;
+        }
+    }
+
+    std::optional<TValue> try_get(TKey key) const {
+        auto iter = m_storage.find(key);
+        if (iter == m_storage.end()) {
+            return {};
+        }
+        return {iter->second};
+    }
+
+    std::optional<TValue> try_get(TKey key) {
+        _step();
+        _step();
+        return ((const WeakKeyMap*)this)->try_get(std::move(key));
+    }
+};
+
+template <typename TKey, typename TValue>
+class WeakValueMap : public NonCopyableObj {
+public:
+    using storage_t = std::unordered_map<TKey, TValue>;
+
+private:
+    storage_t m_storage;
+    typename storage_t::iterator m_cursor = m_storage.begin();
+
+    /**
+     * \brief select a key and verify that whether it is invalid. If yes, erase it
+     *
+     */
+    void _step() {
+        if (m_cursor == m_storage.end()) {
+            m_cursor = m_storage.begin();
+            return;
+        }
+        auto value = m_cursor->second;
+        if (!value.lock()) {
+            m_cursor = m_storage.erase(m_cursor);
+        } else {
+            ++m_cursor;
+        }
+    }
+
+public:
+    size_t count(TKey key) {
+        _step();
+        _step();
+        return m_storage.count(key);
+    }
+
+    TValue& at(TKey key) const { return m_storage.at(key); }
+
+    TValue& at(TKey key) {
+        _step();
+        _step();
+        return m_storage.at(key);
+    }
+
+    TValue& operator[](TKey key) {
+        _step();
+        _step();
+        if (m_storage.count(key)) {
+            return m_storage.at(key);
+        } else {
+            size_t bucket_count = m_storage.bucket_count();
+            TValue& result = m_storage[key];
+            if (bucket_count != m_storage.bucket_count()) {
+                m_cursor = m_storage.begin();
+            }
+            return result;
+        }
+    }
+};
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/mempool.h

@@ -0,0 +1,70 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/mempool.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2021 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <mutex>
+#include <thread>
+#include <unordered_map>
+
+#include "megbrain/utils/mempool.h"
+#include "megbrain/utils/metahelper.h"
+
+namespace mgb::imperative {
+
+template <typename T>
+class MemPoolUtils {
+private:
+    static std::mutex sm_mutex;
+    static std::unordered_map<std::thread::id, std::unique_ptr<MemPool<T>>>
+            sm_instances;
+    static thread_local MemPool<T>* tm_instance;
+    static MemPool<T>* sm_instance;
+
+public:
+    static MemPool<T>& get_thread_local() {
+        if (!tm_instance) {
+            MGB_LOCK_GUARD(sm_mutex);
+            auto& instance = sm_instances[std::this_thread::get_id()];
+            if (!instance) {  // thread id may be duplicated
+                instance = std::make_unique<MemPool<T>>();
+            }
+            tm_instance = instance.get();
+        }
+        return *tm_instance;
+    }
+    static MemPool<T>& get_static() {
+        if (!sm_instance) {
+            MGB_LOCK_GUARD(sm_mutex);
+            auto& instance = sm_instances[{}];
+            if (!instance) {  // double check
+                instance = std::make_unique<MemPool<T>>();
+                sm_instance = instance.get();
+            }
+            mgb_assert(sm_instance);
+        }
+    }
+};
+
+template <typename T>
+std::mutex MemPoolUtils<T>::sm_mutex;
+
+template <typename T>
+std::unordered_map<std::thread::id, std::unique_ptr<MemPool<T>>>
+        MemPoolUtils<T>::sm_instances;
+
+template <typename T>
+thread_local MemPool<T>* MemPoolUtils<T>::tm_instance;
+
+template <typename T>
+MemPool<T>* MemPoolUtils<T>::sm_instance;
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/span.h

@@ -0,0 +1,69 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/span.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <array>
+#include <vector>
+
+#include "megbrain/utils/small_vector.h"
+
+namespace mgb::imperative {
+
+/**
+ * \brief wrapper for c-style array
+ *
+ * \tparam T value type
+ */
+template <typename T>
+class Span {
+private:
+    const T* m_begin = nullptr;
+    const T* m_end = nullptr;
+
+public:
+    Span() {}
+    Span(const T* begin, const T* end) : m_begin{begin}, m_end{end} {}
+    Span(const T* begin, size_t size) : Span(begin, begin + size) {}
+    template <typename TContainer>
+    Span(TContainer& container) : Span(container.data(), container.size()) {}
+    const T* begin() const { return m_begin; }
+    const T* end() const { return m_end; }
+    const T* data() const { return m_begin; }
+    size_t size() const { return m_end - m_begin; }
+    template <typename TContainer>
+    TContainer copy_into() {
+        return TContainer(m_begin, m_end);
+    }
+    const T& operator[](size_t idx) const { return m_begin[idx]; }
+    const T& at(size_t idx) const { return m_begin[idx]; }
+    const T& item() const {
+        mgb_assert(
+                m_end - m_begin == 1, "size mismatch: %zu vs %zu", (m_end - m_begin),
+                (size_t)1);
+        return m_begin[0];
+    }
+
+    template <size_t N>
+    const std::array<T, N>& as_array() {
+        mgb_assert(
+                m_end - m_begin == N, "size mismatch: %zu vs %zu", (m_end - m_begin),
+                N);
+        return *reinterpret_cast<const std::array<T, N>*>(m_begin);
+    }
+
+    Span sub(size_t begin, size_t length) {
+        mgb_assert(begin + length <= m_end - m_begin);
+        return {m_begin + begin, length};
+    }
+};
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/to_string.h

@@ -16,6 +16,7 @@
 #include <tuple>
 #include <type_traits>
 
+#include "megbrain/imperative/utils/span.h"
 #include "megbrain/tensor.h"
 #include "megbrain/utils/small_vector.h"
 
@@ -60,6 +61,22 @@ struct ToStringTrait<SmallVector<T, N>> {
 };
 
 template <typename T>
+struct ToStringTrait<std::vector<T>> {
+    std::string operator()(const std::vector<T>& v) const {
+        if (v.empty()) {
+            return "[]";
+        }
+        std::string result = "[";
+        result += to_string(v[0]);
+        for (size_t i = 1; i < v.size(); ++i) {
+            result += ", ";
+            result += to_string(v[i]);
+        }
+        return result + "]";
+    }
+};
+
+template <typename T>
 struct ToStringTrait<std::shared_ptr<T>> {
     std::string operator()(const std::shared_ptr<T>& sp) const {
         return to_string(sp.get());
@@ -115,4 +132,36 @@ struct ToStringTrait<CompNode> {
     std::string operator()(CompNode device) const { return device.to_string(); }
 };
 
+inline std::string string_join(Span<std::string> span, char delimiter = ',') {
+    std::string buffer = "[";
+    for (size_t i = 1; i < span.size(); ++i) {
+        if (i) {
+            buffer.push_back(delimiter);
+        }
+        buffer.append(span[0]);
+    }
+    return buffer + "]";
+}
+
+template <typename T>
+struct ToStringTrait<Span<T>> {
+    std::string operator()(Span<T> span) const {
+        if (span.size() == 0) {
+            return "[]";
+        }
+        std::string result = "[";
+        result += to_string(span[0]);
+        for (size_t i = 1; i < span.size(); ++i) {
+            result += ", ";
+            result += to_string(span[i]);
+        }
+        return result + "]";
+    }
+};
+
+template <>
+struct ToStringTrait<std::type_info> {
+    std::string operator()(const std::type_info& info) const { return info.name(); }
+};
+
 }  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/value_shape.h

@@ -0,0 +1,104 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/visit.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <vector>
+
+#include "megbrain/imperative/utils/span.h"
+#include "megbrain/tensor.h"
+
+namespace mgb::imperative {
+
+/**
+ * \brief like TensorShape, but allow real scalar shape.
+ *
+ */
+struct ValueShape {
+    size_t shape[TensorShape::MAX_NDIM];
+    int ndim = 0;
+
+    ValueShape() = default;
+    ValueShape(std::initializer_list<size_t> dims) {
+        for (auto&& dim : dims) {
+            shape[ndim++] = dim;
+        }
+    }
+    ValueShape(Span<size_t> dims) {
+        for (auto&& dim : dims) {
+            shape[ndim++] = dim;
+        }
+    }
+
+    size_t& operator[](int axis) { return shape[axis]; }
+
+    size_t operator[](int axis) const { return shape[axis]; }
+
+    size_t at(int axis) const {
+        mgb_assert(axis < ndim);
+        return shape[axis];
+    }
+
+    size_t total_nr_elems() const {
+        size_t prod = 1;
+        for (int i = 0; i < ndim; ++i) {
+            prod *= shape[i];
+        }
+        return prod;
+    }
+
+    bool is_scalar() const { return ndim == 0; }
+
+    std::string to_string() const {
+        std::string buffer = "{";
+        for (size_t i = 0; i < ndim; ++i) {
+            if (i) {
+                buffer.append(",");
+            }
+            buffer.append(std::to_string(shape[i]));
+        }
+        buffer.append("}");
+        return buffer;
+    }
+
+    static ValueShape from(TensorShape tensor_shape) {
+        mgb_assert(tensor_shape.ndim);
+        return Span<size_t>{tensor_shape.shape, tensor_shape.ndim};
+    }
+
+    TensorShape as_tensor_shape() const {
+        mgb_assert(ndim != 0);
+        TensorShape ret;
+        for (size_t i = 0; i < ndim; ++i) {
+            ret.shape[i] = shape[i];
+        }
+        ret.ndim = ndim;
+        return ret;
+    }
+
+    bool operator==(const ValueShape& rhs) const {
+        if (ndim != rhs.ndim) {
+            return false;
+        }
+        for (size_t i = 0; i < ndim; ++i) {
+            if (shape[i] != rhs.shape[i]) {
+                return false;
+            }
+        }
+        return true;
+    }
+};
+
+static_assert(sizeof(size_t) >= sizeof(int));
+static_assert(TensorShape::MAX_NDIM == 7);
+static_assert(sizeof(ValueShape) <= sizeof(size_t) * 8);
+
+}  // namespace mgb::imperative

imperative/src/include/megbrain/imperative/utils/visit.h

@@ -0,0 +1,26 @@
+/**
+ * \file imperative/src/include/megbrain/imperative/utils/visit.h
+ * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
+ *
+ * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ */
+
+#pragma once
+
+#include <vector>
+
+#include "megbrain/utils/small_vector.h"
+
+namespace mgb::imperative {
+
+template <typename... TVisitors>
+class Visitor : public TVisitors... {
+public:
+    using TVisitors::operator()...;
+};
+
+}  // namespace mgb::imperative

imperative/src/test/profiler.cpp

@@ -28,10 +28,10 @@ TEST(TestProfiler, ImperativeLogProfile) {
     auto results = imperative::Profiler::collect();
     imperative::Profiler::stop_profile();
     mgb_assert(results.entries.size() == 2);
-    auto* event_start = results.entries[0].data.as<profiler::CustomEvent>();
-    auto* event_finish = results.entries[1].data.as<profiler::CustomFinishEvent>();
-    mgb_assert(event_start && event_start->title == "XXX");
-    mgb_assert(event_finish && event_finish->title == "XXX");
+    auto& event_start = results.entries[0].data.cast<profiler::CustomEvent>();
+    auto& event_finish = results.entries[1].data.cast<profiler::CustomFinishEvent>();
+    mgb_assert(event_start.title == "XXX");
+    mgb_assert(event_finish.title == "XXX");
     mgb_assert(results.entries[0].time < results.entries[1].time);
     mgb_assert(results.entries[0].id < results.entries[1].id);
 }