X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/198b09ec16ca1b8fc05053bcae9e75c0ad689711..1d0056178d75e1a88c82c6657833f24153f5ad16:/include/simgrid/kernel/future.hpp

diff --git a/include/simgrid/kernel/future.hpp b/include/simgrid/kernel/future.hpp
index c58f46b164..7b2941e583 100644
--- a/include/simgrid/kernel/future.hpp
+++ b/include/simgrid/kernel/future.hpp
@@ -1,4 +1,4 @@
-/* Copyright (c) 2016. The SimGrid Team.
+/* Copyright (c) 2016-2019. The SimGrid Team.
  * All rights reserved.                                                     */
 
 /* This program is free software; you can redistribute it and/or modify it
@@ -7,16 +7,18 @@
 #ifndef SIMGRID_KERNEL_FUTURE_HPP
 #define SIMGRID_KERNEL_FUTURE_HPP
 
-#include <boost/optional.hpp>
-
-#include <xbt/base.h>
-
 #include <functional>
 #include <future>
 #include <memory>
 #include <utility>
 #include <type_traits>
 
+#include <boost/optional.hpp>
+
+#include <xbt/base.h>
+#include <xbt/functional.hpp>
+#include <xbt/future.hpp>
+
 namespace simgrid {
 namespace kernel {
 
@@ -27,8 +29,6 @@ template<class T> class Promise;
 // Those are implementation details:
 enum class FutureStatus;
 template<class T> class FutureState;
-class FutureContinuation;
-template<class T, class F> class FutureContinuationImpl;
 
 enum class FutureStatus {
   not_ready,
@@ -36,46 +36,10 @@ enum class FutureStatus {
   done,
 };
 
-/** A continuation attached to a future to be executed when it is ready */
-XBT_PUBLIC_CLASS FutureContinuation {
-public:
-  FutureContinuation() {}
-
-  // No copy:
-  FutureContinuation(FutureContinuation&) = delete;
-  FutureContinuation& operator=(FutureContinuation&) = delete;
-
-  virtual ~FutureContinuation() {}
-  virtual void operator()() = 0;
-};
-
-/** Default implementation of `FutureContinuation`
- *
- *  @param T   value type of the future
- *  @param F   type of the wrapped code/callback/continuation
- */
-template<class T, class F>
-class FutureContinuationImpl : public FutureContinuation {
-public:
-  FutureContinuationImpl(std::shared_ptr<FutureState<T>> ptr, F callback)
-    : ptr_(std::move(ptr)), callback_(std::move(callback)) {}
-  ~FutureContinuationImpl() override {}
-  void operator()() override
-  {
-    try {
-      callback_(Future<T>(ptr_));
-    }
-    // Those exceptions are lost.
-    // If we want to implement callback chaining, we'll have to catch them and
-    // foward them to the next future.
-    catch (...) {
-      // We could log this.
-    }
-  }
-private:
-  std::shared_ptr<FutureState<T>> ptr_;
-  F callback_;
-};
+template<class T>
+struct is_future : std::false_type {};
+template<class T>
+struct is_future<Future<T>> : std::true_type {};
 
 /** Bases stuff for all @ref simgrid::kernel::FutureState<T> */
 class FutureStateBase {
@@ -84,6 +48,8 @@ public:
   FutureStateBase(FutureStateBase const&) = delete;
   FutureStateBase& operator=(FutureStateBase const&) = delete;
 
+  XBT_PUBLIC void schedule(simgrid::xbt::Task<void()>&& job);
+
   void set_exception(std::exception_ptr exception)
   {
     xbt_assert(exception_ == nullptr);
@@ -93,9 +59,9 @@ public:
     this->set_ready();
   }
 
-  void set_continuation(std::unique_ptr<FutureContinuation> continuation)
+  void set_continuation(simgrid::xbt::Task<void()>&& continuation)
   {
-    xbt_assert(!continuation_);
+    xbt_assert(not continuation_);
     switch (status_) {
     case FutureStatus::done:
       // This is not supposed to happen if continuation is set
@@ -105,13 +71,15 @@ public:
     case FutureStatus::ready:
       // The future is ready, execute the continuation directly.
       // We might execute it from the event loop instead:
-      (*continuation)();
+      schedule(std::move(continuation));
       break;
     case FutureStatus::not_ready:
-      // The future is not ready so we mast keep the continuation for
+      // The future is not ready so we must keep the continuation for
       // executing it later:
       continuation_ = std::move(continuation);
       break;
+    default:
+      DIE_IMPOSSIBLE;
     }
   }
 
@@ -126,8 +94,8 @@ public:
   }
 
 protected:
-  FutureStateBase() {}
-  ~FutureStateBase() {};
+  FutureStateBase() = default;
+  ~FutureStateBase() = default;
 
   /** Set the future as ready and trigger the continuation */
   void set_ready()
@@ -135,10 +103,10 @@ protected:
     status_ = FutureStatus::ready;
     if (continuation_) {
       // We unregister the continuation before executing it.
-      // We need to do this becase the current implementation of the
+      // We need to do this because the current implementation of the
       // continuation has a shared_ptr to the FutureState.
       auto continuation = std::move(continuation_);
-      (*continuation)();
+      this->schedule(std::move(continuation));
     }
   }
 
@@ -153,6 +121,7 @@ protected:
     status_ = FutureStatus::done;
     if (exception_) {
       std::exception_ptr exception = std::move(exception_);
+      exception_ = nullptr;
       std::rethrow_exception(std::move(exception));
     }
   }
@@ -160,15 +129,15 @@ protected:
 private:
   FutureStatus status_ = FutureStatus::not_ready;
   std::exception_ptr exception_;
-  std::unique_ptr<FutureContinuation> continuation_;
+  simgrid::xbt::Task<void()> continuation_;
 };
 
 /** Shared state for future and promises
  *
  *  You are not expected to use them directly but to create them
- *  implicitely through a @ref simgrid::kernel::Promise.
+ *  implicitly through a @ref simgrid::kernel::Promise.
  *  Alternatively kernel operations could inherit or contain FutureState
- *  if they are managed with @ref std::shared_ptr.
+ *  if they are managed with std::shared_ptr.
  **/
 template<class T>
 class FutureState : public FutureStateBase {
@@ -188,7 +157,7 @@ public:
     xbt_assert(this->value_);
     auto result = std::move(this->value_.get());
     this->value_ = boost::optional<T>();
-    return std::move(result);
+    return result;
   }
 
 private:
@@ -212,7 +181,7 @@ public:
     xbt_assert(this->value_);
     T* result = value_;
     value_ = nullptr;
-    return *value_;
+    return *result;
   }
 
 private:
@@ -235,14 +204,29 @@ public:
   }
 };
 
+template <class T> void bind_promise(Promise<T>&& promise, Future<T> future)
+{
+  class PromiseBinder {
+  public:
+    explicit PromiseBinder(Promise<T>&& promise) : promise_(std::move(promise)) {}
+    void operator()(Future<T> future) { simgrid::xbt::set_promise(promise_, future); }
+
+  private:
+    Promise<T> promise_;
+  };
+  future.then_(PromiseBinder(std::move(promise)));
+}
+
+template <class T> Future<T> unwrap_future(Future<Future<T>> future);
+
 /** Result of some (probably) asynchronous operation in the SimGrid kernel
  *
  * @ref simgrid::simix::Future and @ref simgrid::simix::Future provide an
- * abstration for asynchronous stuff happening in the SimGrid kernel. They
+ * abstraction for asynchronous stuff happening in the SimGrid kernel. They
  * are based on C++1z futures.
  *
  * The future represents a value which will be available at some point when this
- * asynchronous operaiont is finished. Alternatively, if this operations fails,
+ * asynchronous operation is finished. Alternatively, if this operations fails,
  * the result of the operation might be an exception.
  *
  *  As the operation is possibly no terminated yet, we cannot get the result
@@ -263,7 +247,7 @@ public:
  *    // available:
  *    try {
  *      // Try to get value, this might throw an exception if the operation
- *      // failed (such as an exception throwed by the worker process):
+ *      // failed (such as an exception thrown by the worker process):
  *      std::string value = result.get();
  *      XBT_INFO("Value: %s", value.c_str());
  *    }
@@ -274,7 +258,7 @@ public:
  *  );
  *  </pre>
  *
- *  This is based on C++1z @ref std::future but with some differences:
+ *  This is based on C++1z std::future but with some differences:
  *
  *  * there is no thread synchronization (atomic, mutex, condition variable,
  *    etc.) because everything happens in the SimGrid event loop;
@@ -284,7 +268,7 @@ public:
  *  * inside the `.then()`, `.get()` can be used;
  *
  *  * `.get()` can only be used when `.is_ready()` (as everything happens in
- *     a single-thread, the future would be guaranted to deadlock if `.get()`
+ *     a single-thread, the future would be guaranteed to deadlock if `.get()`
  *     is called when the future is not ready);
  *
  *  * there is no future chaining support for now (`.then().then()`);
@@ -294,8 +278,9 @@ public:
 template<class T>
 class Future {
 public:
-  Future() {}
-  Future(std::shared_ptr<FutureState<T>> state): state_(std::move(state)) {}
+  Future() = default;
+  explicit Future(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
+  ~Future() = default;
 
   // Move type:
   Future(Future&) = delete;
@@ -303,7 +288,8 @@ public:
   Future(Future&& that) : state_(std::move(that.state_)) {}
   Future& operator=(Future&& that)
   {
-    state_ = std::move(that.stat_);
+    state_ = std::move(that.state_);
+    return *this;
   }
 
   /** Whether the future is valid:.
@@ -328,36 +314,76 @@ public:
     return state_ != nullptr && state_->is_ready();
   }
 
+  /** Attach a continuation to this future
+   *
+   *  This is like .then() but avoid the creation of a new future.
+   */
+  template<class F>
+  void then_(F continuation)
+  {
+    if (state_ == nullptr)
+      throw std::future_error(std::future_errc::no_state);
+    // Give shared-ownership to the continuation:
+    auto state = std::move(state_);
+    state->set_continuation(simgrid::xbt::make_task(std::move(continuation), state));
+  }
+
+  /** Attach a continuation to this future
+   *
+   *  This version never does future unwrapping.
+   */
+  template <class F> auto then_no_unwrap(F continuation) -> Future<decltype(continuation(std::move(*this)))>
+  {
+    typedef decltype(continuation(std::move(*this))) R;
+    if (state_ == nullptr)
+      throw std::future_error(std::future_errc::no_state);
+    auto state = std::move(state_);
+    // Create a new future...
+    Promise<R> promise;
+    Future<R> future = promise.get_future();
+    // ...and when the current future is ready...
+    state->set_continuation(simgrid::xbt::make_task(
+        [](Promise<R> promise, std::shared_ptr<FutureState<T>> state, F continuation) {
+          // ...set the new future value by running the continuation.
+          Future<T> future(std::move(state));
+          simgrid::xbt::fulfill_promise(promise, [&continuation, &future] { return continuation(std::move(future)); });
+        },
+        std::move(promise), state, std::move(continuation)));
+    return future;
+  }
+
   /** Attach a continuation to this future
    *
    *  The future must be valid in order to make this call.
    *  The continuation is executed when the future becomes ready.
    *  The future becomes invalid after this call.
    *
-   *  We don't support future chaining for now (`.then().then()`).
-   *
    * @param continuation This function is called with a ready future
    *                     the future is ready
    * @exception std::future_error no state is associated with the future
    */
+  template <class F>
+  auto then(F continuation) -> typename std::enable_if<not is_future<decltype(continuation(std::move(*this)))>::value,
+                                                       Future<decltype(continuation(std::move(*this)))>>::type
+  {
+    return this->then_no_unwrap(std::move(continuation));
+  }
+
+  /** Attach a continuation to this future (future chaining) */
   template<class F>
-  void then(F continuation)
+  auto then(F continuation)
+  -> typename std::enable_if<
+       is_future<decltype(continuation(std::move(*this)))>::value,
+       decltype(continuation(std::move(*this)))
+     >::type
   {
-    if (state_ == nullptr)
-      throw std::future_error(std::future_errc::no_state);
-    std::unique_ptr<FutureContinuation> ptr =
-      std::unique_ptr<FutureContinuation>(
-        new FutureContinuationImpl<T,F>(state_, std::move(continuation)));
-    state_->set_continuation(std::move(ptr));
-    state_ = nullptr;
+    return unwrap_future(this->then_no_unwrap(std::move(continuation)));
   }
 
   /** Get the value from the future
-   *
-   *  This is expected to be called
    *
    *  The future must be valid and ready in order to make this call.
-   *  @ref std::future blocks when the future is not ready but we are
+   *  std::future blocks when the future is not ready but we are
    *  completely single-threaded so blocking would be a deadlock.
    *  After the call, the future becomes invalid.
    *
@@ -377,19 +403,27 @@ private:
   std::shared_ptr<FutureState<T>> state_;
 };
 
-/** Producer side of a @simgrid::kernel::Future
+template <class T> Future<T> unwrap_future(Future<Future<T>> future)
+{
+  Promise<T> promise;
+  Future<T> result = promise.get_future();
+  bind_promise(std::move(promise), std::move(future));
+  return result;
+}
+
+/** Producer side of a @ref simgrid::kernel::Future
  *
  *  A @ref Promise is connected to some `Future` and can be used to
  *  set its result.
  *
- *  Similar to @ref std::promise
+ *  Similar to std::promise
  *
  *  <code>
  *  // Create a promise and a future:
  *  auto promise = std::make_shared<simgrid::kernel::Promise<T>>();
  *  auto future = promise->get_future();
  *
- *  SIMIX_timer_set(date, [promise] {
+ *  simgrid::simix::Timer::set(date, [promise] {
  *    try {
  *      int value = compute_the_value();
  *      if (value < 0)
@@ -399,8 +433,8 @@ private:
  *      promise.set_value(value);
  *    }
  *    catch (...) {
- *      // If an error occured, we can set an exception which
- *      // will be throwed buy future.get():
+ *      // If an error occurred, we can set an exception which
+ *      // will be thrown by future.get():
  *      promise.set_exception(std::current_exception());
  *    }
  *  });
@@ -413,13 +447,13 @@ template<class T>
 class Promise {
 public:
   Promise() : state_(std::make_shared<FutureState<T>>()) {}
-  Promise(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
+  explicit Promise(std::shared_ptr<FutureState<T>> state) : state_(std::move(state)) {}
 
   // Move type
-  Promise(Promise&) = delete;
-  Promise& operator=(Promise&) = delete;
+  Promise(Promise const&) = delete;
+  Promise& operator=(Promise const&) = delete;
   Promise(Promise&& that) :
-    state_(std::move(that.state_)), future_get_(that.future_set)
+    state_(std::move(that.state_)), future_get_(that.future_get_)
   {
     that.future_get_ = false;
   }
@@ -468,7 +502,7 @@ template<>
 class Promise<void> {
 public:
   Promise() : state_(std::make_shared<FutureState<void>>()) {}
-  Promise(std::shared_ptr<FutureState<void>> state) : state_(std::move(state)) {}
+  explicit Promise(std::shared_ptr<FutureState<void>> state) : state_(std::move(state)) {}
   ~Promise()
   {
     if (state_ && state_->get_status() == FutureStatus::not_ready)
@@ -477,8 +511,8 @@ public:
   }
 
   // Move type
-  Promise(Promise&) = delete;
-  Promise& operator=(Promise&) = delete;
+  Promise(Promise const&) = delete;
+  Promise& operator=(Promise const&) = delete;
   Promise(Promise&& that) :
     state_(std::move(that.state_)), future_get_(that.future_get_)
   {