NOT INTENDED FOR LANDING: A promises demo

components/scheduler/promises/promise_internal.h

Index: components/scheduler/promises/promise_internal.h
diff --git a/components/scheduler/promises/promise_internal.h b/components/scheduler/promises/promise_internal.h
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+++ b/components/scheduler/promises/promise_internal.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_SCHEDULER_PROMISES_PROMISE_INTERNAL_H_
+#define COMPONENTS_SCHEDULER_PROMISES_PROMISE_INTERNAL_H_
+
+#include <set>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
+#include "base/single_thread_task_runner.h"
+#include "components/scheduler/promises/rejectable.h"
+
+namespace promise {
+template <typename R>
+class Promise;
+
+namespace internal {
+
+class PromiseExecutor;
+class ThreadPoolPromiseExecutor;
+
+template <typename R>
+class Promise;
+
+class SCHEDULER_EXPORT PromiseBase : public base::RefCounted<PromiseBase> {
+ public:
+  enum class PrerequisitePolicy { ALL, ANY, ALWAYS, NEVER };
+
+  explicit PromiseBase(PrerequisitePolicy prerequisite_policy);
+
+  PromiseBase(std::vector<scoped_refptr<PromiseBase>> prerequisites,
+              PrerequisitePolicy prerequisite_policy);
+
+  enum class State {
+    NEW,
+    PENDING,
+    PARTIALLY_RESOLVED,
+    RESOLVED,
+    REJECTED,
+    DEPENDENCY_REJECTED,
+    CANCELLED
+  };
+
+  State state() const { return state_; }
+
+  void SetThisAndPrerequisitesAsEager(bool eager);
+
+  void Cancel();
+
+  std::vector<scoped_refptr<PromiseBase>>& prerequisites() {
+    return prerequisites_;
+  }
+
+  std::set<PromiseBase*>& dependants() { return dependants_; }
+
+  bool can_run_now() const { return can_run_now_; }
+
+  bool is_resolved() const { return state() == PromiseBase::State::RESOLVED; }
+
+ protected:
+  friend class base::RefCounted<PromiseBase>;
+  friend class PromiseExecutor;
+  friend class ThreadPoolPromiseExecutor;
+
+  virtual ~PromiseBase();
+
+  virtual void ExecutorDrivenResolve() = 0;
+
+  void set_state(State state) { state_ = state; }
+
+  void SetThisAndPrerequisitesAsShouldRun(PromiseExecutor* executor,
+                                          bool should_run);
+
+  void RegisterDynamicDependancy(scoped_refptr<PromiseBase> dependency);
+
+  bool AllPrerequisitesSatisfied() const;
+
+  void SchedulePromiseForResolve();
+
+  void MarkAsResolved();
+  void MarkAsRejected();
+
+  std::vector<scoped_refptr<PromiseBase>> prerequisites_;
+  std::set<PromiseBase*> dependants_;
+  PromiseExecutor* executor_;
+  State state_;
+  PrerequisitePolicy prerequisite_policy_;
+  bool can_run_now_;
+  int should_run_refcount_;
+  int eager_refcount_;
+
+  DISALLOW_COPY_AND_ASSIGN(PromiseBase);
+};
+
+template <typename R>
+class SCHEDULER_EXPORT Promise : public PromiseBase {
+ public:
+  using ReturnType = R;
+
+  // RStorageType = (R == void) ? bool : R;
+  // This is useful to avoid the need for partial template specalization.
+  using RStorageType =
+      typename std::conditional<std::is_void<R>::value, bool, R>::type;
+
+  explicit Promise(PrerequisitePolicy prerequisite_policy)
+      : PromiseBase(prerequisite_policy) {}
+
+  Promise(std::vector<scoped_refptr<PromiseBase>> prerequisites,
+          PrerequisitePolicy prerequisite_policy)
+      : PromiseBase(std::move(prerequisites), prerequisite_policy) {}
+
+  template <typename RR = R>
+  enable_if_not_void_t<RR, RR&> GetResolved() {
+    if (r_promise_)
+      return r_promise_->GetResolved();
+    DCHECK(state() == PromiseBase::State::RESOLVED);
+    return r_;
+  }
+
+  template <typename RR = R>
+  enable_if_not_void_t<RR, void> Resolve(const RR&& r) {
+    r_ = std::move(r);
+    PromiseBase::MarkAsResolved();
+  }
+
+  template <typename RR = R>
+  enable_if_not_void_t<RR, void> Resolve(RR&& r) {
+    r_ = std::move(r);
+    PromiseBase::MarkAsResolved();
+  }
+
+  template <typename RR = R>
+  enable_if_void_t<RR, void> Resolve() {
+    PromiseBase::MarkAsResolved();
+  }
+
+  void Resolve(::promise::Promise<R> promise) {
+    r_promise_ = std::move(promise.promise_);
+    prerequisite_policy_ = PrerequisitePolicy::ALL;
+    state_ = State::PARTIALLY_RESOLVED;
+    RegisterDynamicDependancy(r_promise_);
+  }
+
+  bool is_rejected() const { return false; }
+
+ protected:
+  void ExecutorDrivenResolve() override { NOTREACHED(); }
+
+  RStorageType r_;
+  scoped_refptr<Promise<R>> r_promise_;
+
+  virtual ~Promise() {}
+};
+
+// Partial template specilazation to provide syntatic sugar for Rejectable
+// promises.
+template <typename ResolveT, typename RejectT>
+class SCHEDULER_EXPORT Promise<Rejectable<ResolveT, RejectT>>
+    : public PromiseBase {
+ public:
+  using ReturnType = Rejectable<ResolveT, RejectT>;
+
+  explicit Promise(PrerequisitePolicy prerequisite_policy)
+      : PromiseBase(prerequisite_policy) {}
+
+  Promise(std::vector<scoped_refptr<PromiseBase>> prerequisites,
+          PrerequisitePolicy prerequisite_policy)
+      : PromiseBase(std::move(prerequisites), prerequisite_policy) {}
+
+  ReturnType& GetResolved() {
+    if (r_promise_)
+      return r_promise_->GetResolved();
+    return r_;
+  }
+
+  bool is_rejected() const {
+    if (r_promise_)
+      return r_promise_->is_rejected();
+    return state() == PromiseBase::State::REJECTED;
+  }
+
+  template <typename RR = ResolveT>
+  enable_if_not_void_t<RR, void> Resolve(const RR& r) {
+    r_.Resolve(r);
+    PromiseBase::MarkAsResolved();
+  }
+
+  template <typename RR = ResolveT>
+  enable_if_not_void_t<RR, void> Resolve(RR&& r) {
+    r_.Resolve(std::move(r));
+    PromiseBase::MarkAsResolved();
+  }
+
+  template <typename RR = ResolveT>
+  enable_if_void_t<RR, void> Resolve() {
+    r_.Resolve();
+    PromiseBase::MarkAsResolved();
+  }
+
+  void Resolve(const ReturnType& r) {
+    r_ = r;
+    if (r_.is_resolved()) {
+      PromiseBase::MarkAsResolved();
+    } else {
+      PromiseBase::MarkAsRejected();
+    }
+  }
+
+  void Resolve(ReturnType&& r) {
+    r_ = std::move(r);
+    if (r_.is_resolved()) {
+      PromiseBase::MarkAsResolved();
+    } else {
+      PromiseBase::MarkAsRejected();
+    }
+  }
+
+  template <typename RR = RejectT>
+  enable_if_not_void_t<RR, void> Reject(const RR& r) {
+    r_.Reject(r);
+    PromiseBase::MarkAsRejected();
+  }
+
+  template <typename RR = RejectT>
+  enable_if_not_void_t<RR, void> Reject(RR&& r) {
+    r_.Reject(std::move(r));
+    PromiseBase::MarkAsRejected();
+  }
+
+  template <typename RR = RejectT>
+  enable_if_void_t<RR, void> Reject() {
+    r_.Reject();
+    PromiseBase::MarkAsRejected();
+  }
+
+  void Resolve(::promise::Promise<ReturnType> promise) {
+    r_promise_ = std::move(promise.promise_);
+    prerequisite_policy_ = PrerequisitePolicy::ALL;
+    state_ = State::PARTIALLY_RESOLVED;
+    RegisterDynamicDependancy(r_promise_);
+  }
+
+ protected:
+  void ExecutorDrivenResolve() override {
+    // This can get called if r_promise_ rejects.
+    DCHECK(state_ == PromiseBase::State::DEPENDENCY_REJECTED);
+  }
+
+  ReturnType r_;
+  scoped_refptr<Promise<ReturnType>> r_promise_;
+
+  virtual ~Promise() {}
+};
+
+template <typename R, typename... Args>
+class FunctionPromise final : public Promise<R> {
+ public:
+  FunctionPromise(base::Callback<R(Args...)> cb)
+      : Promise<R>(PromiseBase::PrerequisitePolicy::ALWAYS), cb_(cb) {}
+
+ private:
+  ~FunctionPromise() override {}
+
+  void ExecutorDrivenResolve() override {
+    Promise<R>::Resolve(std::move(cb_.Run()));
+  }
+
+  base::Callback<R(Args...)> cb_;
+};
+
+template <typename... Args>
+class FunctionPromise<void, Args...> final : public Promise<void> {
+ public:
+  FunctionPromise(base::Callback<void(Args...)> cb)
+      : Promise<void>(PromiseBase::PrerequisitePolicy::ALWAYS), cb_(cb) {}
+
+ private:
+  ~FunctionPromise() override {}
+
+  void ExecutorDrivenResolve() override {
+    cb_.Run();
+    Promise<void>::Resolve();
+  }
+
+  base::Callback<void(Args...)> cb_;
+};
+
+// === promise::Race().Then() implementation
+
+template <typename ThenR, typename CallbackR, typename AnyPromise>
+class SCHEDULER_EXPORT RacePromises final : public Promise<ThenR> {
+ public:
+  RacePromises(base::Callback<CallbackR(typename AnyPromise::ReturnType)>&& cb,
+               std::vector<scoped_refptr<PromiseBase>>&& promises)
+      : Promise<ThenR>(std::move(promises),
+                       PromiseBase::PrerequisitePolicy::ANY),
+        cb_(std::move(cb)) {}
+
+ private:
+  template <typename CB = CallbackR>
+  enable_if_not_void_t<CB, void> ResolveInternal(PromiseBase* prerequisite) {
+    Promise<ThenR>::Resolve(std::move(cb_.Run(
+        std::move(static_cast<AnyPromise*>(prerequisite)->GetResolved()))));
+  }
+
+  template <typename CB = CallbackR>
+  enable_if_void_t<CB, void> ResolveInternal(PromiseBase* prerequisite) {
+    cb_.Run(std::move(static_cast<AnyPromise*>(prerequisite)->GetResolved()));
+    Promise<ThenR>::Resolve();
+  }
+
+  void ExecutorDrivenResolve() override {
+    for (const scoped_refptr<PromiseBase>& prerequisite :
+         PromiseBase::prerequisites_) {
+      if (prerequisite->state() == PromiseBase::State::RESOLVED ||
+          prerequisite->state() == PromiseBase::State::REJECTED) {
+        ResolveInternal(std::move(prerequisite.get()));
+        return;
+      }
+    }
+    NOTREACHED();
+  }
+
+  ~RacePromises() override {}
+
+  base::Callback<CallbackR(typename AnyPromise::ReturnType)> cb_;
+};
+
+template <typename ThenR, typename CallbackR>
+class SCHEDULER_EXPORT RaceVoidPromises final : public Promise<ThenR> {
+ public:
+  RaceVoidPromises(base::Callback<CallbackR()>&& cb,
+                   std::vector<scoped_refptr<PromiseBase>>&& promises)
+      : Promise<ThenR>(std::move(promises),
+                       PromiseBase::PrerequisitePolicy::ANY),
+        cb_(std::move(cb)) {}
+
+ private:
+  template <typename CB = CallbackR>
+  enable_if_not_void_t<CB, void> ResolveInternal() {
+    Promise<ThenR>::Resolve(std::move(cb_.Run()));
+  }
+
+  template <typename CB = CallbackR>
+  enable_if_void_t<CB, void> ResolveInternal() {
+    cb_.Run();
+    Promise<ThenR>::Resolve();
+  }
+
+  void ExecutorDrivenResolve() override {
+    for (const scoped_refptr<PromiseBase>& prerequisite :
+         PromiseBase::prerequisites_) {
+      if (prerequisite->state() == PromiseBase::State::RESOLVED) {
+        ResolveInternal();
+        return;
+      }
+    }
+    NOTREACHED();
+  }
+
+  ~RaceVoidPromises() override {}
+
+  base::Callback<CallbackR()> cb_;
+};
+
+template <typename R>
+class SCHEDULER_EXPORT RaceSpec {
+ public:
+  template <typename RR>
+  static PromiseBase* GetPromiseBase(RR r) {
+    return r.promise();
+  }
+
+  template <typename... Promises>
+  RaceSpec(::promise::Promise<R> r, Promises... promises)
+      : promises_({r.promise(), GetPromiseBase(promises)...}) {}
+
+  template <typename RR = R, typename ThenR>
+  enable_if_not_void_t<RR, ::promise::Promise<ThenR>> Then(
+      base::Callback<ThenR(RR)>&& cb) {
+    return ::promise::Promise<ThenR>(new RacePromises<ThenR, ThenR, Promise<R>>(
+        std::move(cb), std::move(promises_)));
+  }
+
+  template <typename ThenR>
+  ::promise::Promise<ThenR> Then(base::Callback<ThenR()>&& cb) {
+    return ::promise::Promise<ThenR>(new RaceVoidPromises<ThenR, ThenR>(
+        std::move(cb), std::move(promises_)));
+  }
+
+  template <typename RR = R, typename ThenR>
+  enable_if_not_void_t<RR, ::promise::Promise<ThenR>> Then(
+      base::Callback<::promise::Promise<ThenR>(RR)>&& cb) {
+    return ::promise::Promise<ThenR>(
+        new RacePromises<ThenR, ::promise::Promise<ThenR>, Promise<RR>>(
+            std::move(cb), std::move(promises_)));
+  }
+
+  template <typename ThenR>
+  ::promise::Promise<ThenR> Then(
+      base::Callback<::promise::Promise<ThenR>()>&& cb) {
+    return ::promise::Promise<ThenR>(
+        new RaceVoidPromises<ThenR, ::promise::Promise<ThenR>>(
+            std::move(cb), std::move(promises_)));
+  }
+
+ private:
+  std::vector<scoped_refptr<PromiseBase>> promises_;
+};
+
+// === promise::All().Then() implementation
+
+template <typename ThenR, typename CB, typename... Promises>
+class SCHEDULER_EXPORT RunAfterAllPromises final : public Promise<ThenR> {
+ public:
+  RunAfterAllPromises(base::Callback<CB>&& cb,
+                      std::vector<scoped_refptr<PromiseBase>>&& promises)
+      : Promise<ThenR>(std::move(promises),
+                       PromiseBase::PrerequisitePolicy::ALL),
+        cb_(std::move(cb)) {}
+
+ private:
+  template <size_t... Indices, class... Args>
+  ThenR forward(indices<Indices...>) {
+    // The PromiseResolver is evaluated for each index in the Indices parameter
+    // pack.  The trailing '...' is the template magic that makes that work.
+    return cb_.Run(std::move(PromiseResolver<Indices, Promises...>::GetResolved(
+        PromiseBase::prerequisites_))...);
+  }
+
+  template <size_t... Indices, class... Args>
+  void forward_void(indices<Indices...>) {
+    // The PromiseResolver is evaluated for each index in the Indices parameter
+    // pack.  The trailing '...' is the template magic that makes that work.
+    cb_.Run(std::move(PromiseResolver<Indices, Promises...>::GetResolved(
+        PromiseBase::prerequisites_))...);
+  }
+
+  template <typename ThenRR = ThenR>
+  enable_if_not_void_t<ThenRR, void> ResolveInternal() {
+    using Indices = typename make_indices<sizeof...(Promises)>::type;
+    Promise<ThenRR>::Resolve(std::move(forward(Indices())));
+  }
+
+  template <typename ThenRR = ThenR>
+  enable_if_void_t<ThenRR, void> ResolveInternal() {
+    using Indices = typename make_indices<sizeof...(Promises)>::type;
+    forward_void(Indices());
+    Promise<ThenRR>::Resolve();
+  }
+
+  void ExecutorDrivenResolve() override { ResolveInternal(); }
+
+  ~RunAfterAllPromises() override {}
+
+  base::Callback<CB> cb_;
+};
+
+template <typename ThenR, typename CB, typename... Promises>
+class SCHEDULER_EXPORT RunAfterAllVoidPromises final : public Promise<ThenR> {
+ public:
+  RunAfterAllVoidPromises(base::Callback<CB>&& cb,
+                          std::vector<scoped_refptr<PromiseBase>>&& promises)
+      : Promise<ThenR>(std::move(promises),
+                       PromiseBase::PrerequisitePolicy::ALL),
+        cb_(std::move(cb)) {}
+
+ private:
+  template <typename ThenRR = ThenR>
+  enable_if_not_void_t<ThenRR, void> ResolveInternal() {
+    Promise<ThenR>::Resolve(std::move(std::move(cb_.Run())));
+  }
+
+  template <typename ThenRR = ThenR>
+  enable_if_void_t<ThenRR, void> ResolveInternal() {
+    cb_.Run();
+    Promise<ThenR>::Resolve();
+  }
+
+  void ExecutorDrivenResolve() override { ResolveInternal(); }
+
+  ~RunAfterAllVoidPromises() override {}
+
+  base::Callback<CB> cb_;
+};
+
+template <typename... Promises>
+class SCHEDULER_EXPORT AllSpec {
+ public:
+  template <typename R>
+  static PromiseBase* GetPromiseBase(R r) {
+    return r.promise();
+  }
+
+  AllSpec(Promises... promises) : promises_({GetPromiseBase(promises)...}) {}
+
+  template <typename ThenR, typename... ThenArgs>
+  scoped_refptr<Promise<ThenR>> Then(base::Callback<ThenR(ThenArgs...)>&& cb) {
+    static_assert(
+        sizeof...(ThenArgs) == sizeof...(Promises),
+        "Must have the same number of promises and callback arguments");
+    static_assert(sizeof...(Promises) > 0,
+                  "Must have at least one promise to wait on");
+    return make_scoped_refptr<Promise<ThenR>>(
+        new RunAfterAllPromises<ThenR, ThenR(ThenArgs...), Promises...>(
+            std::move(cb), std::move(promises_)));
+  }
+
+  template <typename ThenR>
+  scoped_refptr<Promise<ThenR>> Then(base::Callback<ThenR()>&& cb) {
+    static_assert(sizeof...(Promises) > 0,
+                  "Must have at least one promise to wait on");
+    return make_scoped_refptr<Promise<ThenR>>(
+        new RunAfterAllVoidPromises<ThenR, ThenR(), Promises...>(
+            std::move(cb), std::move(promises_)));
+  }
+
+ private:
+  std::vector<scoped_refptr<PromiseBase>> promises_;
+};
+
+}  // namespace internal
+}  // namespace promise
+
+#endif  // COMPONENTS_SCHEDULER_PROMISES_PROMISE_INTERNAL_H_