X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FMemory.h;h=272d64dc68da5b6e997f6acb49e92be5d0d0a4b2;hb=5ba3126fb76f1d81100b34e429c79cd21f8cd142;hp=5a1059bd5fa70fa09449bb4f22556d26e971fbc5;hpb=a2d09ab3345f5f8c4ddb2e5db47c4b8366ed5669;p=folly.git

diff --git a/folly/Memory.h b/folly/Memory.h
index 5a1059bd..272d64dc 100644
--- a/folly/Memory.h
+++ b/folly/Memory.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,18 +14,17 @@
  * limitations under the License.
  */
 
-#ifndef FOLLY_MEMORY_H_
-#define FOLLY_MEMORY_H_
+#pragma once
 
-#include "folly/Traits.h"
+#include <folly/Traits.h>
 
-#include <memory>
-#include <limits>
-#include <utility>
+#include <cstddef>
+#include <cstdlib>
 #include <exception>
+#include <limits>
+#include <memory>
 #include <stdexcept>
-
-#include <cstddef>
+#include <utility>
 
 namespace folly {
 
@@ -37,17 +36,125 @@ namespace folly {
  * @author Xu Ning (xning@fb.com)
  */
 
-template<typename T, typename Dp = std::default_delete<T>, typename... Args>
-std::unique_ptr<T, Dp> make_unique(Args&&... args) {
-  return std::unique_ptr<T, Dp>(new T(std::forward<Args>(args)...));
+#if __cplusplus >= 201402L || __cpp_lib_make_unique >= 201304L || \
+    (__ANDROID__ && __cplusplus >= 201300L) || _MSC_VER >= 1900
+
+/* using override */ using std::make_unique;
+
+#else
+
+template<typename T, typename... Args>
+typename std::enable_if<!std::is_array<T>::value, std::unique_ptr<T>>::type
+make_unique(Args&&... args) {
+  return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
 }
 
-/*
- * StlAllocator wraps a SimpleAllocator into a STL-compliant
- * allocator, maintaining an instance pointer to the simple allocator
- * object.  The underlying SimpleAllocator object must outlive all
- * instances of StlAllocator using it.
+// Allows 'make_unique<T[]>(10)'. (N3690 s20.9.1.4 p3-4)
+template<typename T>
+typename std::enable_if<std::is_array<T>::value, std::unique_ptr<T>>::type
+make_unique(const size_t n) {
+  return std::unique_ptr<T>(new typename std::remove_extent<T>::type[n]());
+}
+
+// Disallows 'make_unique<T[10]>()'. (N3690 s20.9.1.4 p5)
+template<typename T, typename... Args>
+typename std::enable_if<
+  std::extent<T>::value != 0, std::unique_ptr<T>>::type
+make_unique(Args&&...) = delete;
+
+#endif
+
+/**
+ * static_function_deleter
+ *
+ * So you can write this:
+ *
+ *      using RSA_deleter = folly::static_function_deleter<RSA, &RSA_free>;
+ *      auto rsa = std::unique_ptr<RSA, RSA_deleter>(RSA_new());
+ *      RSA_generate_key_ex(rsa.get(), bits, exponent, nullptr);
+ *      rsa = nullptr;  // calls RSA_free(rsa.get())
+ *
+ * This would be sweet as well for BIO, but unfortunately BIO_free has signature
+ * int(BIO*) while we require signature void(BIO*). So you would need to make a
+ * wrapper for it:
+ *
+ *      inline void BIO_free_fb(BIO* bio) { CHECK_EQ(1, BIO_free(bio)); }
+ *      using BIO_deleter = folly::static_function_deleter<BIO, &BIO_free_fb>;
+ *      auto buf = std::unique_ptr<BIO, BIO_deleter>(BIO_new(BIO_s_mem()));
+ *      buf = nullptr;  // calls BIO_free(buf.get())
+ */
+
+template <typename T, void(*f)(T*)>
+struct static_function_deleter {
+  void operator()(T* t) const {
+    f(t);
+  }
+};
+
+/**
+ *  to_shared_ptr
+ *
+ *  Convert unique_ptr to shared_ptr without specifying the template type
+ *  parameter and letting the compiler deduce it.
+ *
+ *  So you can write this:
+ *
+ *      auto sptr = to_shared_ptr(getSomethingUnique<T>());
+ *
+ *  Instead of this:
+ *
+ *      auto sptr = shared_ptr<T>(getSomethingUnique<T>());
+ *
+ *  Useful when `T` is long, such as:
+ *
+ *      using T = foobar::FooBarAsyncClient;
+ */
+template <typename T, typename D>
+std::shared_ptr<T> to_shared_ptr(std::unique_ptr<T, D>&& ptr) {
+  return std::shared_ptr<T>(std::move(ptr));
+}
+
+/**
+ *  to_weak_ptr
+ *
+ *  Make a weak_ptr and return it from a shared_ptr without specifying the
+ *  template type parameter and letting the compiler deduce it.
+ *
+ *  So you can write this:
+ *
+ *      auto wptr = to_weak_ptr(getSomethingShared<T>());
+ *
+ *  Instead of this:
+ *
+ *      auto wptr = weak_ptr<T>(getSomethingShared<T>());
  *
+ *  Useful when `T` is long, such as:
+ *
+ *      using T = foobar::FooBarAsyncClient;
+ */
+template <typename T>
+std::weak_ptr<T> to_weak_ptr(const std::shared_ptr<T>& ptr) {
+  return std::weak_ptr<T>(ptr);
+}
+
+namespace detail {
+/**
+ * Not all STL implementations define ::free in a way that its address can be
+ * determined at compile time. So we must wrap ::free in a function whose
+ * address can be determined.
+ */
+inline void SysFree(void* p) {
+  ::free(p);
+}
+}
+
+using SysBufferDeleter = static_function_deleter<void, &detail::SysFree>;
+using SysBufferUniquePtr = std::unique_ptr<void, SysBufferDeleter>;
+inline SysBufferUniquePtr allocate_sys_buffer(size_t size) {
+  return SysBufferUniquePtr(::malloc(size));
+}
+
+/**
  * A SimpleAllocator must provide two methods:
  *
  *    void* allocate(size_t size);
@@ -58,26 +165,31 @@ std::unique_ptr<T, Dp> make_unique(Args&&... args) {
  * if the allocation can't be satisfied, and free a previously
  * allocated block.
  *
- * Note that the following allocator resembles the standard allocator
- * quite well:
- *
- * class MallocAllocator {
- *  public:
- *   void* allocate(size_t size) {
- *     void* p = malloc(size);
- *     if (!p) throw std::bad_alloc();
- *     return p;
- *   }
- *   void deallocate(void* p) {
- *     free(p);
- *   }
- * };
+ * SysAlloc resembles the standard allocator.
+ */
+class SysAlloc {
+ public:
+  void* allocate(size_t size) {
+    void* p = ::malloc(size);
+    if (!p) throw std::bad_alloc();
+    return p;
+  }
+  void deallocate(void* p) {
+    ::free(p);
+  }
+};
+
+/**
+ * StlAllocator wraps a SimpleAllocator into a STL-compliant
+ * allocator, maintaining an instance pointer to the simple allocator
+ * object.  The underlying SimpleAllocator object must outlive all
+ * instances of StlAllocator using it.
  *
  * But note that if you pass StlAllocator<MallocAllocator,...> to a
  * standard container it will be larger due to the contained state
  * pointer.
  *
- * author: Tudor Bosman <tudorb@fb.com>
+ * @author: Tudor Bosman <tudorb@fb.com>
  */
 
 // This would be so much simpler with std::allocator_traits, but gcc 4.6.2
@@ -91,7 +203,7 @@ template <class Alloc> class StlAllocator<Alloc, void> {
   typedef const void* const_pointer;
 
   StlAllocator() : alloc_(nullptr) { }
-  explicit StlAllocator(Alloc* alloc) : alloc_(alloc) { }
+  explicit StlAllocator(Alloc* a) : alloc_(a) { }
 
   Alloc* alloc() const {
     return alloc_;
@@ -126,18 +238,16 @@ class StlAllocator {
   typedef size_t size_type;
 
   StlAllocator() : alloc_(nullptr) { }
-  explicit StlAllocator(Alloc* alloc) : alloc_(alloc) { }
+  explicit StlAllocator(Alloc* a) : alloc_(a) { }
 
   template <class U> StlAllocator(const StlAllocator<Alloc, U>& other)
     : alloc_(other.alloc()) { }
 
-  T* allocate(size_t n, const void* hint = nullptr) {
+  T* allocate(size_t n, const void* /* hint */ = nullptr) {
     return static_cast<T*>(alloc_->allocate(n * sizeof(T)));
   }
 
-  void deallocate(T* p, size_t n) {
-    alloc_->deallocate(p);
-  }
+  void deallocate(T* p, size_t /* n */) { alloc_->deallocate(p); }
 
   size_t max_size() const {
     return std::numeric_limits<size_t>::max();
@@ -341,6 +451,99 @@ std::shared_ptr<T> allocate_shared(Allocator&& allocator, Args&&... args) {
   );
 }
 
-}  // namespace folly
+/**
+ * IsArenaAllocator<T>::value describes whether SimpleAllocator has
+ * no-op deallocate().
+ */
+template <class T> struct IsArenaAllocator : std::false_type { };
+
+/*
+ * folly::enable_shared_from_this
+ *
+ * To be removed once C++17 becomes a minimum requirement for folly.
+ */
+#if __cplusplus >= 201700L || \
+    __cpp_lib_enable_shared_from_this >= 201603L
+
+// Guaranteed to have std::enable_shared_from_this::weak_from_this(). Prefer
+// type alias over our own class.
+/* using override */ using std::enable_shared_from_this;
 
-#endif /* FOLLY_MEMORY_H_ */
+#else
+
+/**
+ * Extends std::enabled_shared_from_this. Offers weak_from_this() to pre-C++17
+ * code. Use as drop-in replacement for std::enable_shared_from_this.
+ *
+ * C++14 has no direct means of creating a std::weak_ptr, one must always
+ * create a (temporary) std::shared_ptr first. C++17 adds weak_from_this() to
+ * std::enable_shared_from_this to avoid that overhead. Alas code that must
+ * compile under different language versions cannot call
+ * std::enable_shared_from_this::weak_from_this() directly. Hence this class.
+ *
+ * @example
+ *   class MyClass : public folly::enable_shared_from_this<MyClass> {};
+ *
+ *   int main() {
+ *     std::shared_ptr<MyClass> sp = std::make_shared<MyClass>();
+ *     std::weak_ptr<MyClass> wp = sp->weak_from_this();
+ *   }
+ */
+template <typename T>
+class enable_shared_from_this : public std::enable_shared_from_this<T> {
+public:
+  constexpr enable_shared_from_this() noexcept = default;
+
+  std::weak_ptr<T> weak_from_this() noexcept {
+    return weak_from_this_<T>(this);
+  }
+
+  std::weak_ptr<T const> weak_from_this() const noexcept {
+    return weak_from_this_<T>(this);
+  }
+
+private:
+  // Uses SFINAE to detect and call
+  // std::enable_shared_from_this<T>::weak_from_this() if available. Falls
+  // back to std::enable_shared_from_this<T>::shared_from_this() otherwise.
+  template <typename U>
+  auto weak_from_this_(std::enable_shared_from_this<U>* base_ptr)
+  noexcept -> decltype(base_ptr->weak_from_this()) {
+    return base_ptr->weak_from_this();
+  }
+
+  template <typename U>
+  auto weak_from_this_(std::enable_shared_from_this<U> const* base_ptr)
+  const noexcept -> decltype(base_ptr->weak_from_this()) {
+    return base_ptr->weak_from_this();
+  }
+
+  template <typename U>
+  std::weak_ptr<U> weak_from_this_(...) noexcept {
+    try {
+      return this->shared_from_this();
+    } catch (std::bad_weak_ptr const&) {
+      // C++17 requires that weak_from_this() on an object not owned by a
+      // shared_ptr returns an empty weak_ptr. Sadly, in C++14,
+      // shared_from_this() on such an object is undefined behavior, and there
+      // is nothing we can do to detect and handle the situation in a portable
+      // manner. But in case a compiler is nice enough to implement C++17
+      // semantics of shared_from_this() and throws a bad_weak_ptr, we catch it
+      // and return an empty weak_ptr.
+      return std::weak_ptr<U>{};
+    }
+  }
+
+  template <typename U>
+  std::weak_ptr<U const> weak_from_this_(...) const noexcept {
+    try {
+      return this->shared_from_this();
+    } catch (std::bad_weak_ptr const&) {
+      return std::weak_ptr<U const>{};
+    }
+  }
+};
+
+#endif
+
+}  // namespace folly