feat add future

CMakeLists.txt

@@ -61,6 +61,8 @@ target_sources(
           src/sled/debugging/demangle.cc
           src/sled/debugging/symbolize.cc
           src/sled/event_bus/event_bus.cc
+          src/sled/futures/future.cc
+          src/sled/futures/internal/failure_handling.cc
           src/sled/filesystem/path.cc
           src/sled/log/log.cc
           src/sled/network/async_resolver.cc
@@ -210,6 +212,7 @@ if(SLED_BUILD_TESTS)
   sled_add_test(NAME sled_inja_test SRCS src/sled/nonstd/inja_test.cc)
   sled_add_test(NAME sled_fsm_test SRCS src/sled/nonstd/fsm_test.cc)
   sled_add_test(NAME sled_timestamp_test SRCS src/sled/units/timestamp_test.cc)
+  sled_add_test(NAME sled_future_test SRCS src/sled/futures/future_test.cc)
   sled_add_test(
     NAME sled_cache_test SRCS src/sled/cache/lru_cache_test.cc
     src/sled/cache/fifo_cache_test.cc src/sled/cache/expire_cache_test.cc)

src/sled/async/async_test.cc

@@ -11,7 +11,7 @@ TEST_SUITE("Async")
             CHECK_EQ(value, 126);
             return value;
         });
-        task1.wait();
+        // task1.wait();
         CHECK_EQ(126, task1.get());
     }
 

src/sled/futures/detail/delay.h

@@ -1,92 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_DELAY_H
-#define SLED_FUTURES_DETAIL_DELAY_H
-
-#include "sled/units/time_delta.h"
-#include "traits.h"
-#include <exception>
-
-namespace sled {
-namespace detail {
-
-template<typename R>
-struct DelayReceiver {
-    R receiver;
-    sled::TimeDelta delta;
-    bool stopped = false;
-
-    template<typename U>
-    void SetValue(U &&val)
-    {
-        if (stopped) { return; }
-        receiver.SetValue(std::forward<U>(val));
-    }
-
-    void SetError(std::exception_ptr e)
-    {
-        if (stopped) { return; }
-        receiver.SetError(e);
-    }
-
-    void SetStopped()
-    {
-        if (stopped) { return; }
-        stopped = true;
-        receiver.SetStopped();
-    }
-};
-
-template<typename S, typename R>
-struct DelayOperation {
-    ConnectResultT<S, R> op;
-
-    void Start() { op.Start(); }
-
-    void Stop() { op.Stop(); }
-};
-
-template<typename S>
-struct DelaySender {
-    using result_t  = typename S::result_t;
-    using this_type = DelaySender<S>;
-    S sender;
-    sled::TimeDelta delta;
-
-    template<typename R>
-    DelayOperation<S, DelayReceiver<R>> Connect(R receiver)
-    {
-        return {sender.Connect(DelayReceiver<R>{receiver, delta})};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename S>
-DelaySender<S>
-Delay(S sender, sled::TimeDelta const &delta)
-{
-    return {sender, delta};
-}
-
-struct DelayLazy {
-    sled::TimeDelta delta;
-
-    template<typename S>
-    DelaySender<S> Continue(S sender) const
-    {
-        return {sender, delta};
-    }
-};
-
-inline DelayLazy
-Delay(sled::TimeDelta const &delta)
-{
-    return {delta};
-}
-
-}// namespace detail
-}// namespace sled
-#endif//  SLED_FUTURES_DETAIL_DELAY_H

src/sled/futures/detail/future.h

@@ -1,103 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_FUTURE_H
-#define SLED_FUTURES_DETAIL_FUTURE_H
-#include "sled/synchronization/mutex.h"
-#include "traits.h"
-
-namespace sled {
-namespace detail {
-
-namespace {
-enum class State {
-    kPending,
-    kError,
-    kValue,
-};
-
-template<typename T>
-struct FutureState {
-
-    sled::Mutex mutex;
-    sled::ConditionVariable cv;
-    State state = State::kPending;
-
-    union {
-        T value;
-        std::exception_ptr error;
-    };
-};
-}// namespace
-
-template<typename R>
-struct FutureOperation {
-    std::shared_ptr<FutureState<typename R::result_t>> state;
-    R receiver;
-    mutable bool stopped = false;
-
-    void Start()
-    {
-        if (stopped) { return; }
-        sled::MutexLock lock(&state->mutex);
-        state->cv.Wait(lock, [&] { return state->state != State::kPending; });
-        if (state->state == State::kValue) {
-            receiver.SetValue(std::move(state->value));
-        } else {
-            receiver.SetError(state->error);
-        }
-    }
-
-    void Stop()
-    {
-        if (stopped) { return; }
-        stopped = true;
-        receiver.SetStopped();
-    }
-};
-
-template<typename T>
-struct FutureSender {
-    using result_t  = T;
-    using this_type = FutureSender<T>;
-    std::shared_ptr<FutureState<T>> state;
-
-    template<typename R>
-    FutureOperation<R> Connect(R receiver)
-    {
-        return {state, receiver};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename T>
-struct Promise {
-    std::shared_ptr<FutureState<T>> state;
-
-    Promise() : state(std::make_shared<FutureState<T>>()) {}
-
-    template<typename U = T>
-    typename std::enable_if<std::is_convertible<U, T>::value>::type SetValue(U &&val)
-    {
-        sled::MutexLock lock(&state->mutex);
-        state->value = std::forward<T>(val);
-        state->state = State::kValue;
-        state->cv.NotifyAll();
-    }
-
-    void SetError(std::exception_ptr e)
-    {
-        sled::MutexLock lock(&state->mutex);
-        state->error = e;
-        state->state = State::kError;
-        state->cv.NotifyAll();
-    }
-
-    FutureSender<T> GetFuture() { return {state}; }
-};
-
-}// namespace detail
-}// namespace sled
-#endif// SLED_FUTURES_DETAIL_FUTURE_H

src/sled/futures/detail/just.h

@@ -1,48 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_JUST_H
-#define SLED_FUTURES_DETAIL_JUST_H
-
-#include "traits.h"
-#include <memory>
-
-namespace sled {
-namespace detail {
-
-template<typename T, typename R>
-struct JustOperation {
-    T value;
-    R receiver;
-
-    void Start() { receiver.SetValue(std::forward<T>(value)); }
-
-    void Stop() { receiver.SetStopped(); }
-};
-
-template<typename T>
-struct JustSender {
-    using result_t  = T;
-    using this_type = JustSender<T>;
-    T value;
-
-    template<typename R>
-    JustOperation<T, R> Connect(R receiver)
-    {
-        return {std::forward<T>(value), receiver};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename T>
-JustSender<T>
-Just(T &&value)
-{
-    return {std::forward<T>(value)};
-}
-
-}// namespace detail
-}// namespace sled
-#endif//  SLED_FUTURES_DETAIL_JUST_H

src/sled/futures/detail/just_test.cc

@@ -1,3 +0,0 @@
-#include <sled/futures/detail/just.h>
-
-TEST(Just, basic) { auto s1 = sled::detail::Just(42); }

src/sled/futures/detail/on.h

@@ -1,114 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_VIA_H
-#define SLED_FUTURES_DETAIL_VIA_H
-#include "traits.h"
-#include <exception>
-#include <functional>
-#include <memory>
-
-namespace sled {
-namespace detail {
-template<typename R, typename F>
-struct OnReceiver {
-    R receiver;
-    F schedule;
-    bool stopped = false;
-
-    template<typename U>
-    typename std::enable_if<std::is_rvalue_reference<U>::value
-                            || (!std::is_copy_assignable<U>::value && !std::is_copy_constructible<U>::value)>::type
-    SetValue(U &&val)
-    {
-        static_assert(std::is_rvalue_reference<decltype(val)>::value, "U must be an rvalue reference");
-        if (stopped) { return; }
-        try {
-            auto moved = make_move_on_copy(val);
-            schedule([this, moved]() mutable { receiver.SetValue(std::move(moved.value)); });
-        } catch (...) {
-            SetError(std::current_exception());
-        }
-    }
-
-    template<typename U>
-    typename std::enable_if<!std::is_rvalue_reference<U>::value
-                            && (std::is_copy_assignable<U>::value || std::is_copy_constructible<U>::value)>::type
-    SetValue(U &&val)
-    {
-        if (stopped) { return; }
-        try {
-            schedule([this, val] { receiver.SetValue(val); });
-        } catch (...) {
-            SetError(std::current_exception());
-        }
-    }
-
-    void SetError(std::exception_ptr e)
-    {
-        if (stopped) { return; }
-        receiver.SetError(e);
-    }
-
-    void SetStopped()
-    {
-        if (stopped) { return; }
-        stopped = true;
-        receiver.SetStopped();
-    }
-};
-
-template<typename S, typename R>
-struct OnOperation {
-    ConnectResultT<S, R> op;
-
-    void Start() { op.Start(); }
-
-    void Stop() { op.Stop(); }
-};
-
-template<typename S, typename F>
-struct OnSender {
-    using result_t  = typename S::result_t;
-    using this_type = OnSender<S, F>;
-    S sender;
-    F schedule;
-
-    template<typename R>
-    OnOperation<S, OnReceiver<R, F>> Connect(R receiver)
-    {
-        return {sender.Connect(OnReceiver<R, F>{receiver, schedule})};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename F>
-struct OnLazy {
-    F func;
-
-    template<typename S>
-    OnSender<S, F> Continue(S sender) const
-    {
-        return {sender, func};
-    }
-};
-
-template<typename S, typename F>
-OnSender<S, F>
-On(S sender, F &&schedule)
-{
-    return {sender, std::forward<F>(schedule)};
-}
-
-template<typename F>
-OnLazy<F>
-On(F &&schedule)
-{
-    return {schedule};
-}
-
-}// namespace detail
-}// namespace sled
-#endif// SLED_FUTURES_DETAIL_VIA_H

src/sled/futures/detail/retry.h

@@ -1,144 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_RETRY_H
-#define SLED_FUTURES_DETAIL_RETRY_H
-
-#include "sled/log/log.h"
-#include "sled/synchronization/mutex.h"
-#include "traits.h"
-#include <memory>
-
-namespace sled {
-namespace detail {
-
-namespace {
-struct RetryState {
-    enum State { kPending, kDone, kRetry };
-
-    sled::Mutex mutex;
-    sled::ConditionVariable cv;
-    int retry_count = 0;
-    State state     = kPending;
-};
-}// namespace
-
-template<typename R>
-struct RetryReceiver {
-    std::shared_ptr<RetryState> state;
-    R receiver;
-    bool stopped = false;
-
-    template<typename U>
-    void SetValue(U &&val)
-    {
-        {
-            sled::MutexLock lock(&state->mutex);
-            if (stopped) { return; }
-            state->state = RetryState::kDone;
-            state->cv.NotifyAll();
-        }
-        receiver.SetValue(std::forward<U>(val));
-    }
-
-    void SetError(std::exception_ptr e)
-    {
-        // notify
-        {
-            sled::MutexLock lock(&state->mutex);
-            if (stopped) { return; }
-            if (state->retry_count > 0) {
-                --state->retry_count;
-                state->state = RetryState::kRetry;
-                return;
-            } else {
-                state->state = RetryState::kDone;
-                state->cv.NotifyAll();
-            }
-        }
-        receiver.SetError(e);
-    }
-
-    void SetStopped()
-    {
-        {
-            sled::MutexLock lock(&state->mutex);
-            if (stopped) { return; }
-            stopped      = true;
-            state->state = RetryState::kDone;
-            state->cv.NotifyAll();
-        }
-        receiver.SetStopped();
-    }
-};
-
-template<typename S, typename R>
-struct RetryOperation {
-    int retry_count;
-    std::shared_ptr<RetryState> state;
-    ConnectResultT<S, R> op;
-
-    void Start()
-    {
-        {
-            sled::MutexLock lock(&state->mutex);
-            state->retry_count = retry_count;
-            state->state       = RetryState::kPending;
-        }
-        do {
-            op.Start();
-            sled::MutexLock lock(&state->mutex);
-            state->cv.Wait(lock, [this] { return state->state != RetryState::kPending; });
-            if (state->state == RetryState::kDone) { break; }
-            state->state = RetryState::kPending;
-        } while (true);
-    }
-
-    void Stop() { op.Stop(); }
-};
-
-template<typename S>
-struct RetrySender {
-    using result_t  = typename S::result_t;
-    using this_type = RetrySender<S>;
-    S sender;
-    int retry_count;
-
-    template<typename R>
-    RetryOperation<S, RetryReceiver<R>> Connect(R receiver)
-    {
-        auto state = std::make_shared<RetryState>();
-        auto op    = sender.Connect(RetryReceiver<R>{state, receiver});
-        return {retry_count, state, op};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename S>
-RetrySender<S>
-Retry(S sender, int retry_count)
-{
-    return {sender, retry_count};
-}
-
-struct RetryLazy {
-    int retry_count;
-
-    template<typename S>
-    RetrySender<S> Continue(S sender) const
-    {
-        return {sender, retry_count};
-    }
-};
-
-inline RetryLazy
-Retry(int retry_count)
-{
-    return {retry_count};
-}
-
-}// namespace detail
-}// namespace sled
-#endif//  SLED_FUTURES_DETAIL_RETRY_H

src/sled/futures/detail/then.h

@@ -1,97 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_THEN_H
-#define SLED_FUTURES_DETAIL_THEN_H
-
-#include "traits.h"
-#include <memory>
-
-namespace sled {
-namespace detail {
-
-template<typename R, typename F>
-struct ThenReceiver {
-    R receiver;
-    F func;
-    bool stopped = false;
-
-    template<typename U, typename Ret = invoke_result_t<F, U>>
-    void SetValue(U &&val)
-    {
-        if (stopped) { return; }
-        try {
-            receiver.SetValue(std::forward<Ret>(func(std::forward<U>(val))));
-        } catch (...) {
-            SetError(std::current_exception());
-        }
-    }
-
-    void SetError(std::exception_ptr e)
-    {
-        if (stopped) { return; }
-        receiver.SetError(e);
-    }
-
-    void SetStopped()
-    {
-        if (stopped) { return; }
-        stopped = true;
-        receiver.SetStopped();
-    }
-};
-
-template<typename S, typename R>
-struct ThenOperation {
-    ConnectResultT<S, R> op;
-
-    void Start() { op.Start(); }
-
-    void Stop() { op.Stop(); }
-};
-
-template<typename S, typename F>
-struct ThenSender {
-    using result_t  = invoke_result_t<F, typename decay_t<S>::result_t>;
-    using this_type = ThenSender<S, F>;
-    S sender;
-    F func;
-
-    template<typename R>
-    ThenOperation<S, ThenReceiver<R, F>> Connect(R receiver)
-    {
-        return {sender.Connect(ThenReceiver<R, F>{receiver, func})};
-    }
-
-    template<typename Lazy>
-    friend ContinueResultT<this_type, Lazy> operator|(this_type sender, Lazy lazy)
-    {
-        return lazy.Continue(sender);
-    }
-};
-
-template<typename S, typename F>
-ThenSender<S, F>
-Then(S &&sender, F &&func)
-{
-    return {std::forward<S>(sender), std::forward<F>(func)};
-}
-
-template<typename F>
-struct ThenLazy {
-    F func;
-
-    template<typename S>
-    ThenSender<S, F> Continue(S sender) const
-    {
-        return {sender, func};
-    }
-};
-
-template<typename F>
-ThenLazy<F>
-Then(F &&func)
-{
-    return {func};
-}
-
-}// namespace detail
-}// namespace sled
-#endif//  SLED_FUTURES_DETAIL_THEN_H

src/sled/futures/detail/traits.h

@@ -1,56 +0,0 @@
-#ifndef SLED_FUTURES_DETAIL_TRAITS_H
-#define SLED_FUTURES_DETAIL_TRAITS_H
-
-#include "sled/exec/detail/invoke_result.h"
-
-#include <memory>
-#include <type_traits>
-
-namespace sled {
-namespace detail {
-template<typename S, typename R>
-struct ConnectResult {
-    typedef decltype(std::declval<S>().Connect(std::declval<R>())) type;
-};
-
-template<typename S, typename R>
-using ConnectResultT = typename ConnectResult<S, R>::type;
-
-template<typename S, typename Lazy>
-struct ContinueResult {
-    typedef decltype(std::declval<Lazy>().Continue(std::declval<S>())) type;
-};
-
-template<typename S, typename Lazy>
-using ContinueResultT = typename ContinueResult<S, Lazy>::type;
-
-template<typename F, typename... Args>
-using invoke_result_t = eggs::invoke_result_t<F, Args...>;
-
-template<typename T>
-using decay_t = typename std::decay<T>::type;
-
-template<typename T>
-struct move_on_copy {
-    using type = typename std::remove_reference<T>::type;
-
-    move_on_copy(type &&value) : value(std::move(value)) {}
-
-    move_on_copy(const move_on_copy &other) : value(std::move(other.value)) {}
-
-    move_on_copy(move_on_copy &&)                 = delete;
-    move_on_copy &operator=(const move_on_copy &) = delete;
-
-    mutable type value;
-};
-
-template<typename T>
-move_on_copy<T>
-make_move_on_copy(T &&value)
-{
-    return {std::move<T>(value)};
-}
-
-}// namespace detail
-}// namespace sled
-#endif// SLED_FUTURES_DETAIL_TRAITS_H

src/sled/futures/future.cc

@@ -0,0 +1,15 @@
+
+#include "sled/futures/future.h"
+
+namespace sled {
+namespace detail {
+void
+IncrementFuturesUsage()
+{}
+
+void
+DecrementFuturesUsage()
+{}
+
+}// namespace detail
+}// namespace sled

src/sled/futures/future.h

@@ -1,6 +1,327 @@
 #ifndef SLED_FUTURES_FUTURE_H
 #define SLED_FUTURES_FUTURE_H
 
-namespace sled {}
+#pragma once
+#include "sled/futures/internal/failure_handling.h"
+#include "sled/futures/internal/promise.h"
+#include "sled/lang/attributes.h"
+#include "sled/log/log.h"
+#include "sled/synchronization/event.h"
+#include "sled/synchronization/mutex.h"
+#include "sled/variant.h"
+#include <atomic>
+#include <list>
+
+namespace sled {
+namespace detail {
+template<typename F, typename... Args>
+struct is_invocable : std::is_constructible<std::function<void(Args...)>,
+                                            std::reference_wrapper<typename std::remove_reference<F>::type>> {};
+
+template<typename R, typename F, typename... Args>
+struct is_invocable_r : std::is_constructible<std::function<R(Args...)>,
+                                              std::reference_wrapper<typename std::remove_reference<F>::type>> {};
+
+enum FutureState {
+    kNotCompletedFuture = 0,
+    kSuccessFuture      = 1,
+    kFailedFuture       = 2,
+};
+
+SLED_EXPORT void IncrementFuturesUsage();
+SLED_EXPORT void DecrementFuturesUsage();
+
+template<typename T, typename FailureT>
+struct FutureData {
+    FutureData() { IncrementFuturesUsage(); }
+
+    FutureData(const FutureData &)            = delete;
+    FutureData(FutureData &&)                 = delete;
+    FutureData &operator=(const FutureData &) = delete;
+    FutureData &operator=(FutureData &&)      = delete;
+
+    ~FutureData() { DecrementFuturesUsage(); }
+
+    std::atomic_int state{kNotCompletedFuture};
+    sled::variant<sled::monostate, T, FailureT> value;
+    std::list<std::function<void(const T &)>> success_callbacks;
+    std::list<std::function<void(const FailureT &)>> failure_callbacks;
+    sled::Mutex mutex_;
+};
+}// namespace detail
+
+//
+
+template<typename T, typename FailureT>
+class Future {
+    static_assert(!std::is_same<T, void>::value, "Future<void, _> is not allowed. Use Future<bool, _> instead");
+    static_assert(!std::is_same<FailureT, void>::value, "Future<_, void> is not allowed. Use Future<_, bool> instead");
+    template<typename T2, typename FailureT2>
+    friend class Future;
+    friend class Promise<T, FailureT>;
+    friend struct detail::FutureData<T, FailureT>;
+
+public:
+    using Value   = T;
+    using Failure = FailureT;
+
+    Future() noexcept = default;
+
+    explicit Future(const Promise<T, FailureT> &promise) { data_ = promise.future().data_; }
+
+    Future(const Future<T, FailureT> &) noexcept                         = default;
+    Future(Future<T, FailureT> &&) noexcept                              = default;
+    Future<T, FailureT> &operator=(const Future<T, FailureT> &) noexcept = default;
+    Future<T, FailureT> &operator=(Future<T, FailureT> &&) noexcept      = default;
+    ~Future()                                                            = default;
+
+    bool operator==(const Future<T, FailureT> &other) const noexcept { return data_ == other.data_; }
+
+    bool operator!=(const Future<T, FailureT> &other) const noexcept { return !operator==(other); }
+
+    bool IsCompleted() const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        int value = data_->state.load(std::memory_order_acquire);
+        return value == detail::kSuccessFuture || value == detail::kFailedFuture;
+    }
+
+    bool IsFailed() const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        return data_->state.load(std::memory_order_acquire) == detail::kFailedFuture;
+    }
+
+    bool IsSucceeded() const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        return data_->state.load(std::memory_order_acquire) == detail::kSuccessFuture;
+    }
+
+    bool IsValid() const noexcept { return static_cast<bool>(data_); }
+
+    bool Wait(int64_t timeout_ms) const noexcept { return Wait(sled::TimeDelta::Millis(timeout_ms)); }
+
+    bool Wait(sled::TimeDelta timeout = sled::Event::kForever) const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        if (IsCompleted()) { return true; }
+
+        bool wait_forever         = timeout <= sled::TimeDelta::Zero();
+        sled::TimeDelta wait_time = wait_forever ? sled::Event::kForever : timeout;
+
+        auto event_ptr = std::make_shared<sled::Event>();
+        OnComplete([event_ptr]() { event_ptr->Set(); });
+        event_ptr->Wait(wait_time);
+
+        return IsCompleted();
+    }
+
+    template<typename Dummy = void,
+             typename       = typename std::enable_if<std::is_copy_constructible<T>::value, Dummy>::type>
+    T Result() const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        if (!IsCompleted()) Wait();
+        if (IsSucceeded()) {
+            try {
+                return sled::get<T>(data_->value);
+            } catch (...) {}
+        }
+        return T();
+    }
+
+    const T &ResultRef() const
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        if (!IsCompleted()) { Wait(); }
+        return sled::get<T>(data_->value);
+    }
+
+    FailureT FailureReason() const
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        if (!IsCompleted()) { Wait(); }
+        if (IsFailed()) {
+            try {
+                return sled::get<FailureT>(data_->value);
+            } catch (...) {}
+        }
+        return FailureT();
+    }
+
+    template<typename Func, typename = typename std::enable_if<detail::is_invocable<Func, T>::value>::type>
+    Future<T, FailureT> OnSuccess(Func &&f) const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        bool call_it = false;
+        {
+            sled::MutexLock lock(&data_->mutex_);
+            if (IsCompleted()) {
+                call_it = IsSucceeded();
+            } else {
+                try {
+                    data_->success_callbacks.emplace_back(std::forward<Func>(f));
+                } catch (std::exception &e) {
+                    return Future<T, FailureT>::Failed(detail::ExceptionFailure<FailureT>(e));
+                } catch (...) {
+                    return Future<T, FailureT>::Failed(detail::ExceptionFailure<FailureT>());
+                }
+            }
+        }
+        if (call_it) {
+            try {
+                f(sled::get<T>(data_->value));
+            } catch (...) {}
+        }
+        return Future<T, FailureT>(data_);
+    }
+
+    template<typename Func, typename = typename std::enable_if<detail::is_invocable<Func, FailureT>::value>::type>
+    Future<T, FailureT> OnFailure(Func &&f) const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        bool call_it = false;
+        {
+            sled::MutexLock lock(&data_->mutex_);
+            if (IsCompleted()) {
+                call_it = IsFailed();
+            } else {
+                try {
+                    data_->failure_callbacks.emplace_back(std::forward<Func>(f));
+                } catch (std::exception &e) {
+                    return Future<T, FailureT>::Failed(detail::ExceptionFailure<FailureT>(e));
+                } catch (...) {
+                    return Future<T, FailureT>::Failed(detail::ExceptionFailure<FailureT>());
+                }
+            }
+        }
+        if (call_it) {
+            try {
+                f(sled::get<FailureT>(data_->value));
+            } catch (...) {}
+        }
+        return Future<T, FailureT>(data_);
+    }
+
+    template<typename Func, typename = typename std::enable_if<detail::is_invocable<Func>::value>::type>
+    Future<T, FailureT> OnComplete(Func &&f) const noexcept
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        OnSuccess([f](const T &) noexcept { f(); });
+        OnFailure([f](const FailureT &) noexcept { f(); });
+        return Future<T, FailureT>(data_);
+    }
+
+    // template<typename Func, typename = typename std::enable_if<detail::is_invocable<Func>::value>::type>
+    // Future<T, FailureT> OnComplete(Func &&F) const noexcept
+    // {
+    //     SLED_ASSERT(data_ != nullptr, "Future is not valid");
+    //     OnSuccess([f](const auto &) noexcept { f(); })
+    // }
+
+    static Future<typename std::decay<T>::type, FailureT> Successful(T &&value) noexcept
+    {
+        Future<typename std::decay<T>::type, FailureT> result
+            = Future<typename std::decay<T>::type, FailureT>::Create();
+        result.FillSuccess(std::forward<T>(value));
+        return result;
+    }
+
+    static Future<T, FailureT> successful(const T &value) noexcept
+    {
+        Future<T, FailureT> result = Future<T, FailureT>::Create();
+        result.FillSuccess(value);
+        return result;
+    }
+
+    static Future<T, FailureT> Successful() { return Future<T, FailureT>::Successful(T()); }
+
+    static Future<T, FailureT> Failed(const FailureT &failure) noexcept
+    {
+        Future<T, FailureT> result = Future<T, FailureT>::Create();
+        result.FillFailure(failure);
+        return result;
+    }
+
+private:
+    explicit Future(std::shared_ptr<detail::FutureData<T, FailureT>> other_data) { data_ = other_data; }
+
+    inline static Future<T, FailureT> Create()
+    {
+        Future<T, FailureT> result;
+        result.data_ = std::make_shared<detail::FutureData<T, FailureT>>();
+        return result;
+    }
+
+    void FillSuccess(const T &value)
+    {
+        T copy = value;
+        FillSuccess(std::move(copy));
+    }
+
+    void FillSuccess(T &&value)
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        if (detail::HasLastFailure()) {
+            FailureT failure = detail::LastFailure<FailureT>();
+            detail::InvalidateLastFailure();
+            FillFailure(std::move(failure));
+            return;
+        }
+
+        std::list<std::function<void(const T &)>> callbacks;
+        {
+            sled::MutexLock lock(&data_->mutex_);
+            if (IsCompleted()) { return; }
+
+            try {
+                data_->value.template emplace<T>(std::move(value));
+            } catch (...) {}
+            data_->state.store(detail::kSuccessFuture, std::memory_order_release);
+            callbacks                = std::move(data_->success_callbacks);
+            data_->success_callbacks = std::list<std::function<void(const T &)>>();
+            data_->failure_callbacks.clear();
+        }
+
+        for (const auto &f : callbacks) {
+            try {
+                f(sled::get<T>(data_->value));
+            } catch (...) {}
+        }
+    }
+
+    void FillFailure(const FailureT &reason)
+    {
+        FailureT copy = reason;
+        FillFailure(std::move(copy));
+    }
+
+    void FillFailure(FailureT &&reason)
+    {
+        SLED_ASSERT(data_ != nullptr, "Future is not valid");
+        std::list<std::function<void(const FailureT &)>> callbacks;
+        {
+            sled::MutexLock lock(&data_->mutex_);
+            if (IsCompleted()) { return; }
+            try {
+                data_->value.template emplace<FailureT>(std::move(reason));
+            } catch (...) {}
+            data_->state.store(detail::kFailedFuture, std::memory_order_release);
+            callbacks                = std::move(data_->failure_callbacks);
+            data_->failure_callbacks = std::list<std::function<void(const FailureT &)>>();
+            data_->success_callbacks.clear();
+        }
+
+        for (const auto &f : callbacks) {
+            try {
+                f(sled::get<FailureT>(data_->value));
+            } catch (...) {}
+        }
+    }
+
+    std::shared_ptr<detail::FutureData<T, FailureT>> data_;
+};
+}// namespace sled
 
 #endif// SLED_FUTURES_FUTURE_H

src/sled/futures/future_test.cc

@@ -0,0 +1,26 @@
+#include <sled/futures/future.h>
+
+TEST_SUITE("future")
+{
+    TEST_CASE("base success")
+    {
+        sled::Promise<int, std::string> p;
+        auto f = p.GetFuture();
+        p.Success(42);
+        CHECK(f.Wait(-1));
+        CHECK(f.IsValid());
+        CHECK_EQ(f.Result(), 42);
+    }
+    TEST_CASE("base failed")
+    {
+        sled::Promise<int, std::string> p;
+        auto f = p.GetFuture();
+        p.Failure("error");
+        REQUIRE(p.IsFilled());
+        REQUIRE(f.IsCompleted());
+        CHECK(f.Wait(-1));
+        CHECK(f.IsValid());
+        CHECK_EQ(f.FailureReason(), "error");
+    }
+    TEST_CASE("thread success") {}
+}

src/sled/futures/internal/failure_handling.cc

@@ -0,0 +1,32 @@
+#include "sled/futures/internal/failure_handling.h"
+
+namespace sled {
+namespace detail {
+static thread_local sled::any last_failure;
+
+bool
+HasLastFailure() noexcept
+{
+    return last_failure.has_value();
+}
+
+void
+InvalidateLastFailure() noexcept
+{
+    last_failure.reset();
+}
+
+const sled::any &
+LastFailureAny() noexcept
+{
+    return last_failure;
+}
+
+void
+SetLastFailure(const sled::any &failure) noexcept
+{
+    last_failure = failure;
+}
+
+}// namespace detail
+}// namespace sled

src/sled/futures/internal/failure_handling.h

@@ -0,0 +1,108 @@
+#ifndef SLED_FUTURES_INTERNAL_FAILURE_HANDLING_H
+#define SLED_FUTURES_INTERNAL_FAILURE_HANDLING_H
+
+#pragma once
+#include "sled/any.h"
+#include <string>
+
+namespace sled {
+namespace failure {
+template<typename FailureT>
+inline FailureT
+FailureFromString(std::string &&)
+{
+    return FailureT();
+}
+
+template<typename FailureT>
+inline FailureT
+FailureFromString(const std::string &str)
+{
+    std::string copy = str;
+    return FailureFromString<FailureT>(std::move(copy));
+}
+
+template<>
+inline std::string
+FailureFromString<std::string>(std::string &&str)
+{
+    return std::move(str);
+}
+
+}// namespace failure
+
+namespace detail {
+bool HasLastFailure() noexcept;
+void InvalidateLastFailure() noexcept;
+const sled::any &LastFailureAny() noexcept;
+void SetLastFailure(const sled::any &) noexcept;
+
+template<typename FailureT>
+inline FailureT
+LastFailure() noexcept
+{
+    if (!HasLastFailure()) { return FailureT(); }
+    try {
+        return sled::any_cast<FailureT>(LastFailureAny());
+    } catch (...) {
+        return FailureT();
+    }
+}
+
+template<typename FailureT>
+inline void
+SetLastFailure(const FailureT &failure) noexcept
+{
+    SetLastFailure(sled::any(failure));
+}
+
+template<typename FailureT>
+FailureT
+ExceptionFailure(const std::exception &e)
+{
+    return failure::FailureFromString<FailureT>(e.what());
+}
+
+template<typename FailureT>
+FailureT
+ExceptionFailure()
+{
+    return failure::FailureFromString<FailureT>("Exception");
+}
+}// namespace detail
+
+template<typename T, typename FailureT>
+class Future;
+
+template<typename FailureT>
+struct WithFuture {
+    explicit WithFuture(const FailureT &f = FailureT()) noexcept : failure_(f) {}
+
+    explicit WithFuture(FailureT &&f) noexcept : failure_(std::move(f)) {}
+
+    template<typename... Args>
+    explicit WithFuture(Args &&...args) noexcept : failure_(std::forward<Args>(args)...)
+    {}
+
+    template<typename T>
+    operator T() const noexcept
+    {
+        detail::SetLastFailure(std::move(failure_));
+        return T();
+    }
+
+    template<typename T>
+    operator Future<T, FailureT>() noexcept
+    {
+        Future<T, FailureT> result = Future<T, FailureT>::Create();
+        result.Faillure(failure_);
+        return result;
+    }
+
+private:
+    FailureT failure_;
+};
+
+}// namespace sled
+
+#endif// SLED_FUTURES_INTERNAL_FAILURE_HANDLING_H

src/sled/futures/internal/promise.h

@@ -0,0 +1,43 @@
+#ifndef SLED_FUTURES_INTERNAL_PROMISE_H
+#define SLED_FUTURES_INTERNAL_PROMISE_H
+
+#pragma once
+
+#include <memory>
+#include <type_traits>
+
+namespace sled {
+template<typename T, typename FailureT>
+class Future;
+
+template<typename T, typename FailureT>
+class Promise {
+    static_assert(!std::is_same<T, void>::value, "Promise<void, _> is not allowed. Use Promise<bool, _> instead");
+    static_assert(!std::is_same<FailureT, void>::value,
+                  "Promise<_, void> is not allowed. Use Promise<_, bool> instead");
+
+public:
+    using Value                                  = T;
+    Promise()                                    = default;
+    Promise(const Promise &) noexcept            = default;
+    Promise(Promise &&) noexcept                 = default;
+    Promise &operator=(const Promise &) noexcept = default;
+    Promise &operator=(Promise &&) noexcept      = default;
+    ~Promise()                                   = default;
+
+    Future<T, FailureT> GetFuture() const { return future_; };
+
+    bool IsFilled() const noexcept { return future_.IsCompleted(); }
+
+    void Failure(const FailureT &reason) { return future_.FillFailure(reason); }
+
+    void Success(const T &value) { return future_.FillSuccess(value); }
+
+    void Success(T &&value) { return future_.FillSuccess(std::move(value)); }
+
+private:
+    Future<T, FailureT> future_ = Future<T, FailureT>::Create();
+};
+}// namespace sled
+
+#endif// SLED_FUTURES_INTERNAL_PROMISE_H

src/sled/futures/promise_test.cc

@@ -1,57 +0,0 @@
-#include <gtest/gtest.h>
-#include <sled/futures/promise.h>
-
-TEST(Promise, Basic)
-{
-    auto p = sled::Promise<int>();
-    auto v = p.Then([](int v) {
-                  EXPECT_EQ(v, 1);
-                  return v + 10;
-              })
-                 .Tap([](int v) {
-                     EXPECT_EQ(v, 11);
-                     // no effect
-                     return v + 1;
-                 })
-                 .Then([](int v) {
-                     EXPECT_EQ(v, 11);
-                     return v + 10;
-                 });
-    p.Resolve(1);
-}
-
-TEST(Future, Basic)
-{
-    auto p      = sled::Promise<int>();
-    auto future = p.GetFuture()
-                      .Then([](int v) {
-                          EXPECT_EQ(v, 1);
-                          return v + 10;
-                      })
-                      .Then([](int v) {
-                          EXPECT_EQ(v, 11);
-                          return v + 10;
-                      });
-    p.Resolve(1);
-    EXPECT_EQ(future.Get(), 21);
-}
-
-TEST(Future, Except)
-{
-    auto p = sled::Promise<int>();
-    p.Resolve(1);
-    p.GetFuture()
-        .Then([](int) {
-            return 1;
-            // throw std::runtime_error("test");
-        })
-        .Except([](std::exception_ptr e) {
-            try {
-                std::rethrow_exception(e);
-            } catch (const std::exception &e) {
-                EXPECT_STREQ(e.what(), "test");
-            }
-            return false;
-        })
-        .Get();
-}