X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2Ffutures%2Fdetail%2FCore.h;h=a41059009d48cf87d8b600e530141ad2a2bcfd98;hb=76663af23df01607f74c00c449852f71e5d3f771;hp=27842b55d2e92062359b341d1dea5f8ff6ded81f;hpb=dce6e23d30d9330889bb5fb83c2c4b7383fe21fb;p=folly.git

diff --git a/folly/futures/detail/Core.h b/folly/futures/detail/Core.h
index 27842b55..a4105900 100644
--- a/folly/futures/detail/Core.h
+++ b/folly/futures/detail/Core.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2016 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,13 +21,13 @@
 #include <stdexcept>
 #include <vector>
 
+#include <folly/Executor.h>
+#include <folly/Function.h>
+#include <folly/MicroSpinLock.h>
 #include <folly/Optional.h>
-#include <folly/SmallLocks.h>
-
-#include <folly/futures/Try.h>
-#include <folly/futures/Promise.h>
 #include <folly/futures/Future.h>
-#include <folly/Executor.h>
+#include <folly/futures/Promise.h>
+#include <folly/futures/Try.h>
 #include <folly/futures/detail/FSM.h>
 
 #include <folly/io/async/Request.h>
@@ -74,19 +74,21 @@ enum class State : uint8_t {
 /// time there won't be any problems.
 template<typename T>
 class Core {
+  static_assert(!std::is_void<T>::value,
+                "void futures are not supported. Use Unit instead.");
  public:
   /// This must be heap-constructed. There's probably a way to enforce that in
   /// code but since this is just internal detail code and I don't know how
   /// off-hand, I'm punting.
-  Core() {}
+  Core() : result_(), fsm_(State::Start), attached_(2) {}
 
   explicit Core(Try<T>&& t)
-    : fsm_(State::OnlyResult),
-      attached_(1),
-      result_(std::move(t)) {}
+    : result_(std::move(t)),
+      fsm_(State::OnlyResult),
+      attached_(1) {}
 
   ~Core() {
-    assert(attached_ == 0);
+    DCHECK(attached_ == 0);
   }
 
   // not copyable
@@ -97,6 +99,26 @@ class Core {
   Core(Core&&) noexcept = delete;
   Core& operator=(Core&&) = delete;
 
+  // Core is assumed to be convertible only if the type is convertible
+  // and the size is the same. This is a compromise for the complexity
+  // of having to make Core truly have a conversion constructor which
+  // would cause various other problems.
+  // If we made Core move constructible then we would need to update the
+  // Promise and Future with the location of the new Core. This is complex
+  // and may be inefficient.
+  // Core should only be modified so that for size(T) == size(U),
+  // sizeof(Core<T>) == size(Core<U>).
+  // This assumption is used as a proxy to make sure that
+  // the members of Core<T> and Core<U> line up so that we can use a
+  // reinterpret cast.
+  template <
+      class U,
+      typename = typename std::enable_if<std::is_convertible<U, T>::value &&
+                                         sizeof(U) == sizeof(T)>::type>
+  static Core<T>* convert(Core<U>* from) {
+    return reinterpret_cast<Core<T>*>(from);
+  }
+
   /// May call from any thread
   bool hasResult() const {
     switch (fsm_.getState()) {
@@ -125,33 +147,13 @@ class Core {
     }
   }
 
-  template <typename F>
-  class LambdaBufHelper {
-   public:
-    explicit LambdaBufHelper(F&& func) : func_(std::forward<F>(func)) {}
-    void operator()(Try<T>&& t) {
-      SCOPE_EXIT { this->~LambdaBufHelper(); };
-      func_(std::move(t));
-    }
-   private:
-    F func_;
-  };
-
   /// Call only from Future thread.
   template <typename F>
-  void setCallback(F func) {
+  void setCallback(F&& func) {
     bool transitionToArmed = false;
     auto setCallback_ = [&]{
       context_ = RequestContext::saveContext();
-
-      // Move the lambda into the Core if it fits
-      if (sizeof(LambdaBufHelper<F>) <= lambdaBufSize) {
-        auto funcLoc = static_cast<LambdaBufHelper<F>*>((void*)lambdaBuf_);
-        new (funcLoc) LambdaBufHelper<F>(std::forward<F>(func));
-        callback_ = std::ref(*funcLoc);
-      } else {
-        callback_ = std::move(func);
-      }
+      callback_ = std::forward<F>(func);
     };
 
     FSM_START(fsm_)
@@ -212,71 +214,97 @@ class Core {
   void detachPromise() {
     // detachPromise() and setResult() should never be called in parallel
     // so we don't need to protect this.
-    if (!result_) {
-      setResult(Try<T>(exception_wrapper(BrokenPromise())));
+    if (UNLIKELY(!result_)) {
+      setResult(Try<T>(exception_wrapper(BrokenPromise(typeid(T).name()))));
     }
     detachOne();
   }
 
   /// May call from any thread
   void deactivate() {
-    active_ = false;
+    active_.store(false, std::memory_order_release);
   }
 
   /// May call from any thread
   void activate() {
-    active_ = true;
+    active_.store(true, std::memory_order_release);
     maybeCallback();
   }
 
   /// May call from any thread
-  bool isActive() { return active_; }
+  bool isActive() { return active_.load(std::memory_order_acquire); }
 
   /// Call only from Future thread
-  void setExecutor(Executor* x, int8_t priority) {
-    folly::MSLGuard g(executorLock_);
+  void setExecutor(Executor* x, int8_t priority = Executor::MID_PRI) {
+    if (!executorLock_.try_lock()) {
+      executorLock_.lock();
+    }
+    executor_ = x;
+    priority_ = priority;
+    executorLock_.unlock();
+  }
+
+  void setExecutorNoLock(Executor* x, int8_t priority = Executor::MID_PRI) {
     executor_ = x;
     priority_ = priority;
   }
 
   Executor* getExecutor() {
-    folly::MSLGuard g(executorLock_);
     return executor_;
   }
 
   /// Call only from Future thread
   void raise(exception_wrapper e) {
-    folly::MSLGuard guard(interruptLock_);
+    if (!interruptLock_.try_lock()) {
+      interruptLock_.lock();
+    }
     if (!interrupt_ && !hasResult()) {
       interrupt_ = folly::make_unique<exception_wrapper>(std::move(e));
       if (interruptHandler_) {
         interruptHandler_(*interrupt_);
       }
     }
+    interruptLock_.unlock();
   }
 
   std::function<void(exception_wrapper const&)> getInterruptHandler() {
-    folly::MSLGuard guard(interruptLock_);
-    return interruptHandler_;
+    if (!interruptHandlerSet_.load(std::memory_order_acquire)) {
+      return nullptr;
+    }
+    if (!interruptLock_.try_lock()) {
+      interruptLock_.lock();
+    }
+    auto handler = interruptHandler_;
+    interruptLock_.unlock();
+    return handler;
   }
 
   /// Call only from Promise thread
   void setInterruptHandler(std::function<void(exception_wrapper const&)> fn) {
-    folly::MSLGuard guard(interruptLock_);
+    if (!interruptLock_.try_lock()) {
+      interruptLock_.lock();
+    }
     if (!hasResult()) {
       if (interrupt_) {
         fn(*interrupt_);
       } else {
-        interruptHandler_ = std::move(fn);
+        setInterruptHandlerNoLock(std::move(fn));
       }
     }
+    interruptLock_.unlock();
+  }
+
+  void setInterruptHandlerNoLock(
+      std::function<void(exception_wrapper const&)> fn) {
+    interruptHandlerSet_.store(true, std::memory_order_relaxed);
+    interruptHandler_ = std::move(fn);
   }
 
  protected:
   void maybeCallback() {
     FSM_START(fsm_)
       case State::Armed:
-        if (active_) {
+        if (active_.load(std::memory_order_acquire)) {
           FSM_UPDATE2(fsm_, State::Done, []{}, [this]{ this->doCallback(); });
         }
         FSM_BREAK
@@ -287,36 +315,48 @@ class Core {
   }
 
   void doCallback() {
-    RequestContext::setContext(context_);
-
-    // TODO(6115514) semantic race on reading executor_ and setExecutor()
-    Executor* x;
+    Executor* x = executor_;
     int8_t priority;
-    {
-      folly::MSLGuard g(executorLock_);
+    if (x) {
+      if (!executorLock_.try_lock()) {
+        executorLock_.lock();
+      }
       x = executor_;
       priority = priority_;
+      executorLock_.unlock();
     }
 
+    // keep Core alive until callback did its thing
+    ++attached_;
+
     if (x) {
-      ++attached_; // keep Core alive until executor did its thing
       try {
         if (LIKELY(x->getNumPriorities() == 1)) {
           x->add([this]() mutable {
             SCOPE_EXIT { detachOne(); };
+            RequestContext::setContext(context_);
+            SCOPE_EXIT { callback_ = {}; };
             callback_(std::move(*result_));
           });
         } else {
           x->addWithPriority([this]() mutable {
             SCOPE_EXIT { detachOne(); };
+            RequestContext::setContext(context_);
+            SCOPE_EXIT { callback_ = {}; };
             callback_(std::move(*result_));
           }, priority);
         }
       } catch (...) {
+        --attached_; // Account for extra ++attached_ before try
+        RequestContext::setContext(context_);
         result_ = Try<T>(exception_wrapper(std::current_exception()));
+        SCOPE_EXIT { callback_ = {}; };
         callback_(std::move(*result_));
       }
     } else {
+      SCOPE_EXIT { detachOne(); };
+      RequestContext::setContext(context_);
+      SCOPE_EXIT { callback_ = {}; };
       callback_(std::move(*result_));
     }
   }
@@ -330,17 +370,26 @@ class Core {
     }
   }
 
-  FSM<State> fsm_ {State::Start};
-  std::atomic<unsigned char> attached_ {2};
+  // Core should only be modified so that for size(T) == size(U),
+  // sizeof(Core<T>) == size(Core<U>).
+  // See Core::convert for details.
+
+  folly::Function<
+      void(Try<T>&&),
+      folly::FunctionMoveCtor::MAY_THROW,
+      8 * sizeof(void*)>
+      callback_;
+  // place result_ next to increase the likelihood that the value will be
+  // contained entirely in one cache line
+  folly::Optional<Try<T>> result_;
+  FSM<State> fsm_;
+  std::atomic<unsigned char> attached_;
   std::atomic<bool> active_ {true};
+  std::atomic<bool> interruptHandlerSet_ {false};
   folly::MicroSpinLock interruptLock_ {0};
   folly::MicroSpinLock executorLock_ {0};
   int8_t priority_ {-1};
   Executor* executor_ {nullptr};
-  folly::Optional<Try<T>> result_ {};
-  std::function<void(Try<T>&&)> callback_ {nullptr};
-  static constexpr size_t lambdaBufSize = 8 * sizeof(void*);
-  char lambdaBuf_[lambdaBufSize];
   std::shared_ptr<RequestContext> context_ {nullptr};
   std::unique_ptr<exception_wrapper> interrupt_ {};
   std::function<void(exception_wrapper const&)> interruptHandler_ {nullptr};
@@ -371,22 +420,41 @@ struct CollectVariadicContext {
          p.setException(std::move(t.exception()));
        }
      } else if (!threw) {
-       std::get<I>(results) = std::move(t.value());
+       std::get<I>(results) = std::move(t);
      }
   }
   ~CollectVariadicContext() {
     if (!threw.exchange(true)) {
-      p.setValue(std::move(results));
+      p.setValue(unwrap(std::move(results)));
     }
   }
   Promise<std::tuple<Ts...>> p;
-  std::tuple<Ts...> results;
-  std::atomic<bool> threw;
+  std::tuple<folly::Try<Ts>...> results;
+  std::atomic<bool> threw {false};
   typedef Future<std::tuple<Ts...>> type;
+
+ private:
+  template <typename... Ts2>
+  static std::tuple<Ts...> unwrap(std::tuple<folly::Try<Ts>...>&& o,
+                                  Ts2&&... ts2) {
+    static_assert(sizeof...(ts2) <
+                  std::tuple_size<std::tuple<folly::Try<Ts>...>>::value,
+                  "Non-templated unwrap should be used instead");
+    assert(std::get<sizeof...(ts2)>(o).hasValue());
+
+    return unwrap(std::move(o),
+                  std::forward<Ts2>(ts2)...,
+                  std::move(*std::get<sizeof...(ts2)>(o)));
+  }
+
+  static std::tuple<Ts...> unwrap(std::tuple<folly::Try<Ts>...>&& /* o */,
+                                  Ts&&... ts) {
+    return std::tuple<Ts...>(std::forward<Ts>(ts)...);
+  }
 };
 
-template <template <typename ...> class T, typename... Ts>
-void collectVariadicHelper(const std::shared_ptr<T<Ts...>>& ctx) {
+template <template <typename...> class T, typename... Ts>
+void collectVariadicHelper(const std::shared_ptr<T<Ts...>>& /* ctx */) {
   // base case
 }